Focus on biological processes does not capture the whole picture

The ocean contains about 60 times more carbon than the atmosphere, in part due to a key process in the marine carbon cycle called the biological carbon pump (BCP). In this process, carbon dioxide (CO2) is converted to organic matter through photosynthesis and subsequently sinks as the so-called "export flux" from the surface ocean waters to the deep sea. As it sinks, bacterial decomposition processes break down the organic matter back into inorganic carbon, thus storing CO2 in the interior ocean. The BCP keeps atmospheric CO2 levels significantly lower than they would be in a hypothetical world without the BCP. So far, so good.

But one crucial aspect is often overlooked, says Dr Ivy Frenger, a climate researcher at the GEOMAR Helmholtz Centre for Ocean Research Kiel: "You have to consider the ocean circulation, because it determines how much of the biologically produced CO2 can actually accumulate in the interior ocean in the long term, isolated from exchange with the atmosphere." Looking at the effect of the BCP only in terms of the export flux is like trying to explain the balance of a bank account by looking only at the deposits.

"But there are gains and losses."

Changes in the BCP are an important research topic in the context of climate change.

Ivy Frenger notes that when considering the impact of the BCP on atmospheric CO2, it is common to focus on the export flux and neglect the ocean circulation.

She and six international colleagues have therefore published an opinion paper entitled "Misconceptions of the marine biological carbon pump in a changing climate: Thinking outside the 'export' box."

In their paper, the scientists aim to address the misconception that there is a direct link between the global export flux -- equivalent to deposits -- and the biogenic storage of CO2 in the ocean, and hence, atmospheric CO2 -- the equivalent to the bank account balance.

"There is no such simple correlation," says Dr Frenger. The "withdrawal" side also needs to be taken into account.

A much simpler and scientifically more accurate approach, she says, would be to directly estimate the CO2 reservoir resulting from biological processes in the interior ocean.

Such an estimate can be made by measuring the oxygen content of the ocean's interior along with its physical state, such as temperature.

Changes in these variables under climate change would also explain a seemingly paradoxical response of the BCP under anthropogenic climate change: Despite a decreasing export flux, carbon storage due to the biological pump in the interior ocean increases.

This is because changes in ocean circulation delay the return of biologically stored carbon from the ocean interior to the surface.

As in the bank account analogy: while the deposits are lower, if the withdrawals are reduced to an even greater extent there will be a net increase.

Accordingly, for climate change, this feedback results in more CO2 being stored in the ocean's interior than would be the case without the biological carbon pump.

Co-author Angela Landolfi remarks: "It is important to note that this effect is small when compared to the continuing massive anthropogenic CO2 emissions from fossil fuels."

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Fossil CO2 emissions at record high in 2023

Global carbon emissions from fossil fuels have risen again in 2023 -- reaching record levels, according to new research from the Global Carbon Project science team.

The annual Global Carbon Budget projects fossil carbon dioxide (CO2 emissions of 36.8 billion tonnes in 2023, up 1.1% from 2022.

Fossil CO2 emissions are falling in some regions, including Europe and the USA, but rising overall -- and the scientists say global action to cut fossil fuels is not happening fast enough to prevent dangerous climate change.

Emissions from land-use change (such as deforestation) are projected to decrease slightly but are still too high to be offset by current levels of reforestation and afforestation (new forests).

The report projects that total global CO2 emissions (fossil + land-use change) will be 40.9 billion tonnes in 2023.

This is about the same as 2022 levels, and part of a 10-year "plateau" -- far from the steep reduction in emissions that is urgently needed to meet global climate targets.

The research team included the University of Exeter, the University of East Anglia (UEA), CICERO Center for International Climate Research, Ludwig-Maximilian-University Munich and 90 other institutions around the world.

"The impacts of climate change are evident all around us, but action to reduce carbon emissions from fossil fuels remains painfully slow," said Professor Pierre Friedlingstein, of Exeter's Global Systems Institute, who led the study.

"It now looks inevitable we will overshoot the 1.5°C target of the Paris Agreement, and leaders meeting at COP28 will have to agree rapid cuts in fossil fuel emissions even to keep the 2°C target alive."

Professor Corinne Le Quéré, Royal Society Research Professor at UEA's School of Environmental Sciences said: "The latest CO2 data shows that current efforts are not profound or widespread enough to put global emissions on a downward trajectory towards Net Zero, but some trends in emissions are beginning to budge, showing climate policies can be effective.

"Global emissions at today's level are rapidly increasing the CO2 concentration in our atmosphere, causing additional climate change and increasingly serious and growing impacts."

"All countries need to decarbonise their economies faster than they are at present to avoid the worse impacts of climate change."

How long until we cross 1.5°C of global warming?

This study also estimates the remaining carbon budget before the 1.5°C target is breached consistently over multiple years, not just for a single year.

At the current emissions level, the Global Carbon Budget team estimates a 50% chance global warming will exceed 1.5°C consistently in about seven years.

This estimate is subject to large uncertainties, primarily due to the uncertainty on the additional warming coming from non-CO2 agents, especially for the 1.5°C targets which is getting close to the current warming level.

However, it's clear that the remaining carbon budget -- and therefore the time left to meet the 1.5°C target and avoid the worse impacts of climate change -- is running out fast.

Other key findings from the 2023 Global Carbon Budget include:

• Regional trends vary dramatically. Emissions in 2023 are projected to increase in India (8.2%) and China (4.0%), and decline in the EU (-7.4%), the USA (-3.0%) and the rest of the world (-0.4%).
• Global emissions from coal (1.1%), oil (1.5%) and gas (0.5%) are all projected to increase.
• Atmospheric CO2 levels are projected to average 419.3 parts per million in 2023, 51% above pre-industrial levels.
• About half of all CO2 emitted continues to be absorbed by land and ocean "sinks," with the rest remaining in the atmosphere where it causes climate change.
• Global CO2 emissions from fires in 2023 have been larger than the average (based on satellite records since 2003) due to an extreme wildfire season in Canada, where emissions were six to eight times higher than average.
• Current levels of technology-based Carbon Dioxide Removal (ie excluding nature-based means such as reforestation) amount to about 0.01 million tonnes CO2, more than a million times smaller than current fossil CO2 emissions.

The Global Carbon Budget report, produced by an international team of more than 120 scientists, provides an annual, peer-reviewed update, building on established methodologies in a fully transparent manner.

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Climate report: 'Uncharted territory' imperils life on Earth

An international coalition of climate scientists says in a paper published today that the Earth's vital signs have worsened beyond anything humans have yet seen, to the point that life on the planet is imperiled.

William Ripple, a distinguished professor in the Oregon State University College of Forestry, and former OSU postdoctoral researcher Christopher Wolf are the lead authors of the report, and 10 other U.S. and global scientists are co-authors.

"Without actions that address the root problem of humanity taking more from the Earth than it can safely give, we're on our way to the potential collapse of natural and socioeconomic systems and a world with unbearable heat and shortages of food and freshwater," Wolf said.

Published in BioScience, "The 2023 State of the climate report: Entering uncharted territory" notes that 20 of 35 planetary vital signs the authors use to track climate change are at record extremes.

The authors share new data illustrating that many climate-related records were broken by "enormous margins" in 2023, particularly those relating to ocean temperatures and sea ice. They also note an extraordinary Canadian wildfire season that produced unprecedented carbon dioxide emissions.

The report follows by four years the "World Scientists' Warning of a Climate Emergency" published by Ripple and collaborators in BioScience and co-signed by more than 15,000 scientists in 161 countries.

"Life on our planet is clearly under siege," Ripple said. "The statistical trends show deeply alarming patterns of climate-related variables and disasters. We also found little progress to report as far as humanity combating climate change."

Among the key numbers in the report:
 

• Fossil fuel subsidies -- actions by governments that artificially lower the cost of energy production, raise the price received by producers or lower the price paid by consumers -- roughly doubled between 2021 and 2022, from $531 billion to just over $1 trillion.
• Already this year wildfires in Canada have pumped more than 1 gigaton of carbon dioxide into the atmosphere, greater than Canada's total 2021 greenhouse gas emissions of 0.67 gigatons.
• In 2023, there have already been 38 days with global average temperatures more than 1.5 degrees Celsius above pre-industrial levels. Until this year, such days were a rarity, the authors note.
• The highest average Earth surface temperature ever recorded came this past July, and there's reason to believe it was the highest surface temperature the planet has seen in the last 100,000 years.

"As scientists, we are hugely troubled by the sudden increases in the frequency and severity of climate-related disasters," said Wolf, now a scientist with Corvallis-based Terrestrial Ecosystems Research Associates. "The frequency and severity of those disasters might be outpacing rising temperatures. By the end of the 21st century, as many as 3 to 6 billion people may find themselves outside the Earth's livable regions, meaning they will be encountering severe heat, limited food availability and elevated mortality rates."

The authors say policies are needed that take aim at the underlying issue of "ecological overshoot." When human demand on the Earth's resources is too large, the result in an array of environmental crises, including biodiversity decline. As long as humanity continues to put extreme pressure on the planet, any strategy that focuses only on carbon or climate will simply redistribute the pressure, they note.

"Our goal is to communicate climate facts and make policy recommendations," Ripple said. "It is a moral duty of scientists and our institutions to alert humanity of any potential existential threat and to show leadership in taking action."

The authors urge transitioning to a global economy that prioritizes human well-being and curtails overconsumption and excessive emissions by the rich. Specific recommendations include phasing out fossil fuel subsidies, transitioning toward plant-based diets, scaling up forest protection efforts and adopting international coal elimination and fossil fuel non-proliferation treaties.

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Increased West Antarctic Ice Sheet melting 'unavoidable'

Scientists ran simulations on the UK's national supercomputer to investigate ocean-driven melting of the West Antarctic Ice Sheet: how much is unavoidable and must be adapted to, and how much melting the international community still has control over through reduction of greenhouse gas emissions.

Taking into account climate variability like El Niño, they found no significant difference between mid-range emissions scenarios and the most ambitious targets of the 2015 Paris Agreement. Even under a best-case scenario of 1.5°C global temperature rise, melting will increase three times faster than during the 20th century.

The West Antarctic Ice Sheet is losing ice and is Antarctica's largest contributor to sea-level rise. Previous modelling finds this loss could be driven by warming of the Southern Ocean, particularly the Amundsen Sea region. Collectively the West Antarctic Ice Sheet contains enough ice to raise global mean sea-level by up to five metres.

Around the world millions of people live near the coast and these communities will be greatly impacted by sea level rise. A better understanding of the future changes will allow policymakers to plan ahead and adapt more readily.

Lead author Dr Kaitlin Naughten, a researcher at the British Antarctic Survey says:

"It looks like we've lost control of melting of the West Antarctic Ice Sheet. If we wanted to preserve it in its historical state, we would have needed action on climate change decades ago. The bright side is that by recognising this situation in advance, the world will have more time to adapt to the sea level rise that's coming. If you need to abandon or substantially re-engineer a coastal region, having 50 years lead time is going to make all the difference."

The team simulated four future scenarios of the 21st century, plus one historical scenario of the 20th century. The future scenarios either stabilised global temperature rise at the targets set out by the Paris Agreement, 1.5°C and 2°C, or followed standard scenarios for medium and high carbon emissions.

All scenarios resulted in significant and widespread future warming of the Amundsen Sea and increased melting of its ice-shelves. The three lower-range scenarios followed nearly identical pathways over the 21st century. Even under the best-case scenario, warming of the Amundsen Sea sped up by about a factor of three, and melting of the floating ice shelves which stabilise the inland glaciers followed, though it did begin to flatten by the end of the century.

The worst-case scenario had more ice shelf melting than the others, but only after 2045. The authors heed that this high fossil fuel scenario, where emissions increase rapidly, is considered unlikely to occur.

This study presents sobering future projections of Amundsen Sea ice-shelf melting but does not undermine the importance of mitigation in limiting the impacts of climate change.

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Making hydrogen from waste plastic could pay for itself

Hydrogen is viewed as a promising alternative to fossil fuel, but the methods used to make it either generate too much carbon dioxide or are too expensive. Rice University researchers have found a way to harvest hydrogen from plastic waste using a low-emissions method that could more than pay for itself.

"In this work, we converted waste plastics -- including mixed waste plastics that don't have to be sorted by type or washed -- into high-yield hydrogen gas and high-value graphene," said Kevin Wyss, a Rice doctoral alumnus and lead author on a study published in Advanced Materials. "If the produced graphene is sold at only 5% of current market value -- a 95% off sale! -- clean hydrogen could be produced for free."

By comparison, 'green' hydrogen -- produced using renewable energy sources to split water into its two component elements -- costs roughly $5 for just over two pounds. Though cheaper, most of the nearly 100 million tons of hydrogen used globally in 2022 was derived from fossil fuels, its production generating roughly 12 tons of carbon dioxide per ton of hydrogen.

"The main form of hydrogen used today is 'gray' hydrogen, which is produced through steam-methane reforming, a method that generates a lot of carbon dioxide" said James Tour, Rice's T. T. and W. F. Chao Professor of Chemistry and a professor of materials science and nanoengineering. "Demand for hydrogen will likely skyrocket over the next few decades, so we can't keep making it the same way we have up until now if we're serious about reaching net zero emissions by 2050."

The researchers exposed plastic waste samples to rapid flash Joule heating for about four seconds, bringing their temperature up to 3100 degrees Kelvin. The process vaporizes the hydrogen present in plastics, leaving behind graphene -- an extremely light, durable material made up of a single layer of carbon atoms.

"When we first discovered flash Joule heating and applied it to upcycle waste plastic into graphene, we observed a lot of volatile gases being produced and shooting out of the reactor," Wyss said. "We wondered what they were, suspecting a mix of small hydrocarbons and hydrogen, but lacked the instrumentation to study their exact composition."

Using funding from the United States Army Corps of Engineers, the Tour lab acquired the necessary equipment to characterize the vaporized contents.

"We know that polyethylene, for example, is made of 86% carbon and 14% hydrogen, and we demonstrated that we are able to recover up to 68% of that atomic hydrogen as gas with a 94% purity," Wyss said. "Developing the methods and expertise to characterize and quantify all the gases, including hydrogen, produced by this method was a difficult but rewarding process for me.

"I am glad that techniques I learned and used in this work -- specifically life-cycle assessment and gas chromatography -- can be applied to other projects in our group. I hope that this work will allow for the production of clean hydrogen from waste plastics, possibly solving major environmental problems like plastic pollution and the greenhouse gas-intensive production of hydrogen by steam methane reforming."

Read more at Science Daily

Switching to hydrogen fuel could prolong the methane problem

Hydrogen's potential as a clean fuel could be limited by a chemical reaction in the lower atmosphere, according to research from Princeton University and the National Oceanic and Atmospheric Association.

This is because hydrogen gas easily reacts in the atmosphere with the same molecule primarily responsible for breaking down methane, a potent greenhouse gas. If hydrogen emissions exceed a certain threshold, that shared reaction will likely lead to methane accumulating in the atmosphere -- with decades-long climate consequences.

"Hydrogen is theoretically the fuel of the future," said Matteo Bertagni, a postdoctoral researcher at the High Meadows Environmental Institute working on the Carbon Mitigation Initiative. "In practice, though, it poses many environmental and technological concerns that still need to be addressed."

Bertagni is the first author of a research article published in Nature Communications, in which researchers modeled the effect of hydrogen emissions on atmospheric methane. They found that above a certain threshold, even when replacing fossil fuel usage, a leaky hydrogen economy could cause near-term environmental harm by increasing the amount of methane in the atmosphere. The risk for harm is compounded for hydrogen production methods using methane as an input, highlighting the critical need to manage and minimize emissions from hydrogen production.

"We have a lot to learn about the consequences of using hydrogen, so the switch to hydrogen, a seemingly clean fuel, doesn't create new environmental challenges," said Amilcare Porporato, Thomas J. Wu '94 Professor of Civil and Environmental Engineering and the High Meadows Environmental Institute. Porporato is a principal investigator and member of the Leadership Team for the Carbon Mitigation Initiative and is also associated faculty at the Andlinger Center for Energy and the Environment.

The problem boils down to one small, difficult-to-measure molecule known as the hydroxyl radical (OH). Often dubbed "the detergent of the troposphere," OH plays a critical role in eliminating greenhouse gases such as methane and ozone from the atmosphere.

The hydroxyl radical also reacts with hydrogen gas in the atmosphere. And since a limited amount of OH is generated each day, any spike in hydrogen emissions means that more OH would be used to break down hydrogen, leaving less OH available to break down methane. As a consequence, methane would stay longer in the atmosphere, extending its warming impacts.

According to Bertagni, the effects of a hydrogen spike that might occur as government incentives for hydrogen production expand could have decades-long climate consequences for the planet.

"If you emit some hydrogen into the atmosphere now, it will lead to a progressive build-up of methane in the following years," Bertagni said. "Even though hydrogen only has a lifespan of around two years in the atmosphere, you'll still have the methane feedback from that hydrogen in 30 years from now."

In the study, the researchers identified the tipping point at which hydrogen emissions would lead to an increase in atmospheric methane and thereby undermine some of the near-term benefits of hydrogen as a clean fuel. By identifying that threshold, the researchers established targets for managing hydrogen emissions.

"It's imperative that we are proactive in establishing thresholds for hydrogen emissions, so that they can be used to inform the design and implementation of future hydrogen infrastructure," said Porporato.

For hydrogen referred to as green hydrogen, which is produced by splitting water into hydrogen and oxygen using electricity from renewable sources, Bertagni said that the critical threshold for hydrogen emissions sits at around 9%. That means that if more than 9% of the green hydrogen produced leaks into the atmosphere -- whether that be at the point of production, sometime during transport, or anywhere else along the value chain -- atmospheric methane would increase over the next few decades, canceling out some of the climate benefits of switching away from fossil fuels.

And for blue hydrogen, which refers to hydrogen produced via methane reforming with subsequent carbon capture and storage, the threshold for emissions is even lower. Because methane itself is the primary input for the process of methane reforming, blue hydrogen producers have to consider direct methane leakage in addition to hydrogen leakage. For example, the researchers found that even with a methane leakage rate as low as 0.5%, hydrogen leakages would have to be kept under around 4.5% to avoid increasing atmospheric methane concentrations.

"Managing leakage rates of hydrogen and methane will be critical," Bertagni said. "If you have just a small amount of methane leakage and a bit of hydrogen leakage, then the blue hydrogen that you produce really might not be much better than using fossil fuels, at least for the next 20 to 30 years."

The researchers emphasized the importance of the time scale over which the effect of hydrogen on atmospheric methane is considered. Bertagni said that in the long-term (over the course of a century, for instance), the switch to a hydrogen economy would still likely deliver net benefits to the climate, even if methane and hydrogen leakage levels are high enough to cause near-term warming. Eventually, he said, atmospheric gas concentrations would reach a new equilibrium, and the switch to a hydrogen economy would demonstrate its climate benefits. But before that happens, the potential near-term consequences of hydrogen emissions might lead to irreparable environmental and socioeconomic damage.

Thus, if institutions hope to meet mid-century climate goals, Bertagni cautioned that hydrogen and methane leakage to the atmosphere must be held in check as hydrogen infrastructure begins to roll out. And because hydrogen is a small molecule that is notoriously difficult to control and measure, he explained that managing emissions will likely require researchers to develop better methods for tracking hydrogen losses across the value chain.

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New technology creates carbon neutral chemicals out of thin air

It is possible to capture carbon dioxide (CO2) from the surrounding atmosphere and repurpose it into useful chemicals usually made from fossil fuels, according to a study from the University of Surrey.

The technology could allow scientists to both capture CO2 and transform it into useful chemicals such as carbon monoxide and synthetic natural gas in one circular process.

Dr Melis Duyar, Senior Lecturer of Chemical Engineering at the University of Surrey commented:

"Capturing CO2 from the surrounding air and directly converting it into useful products is exactly what we need to approach carbon neutrality in the chemicals sector. This could very well be a milestone in the steps needed for the UK to reach its 2050 net-zero goals.

"We need to get away from our current thinking on how we produce chemicals, as current practices rely on fossil fuels which are not sustainable. With this technology we can supply chemicals with a much lower carbon footprint and look at replacing fossil fuels with carbon dioxide and renewable hydrogen as the building blocks of other important chemicals."

The technology uses patent-pending switchable Dual Function Materials (DFMs), that capture carbon dioxide on their surface and catalyse the conversion of captured CO2 directly into chemicals. The "switchable" nature of the DFMs comes from their ability to produce multiple chemicals depending on the operating conditions or the composition of the added reactant. This makes the technology responsive to variations in demand for chemicals as well as availability of renewable hydrogen as a reactant.

Dr Duyar continued:

"These outcomes are a testament to the research excellence at Surrey, with continuously improving facilities, internal funding schemes and a collaborative culture."

Loukia-Pantzechroula Merkouri, Postgraduate student leading this research at the University of Surrey added:

"Not only does this research demonstrate a viable solution to the production of carbon neutral fuels and chemicals, but it also offers an innovative approach to combat the ever-increasing CO2 emissions contributing to global warming."

Read more at Science Daily

Just 10 financial actors hold the key to climate change

A new report has identified the 10 financial actors with the most influence on the fossil fuel economy and outlines the decisive role they can play in helping de-carbonize our future.

The study found that the top 10 most influential actors, including investment advisors, governments, and sovereign wealth funds from around the world, own 49.5 per cent of potential emissions from the world's largest energy firms.

"This shows us that both investors and governments can be at the forefront of change if citizens and clients urge them to de-carbonize," said Truzaar Dordi, lead researcher from the University of Waterloo. "A concentrated number of investors with the potential to influence the trajectory of the fossil fuel industry is either a problem, or an opportunity, depending on how you see things."

To arrive at their list, the researchers used a novel scoring mechanism blending the financial actor's fossil fuel holdings and investment in the world's 200 largest fossil fuel firms.

"If they're serious, capital markets can enable a low-carbon transition within the top coal, oil and gas reserve owners in the world," said Dordi. "Recent pledges to reduce carbon exposure in investment portfolios and engagement with the fossil fuel industry indicate we may already be moving in that direction."

The paper outlines specific ways these 10 governments and private investment advisors can make changes that will have a transformative impact in the fight against climate change. Some recommendations include public disclosure of a scheduled phase-out of fossil fuel financing, an assessment of a portfolio's exposure to climate risk in a 2°C world, and an alignment of investment portfolios with a 1.5°C scenario.

"Individually, reducing the demand for fossil fuels by driving and flying less and turning off the air-conditioner are great. We should keep doing that. But we also need to reduce our production of fossil fuels, which these 10 actors can lead. Without them, we simply won't have what it takes to meet our emissions targets and avoid catastrophe."

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Once seen as fleeting, a new solar tech proves its lasting power

Princeton Engineering researchers have developed the first perovskite solar cell with a commercially viable lifetime, marking a major milestone for an emerging class of renewable energy technology. The team projects their device can perform above industry standards for around 30 years, far more than the 20 years used as a threshold for viability for solar cells.

The device is not only highly durable, it also meets common efficiency standards. It is the first of its kind to rival the performance of silicon-based cells, which have dominated the market since their introduction in 1954.

Perovskites are semiconductors with a special crystal structure that makes them well suited for solar cell technology. They can be manufactured at room temperature, using much less energy than silicon, making them cheaper and more sustainable to produce. And whereas silicon is stiff and opaque, perovskites can be made flexible and transparent, extending solar power well beyond the iconic panels that populate hillsides and rooftops across America.

But unlike silicon, perovskites are notoriously fragile. Early perovskite solar cells (PSC), created between 2009 and 2012, lasted only minutes. The projected lifetime of the new device represents a five-fold increase over the previous record, set by a lower efficiency PSC in 2017. (That device operated under continuous illumination at room temperature for one year. The new device would operate for five years under similar lab conditions.)

The Princeton team, led by Lynn Loo, the Theodora D. '78 and William H. Walton III '74 Professor in Engineering, revealed their new device and their new method for testing such devices in a paper published June 16 in Science.

Loo said the record-setting design has highlighted the durable potential of PSCs, especially as a way to push solar cell technology beyond the limits of silicon. But she also pointed past the headline result to her team's new accelerated aging technique as the work's deeper significance.

"We might have the record today," she said, "but someone else is going to come along with a better record tomorrow. The really exciting thing is that we now have a way to test these devices and know how they will perform in the long term."

Due to perovskites' well-known frailty, long-term testing hasn't been much of a concern until now. But as the devices get better and last longer, testing one design against another will become crucial in rolling out durable, consumer-friendly technologies.

"This paper is likely going to be a prototype for anyone looking to analyze performance at the intersection of efficiency and stability," said Joseph Berry, a senior fellow at the National Renewable Energy Laboratory who specializes in the physics of solar cells and who was not involved in this study. "By producing a prototype to study stability, and showing what can be extrapolated [through accelerated testing], it's doing the work everyone wants to see before we start field testing at scale. It allows you to project in a way that's really impressive."

While efficiency has accelerated at a remarkable pace over the past decade, Berry said, the stability of these devices has improved more slowly. For them to become widespread and rolled out by industry, testing will need to become more sophisticated. That's where Loo's accelerated aging process comes in.

"These kinds of tests are going to be increasingly important," Loo said. "You can make the most efficient solar cells, but it won't matter if they aren't stable."

How they got here

Early in 2020, Loo's team was working on various device architectures that would maintain relatively strong efficiency -- converting enough sunlight to electric power to make them valuable -- and survive the onslaught of heat, light and humidity that bombard a solar cell during its lifetime.

Xiaoming Zhao, a postdoctoral researcher in Loo's lab, had been working on a number of designs with colleagues. The efforts layered different materials in order to optimize light absorption while protecting the most fragile areas from exposure. They developed an ultra-thin capping layer between two crucial components: the absorbing perovskite layer and a charge-carrying layer made from cupric salt and other substances. The goal was to keep the perovskite semiconductor from burning out in a matter of weeks or months, the norm at that time.

It's hard to comprehend how thin this capping layer is. Scientists use the term 2D to describe it, meaning two dimensions, as in something that has no thickness at all. In reality, it's merely a few atoms thick -- more than a million times smaller than the smallest thing a human eye can see. While the idea of a 2D capping layer isn't new, it is still considered a promising, emerging technique. Scientists at NREL have shown that 2D layers can greatly improve long-haul performance, but no one had developed a device that pushed perovskites anywhere close to the commercial threshold of a 20-year lifetime.

Zhao and his colleagues went through scores of permutations of these designs, shifting minute details in the geometry, varying the number of layers, and trying out dozens of material combinations. Each design went into the light box, where they could irradiate the sensitive devices in relentless bright light and measure their drop in performance over time.

In the fall of that year, as the first wave of the pandemic subsided and researchers to returned to their labs to tend to their experiments in carefully coordinated shifts, Zhao noticed something odd in the data. One set of the devices still seemed to be operating near its peak efficiency.

"There was basically zero drop after nearly half a year," he said.

That's when he realized he needed a way to stress test his device faster than his real-time experiment allowed.

"The lifetime we want is about 30 years, but you can't take 30 years to test your device," Zhao said. "So we need some way to predict this lifetime within a reasonable timeframe. That's why this accelerated aging is very important."

The new testing method speeds up the aging process by illuminating the device while blasting it with heat. This process speeds up what would happen naturally over years of regular exposure. The researchers chose four aging temperatures and measured results across these four different data streams, from the baseline temperature of a typical summer day to an extreme of 230 degrees Fahrenheit, higher than the boiling point of water.

They then extrapolated from the combined data and forecast the device's performance at room temperature over tens of thousands of hours of continuous illumination. The results showed a device that would perform above 80 percent of its peak efficiency under continuous illumination for at least five years at an average temperature of 95 degrees Fahrenheit. Using standard conversion metrics, Loo said that's the lab equivalent of 30 years of outdoor operation in an area like Princeton, NJ.

Berry of NREL concurred. "It's very credible," he said. "Some people are still going to want to see it play out. But this is much more credible science than a lot of other attempts at forecasting."

The Michael Jordan of solar cells

Perovskite solar cells were pioneered in 2006, with the first published devices following in 2009. Some of the earliest devices lasted only seconds. Others minutes. In the 2010s the device lifetimes grew to days and weeks and finally months. Then in 2017, a group from Switzerland published a groundbreaking paper on a PSC that lasted for one full year of continuous illumination.

Meanwhile, the efficiency of these devices has skyrocketed over the same period. While the first PSC showed a power-conversion efficiency of less than 4 percent, researchers boosted that metric nearly tenfold in as many years. It was the fastest improvement scientists had seen in any class of renewable-energy technology to date.

So why the push for perovskites? Berry said a combination of recent advances make them uniquely desirable: newly high efficiencies, an extraordinary "tunability" that allows scientists to make highly specific applications, the ability to manufacture them locally with low energy inputs, and now a credible forecast of extended life coupled with a sophisticated aging process to test a wide array of designs.

Loo said it's not that PSCs will replace silicon devices so much that the new technology will complement the old, making solar panels even cheaper, more efficient and more durable than they are now, and expanding solar energy into untold new areas of modern life. For example, her group recently demonstrated a completely transparent perovskite film (having different chemistry) that can turn windows into energy producing devices without changing their appearance. Other groups have found ways to print photovoltaic inks using perovskites, allowing formfactors scientists are only now dreaming up.

But the main advantage in the long run, according to both Berry and Loo: Perovskites can be manufactured at room temperature, whereas silicon is forged at around 3000 degrees Fahrenheit. That energy has to come from somewhere, and at the moment that means burning a lot of fossil fuels.

Read more at Science Daily

Confirmed: Atmospheric helium levels are rising

Scientists at Scripps Institution of Oceanography at UC San Diego used an unprecedented technique to detect that levels of helium are rising in the atmosphere, resolving an issue that has lingered among atmospheric chemists for decades.

The atmospheric abundance of the 4-helium (4He) isotope is rising because 4He is released during the burning and extraction of fossil fuels. The researchers report that it is increasing at a very small but, for the first time, clearly measurable rate. The 4He isotope itself does not add to the greenhouse effect that is making the planet warmer, but measures of it could serve as indirect markers of fossil-fuel use.

The National Science Foundation-supported study appears today in the journal Nature Geoscience.

"The main motivation was to resolve a longstanding controversy in the science community about atmospheric helium concentrations," said study lead author Benni Birner, a former graduate student and now postdoctoral researcher at Scripps Institution of Oceanography at UC San Diego.

The isotope 4He is produced by radioactive decay in the Earth's crust and accumulates in the same reservoirs as fossil fuels, in particular those of natural gas. During the extraction and combustion of fossil fuels, 4He is coincidentally released, which creates another means to evaluate the scale of industrial activity.

The study's breakthrough is in the technique the Scripps Oceanography team used to measure how much helium is in the atmosphere. Birner and Scripps geoscientists Jeff Severinghaus, Bill Paplawsky, and Ralph Keeling created a precise method to compare the 4He isotope to levels of the common atmospheric gas nitrogen. Because nitrogen levels in the atmosphere are constant, an increase in He/N2 is indicative of the rate of 4He buildup in the atmosphere.

Study co-author and Scripps Oceanography geochemist Ralph Keeling, overseer of the famed carbon dioxide measurement known as the Keeling Curve, describes the study as a "masterpiece of fundamental geochemistry." Though helium is relatively easy for scientists to detect in air samples, present at levels of five parts per million of air, no one had done the work to measure it carefully enough to observe an atmospheric increase, he said.

The study also provides a foundation for scientists to better understand the valuable 3-helium (3He) isotope, which has uses for nuclear fusion, cryogenics, and other applications. Proposals to acquire the scarce gas from the moon are an indication of the lengths to which manufacturers will go to harvest it.

According to previous work by other researchers, the 4He isotope exists in the atmosphere in what appears to be an unvarying ratio with 3He. The atmospheric rise of 4He isotope measured at Scripps therefore implies that the 3He isotope must be rising at a comparable rate as 4He. The research by Birner's team raises several questions about the accuracy of scientists' previous assumptions about how 3He is produced and in what quantity.

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Microbes can provide sustainable hydrocarbons for the petrochemical industry

If the petrochemical industry is ever to wean itself off oil and gas, it has to find sustainably-sourced chemicals that slip effortlessly into existing processes for making products such as fuels, lubricants and plastics.

Making those chemicals biologically is the obvious option, but microbial products are different from fossil fuel hydrocarbons in two key ways: They contain too much oxygen, and they have too many other atoms hanging off the carbons. In order for microbial hydrocarbons to work in existing synthetic processes, they often have to be de-oxygenated -- in chemical parlance, reduced -- and stripped of extraneous chemical groups, all of which takes energy.

A team of chemists from the University of California, Berkeley, and the University of Minnesota has now engineered microbes to make hydrocarbon chains that can be deoxygenated more easily and using less energy -- basically just the sugar glucose that the bacteria eat, plus a little heat.

The process allows microbial production of a broad range of chemicals currently made from oil and gas -- in particular, products like lubricants made from medium-chain hydrocarbons, which contain between eight and 10 carbon atoms in the chain.

"Part of the issue with trying to move to something like glucose as a feedstock for making molecules or to drive the chemical industry is that the fossil fuel structures of petrochemicals are so different -- they're usually fully reduced, with no oxygen substitutions," said Michelle Chang, UC Berkeley professor of chemistry and of chemical and biomolecular engineering. "Bacteria know how to make all these complex molecules that have all these functional groups sticking out from them, like all natural products, but making petrochemicals that we're used to using as precursors for the chemical industry is a bit of a challenge for them."

"This process is one step towards deoxygenating these microbial products, and it allows us to start making things that can replace petrochemicals, using just glucose from plant biomass, which is more sustainable and renewable," she said. "That way we can get away from petrochemicals and other fossil fuels."

The bacteria were engineered to make hydrocarbon chains of medium length, which has not been achieved before, though others have developed microbial processes for making shorter and longer chains, up to about 20 carbons. But the process can be readily adapted to make chains of other lengths, Chang said, including short-chain hydrocarbons used as precursors to the most popular plastics, such as polyethylene.

She and her colleagues published their results this week in the journal Nature Chemistry.

A bioprocess to make olefins

Fossil hydrocarbons are simple linear chains of carbon atoms with a hydrogen atom attached to each carbon. But the chemical processes optimized for turning these into high-value products don't easily allow substitution by microbially produced precursors that are oxygenated and have carbon atoms decorated with lots of other atoms and small molecules.

To get bacteria to produce something that can replace these fossil fuel precursors, Chang and her team, including co-first authors Zhen Wang and Heng Song, former UC Berkeley postdoctoral fellows, searched databases for enzymes from other bacteria that can synthesize medium-chain hydrocarbons. They also sought an enzyme that could add a special chemical group, carboxylic acid, at one end of the hydrocarbon, turning it into what's called a fatty acid.

All told, the researchers inserted five separate genes into E. coli bacteria, forcing the bacteria to ferment glucose and produce the desired medium-chain fatty acid. The added enzymatic reactions were independent of, or orthogonal to, the bacteria's own enzyme pathways, which worked better than trying to tweak the bacteria's complex metabolic network.

"We identified new enzymes that could actually make these mid-size hydrocarbon chains and that were orthogonal, so separate from fatty acid biosynthesis by the bacteria. That allows us to run it separately, and it uses less energy than it would if you use the native synthase pathway," Chang said. "The cells consume enough glucose to survive, but then alongside that, you have your pathway chewing through all the sugar to get higher conversions and a high yield."

That final step to create a medium-chain fatty acid primed the product for easy conversion by catalytic reaction to olefins, which are precursors to polymers and lubricants.

The UC Berkeley group collaborated with the Minnesota group led by Paul Dauenhauer, which showed that a simple, acid-based catalytic reaction called a Lewis acid catalysis (after famed UC Berkeley chemist Gilbert Newton Lewis) easily removed the carboxylic acid from the final microbial products -- 3-hydroxyoctanoic and 3-hydroxydecanoic acids -- to produce the olefins heptene and nonene, respectively. Lewis acid catalysis uses much less energy than the redox reactions typically needed to remove oxygen from natural products to produce pure hydrocarbons.

"The biorenewable molecules that Professor Chang's group made were perfect raw materials for catalytic refining," said Dauenhauer, who refers to these precursor molecules as bio-petroleum. "These molecules contained just enough oxygen that we could readily convert them to larger, more useful molecules using metal nanoparticle catalysts. This allowed us to tune the distribution of molecular products as needed, just like conventional petroleum products, except this time we were using renewable resources."

Heptene, with seven carbons, and nonene, with nine, can be employed directly as lubricants, cracked to smaller hydrocarbons and used as precursors to plastic polymers, such as polyethylene or polypropylene, or linked to form even longer hydrocarbons, like those in waxes and diesel fuel.

"This is a general process for making target compounds, no matter what chain length they are," Chang said. "And you don't have to engineer an enzyme system every time you want to change a functional group or the chain length or how branched it is."

Despite their feat of metabolic engineering, Chang noted that the long-term and more sustainable goal would be to completely redesign processes for synthesizing industrial hydrocarbons, including plastics, so that they are optimized to use the types of chemicals that microbes normally produce, rather than altering microbial products to fit into existing synthetic processes.

"There's a lot of interest in the question, 'What if we look at entirely new polymer structures?'," she said. "Can we make monomers from glucose by fermentation for plastics with similar properties to the plastics that we use today, but not the same structures as polyethylene or polypropylene, which are not easy to recycle."

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Stinkweed could make a cleaner bio-jet fuel, study finds

A common farm weed could make a "greener" jet fuel with fewer production-related environmental impacts than other biofuels, a new study indicates.

Growing the weed, pennycress -- often called stinkweed -- as a crop requires less fertilizer and fewer pesticides than other plants that can be used to make renewable jet fuel, according to the study. Pennycress also requires fewer farm operations, such as soil tilling, than other potential biofuel crops, reducing the associated environmental costs. Those costs include carbon dioxide emissions that cause the climate to change, as well as other emissions that pollute the air.

Environmental impacts could be further mitigated through farm management techniques that keep fertilizer on fields, rather than allowing it to run off into nearby watersheds, the study suggests. Such techniques can add to the financial cost of growing crops, but reduce their environmental footprints.

"Reducing greenhouse gas emissions from air travel will mean not just incremental changes, but a fundamental change in how we have been producing fuel and where that fuel comes from," said Ajay Shah, senior author of the study and associate professor of food, agricultural and biological engineering at The Ohio State University in Wooster. "And what we found is that pennycress might make a very good alternative fuel, especially when you consider the environmental costs of producing it."

The study was published recently online in the journal Applied Energy.

For this study, the researchers estimated the environmental impacts of growing pennycress, transporting it to a biorefinery and converting it to a usable jet fuel. They also accounted for the environmental costs of burning leftover byproducts of refining the pennycress seed into fuel.

Those environmental costs include fertilizer and pesticide use, water consumption and the energy required to harvest and transport pennycress seeds from a farm to a biorefinery and process them into usable fuel.

The researchers built computer models to determine how much total energy it would take to produce jet fuel from pennycress seeds and compared those estimates with the energy needed for producing biofuels from other crops. The data for the models came from existing studies about biofuel production.

Their models showed that it took about half as much energy to produce jet fuel from pennycress as it did to produce jet fuel from canola or sunflowers, two other potential bio-jet fuel crops. Pennycress oil production used about a third as much energy as soybean oil production, the researchers found, and the energy needed for turning pennycress into jet fuel was about the same as that used to produce fuel from the flowering plant camelina, another biofuel crop.

Renewable jetfuels are not yet financially competitive with fossil fuel-based fuels, Shah said. But calculating the environmental impacts of alternative bio-based fuels should help both farmers and policymakers as they try to limit carbon dioxide in the Earth's atmosphere and, hopefully, to slow or stop climate change.

"Pennycress also makes an appealing alternative jet fuel because of its growing season," Shah said. "It is a winter cover crop that can be grown between corn season and soybean season, giving the same body of farmland an extra production cycle each year.

"Pennycress can be planted when corn is still standing in the field, before the corn harvest," he said. "And it can be harvested before the soybean crops are planted. The bottom line is it can be used as a cover crop, it doesn't divert any agricultural production land, and it has suitable properties for renewable jet fuel production."

Greenhouse gas emissions from air travel contribute to climate change, accounting for about 2% of all human-induced carbon-dioxide emissions, according to various groups that study the effects of transportation on climate change.

"Reducing those emissions will almost certainly mean finding cleaner alternatives to jet fuels made from fossil fuels," Shah said. "Studies like this one can help determine the best alternative.

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Banning the sale of fossil-fuel cars benefits the climate when replaced by electric cars

If a ban were introduced on the sale of new petrol and diesel cars, and they were replaced by electric cars, the result would be a great reduction in carbon dioxide emissions. That is the finding of new research from Chalmers University of Technology, Sweden, looking at emissions from the entire life cycle -- from manufacture of electric cars and batteries, to electricity used for operation. However, the total effect of a phasing out of fossil-fuelled cars will not be felt until the middle of the century -- and how the batteries are manufactured will affect the extent of the benefit.

A rapid and mandatory phasing in of electric cars could cause emissions from Swedish passenger cars' exhausts to approach zero by 2045. The Swedish government has proposed an outright ban on the sale of new fossil fuel cars from the year 2030 -- but that alone will not be enough to achieve Sweden's climate targets on schedule.

"The lifespan of the cars currently on the roads and those which would be sold before the introduction of such a restriction mean that it would take some time -- around 20 years -- before the full effect becomes visible," says Johannes Morfeldt, researcher in Physical Resource Theory at Chalmers University of Technology and lead author of the recently published scientific study.

To have the desired effect, a ban would either need to be introduced earlier, by the year 2025, or, if the ban is not brought in until 2030, then the use of biofuels in petrol and diesel cars needs to increase significantly before then -- in accordance with the revised Swedish "reduction obligation." The combination of these two measures would have the effect of achieving zero emissions from passenger vehicles and keeping to Sweden's climate targets.

"The results from our study show that rapid electrification of the Swedish car fleet would reduce life cycle emissions, from 14 million tonnes of carbon dioxide in 2020 to between 3 and 5 million tonnes by the year 2045. The end result in 2045 will depend mainly on the extent to which possible emission reductions in the manufacturing industry are realised," says Johannes Morfeldt.

A transition from petrol and diesel cars to electric cars will mean an increased demand for batteries. Batteries for electric cars are often criticised, not least for the fact that they result in high levels of greenhouse gas emissions during manufacture.

"There are relatively good opportunities to reduce emissions from global battery manufacturing. Our review of the literature on this shows that average emissions from global battery manufacturing could decrease by about two thirds per kilowatt hour of battery capacity by the year 2045. However, most battery manufacturing takes place overseas, so Swedish decision-makers have more limited opportunities to influence this question," says Johannes Morfeldt.

From a climate perspective, it does not matter where the emissions take place, and the risk with decisions taken at a national level for lowering passenger-vehicle emissions is that they could lead to increased emissions elsewhere -- a phenomenon sometimes termed 'carbon leakage'. In this case, the increase in emissions would result from greater demand for batteries, and the risk is thus greater the higher the emissions from battery production.

In that case, the Swedish decision would not have as great an effect on reducing the climate impact as desired. The life-cycle emissions would end up in the upper range -- around 5 million tonnes of carbon dioxide instead of around 3 million tonnes. Due to this, there may be reason to regulate emissions in both vehicle and battery production, from a life cycle perspective.

"Within the EU, for example, there is a discussion about setting a common standard for the manufacture of batteries and vehicles -- in a similar way as there is a standard that regulates what may be emitted from exhausts," says Johannes Morfeldt.

But, given Sweden's low emissions from electricity production, a ban on sales of new fossil-fuel cars would indeed result in a sharp reduction of the total climate impact, regardless of how the manufacturing industry develops.

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How will we achieve carbon-neutral flight in future?

 Carbon-neutral aviation is possible, but in future, aircraft are likely to continue to be powered by fossil fuels. The CO2 they emit must be systematically stored underground. This is the most economical of various approaches researchers have compared in detail.

It is politically agreed and necessary for climate protection reasons that our entire economy becomes climate-neutral in the coming decades -- and that applies to air travel, too. This is a technically feasible goal, and there are numerous ways to achieve it. ETH Professor Marco Mazzotti and his team have now compared the options that appear to be the easiest to implement in the short and medium term and evaluated them according to factors such as cost-effectiveness.

The ETH researchers conclude that the most favourable option is to continue powering aircraft with fossil fuels in future, but then remove the associated CO2 emissions from the atmosphere using CO2 capture plants and store that CO2 permanently underground (carbon capture and storage, CCS). "The necessary technology already exists, and underground storage facilities have been operating for years in the North Sea and elsewhere," says Viola Becattini, a postdoc in Mazzotti's group and the study's first author.

"The approach may become a cost-competitive mitigation solution for air travel in case, for example, a carbon tax or a cap-and-trade system were imposed on emissions from fossil jet fuels, or if governments were to provide financial incentives for deploying CCS technologies and achieving climate goals," says ETH professor Mazzotti.

Directly or indirectly from the air

Basically, there are two ways to capture CO2: either directly from the air or indirectly at a site where organic material is burned, for example in a waste incineration plant. "Roughly speaking, half of the carbon in the waste burned in municipal incinerators comes from fossil sources, such as plastic that has been produced from petroleum. The other half is organic material, such as wood or wood products like paper and cardboard," Mazzotti says.

From a climate action perspective, capturing and storing the share of carbon that has fossil origin is a zero-sum game: it simply sends carbon that originated underground back to where it came from. As to the share of carbon from organic sources, this was originally absorbed from the air as CO2 by plants, so capturing and storing this carbon is an indirect way to remove CO2 from the air. This means CCS is a suitable method for putting carbon from fossil aviation fuels back underground -- and effectively making air travel carbon-neutral.

In their study, the ETH scientists were able to show that indirect carbon capture from waste incineration gases costs significantly less than direct carbon capture from the air, which is also already technically feasible.

Synthetic fuels more expensive

As a further option, the scientists investigated producing synthetic aviation fuel from CO2 captured directly or indirectly from the air (carbon capture and utilisation, CCU). Because the chemical synthesis of fuel from CO2 is energy-intensive and therefore expensive, this approach is in any case less economical than using fossil fuel and CCS. Regardless of whether the CO2 is captured directly or indirectly, CCU is about three times more expensive than CCS.

ETH Professor Mazzotti also points out one of CCU's pitfalls: depending on the energy source, this approach may even be counterproductive from a climate action perspective, namely if the electricity used to produce the fuel is from fossil fuel-fired power plants. "With Switzerland's current electricity mix or with France's, which has a high proportion of nuclear power, energy-intensive CCU is already more harmful to the climate than the status quo with fossil aviation fuels -- and even more so with the average electricity mix in the EU, which has a higher proportion of fossil fuel-fired power plants," Mazzotti says. The only situation in which CCU would make sense from a climate action perspective is if virtually all the electricity used comes from carbon-neutral sources.

More profitable over time

"Despite this limitation and the fundamentally high cost of CCU, there may be regions of the world where it makes sense. For example, where a lot of renewable electricity is generated and there are no suitable CO2 storage sites," Becattini says.

The ETH researchers calculated the costs of the various options for carbon-neutral aviation not only in the present day, but also for the period out to 2050. They expect CCS and CCU technologies to become less expensive both as technology advances and through economies of scale. The price of CO2 emissions levied as carbon taxes is likely to rise. Because of these two developments, the researchers expect CCS and CCU to become more profitable over time.

Infrastructure required

The researchers emphasise that there are other ways to make air travel carbon-neutral. For instance, there is much research underway into aircraft that run on either electricity or hydrogen. Mazzotti says that while these efforts should be taken seriously, there are drawbacks with both approaches. For one thing, electrically powered aircraft are likely to be unsuitable for long-haul flights because of how much their batteries will weigh. And before hydrogen can be used as a fuel, both the aircraft and their supply infrastructure will have to be completely developed and built from scratch. Because these approaches are currently still in the development stage, with many questions still open, the ETH scientists didn't include them in their analysis and instead focused on drop-in liquid fuels.

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Paper recycling must be powered by renewables to save climate

 Recycling paper may only be helpful to the climate if it is powered by renewable energy, according to a new modelling study by researchers at UCL and Yale.

The study, published in Nature Sustainability, found that greenhouse gas emissions would increase by 2050 if we recycled more paper, as current methods rely on fossil fuels and electricity from the grid.

The researchers modelled various scenarios for increasing recycling of wastepaper by 2050 and the impact this would have on greenhouse emissions. They found that if all wastepaper was recycled, emissions could increase by 10%, as recycling paper tends to rely more on fossil fuels than making new paper.

However, the researchers found that emissions would radically reduce if paper production and disposal were carried out using renewable energy sources rather than fossil fuels.

Making new paper from trees requires more energy than paper recycling, but the energy for this process is generated from black liquor -- the low-carbon by-product of the wood pulping process. In contrast, paper recycling relies on fuels and electricity from the grid.

Researchers found that modernising landfill practices, for instance by capturing methane emissions and using them for energy, also had a positive effect -- although not as profound as moving to renewables.

Lead author Dr Stijn van Ewijk (UCL Institute for Sustainable Resources and Yale Center for Industrial Ecology) said: "Our study shows that recycling is not a guaranteed way to address climate change. Recycling of paper may not be helpful unless it is powered by renewable energy.

"We looked at global averages, but trends may vary considerably in different parts of the world. Our message isn't to stop recycling, but to point out the risk of investing in recycling at the expense of decarbonising the energy supply and seeing very little change to emissions as a result."

Senior author Professor Paul Ekins (UCL Institute for Sustainable Resources) said: "The recycling of some materials, for instance metals, can lead to a very large reduction in emissions. But we need to be careful about assumptions that recycling, or a circular economy in general, will always have a positive effect on climate change."

The researchers emphasized that recycling has benefits beyond combatting global warming. Co-author Professor Julia Stegemann (UCL Civil, Environmental & Geomatic Engineering) said: "Our exponentially increasing consumption of global resources has many seriously damaging environmental impacts beyond climate change, and conserving resources, including by paper recycling, remains critical for sustainability."

The researchers reported that paper accounted for 1.3% of global greenhouse gas emissions in 2012. About a third of these emissions came from the disposal of paper in landfills. Researchers said that in coming years, use of paper would likely rise, with the move away from plastics leading to increased demand for paper packaging.

The study looked at how different levels of recycling, renewable energy use and more environmentally friendly landfill practices might affect our ability to reduce emissions in line with a target to avoid a 2-degrees Celsius temperature rise by 2050.

It found that if past trends continued, emissions would slightly increase from the 2012 level (721 metric tonnes of carbon dioxide equivalent in a year) to 736 metric tonnes in 2050, with efforts to reduce emissions outweighed by increased demand for paper.

A radical programme of recycling, with landfill and energy uses remaining on the same path, would increase this still further by 10% (to 808 metric tonnes), with savings due to a decrease in total energy use outweighed by an increase in the use of high-carbon electricity.

On the other hand, radically modernising landfill practices would reduce emissions to 591 metric tonnes, while moving to renewables, with recycling and landfill practices remaining on the standard path, would reduce emissions by 96% to 28 tonnes.

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Satellite tracking shows how ships affect clouds and climate

By matching the movement of ships to the changes in clouds caused by their emissions, researchers have shown how strongly the two are connected.

When ships burn fossil fuels, they release airborne particles containing various naturally occurring chemicals, including sulphur. These particles are known to modify certain types of clouds, which can affect climate.

Better knowledge of how these particles, and particularly the sulphur components, affect clouds could help scientists create more accurate climate models.

In the latest study, satellite tracking was also used to show the impact of restrictions on sulphur in fuels, revealing the impact of ships on clouds largely disappears in restricted zones.

This information can be used to build a relationship between cloud properties and the sulphur content of shipping fuels. Importantly, this could help shipping companies monitor compliance with sulphur regulations that come into force on 1 January 2020.

The study, published today in Geophysical Research Letters, was led by researchers from Imperial College London, together with University College London and the University of Oxford.

Emissions from ships contain several chemicals, including sulphate aerosols -- small particles of sulphur and oxygen. The aerosols can act as 'seeds' around which water droplets accumulate, causing changes in cloud properties that are visible to satellites.

This means that ships can change clouds, leaving lines -- known as ship tracks -- in the clouds behind them as they sail.

However, exactly how these aerosols impact the properties of the clouds is not precisely known. This knowledge is important because the kinds of clouds that the emissions affect can influence climate warming, and is therefore important to capture in climate models.

Aerosol are emitted from many sources, such as factories and cars, but it has been difficult to match these outputs with the influence on clouds, as there are many other factors at play.

However, with ship tracks, the relationship is more straightforward, enabling researchers to tease out the links between aerosols and clouds more easily.

Lead researcher Dr Edward Gryspeerdt, from the Department of Physics at Imperial, said: "Ship tracks act like an experiment that would be impossible for us to do otherwise -- we cannot inject sulphate aerosols into the atmosphere at such scale to see what happens.

"Instead, restrictions on the amount of ship sulphate emissions can contain provide us with a perfect experiment for determining just how important the aerosols are in cloud formation. By analysing a huge dataset of ship tracks observed from satellites, we can see that they largely disappear when restrictions are introduced, demonstrating the strong impact of aerosols."

The team studied more than 17,000 ship tracks from satellite observations and matched them to the movements of individual ships using their onboard GPS.

The study period covered the introduction of emission control areas around the coast of North America, the North Sea, the Baltic Sea and the English Channel, which restricted sulphur in ship fuel to 0.5 percent, leading to fewer sulphate aerosol emissions.

The researchers found that in these areas, ship tracks nearly completely disappeared compared to before the restrictions, under similar weather conditions.

This shows that sulphate aerosols have the most significant impact on cloud formation, as opposed to other components of the ship exhaust, such as black carbon.

The result also means that a ship not in compliance with the regulations, by burning the current high-sulphur fuels without exhaust treatment, could be detected because it would create a measurable difference in the satellite-observed cloud properties.

Co-author Dr Tristan Smith, from UCL's Energy Institute, said: "Currently, it is hard for regulators to know what ships are doing in the middle of the ocean. The potential for undetected non-compliance with the 2020 sulphur regulations is a real risk for shipping companies because it can create commercial advantage to those companies who do not comply.

"This study shows that science and technology are producing significant advancements in the transparency of shipping, and helping to reduce risks and unfairness for responsible operators."

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