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When it comes to cooling the planet, forests have more than one trick up their trees.  

Tropical forests help cool the average global temperature by more than 1 degree Celsius, a new study finds. The effect stems largely from forests’ capacity to capture and store atmospheric carbon (SN: 11/18/21). But around one-third of that tropical cooling effect comes from several other processes, such as the release of water vapor and aerosols, researchers report March 24 in Frontiers in Forests and Global Change.

“We tend to focus on carbon dioxide and other greenhouse gases, but forests are not just carbon sponges,” says Deborah Lawrence, an environmental scientist at the University of Virginia in Charlottesville. “It’s time to think about what else forests are doing for us besides just absorbing carbon dioxide.”

Researchers already knew that forests influence their local climates through various physical and chemical processes. Trees release water vapor through pores in their leaves — a process called evapotranspiration — and, like human sweating, this cools the trees and their surroundings. Also, uneven forest canopies can have a cooling effect, as they provide an undulating surface that can bump hot, overpassing fronts of air upward and away. What’s more, trees generate aerosols that can lower temperatures by reflecting sunlight and seeding clouds.

But on a global scale, it wasn’t clear how these other cooling benefits compared with the cooling provided by forests’ capturing of carbon dioxide, Lawrence says.

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So she and her colleagues analyzed how the complete deforestation of different regions would impact global temperatures, using data gathered from other studies. For instance, the researchers used forest biomass data to determine how much the release of carbon stored by those forests would warm the global temperature. They then compared those results with other studies’ estimates of how much the loss of other aspects of forests — such as evapotranspiration, uneven canopies and aerosol production — affected regional and global temperatures.

The researchers found that in forests at latitudes from around 50° S of the equator to 50° N, the primary way that forests influenced the global average temperature was through carbon sequestration. But those other cooling factors still played large roles.

Forests located from 30° N to 30° S provided alternative benefits that cool the planet by over 0.3 degrees C, about half as much cooling as carbon sequestration provided. And the bulk of that cooling, around 0.2 degrees C, came from forests in the core of the tropics (within 10° of the equator). Canopy topography generally provided the greatest cooling, followed by evapotranspiration and then aerosols.

Forests in the far north, however, appear to have a net warming effect, the team reports. Clearing the boreal forests — which stretch across Canada, Alaska, Russia and Scandinavia — would expose more snow cover during the winter. This would decrease ground level temperatures because snow reflects much of the incoming sunlight back into the sky. Still, the researchers found that altogether, the world’s forests cool the global average temperature about 0.5 degrees C.

The findings suggest that global and regional climate action efforts should refrain from focusing solely on carbon emissions, Lawrence says. “There’s this whole service that tropical forests are providing that simply are not visible to us or to policy makers.”

The research shows that clearing tropical forests robs us of many climate-cooling benefits, says Gabriel de Oliveira, a geographer from the University of South Alabama in Mobile. But deforestation isn’t the only way that humans impair forests’ cooling ability, he says. Many forests are damaged by fires or selective logging, and are less able to help with cooling (SN: 9/1/21). It would be useful to consider how forest degradation, in addition to deforestation, impacts regional and global climate temperatures, de Oliveira says, to assess the impact of restoring and protecting forests (SN: 7/13/21). “It’s cool to see beyond carbon dioxide, but it’s also very important to see beyond deforestation.” More

Towers of smoke that rose high into the stratosphere during Australia’s “black summer” fires in 2019 and 2020 destroyed some of Earth’s protective ozone layer, researchers report in the March 18 Science.

Chemist Peter Bernath of Old Dominion University in Norfolk, Va., and his colleagues analyzed data collected in the lower stratosphere during 2020 by a satellite instrument called the Atmospheric Chemistry Experiment. It measures how different particles in the atmosphere absorb light at different wavelengths. Such absorption patterns are like fingerprints, identifying what molecules are present in the particles.

The team’s analyses revealed that the particles of smoke, shot into the stratosphere by fire-fueled thunderstorms called pyrocumulonimbus clouds, contained a variety of mischief-making organic molecules (SN: 12/15/20). The molecules, the team reports, kicked off a series of chemical reactions that altered the balances of gases in Earth’s stratosphere to a degree never before observed in 15 years of satellite measurements. That shuffle included boosting levels of chlorine-containing molecules that ultimately ate away at the ozone.

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Ozone concentrations in the stratosphere initially increased from January to March 2020, due to similar chemical reactions — sometimes with the contribution of wildfire smoke — that produce ozone  pollution at ground level (SN: 12/8/21). But from April to December 2020, the ozone levels not only fell, but sank below the average ozone concentration from 2005 to 2019.

Earth’s ozone layer shields the planet from much of the sun’s ultraviolet radiation. Once depleted by human emissions of chlorofluorocarbons and other ozone-damaging substances, the layer has been showing signs of recovery thanks to the Montreal Protocol, an international agreement to reduce the atmospheric concentrations of those substances (SN: 2/10/21).

But the increasing frequency of large wildfires due to climate change — and their ozone-destroying potential — could become a setback for that rare climate success story, the researchers say (SN: 3/4/20). More

Neither adaptation by humankind nor mitigation alone is enough to reduce the risk from climate impacts, hundreds of the world’s scientists say. Nothing less than a concerted, global effort to both drastically curb carbon emissions and proactively adapt to climate change can stave off the most disastrous consequences, according to the latest report from the United Nations’ Intergovernmental Panel on Climate Change, or IPCC.

That dire warning comes as the effects of climate change on people and nature are playing out across the globe in a more widespread and severe manner than previously anticipated. And the most vulnerable communities — often low-income or Indigenous — are being hit the hardest, the report says.

“It’s the strongest rebuttal that we’ve seen yet of this idea that we can just adapt our way out of climate change and we don’t have to mitigate emissions,” says Anne Christianson, the director of international climate policy at the Center for American Progress in Washington, D.C., who was not involved in the report.

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A consortium of 270 scientists from 67 countries synthesized the report after reviewing over 34,000 studies. Released February 28 as part of the IPCC’s sixth assessment of climate science, the report details how the impacts of climate change are playing out today in different regions, and assessed the capacities of communities and regions to adapt.

Many countries understand the need for climate adaptation. And modern solutions, such as the building of urban gardens or adoption of agroforestry, where implemented, appear to show promise. But, the report finds, efforts to adapt are, by and large, reactionary, small and drastically underfunded. As a result, about 3.3 billion to 3.6 billion people remain highly vulnerable to climate risks such as extreme weather events, sea level rise and food and water shortages. The need for adaptation is greatest — and growing larger — in low-income regions, most notably in parts of Africa, South Asia, small island states and Central and South America.

The report also underscores the importance of involving those who are impacted the most in climate plans. “We can no longer just make these decisions at the highest level; we need to include local stakeholders, Indigenous groups, local communities and those who are most as at risk for climate change, such as women, racial minorities, the elderly and children,” Christianson says.

Last August, a previous report, also part of the IPCC’s sixth assessment, covered the physical science underpinning climate change (SN: 8/9/21). In that report, scientists stated loud and clear that there was no time to waste. By 2030, carbon emissions need to be cut in half, compared with 2017 levels, to prevent global temperatures from climbing 1.5° Celsius above the preindustrial baseline, the report found. Beyond that baseline, the capacity for humankind and nature to adapt severely deteriorates. In a bit of good news, the authors of that 2021 report also found that if all carbon emissions were to cease today, global temperatures would stop rising in about three years, not the 30 to 40 years once thought. In other words, we can make a big difference in very little time.

Still, climate change is already affecting many parts of Earth. And some of the consequences aren’t going away anytime soon. Sea level will continue to rise for decades, driven in part by the runaway melting of Greenland’s ice sheet (SN: 9/30/20). By 2050, sea level along U.S. coastlines will have risen by 25 to 30 centimeters, or roughly one foot, the National Oceanic and Atmospheric Administration estimates.

The latest IPCC report reveals that the effects of climate change, which include an increased frequency of wildfires (such as these in Turkey), are more widespread and severe than had been expected.YASIN AKGUL/AFP via Getty Images

Extreme weather events and climate-fueled wildfires have already caused mass mortalities of corals and other animals and trees, and pushed entire species toward the brink of extinction (SN: 3/9/21). What’s more, climate change is forcing many people to relocate, as well as detrimentally affecting mental health and spreading disease as vectors such as mosquitoes shift to new habitats (SN: 5/12/20; SN: 10/7/19).

Adaptation is especially needed in cities, which are growing and expected to contain two-thirds of the world’s population by 2050, including climate refugees from elsewhere, the new report finds. Urban communities are becoming increasingly vulnerable to extreme heat waves, urban heat island effects, floods and storm surges (SN: 9/18/21).

Outside of cities, the breakdown of ecosystems and loss of biodiversity severely impacts the people who rely on natural systems for their livelihoods, the report emphasizes. Farmers in the global south are finding it increasingly challenging to grow crops as a result of droughts, heat waves, floods and sea-level rise (SN: 9/24/21). People who make their living fishing are being forced to travel greater distances to pursue species that are altering their natural ranges as ocean temperatures warm.

Key to adapting to these impacts is the restoration and preservation of natural ecosystems, the report states. Conserving 30 to 50 percent of the planet’s land, ocean and freshwater ecosystems will help support biodiversity and enhance climate resilience (SN: 4/22/20). Preserving mangrove forests, for instance, along less developed coastlines sequesters large amounts of carbon and protects against storm surges (SN:5/7/21, SN: 6/4/20).

“The truth is that nature can be our savior,” said Inger Andersen, executive director of the U.N. Environment Programme, at a February 28 news conference announcing the report’s release. “But only if we save it first.”

Still, the natural world and many of the “services” it provides to humankind, such as carbon storage and flood control, begin to break down more rapidly at about 1.5° C above preindustrial temperatures, the report notes. And the window to prevent that from happening is closing. “We are on a trajectory to losing many of these systems and the services they provide” says Borja Reguero, a coastal science researcher at the University of California, Santa Cruz who reviewed the report.

What that means is there is no time to waste. “We simultaneously need to reduce our greenhouse gas emissions, adapt to reduce the risks of climate change and also address losses and damages that are already being experienced,” Adelle Thomas, a climate scientist at the University of the Bahamas in Nassau, said at a February 27 news briefing. Thomas is the lead author of the new report’s chapter on key risks across sectors and regions.

“And we have a very limited amount of time left to do this,” she stressed. More