New study points to more climate extremes

A new study has found similarities between long-term climatic changes in South Australia and temperate agricultural areas in Argentina -- highlighting similarities across these Southern Hemisphere countries.

As temperature records tumble, and the threat of bushfires and dry conditions looms large, an international study by Flinders University and Argentinian researchers renews the urgency of calls to make more concerted efforts to prepare for climate extremes in South Australia.

Highs and lows in temperature and rainfall indices over the past 50 years have shown an increase in maximum and minimum temperatures of 1.1°C and 0.7°C and less precipitation while pointing to more intense and extended drought periods, extreme summer heatwaves alongside occasional extremes such as frost and flood.

South Australia -- often cited as the driest state on the driest continent -- is poised to see more weather extremes in temperature and precipitation with more storm events, longer and more severe droughts and higher temperature peaks up to 3-5°C above current averages likely to follow global trends, the study shows.

"We found remarkable warming signal trends in both hot and cold extreme weather events," says Universidad Nacional del Sur researcher Dr Federico Ferrelli in a new article supported by Argentina's National Scientific and Technical Research Council.

"This reminds us that we need to focus on climate change mitigation and adapt sustainable management plans to better buffer ecosystems and human health and wellbeing, particularly in areas most exposed to these extreme weather patterns."

Flinders University co-author Professor Patrick Hesp, an expert in coastal dune systems, says that if SA's rainfall continue to decline according to such forecasts, "we can expect to see increased soil erosion in dryland agricultural regions and greater mobility of coastal dune systems -- especially on western coast areas where mean annual rainfall is already quite low."

The researchers used 24 climate extreme indices based on Bureau of Meteorology data to find a significant increase in extreme hot events -- including summer days and tropical night temperatures -- as well as daily maximum and daily minimum temperatures.

While cold indices such as frost days show negative trends, heavy and extreme storms have become more severe locally while rain decreases regionally.

Land management practices, including less land clearance, native plant revegetation and more sustainable agricultural practices, is one step in the right direction.

While Argentina and Australia are economically different countries, the researchers emphasise that the imminent impacts of climate change are reflected in both temperate climate zones in the Southern Hemisphere and impacting on a global scale.

For instance, the Pampas Region in Argentina has experienced substantial increases in maximum, minimum and mean temperatures (1.8 °C, 1.2 °C, and 1.2 °C respectively), with some areas affected by falling precipitation and rising aridity.

"Therefore it is imperative to develop sustainable land management policies to address these issues," researchers say.

"Global warming effects ecosystems, biodiversity, agriculture and food security, water resources, and human health and wellbeing.

"It also contributes to economic and social inequities as vulnerable populations and developing countries are often the hardest hit by the effects of climate change."

Including SA's rising 1.8 million population, extreme temperatures could severely impact cardiovascular and respiratory diseases, vector-borne diseases and affect mortality rates, the researchers warn.

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Massive 2022 eruption reduced ozone layer levels

When the Hunga Tonga-Hunga Ha'apai volcano erupted on January 15, 2022 in the South Pacific, it produced a shock wave felt around the world and triggered tsunamis in Tonga, Fiji, New Zealand, Japan, Chile, Peru and the United States. It also changed the chemistry and dynamics of the stratosphere in the year following the eruption, leading to unprecedented losses in the ozone layer of up to 7% over large areas of the Southern Hemisphere, according to a recent study published in the Proceedings of the National Academy of Sciences (PNAS) from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and the University of Maryland.

Driving those atmospheric changes, according to the research, was the sheer amount of water vapor injected into the stratosphere by the undersea volcano.

The location of the stratosphere is approximately 8 -- 30 miles above Earth's surface and is where the protective ozone layer resides.

"The Hunga Tonga-Hunga Ha'apai eruption was truly extraordinary in that it injected about 300 billion pounds of water into the normally dry stratosphere, which is just an absolutely incredible amount of water from a single event," said David Wilmouth, a project scientist at SEAS and first author of the paper.

"This eruption put us in uncharted territory," said Ross Salawitch, professor at the University of Maryland's Earth System Science Interdisciplinary Center and co-author of the study.

"We've never seen, in the history of satellite records, this much water vapor injected into the atmosphere and our paper is the first that looks at the downstream consequences over broad regions of both hemispheres in the months following the eruption using satellite data and a global model."

The Hunga Tonga-Hunga Ha'apai eruption was the largest explosion ever recorded in the atmosphere.

The eruption hurled aerosols and gases deep into the stratosphere.

Some material reached the lower mesosphere, more than 30 miles above the Earth's surface, altitudes never recorded from a volcanic eruption.

Previous studies found that the eruption increased water vapor in the stratosphere by 10% worldwide, with even higher concentrations in some areas of the Southern Hemisphere.

Wilmouth, Salawitch and the rest of the research team used data from the Microwave Limb Sounder (MLS) aboard the NASA Aura satellite, to track not only how that water vapor moved across the globe but also monitor temperature and levels of chlorine monoxide (ClO), ozone (O3), nitric acid (HNO3), and hydrogen chloride (HCl) in the stratosphere for the year following the eruption.

They then compared those measurements to data collected by MLS from 2005 to 2021 prior to the eruption.

The team found that the injection of water vapor and sulfur dioxide (SO2) changed both the chemistry and the dynamics of the stratosphere.

In terms of chemistry, the SO2 led to an increase of sulfate aerosols, which provided new surfaces for chemical reactions to occur.

"Certain reactions that might not happen at all or only happen slowly can happen faster if there are aerosols available on which those reactions can take place," said Wilmouth.

"The injection of SO2 from the volcano allowed sulfate aerosols to form and the presence of water vapor led to the additional production of sulfate aerosols."

The increased sulfate aerosols and water vapor kicked off a chain of events in the complex atmospheric chemistry that led to widespread changes in the concentrations of a number of compounds, including ozone.

The extra water vapor also had a cooling effect in the stratosphere, leading to a change in circulation, which drove decreases in ozone in the southern hemisphere and an increase of ozone over the tropics.

The researchers found that the peak decrease in ozone occurred in October, nine months after the eruption.

"We had this enormous increase in water vapor in the stratosphere with modest increases in sulfate that set off a series of events that led to significant changes in temperature and circulation, ClO, HNO3, HCl, O3, and other gases," Wilmouth said.

Next, the researchers hope to continue the study by following the impact of the volcano into 2023 and beyond as the water vapor moves from the tropics and midlatitudes to the Southern Hemisphere pole, where it has the potential to amplify ozone losses in the Antarctic.

The water vapor is expected to stay elevated in the stratosphere for a period of several years.

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Palms at the poles: Fossil plants reveal lush southern hemisphere forests in ancient hothouse climate

For decades, paleobotanist David Greenwood has collected fossil plants from Australia -- some so well preserved it's hard to believe they're millions of years old. These fossils hold details about the ancient world in which they thrived, and Greenwood and a team of researchers including climate modeler and research David Hutchinson, from the University of New South Wales, and UConn Department of Geosciences paleobotanist Tammo Reichgelt, have begun the process of piecing together the evidence to see what more they could learn from the collection. Their findings are published in Paleoceanography & Paleoclimatology.

The fossils date back 55 to 40 million years ago, during the Eocene epoch. At that time, the world was much warmer and wetter, and these hothouse conditions meant there were palms at the North and South Pole and predominantly arid landmasses like Australia were lush and green. Reichgelt and co-authors looked for evidence of differences in precipitation and plant productivity between then and now.

Since different plants thrive under specific conditions, plant fossils can indicate what kinds of environments those plants lived in.

By focusing on the morphology and taxonomic features of 12 different floras, the researchers developed a more detailed view of what the climate and productivity was like in the ancient hothouse world of the Eocene epoch.

Reichgelt explains the morphological method relies on the fact that the leaves of angiosperms -- flowering plants -- in general have a strategy for responding to climate.

"For example, if a plant has large leaves and it is left out in the sun and doesn't get enough water, it starts to shrivel up and die because of excess evaporation," Reichgelt says. "Plants with large leaves also lose heat to its surroundings. Finding a large fossil leaf therefore means that most likely this plant was not growing in an environment that was too dry or too cold for excess evaporation or sensible heat loss to happen. These and other morphological features can be linked to the environment that we can quantify. We can compare fossils to modern floras around the world and find the closest analogy."

The second approach was taxonomic. "If you travel up a mountain, the taxonomic composition of the flora changes. Low on the mountain, there may be a deciduous forest that is dominated by maples and beeches and as you go further up the mountain, you see more spruce and fir forest," says Reichgelt. "Finding fossils of beech and maple therefore likely means a warmer climate then if we find fossils of spruce and fir." Such climatic preferences of plant groups can be used to quantitatively reconstruct the ancient climate in which a group of plants in a fossil assemblage was growing.

The results show that the Eocene climate would have been very different to Australia's modern climate. To sustain a lush green landscape, the continent required a steady supply of precipitation. Warmth means more evaporation, and more rainfall was available to move into Australia's continental interior. Higher levels of carbon dioxide in the atmosphere at the time, 1500 to 2000 parts per million, also contributed to the lushness via a process called carbon fertilization. Reichgelt explains that with the sheer abundance of CO2, plants were basically stuffing their faces.

"Southern Australia seems to have been largely forested, with primary productivity similar to seasonal forests, not unlike those here in New England today," Reichgelt says. "In the Northern Hemisphere summer today, there is a big change in the carbon cycle, because lots of carbon dioxide gets drawn down due to primary productivity in the enormous expanse of forests that exists in a large belt around 40 to 60 degrees north. In the Southern Hemisphere, no such landmass exists at those same latitudes today. But Australia during the Eocene occupied 40 degrees to 60 degrees south. And as a result, there would be a highly productive large landmass during the Southern Hemisphere summer, drawing down carbon, more so than what Australia is doing today since it is largely arid."

Hutchinson says the geological evidence suggests the climate is highly sensitive to CO2 and that this effect may be larger than what our climate models predict, "The data also suggests that polar amplification of warming was very strong, and our climate models also tend to under-represent this effect. So, if we can improve our models of the high-CO2 Eocene world, we might improve our predictions of the future."

Future projects will expand the data set beyond Australia to ask what global productivity does during a hothouse climate on a global scale.

"We have large datasets of plant fossils that have been collected around the world, so we can apply the same methods that we use here to ask what happens to global biosphere productivity," says Reichgelt.

With increasing carbon emissions, there is more research going into studying what happens in the biosphere with increased photosynthetic activity and water use efficiency in plants. Reichgelt explains that modern plants have not had the time to evolve to changing CO2 conditions. However, by looking to the past, we can glean some of that information.

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