In a warming world, climate scientists consider category 6 hurricanes

For more than 50 years, the National Hurricane Center has used the Saffir-Simpson Windscale to communicate the risk of property damage; it labels a hurricane on a scale from Category 1 (wind speeds between 74 -- 95 mph) to Category 5 (wind speeds of 158 mph or greater).

But as increasing ocean temperatures contribute to ever more intense and destructive hurricanes, climate scientists Michael Wehner of Lawrence Berkeley National Laboratory (Berkeley Lab) and James Kossin of the First Street Foundation wondered whether the open-ended Category 5 is sufficient to communicate the risk of hurricane damage in a warming climate.

So they investigated and detailed their extensive research in a new article published in the Proceedings of the National Academy of Sciences (PNAS), where they also introduce a hypothetical Category 6 to the Saffir-Simpson Wind Scale, which would encompass storms with wind speeds greater than 192 mph.

"Our motivation is to reconsider how the open-endedness of the Saffir-Simpson Scale can lead to underestimation of risk, and, in particular, how this underestimation becomes increasingly problematic in a warming world," said Wehner, who has spent his career studying the behavior of extreme weather events in a changing climate and to what extent human influence has contributed to individual events.

According to Wehner, anthropogenic global warming has significantly increased surface ocean and tropospheric air temperatures in regions where hurricanes, tropical cyclones, and typhoons form and propagate, providing additional heat energy for storm intensification.

When the team performed a historical data analysis of hurricanes from 1980 to 2021, they found five storms that would have been classified as Category 6, and all of them occurred in the last nine years of record.

They determined a hypothetical upper bound for Category 5 hurricanes by looking at the expanding range of wind speeds between the lower-category storms.

Hurricanes, tropical storms, and typhoons are essentially the same weather phenomenon; their name difference is purely geographical: storms in the North Atlantic and Northeast Pacific Oceans are called hurricanes, events in the Northwest Pacific Ocean are called typhoons, and occurrences in the South Pacific and Indian Oceans are called tropical cyclones.

In addition to studying the past, the researchers analyzed simulations to explore how warming climates would impact hurricane intensification.

Their models showed that with two degrees Celsius of global warming above pre-industrial levels, the risk of Category 6 storms increases by up to 50% near the Philippines and doubles in the Gulf of Mexico and that the highest risk of these storms is in Southeast Asia, the Philippines, and the Gulf of Mexico.

"Even under the relatively low global warming targets of the Paris Agreement, which seeks to limit global warming to just 1.5°C above preindustrial temperatures by the end of this century, the increased chances of Category 6 storms are substantial in these simulations," said Wehner.

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Unprecedented ocean heating shows risks of a world 3°C warmer

Record-high ocean temperatures observed in 2023 could become the norm if the world moved into a climate that is 3.0°C warmer than pre-industrial levels, according to a new study.

From March 2023, the North Atlantic began to show extremely warm temperatures far exceeding anything seen in the past 40 years.

As of August 2023, the North Atlantic was about 1.4°C warmer than the 1982-2011 average.

Analysis of climate model projections showed that last year's extreme ocean conditions were similar to what scientists expect to be the average if global warming reaches 3°C of warming.

Currently, global temperatures have risen by about 1.2°C above pre-industrial levels.

New research, published this month in the Bulletin of the American Meteorological Society, examines the causes of the record-breaking ocean temperatures witnessed in 2023.

Dr Till Kuhlbrodt, of the University of Reading, led the study.

He said: "The extraordinary heat in the North Atlantic and missing sea ice in the Southern Ocean in 2023 tell us the oceans are sounding an alarm. We urgently need to understand exactly why parts of the ocean are warming rapidly so we can prepare for more frequent weather disruption across the planet. How often we get hit by more of these extremes hangs on figuring out what's driving the Atlantic and Southern Oceans into uncharted territory."

Climate connection?

The study highlights that Earth's energy imbalance is likely a key driver of extreme ocean temperatures, as the planet is currently absorbing more than 1.9 watts per square meter more solar energy than it radiates back to space as heat.

Across Earth, over a time span of one year, this is equivalent to roughly 300 times the global annual consumption of electric energy.

This imbalance has grown fast over recent decades mainly due to heat-trapping gases from human activity.

This increasing energy surplus is propelling ocean warming, with more than 90% of the excess energy accumulated by Earth being funnelled into the oceans.

Since 2016 the Atlantic Ocean has warmed faster than other ocean basins in the top 100 meters of ocean.

This enhanced Atlantic warming may be linked to record low levels of sea ice in the Southern Ocean, the researchers suggest.

The rapid Atlantic warming has coincided with a sharp decline in sea ice cover surrounding Antarctica.

In 2023, Antarctic winter sea ice extent reached by far the lowest levels since satellite monitoring began in the late 1970s.

The researchers emphasise the need to quantify how much the rapid Atlantic warming is impacting sea ice cover.

Reliably attributing the oceanic and sea ice extremes will ensure climate models can accurately predict future extremes, which will inform mitigation policies and resilience measures across the globe.

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Multiple ecosystems in hot water after marine heatwave surges across the Pacific

Rising ocean temperatures are sweeping the seas, breaking records and creating problematic conditions for marine life. Unlike heatwaves on land, periods of abrupt ocean warming can surge for months or years. Around the world these 'marine heatwaves' have led to mass species mortality and displacement events, economic declines and habitat loss. New research reveals that even areas of the ocean protected from fishing are still vulnerable to these extreme events fueled by climate change.

A study published today in Global Change Biology, led by researchers at UC Santa Barbara, found that while California's network of marine protected areas (MPAs) provide many social and ecological benefits, they are not resilient to the effects of ocean warming. MPAs are locations in the ocean where human activities such as fishing are restricted to conserve and protect marine ecosystems, habitats, species and cultural resources. The study, part of a 10-year review of California's MPA network conducted at UCSB's National Center for Ecological Analysis & Synthesis (NCEAS), found that marine heatwaves impact ecological communities regardless of whether they are protected inside MPAs.

"MPAs in California and around the world have many benefits, such as increased fish abundance, biomass and diversity," said Joshua Smith, who led the study while he was a postdoctoral researcher at NCEAS . "But they were never designed to buffer the impacts of climate change or marine heatwaves."

Smith and co-authors from all over the world were part of an NCEAS working group formed to synthesize decades of long-term ecological monitoring data from California's diverse ocean habitats. The group, co-led by Jenn Caselle, a researcher with UCSB's Marine Science Institute, and Kerry Nickols, a professor from Cal State University Northridge who now works with the non-profit Ocean Visions, aimed to provide actionable scientific results to California's policy makers and natural resource managers, as part of a statewide Decadal Evaluation of the MPA network. Their analyses spanned the largest marine heatwave on record, which rolled through the Pacific Ocean toward California from 2014-2016. The monster marine heatwave was formed from an environmental double-whammy -- unusual ocean warming nicknamed "The Blob," followed by a major El Niño event that prolonged the sweltering sea temperatures. The marine heatwave blanketed the West Coast from Alaska to Baja and left a wake of altered food webs, collapsed fisheries, and shifted populations of marine life among various other consequences.

As MPA managers around the world face increasing climate shocks, the extent to which MPAs can buffer the worst of these events has become an important question. The working group scientists asked how the ecological communities in California's protected areas fared after such a severe and prolonged heatwave: Would the communities shift and if so, how? Would they 'bounce back' when the marine heatwave subsided? Could the marine protected areas protect sensitive populations or facilitate recovery?

To find answers to their questions, they synthesized over a decade of data collected from 13 no-take MPAs located in a variety of ecosystems along the Central Coast: rocky intertidal zones, kelp forests, shallow and deep rocky reefs. The team looked at fish, invertebrates and seaweed populations inside and outside these areas, using data from before, during and after the heatwave.

They also focused on two of these habitats, rocky intertidal and kelp forests, at 28 MPAs across the full statewide network to gauge whether these locations promoted one particular form of climate resilience -- maintaining both population and community structure.

"We used no-take MPAs as a type of comparison to see whether the protected ecological communities fared better to the marine heatwave than places where fishing occurred," said Smith, now an Ocean Conservation Research Fellow at Monterey Bay Aquarium.

The results are somewhat sobering, though not altogether unexpected.

"The MPAs did not facilitate resistance or recovery across habitats or across communities," Caselle said. "In the face of this unprecedented marine heatwave, communities did change dramatically in most habitats. But, with one exception, the changes occurred similarly both inside and outside the MPAs. The novelty of this study was that we saw similar results across many different habitats and taxonomic groups, from deepwater to shallow reefs and from fishes to algae."

The implication of these findings, according to Smith, is that every part of the ocean is under threat from climate change. "MPAs are effective in many of the ways they were designed, but our findings suggest that MPAs alone are not sufficient to buffer the effects of climate change."

The key question now is what will happen in the future? At the time of this study using data through 2020, the ecological communities have not returned to their former, pre-heatwave state. According to the paper, these ecological communities shifted toward a "pronounced decline in the relative proportion of cold-water species and an increase in warm water species." For example, increases in the abundance of the señorita fish (Oxyjulis californica), a subtropical species with warm water affinity and previously rare in central California, had an outsized influence on the shift of communities. Whether these species persist in their new locations remains to be seen.

"This study makes it clear why long-term monitoring of California's MPAs is so critical," said Caselle. "Some of these time series are longer than 25 years at this point and the data are critical to understanding and readying human communities for the changes occurring in our marine communities." Continued study will show if future shifts in marine communities occur at different rates or to different base states in MPAs compared to fished areas.

Despite the limited ability of MPAs to resist the grip of the marine heatwave, they do confer benefits, not the least of which is the ability to study the complex effects of climate change in areas not impacted by fishing. As areas of minimal human interference that are regularly monitored, they present opportunities to study the response of marine ecosystems to shifting conditions and potentially tailor management techniques accordingly. Moreover, as Smith stated, "the ecological communities in MPAs are still being protected, even if they are different as a result of the heatwave. Given that marine heatwaves are anticipated to increase in frequency and magnitude into the future, swift climate action and nature-based solutions are needed as additional pathways to enhance the health of our oceans."

Kerry Nickols adds, "With the devastating impacts of climate change already apparent, it is very important that we are upfront about climate solutions -- as long as we are burning fossil fuels and warming the globe marine ecosystems will be at risk, even if they are protected from fishing."

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A once-stable glacier in Greenland is now rapidly disappearing

As climate change causes ocean temperatures to rise, one of Greenland's previously most stable glaciers is now retreating at an unprecedented rate, according to a new study.

Led by researchers at The Ohio State University, a team found that between 2018 and 2021, Steenstrup Glacier in Greenland has retreated about 5 miles, thinned about 20%, doubled in the amount of ice it discharges into the ocean, and quadrupled in velocity. According to the study, such a rapid change is so extraordinary among Greenland ice formations that it now places Steenstrup in the top 10% of glaciers that contribute to the entire region's total ice discharge.

The study was published today in Nature Communications.

The Steenstrup Glacier is part of The Greenland Ice Sheet, a body of ice that covers nearly 80% of the world's largest island, which is also the single largest contributor to global sea rise from the cryosphere, the portion of Earth's ecosystem that includes all of its frozen water. While the region plays a crucial part in balancing the global climate system, the area is steadily shrinking as it sheds hundreds of billions of tons of ice each year because of global warming.

Over the past few decades, much of this loss has been attributed to accelerated ice discharge from tidewater glaciers, glaciers that make contact with the ocean. Many glaciologists believe that this recent uptick in ice discharge can be explained by the intrusion of warming waters that are being swept from the Atlantic into Greenlandic fjords -- critical oceanic gateways that can impact the stability of local glaciers and the health of polar ecosystems.

The research team aimed to test that theory by examining a glacier in the southeastern region of Greenland called K.I.V Steenstrups Nordre Bræ, an entity more colloquially known as the Steenstrup Glacier.

"Up until 2016, there was nothing to suggest Steenstrup was in any way interesting," said Thomas Chudley, lead author of the study, who completed this work as a research associate at the Byrd Polar and Climate Research Center. Chudley is now a Leverhulme research fellow at Durham University in the UK.

"There were plenty of other glaciers in Greenland that had retreated dramatically since the 1990s and increased their contribution to sea level rise, but this really wasn't one of them."

As far as scientists knew, Steenstrup had not only been stable for decades but was generally insensitive to the rising temperatures that had destabilized so many other regional glaciers, likely because of its isolated position in shallow waters.

It wasn't until Chudley and his colleagues compiled observational and modeling data from previous remote sensing analyses on the glacier that the team realized Steenstrup was likely experiencing melt due to anomalies in deeper Atlantic water.

"Our current working hypothesis is that ocean temperatures have forced this retreat," Chudley said. "The fact that the glacier's velocity has quadrupled in just a few years opens up new questions about how fast large ice masses can really respond to climate change."

In recent years, glaciologists have been able to use satellite data to estimate the potential volume of glacial ice stored at the poles and how it might affect current sea levels. For instance, if the Greenland Ice Sheet were to melt, Earth's sea levels could rise by nearly 25 feet. In contrast, if the ice sheet in Antarctica were to fall apart, it's possible that oceans would rise by nearly 200 feet, Chudley said.

While Greenland and Antarctica would take centuries to collapse completely, the global cryosphere has the potential to cause sea levels to rise about six feet this century if the West Antarctic Ice Sheet undergoes collapse.

As around 10% of the planet's population lives in low-lying coastal zones, Chudley said that any significant rise in sea level can cause increased risk to low-lying islands and coastal communities from storm surges and tropical cyclones.

In the United States, sea level rise poses a particular risk to coastal cities in places like Florida or Louisiana, Chudley said. But that doesn't necessarily mean it's too late to stop such a future from happening. If climate policies evolve rapidly, humans might have a chance at halting the worst of sea level rise, Chudley said.

Overall, Steenstrup's unique behavior reveals that even long-term stable glaciers are susceptible to sudden and rapid retreat as warmer waters begin to intrude and influence new environments.

While the research says continued scientific observation of the Steenstrup Glacier should be a priority, it concludes other similar glaciers also deserve attention because of their potential to retreat due to warming waters.

Understanding more about these interactions could provide key insight into how glaciers thrive in other locations around the world and even become an indicator of how these environments might change in the future.

"What's happening in Greenland right now is kind of the canary in the coal mine of what might happen in West Antarctica over the next few centuries," Chudley said. "So it would be great to be able to get into the fjord with real on-the-ground observations and see how and why Steenstrup has changed."

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