Amazing Science

While conducting a study of Petermann Glacier in northwest Greenland, researchers at the University of California, Irvine and NASA's Jet Propulsion Laboratory uncovered a previously unseen way in which the ice and ocean interact. The glaciologists said their findings could mean that the climate community has been vastly underestimating the magnitude of future sea level rise caused by polar ice deterioration.

Using satellite radar data from three European missions, the UCI/NASA team learned that Petermann Glacier's grounding line -- where ice detaches from the land bed and begins floating in the ocean -- shifts substantially during tidal cycles, allowing warm seawater to intrude and melt ice at an accelerated rate. The group's results are the subject of a paper published in Proceedings of the National Academy of Sciences.

"Petermann's grounding line could be more accurately described as a grounding zone, because it migrates between 2 and 6 kilometers as tides come in and out," said lead author Enrico Ciraci, UCI assistant specialist in Earth system science and NASA postdoctoral fellow. "This is an order of magnitude larger than expected for grounding lines on a rigid bed."

He said the traditional view of grounding lines beneath ocean-reaching glaciers was that they did not migrate during tidal cycles, nor did they experience ice melt. But the new study replaces that thinking with knowledge that warm ocean water intrudes beneath the ice through preexisting subglacial channels, with the highest melt rates occurring at the grounding zone.

The researchers found that as Petermann Glacier's grounding line retreated nearly 4 kilometers -- 2½ miles -- between 2016 and 2022, warm water carved a 670-foot-tall cavity in the underside of the glacier, and that abscess remained there for all of 2022. "These ice-ocean interactions make the glaciers more sensitive to ocean warming," said senior co-author Eric Rignot, UCI professor of Earth system science and NASA JPL research scientist.

"These dynamics are not included in models, and if we were to include them, it would increase projections of sea level rise by up to 200 percent -- not just for Petermann but for all glaciers ending in the ocean, which is most of northern Greenland and all of Antarctica."

The Greenland ice sheet has lost billions of tons of ice to the ocean in the past few decades, the PNAS paper stresses, with most of the loss caused by warming of subsurface ocean waters, a product of Earth's changing climate. Exposure to ocean water melts the ice vigorously at the glacier front and erodes resistance to the movement of glaciers over the ground, causing the ice to slide more quickly to the sea, according to Rignot.

As fossil fuel use continues to climb and a hotter planet edges closer to passing any safety limits, some scientists are exploring a controversial technological stopgap: spraying chemicals into the atmosphere to reflect away some of the sun's sunlight. Deploying the technology, using special planes, would be relatively cheap and simple, costing a few billion dollars a year, its backers say. And it could - if maintained - hold down global average temperatures, potentially staving off increasingly deadly climate-change impacts such as heatwaves, they argue.

"I do see it as a likely option" if plans to cut emissions fall short and dangers grow, said Emmi Yonekura, a researcher on the risks of climate "geoengineering" at RAND Corporation, a military-focused policy think-tank, during an online event.  But the technology, which mimics the sky-darkening effect of volcanic eruptions, also carries serious and unpredictable risks, critics say - with some scientists so worried that they believe research should stop and outdoor tests be banned. Threats range from potential shifts in rainfall patterns that could spur worsening hunger to rapid, uncontrollable temperature rise if the technology's use is suddenly stopped. The availability of such a planet-cooling option could also give climate polluters an unwarranted green-light to carry on - even though "stratospheric aerosol injection" (SAI) would only mask the problem, not solve it.

Early efforts to create rules to govern its use show signs of stalling, critics warn, making it more likely that one powerful state or even individual could go it alone, potentially to the detriment of others, sparking conflict. "The more we see extreme events like hurricanes, wildfires, also just heatwaves that have acute impacts - those may motivate key actors to try to protect themselves," said Jonathan Wiener, co-director of the Duke Center on Risk. Unilateral use of the technology "might be very difficult to deal with geopolitically", said Wiener, a law and environmental policy professor at Duke University in the United States. Where scientists and policy experts agree is that, as the world speeds towards the lower 1.5 degree-Celsius warming limit set in the Paris Agreement, serious thinking about what happens if the Earth's climate breaks down must happen - fast.

"We are now entering a situation where the likelihood of overshooting 1.5˚C degrees is higher than not overshooting it," said Janos Pasztor, executive director of the Carnegie Climate Governance Initiative (C2G), a think-tank focused on how to manage "climate-altering technologies".  With the world still "very far" from taking the aggressive steps needed to limit climate change, the impacts of a warming planet will worsen - and in some cases be "catastrophic", he warned. That means more extreme ways to cool the climate are now on the table. Pasztor told an online event it was important to weigh up the risks of taking such measures against not taking them. "Simply not doing either anything or enough ... in itself has huge risks," he said.

Tipping Points

To effectively limit warming, climate-heating emissions - largely from burning fossil fuels - need to fall 45% globally by 2030, scientists say. Instead, they are still rising, as oil and gas use continues to grow and investment in renewable energy alternatives lags. Scientists with the Intergovernmental Panel on Climate Change (IPCC) have warned that if global average temperatures exceed 1.5C above pre-industrial times, the world could see changes that will be hard to adapt to.  Those could include surging hunger as crops fail, as well as growing water shortages, migration and conflict. Deaths and financial losses from worsening heatwaves, wildfires, droughts, floods, hurricanes and sea level rise could also increase, affecting rich countries as well as poor.

More heat could melt Arctic and ocean permafrost that holds climate-heating methane, turbo-charging temperature rise and launching the planet into a vicious heating cycle that would be hard to reverse, scientists say. Some impacts of passing 1.5˚C - such as likely losses of many of the world's coral reefs - "will be irreversible, even if global warming is reduced", warned Thelma Krug, a climate scientist and vice chair of the IPCC.  With the World Meteorological Organization projecting that the 1.5C threshold could be passed, at least temporarily, within five years, a Climate Overshoot Commission of 16 world leaders was launched in May. 

It will look at controversial sun-dimming technologies, alongside efforts to remove carbon dioxide from the atmosphere and to adapt to new conditions.

SAI research has won some powerful financial backers, including Bill Gates and a range of venture capitalists and philanthropists, including at least one former oil executive.

A shutdown would have devastating global impacts and must not be allowed to happen, researchers say

Climate scientists have detected warning signs of the collapse of the Gulf Stream, one of the planet’s main potential tipping points. The research found “an almost complete loss of stability over the last century” of the currents that researchers call the Atlantic meridional overturning circulation (AMOC). The currents are already at their slowest point in at least 1,600 years, but the new analysis shows they may be nearing a shutdown.

Such an event would have catastrophic consequences around the world, severely disrupting the rains that billions of people depend on for food in India, South America and West Africa; increasing storms and lowering temperatures in Europe; and pushing up the sea level in the eastern North America. It would also further endanger the Amazon rainforest and Antarctic ice sheets.

The complexity of the AMOC system and uncertainty over levels of future global heating make it impossible to forecast the date of any collapse for now. It could be within a decade or two, or several centuries away. But the colossal impact it would have means it must never be allowed to happen, the scientists said.

“The signs of destabilization being visible already is something that I wouldn’t have expected and that I find scary,” said Niklas Boers, from the Potsdam Institute for Climate Impact Research in Germany, who did the research. “It’s something you just can’t allow to happen.”

It is not known what level of CO2 would trigger an AMOC collapse, he said. “So the only thing to do is keep emissions as low as possible. The likelihood of this extremely high-impact event happening increases with every gram of CO2 that we put into the atmosphere”.

Three years ago, the place you are reading about now did not exist. Then, suddenly, an underwater volcano erupted in the middle of the South Pacific, and by the time the smoke and ash cleared, a new land mass stood revealed – an island that no-one had ever seen before. That's how the volcanic island of Hunga Tonga-Hunga Ha'apai (Hunga Tonga) came into the world in January 2015, nestling in between two existing, uninhabited Polynesian islands that make up part of the Kingdom of Tonga.

In the last 150 years, only three volcanic islands have emerged like this and survived for more than a few months, with the most famous of them being Surtsey – which appeared off the southern coast of Iceland during a four-year eruption that began in 1963. Scientists have studied Surtsey for decades, but Hunga Tonga – informally named after the submarine volcano above which it sits – is set apart by being the only kind of island like this to emerge in the era of the modern satellite, which gives us a whole new way of studying how these rocky land masses evolve. For example, just for fun, if you do a search for 'Hunga Tonga' in Google Maps' regular Maps view, you'll see an outdated illustration of two islands separated by an expanse of blue water. But if you flick the switch to Satellite view, the newly born island is revealed in all its glory.

That kind of perspective is what intrigues scientists, who are using satellite data to learn what they can about such volcanic upstarts, before erosion inevitably sees Hunga Tonga vanish away again under the waves. "There's a huge amount of material that came out from this eruption, possibly larger than at Surtsey," says geologist Vicki Ferrini from Columbia University, who is studying the island with researchers from NASA. "The other interesting thing is that the two islands that surround this new land mass have some pretty tough substrate, so there's something happening to help make this solidify and stay in place, chemically."

Initially, scientists estimated Hunga Tonga might only last for a few months before disappearing, but researchers now think the island – which covers some 200 hectares (nearly 500 acres) and extends as high as 120 meters (400 feet) above the ocean – could survive for as long as 30 years. Using satellite data updated in real time, the team is developing 3D maps of the island's topography, studying its shifting coastlines and the amount of its land that sits above sea level.

A new study finds that the Atlantic Ocean just had its hottest decade in at least 2,900 years. The new findings are published in the Proceedings of the National Academy of Sciences on Monday, and are another sign the climate is entering an unprecedented state.

More than 20 years after intoning, “The water’s getting warm, so you might as well swim,” Smash Mouth’s “All Star” continues to be prophetic. Case in point: A new study finds that the Atlantic Ocean just had its hottest decade in at least 2,900 years. Someone award Smash Mouth a PhD and calculate the h-index of their discography immediately.

The new findings, published in the Proceedings of the National Academy of Sciences on Monday, rely on a mix of ice and sediment cores as well as thermometer data to track the state of the Atlantic. The ocean has gone through a well-known up-and-down swing in sea surface temperature, known as the Atlantic multidecadal oscillation. Plotted over hundreds of years, the AMO looks like a pretty steady wave pattern. In its warm phase, it can lead to a greater number of intense hurricanes, while the opposite is true in its cool phase. In addition to hurricanes, the phase of the AMO also influences temperature and precipitation over landmasses both immediately adjacent to the ocean and as far away as India.

So the state of the AMO is big deal, especially knowing where it’s heading in a warming climate. To get a handle on where the AMO has been, the researchers turned to a surprising source: the sediment in a lake on Ellesmere Island in the Canadian Arctic. The region is one of the areas heavily influenced by shifts in Atlantic Ocean temperatures. When the Atlantic runs hot, it creates higher pressure over the region, resulting in thinner snowpack; less snowpack means less sediment runoff.

Researchers were able to analyze titanium in layer upon layer of lake sediment to create a time series of the past 2,900 years of Atlantic Ocean temperatures. The finding show the wave pattern of warm and cool periods extends into the past, including a big dip in the heart of the Little Ice Age that ran from 1300 until about 1860. Since then, it’s been rising steadily up, with a sharp peak in the past few decades.

The scientists also compared parts of the new Canadian Arctic to shorter, higher-resolution sediment cores from other locations, including one from off the southern coast of Iceland that covers the past 230 or so years. That record relies on Turborotalita quinqueloba, a tiny, cold-water-loving shelled creature, as a proxy for temperature. The core shows a drop in their numbers over the past century, with the rate of disappearance speeding up.

Taken together, the results show that “recent Atlantic warming is unparalleled” in at least 2,900 years. There are natural factors that could be influencing the shift, but it’s impossible to not consider the impact of climate change. The hallmark of climate change is heat, especially in the oceans. Marine heat waves have become more common and intense. Findings published just last month show rising heat is causing the oceans to stratify. Arctic sea ice plunged to its second lowest levels on record in September as well, again due to hotter oceans.

Industrial emissions of ozone depleting substances (ODSs) during the second half of the twentieth century have led to one of the most visible human impacts on the Earth: the Antarctic ozone hole. The ozone loss intensified in the 1980s and reached the level of saturation (i.e., complete loss of ozone) due to the high levels of ODSs in the atmosphere. Significant changes in the southern hemispheric climate have been observed in the past decades due to this unprecedented ozone loss. Although the most recent studies suggest healing in the Antarctic ozone hole, the status of ozone in the loss saturation layer (~13–21 km) has not been discussed in detail.

Now, a comprehensive analysis of vertical, spatial and temporal evolution of ozone loss saturation (ozone mixing ratio ≤ 0.1 ppmv) in the Antarctic vortex using high resolution measurements for the 1979–2017 period reveals that the loss saturation began in 1987 and continued to occur in all winters thereafter, except in the major warming winters of 1988 and 2002. However, this recent analysis shows a clear reduction in the frequency of occurrence of ozone loss saturation over the period 2001–2017 consistently throughout various datasets (e.g., ozonesonde and satellite measurements of ozone profiles and total columns), thereby revealing the emergence of an important milestone in ozone recovery.

The oldest water in the ocean didn't reach its advanced years by accident. Deep in the North Pacific, a vast stretch of submerged ocean is trapped in a kind of stasis between powerful currents and the sea floor, and for the ancient waters caught in this airless 'shadow zone', it's almost like time stands still.

"What we have found is that at around 2 kilometers (1.2 miles) below the surface of the Indian and Pacific Oceans there is a 'shadow zone' with barely any vertical movement that suspends ocean water in an area for centuries," says oceanographer Casimir de Lavergne from the University of New South Wales in Australia.

"Carbon-14 dating had already told us the most ancient water lied in the deep North Pacific. But until now we had struggled to understand why the very oldest waters huddle around the depth of 2 kilometers."

A team of researchers has discovered a flaw in the way past ocean temperatures have been estimated up to now. Their findings could mean that the current period of climate change is unparalleled over the last 100 million years.

Passengers simmered in Jacuzzis and feasted on gourmet cuisine this summer as the 850-foot cruise ship Crystal Serenity moved through the Northwest Passage.

But in the summer of 1778, when Capt. James Cook tried to find a Western entrance to the route, his men toiled on frost-slicked decks and complained about having to supplement dwindling rations with walrus meat.

The British expedition was halted north of the Bering Strait by "ice which was as compact as a wall and seemed to be 10 or 12 feet high at least," according to the captain's journal. Cook's ships followed the ice edge all the way to Siberia in their futile search for an opening, sometimes guided through fog by the braying of the unpalatable creatures the crew called Sea Horses.

More than two centuries later, scientists are mining meticulous records kept by Cook and his crew for a new perspective on the warming that has opened the Arctic in a way the 18th century explorer could never have imagined. Working with maps and logs from Cook's voyage and other historical records and satellite imagery, University of Washington mathematician Harry Stern has tracked changes in ice cover in the Chukchi Sea, between Alaska and Russia, over nearly 240 years.

The results, published this month in the journal Polar Geography, confirm the significant shrinkage of the summer ice cap and shed new light on the timing of the transformation. The analysis also extends the historical picture back nearly 75 years, building on previous work with ships' records from the 1850s.

"This old data helps us look at what conditions were like before we started global warming, and what the natural variability was," said Jim Overland, a Seattle-based oceanographer for the National Oceanic and Atmospheric Administration who was not involved in Stern's project.

The annual Antarctic ozone hole reached an average area of 8.9 million square miles (23.2 million square kilometers) between Sept. 7 and Oct. 13, 2022. This depleted area of the ozone layer over the South Pole was slightly smaller than last year and generally continued the overall shrinking trend of recent years.

“Over time, steady progress is being made, and the hole is getting smaller,” said Paul Newman, chief scientist for Earth sciences at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “We see some wavering as weather changes and other factors make the numbers wiggle slightly from day to day and week to week. But overall, we see it decreasing through the past two decades. The elimination of ozone-depleting substances through the Montreal Protocol is shrinking the hole.”

The ozone layer – the portion of the stratosphere that protects our planet from the Sun’s ultraviolet rays – thins to form an “ozone hole” above the South Pole every September. Chemically active forms of chlorine and bromine in the atmosphere, derived from human-produced compounds, attach to high-altitude polar clouds each southern winter. The reactive chlorine and bromine then initiate ozone-destroying reactions as the Sun rises at the end of Antarctica’s winter.

Researchers at NASA and NOAA detect and measure the growth and breakup of the ozone hole with instruments aboard the Aura, Suomi NPP, and NOAA-20 satellites. On Oct. 5, 2022, those satellites observed a single-day maximum ozone hole of 10.2 million square miles (26.4 million square kilometers), slightly larger than last year.

WITHOUT THE OCEAN, climate change on land would be even more catastrophic. The seas have absorbed over 90 percent of the excess heat from greenhouse gas emissions, essentially saving humanity from itself. But it’s taking a toll: The ocean, too, is rapidly warming. And just as we have heat waves on land, parts of the ocean can experience temperature spikes too.

New research exposes just how bad the problem has gotten. Researchers from the Monterey Bay Aquarium began their calculation by analyzing surface temperature data from 1870 to 1919, sampled from across the globe. (Yes, ships have been taking the ocean’s temperature for 150 years.) Once they knew the historical high temperatures for each month in different parts of the ocean, they had a baseline for marine temperature extremes before the escalation of climate change. In the 19th century, only 2 percent of the ocean surface experienced such extremes. 

Then they compared this data to readings in the same places taken from 1920 to 2019. Their results show that by the year 2014, half of the ocean surface was logging temperatures once considered extreme—exceeding those historical highs. By 2019, that figure was 57 percent. In 150 years, the occurrence of extreme heat had become the new normal. 

These spikes are different from the overall rise in water temperature, which is also caused by global warming. For one thing, a particular region can come back down off of a high when winter arrives. And the location of the spikes can vary over time, meaning some places were affected earlier than others. So while half the ocean surface was logging temperature extremes by 2014, the South Atlantic had actually crossed that threshold back in 1998. 

“And that is ludicrous,” says ecologist Kyle Van Houtan, president and CEO of the Loggerhead Marinelife Center, who coauthored today’s paper in the journal PLOS Climate describing the findings. (Van Houtan did the research in his previous role as the chief scientist at the aquarium, with marine biologist Kisei Tanaka, now at the National Oceanic and Atmospheric Administration.) “There's some major changes going on right now in the ocean, and we think that this calculation, this index, of marine heat that we built is helping to describe why,” he continues. “I think extreme marine heat is much more of a problem than we thought it was. It's actually common today, which is scary, because historically it was just extreme—it was rare.”

“The trends they're seeing are consistent with results from a lot of other papers that conclude that marine heat waves are becoming more frequent, they're warmer, and they're lasting longer,” says Bridget Seegers, an oceanographer at NASA, who wasn’t involved in the work. (She was, though, among the researchers who recently reported that 2021 was the sixth hottest year ever recorded.)

The global economy's business-as-usual approach to climate change has seen Earth's "vital signs" deteriorate to record levels, an influential group of scientists said Wednesday, warning that several climate tipping points were now imminent. The researchers, part of a group of more than 14,000 scientists who have signed on to an initiative declaring a worldwide climate emergency, said that governments had consistently failed to address the root cause of climate change: "the overexploitation of the Earth".

Since a similar assessment in 2019, they noted an "unprecedented surge" in climate-related disasters, including flooding in South America and Southeast Asia, record-shattering heatwaves and wildfires in Australia and the US, and devastating cyclones in Africa and South Asia. Of 31 "vital signs"—key metrics of planetary health that include greenhouse gas emissions, glacier thickness, sea-ice extent and deforestation—they found that 18 hit record highs or lows. For example, despite a dip in pollution linked to the pandemic, levels of atmospheric CO2 and methane hit all-time highs in 2021.

Greenland and Antarctica both recently showed all-time low levels of ice mass, and glaciers are melting 31 percent faster than they did just 15 years ago, the authors said. Both ocean heat and global sea levels set new records since 2019, and the annual loss rate of the Brazilian Amazon reached a 12-year high in 2020.


Highlights of a landmark Intergovernmental Panel on Climate Change (IPCC) draft report on the effects of a warming planet on nature. Echoing previous research, they said that forest degradation linked to fire, drought and logging was causing parts of the Brazilian Amazon to now act as a source of carbon, rather than absorb the gas from the atmosphere. Livestock such as cows and sheep are now at record levels, numbering more than four billion and with a mass exceeding that of all humans and wild land mammals combined, they said.

Tim Lenton, director of the University of Exeter's Global Systems Institute and study co-author, said the recent record-breaking heatwave in the Western United States and Canada showed that the climate had already begun to "behave in shocking, unexpected ways. We need to respond to the evidence that we are hitting climate tipping points with equally urgent action to decarbonize the global economy and start restoring instead of destroying nature," he said.

Earlier this year, the Earth saw a huge dip in carbon emissions as nations around the globe locked down to slow the spread of the coronavirus. It offered a glimpse into what the world might look like if we took drastic steps to reduce our carbon emissions to slow the spread of global warming: For a brief moment, smog-choked cities around the world had clear skies.

But according to a new modeling study published in Scientific Reports, even if we made such drastic reductions permanent, it would still not be enough. The study suggests that if we stopped all human-made greenhouse gas emissions immediately, the Earth’s temperatures would continue to rise because of self-sustaining melting ice and permafrost. These “feedback loops” — in which melting ice causes less sunlight to be reflected back into space, which in turn raises temperatures and causes more ice melt — have already been set into motion, the researchers argue.

Humanity “is beyond the point-of-no-return when it comes to halt the melting of the permafrost using greenhouse gas cuts as the single tool,” Jørgen Randers, PhD, professor emeritus of climate strategy at BI Norwegian Business School and lead author of the study, tells Future Human in an email. That’s not to say we should give up on reducing emissions: Rather, Randers says that the world "should accelerate its effort to cut greenhouse gas emissions (in order to postpone as much as possible the temperature rise) and start developing the technologies for large scale removal of greenhouse gases from the atmosphere.”

For decades, climate scientists have tried to predict the so-called tipping point at which it would be too late to stop global warming — too late to limit the amount the temperature rises, the amount of sea level rise, and the number of lives claimed by both and other climate-induced ecological disasters — through reducing carbon emissions alone. Climate scientists point to either 2030 or 2050 as deadlines for the world to get to zero emissions before runaway climate change kicks in. But according to the new study, no matter how much we reduce emissions now, warming will continue, and the self-sustained melting of Arctic ice and permafrost that has already begun could continue for 500 years.

“It simply will not stop from cutting manmade greenhouse gasses,” says Randers. “We need to do something more in order to stop it.” He and co-author Ulrich Goluke, an associate professor at Business School Lausanne in Switzerland, make the case that it’s time to pursue more aggressive climate strategies, like carbon sequestration.

Lab-made quakes suggested that we should see hints of activity before a big event, but this pattern has been elusive in nature—until now.

Rising sea levels could become overwhelming sooner than previously believed, according to the authors of the most comprehensive study yet of the accelerating ice melt in Greenland.

Run-off from this vast northern ice sheet – currently the biggest single source of meltwater adding to the volume of the world’s oceans – is 50% higher than pre-industrial levels and increasing exponentially as a result of manmade global warming, says the paper, published in Nature on Wednesday.

Almost all of the increase has occurred in the past two decades – a jolt upwards after several centuries of relative stability. This suggests the ice sheet becomes more sensitive as temperatures go up. “Greenland ice is melting more in recent decades than at any point in at least the last four centuries, and probably more than at any time in the last seven to eight millennia,” said the lead author Luke Trusel, of Rowan University. “We demonstrate that Greenland ice is more sensitive to warming today than in the past – it responds non-linearly due to positive feedbacks inherent to the system. Warming means more today than it did even just a few decades ago.”

According to NASA, the ozone hole reached its peak extent on Sept. 11, covering an area about two and a half times the size of the United States – 7.6 million square miles in extent - and then declined through the remainder of September and into October. NOAA ground- and balloon-based measurements also showed the least amount of ozone depletion above the continent during the peak of the ozone depletion cycle since 1988. NOAA and NASA collaborate to monitor the growth and recovery of the ozone hole every year.

“The Antarctic ozone hole was exceptionally weak this year,” said Paul A. Newman, chief scientist for Earth Sciences at NASA's Goddard Space Flight Center in Greenbelt, Maryland. “This is what we would expect to see given the weather conditions in the Antarctic stratosphere.”

The smaller ozone hole in 2017 was strongly influenced by an unstable and warmer Antarctic vortex – the stratospheric low pressure system that rotates clockwise in the atmosphere above Antarctica. This helped minimize polar stratospheric cloud formation in the lower stratosphere. The formation and persistence of these clouds are important first steps leading to the chlorine- and bromine-catalyzed reactions that destroy ozone, scientists said. These Antarctic conditions resemble those found in the Arctic, where ozone depletion is much less severe.

In 2016, warmer stratospheric temperatures also constrained the growth of the ozone hole. Last year, the ozone hole reached a maximum 8.9 million square miles, 2 million square miles less than in 2015. The average area of these daily ozone hole maximums observed since 1991 has been roughly 10 million square miles.  

Although warmer-than-average stratospheric weather conditions have reduced ozone depletion during the past two years, the current ozone hole area is still large because levels of ozone-depleting substances like chlorine and bromine remain high enough to produce significant ozone loss.

Scientists said the smaller ozone hole extent in 2016 and 2017 is due to natural variability and not a signal of rapid healing.

First detected in 1985, the Antarctic ozone hole forms during the Southern Hemisphere’s late winter as the returning sun’s rays catalyze reactions involving man-made, chemically active forms of chlorine and bromine. These reactions destroy ozone molecules.

Thirty years ago, the international community signed the Montreal Protocol on Substances that Deplete the Ozone Layer and began regulating ozone-depleting compounds. The ozone hole over Antarctica is expected to gradually become less severe as chlorofluorocarbons—chlorine-containing synthetic compounds once frequently used as refrigerants – continue to decline. Scientists expect the Antarctic ozone hole to recover back to 1980 levels around 2070.

Aerosols could cool the planet without ozone damage | To halt the rise of global temperatures, Harvard researchers are looking at solar geoengineering, which would inject light-reflecting sulfate aerosols into the stratosphere to cool the planet.

The planet is warming at an unprecedented rate, and reducing emissions of greenhouse gases alone is not enough to remove the risk. Last year’s historic Paris climate agreement set the goal of keeping global temperatures no higher than 1.5 degrees Celsius above preindustrial levels. Emission reductions will be central to achieving that goal, but supplemental efforts can further reduce risks.

One drastic idea is solar geoengineering — injecting light-reflecting sulfate aerosols into the stratosphere to cool the planet. Researchers know that large amounts of aerosols can significantly cool the planet; the effect has been observed after large volcanic eruptions. But these sulfate aerosols also carry significant risks. The biggest known risk is that they produce sulfuric acid in the stratosphere, which damages ozone. Since the ozone layer absorbs ultraviolet light from the sun, its depletion can lead to increased rates of skin cancer, eye damage, and other adverse consequences.

Now, researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have identified an aerosol for solar geoengineering that may be able to cool the planet while simultaneously repairing ozone damage. The research is published in the Proceedings of the National Academy of Sciences.

“In solar geoengineering research, introducing sulfuric acid into the atmosphere has been the only idea that had any serious traction until now,” said David Keith, the Gordon McKay Professor of Applied Physics at SEAS and professor of public policy at the Harvard Kennedy School, the first author of the paper. “This research is a turning point and an important step in analyzing and reducing certain risks of solar geoengineering.”