Climate

It was the mid-1980s, at a meeting in Switzerland, when Wally Broecker’s ears perked up. Scientist Hans Oeschger was describing an ice core drilled at a military radar station in southern Greenland. Layer by layer, the 2-kilometer-long core revealed what the climate there was like thousands of years ago. Climate shifts, inferred from the amounts of carbon dioxide and of a form of oxygen in the core, played out surprisingly quickly — within just a few decades. It seemed almost too fast to be true.      

Broecker returned home, to Columbia University’s Lamont-Doherty Earth Observatory, and began wondering what could cause such dramatic shifts. Some of Oeschger’s data turned out to be incorrect, but the seed they planted in Broecker’s mind flowered — and ultimately changed the way scientists think about past and future climate.

A geochemist who studied the oceans, Broecker proposed that the shutdown of a major ocean circulation pattern, which he named the great ocean conveyor, could cause the North Atlantic climate to change abruptly. In the past, he argued, melting ice sheets released huge pulses of water into the North Atlantic, turning the water fresher and halting circulation patterns that rely on salty water. The result: a sudden atmospheric cooling that plunged the region, including Greenland, into a big chill. (In the 2004 movie The Day After Tomorrow, an overly dramatized oceanic shutdown coats the Statue of Liberty in ice.)

It was a leap of insight unprecedented for the time, when most researchers had yet to accept that climate could shift abruptly, much less ponder what might cause such shifts.

Broecker not only explained the changes seen in the Greenland ice core, he also went on to found a new field. He prodded, cajoled and brought together other scientists to study the entire climate system and how it could shift on a dime. “He was a really big thinker,” says Dorothy Peteet, a paleoclimatologist at NASA’s Goddard Institute for Space Studies in New York City who worked with Broecker for decades. “It was just his genuine curiosity about how the world worked.”

Broecker was born in 1931 into a fundamentalist family who believed the Earth was 6,000 years old, so he was not an obvious candidate to become a pathbreaking geoscientist. Because of his dyslexia, he relied on conversations and visual aids to soak up information. Throughout his life, he did not use computers, a linchpin of modern science, yet became an expert in radiocarbon dating. And, contrary to the siloing common in the sciences, he worked expansively to understand the oceans, the atmosphere, the land, and thus the entire Earth system.

By the 1970s, scientists knew that humans were pouring excess carbon dioxide into the atmosphere, through burning fossil fuels and cutting down carbon-storing forests, and that those changes were tinkering with Earth’s natural thermostat. Scientists knew that climate had changed in the past; geologic evidence over billions of years revealed hot or dry, cold or wet periods. But many scientists focused on long-term climate changes, paced by shifts in the way Earth rotates on its axis and circles the sun — both of which change the amount of sunlight the planet receives. A highly influential 1976 paper referred to these orbital shifts as the “pacemaker of the ice ages.”

Ice cores from Antarctica and Greenland changed the game. In 1969, Willi Dansgaard of the University of Copenhagen and colleagues reported results from a Greenland ice core covering the last 100,000 years. They found large, rapid fluctuations in oxygen-18 that suggested wild temperature swings. Climate could oscillate quickly, it seemed — but it took another Greenland ice core and more than a decade before Broecker had the idea that the shutdown of the great ocean conveyor system could be to blame.

Pulled from southern Greenland beginning in 1979, the Dye-3 ice core (the drill used to retrieve the core is shown) revealed that abrupt climate change had occurred in the past.The Niels Bohr Institute

Broecker proposed that such a shutdown was responsible for a known cold snap that started around 12,900 years ago. As the Earth began to emerge from its orbitally influenced ice age, water melted off the northern ice sheets and washed into the North Atlantic. Ocean circulation halted, plunging Europe into a sudden chill, he said. The period, which lasted just over a millennium, is known as the Younger Dryas after an Arctic flower that thrived during the cold snap. It was the last hurrah of the last ice age.

Evidence that an ocean conveyor shutdown could cause dramatic climate shifts soon piled up in Broecker’s favor. For instance, Peteet found evidence of rapid Younger Dryas cooling in bogs near New York City — thus establishing that the cooling was not just a European phenomenon but also extended to the other side of the Atlantic. Changes were real, widespread and fast.

By the late 1980s and early ’90s, there was enough evidence supporting abrupt climate change that two major projects — one European, one American — began to drill a pair of fresh cores into the Greenland ice sheet. Richard Alley, a geoscientist at Penn State, remembers working through the layers and documenting small climatic changes over thousands of years. “Then we hit the end of the Younger Dryas and it was like falling off a cliff,” he says. It was “a huge change after many small changes,” he says. “Breathtaking.”

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The new Greenland cores cemented scientific recognition of abrupt climate change. Though the shutdown of the ocean conveyor could not explain all abrupt climate changes that had ever occurred, it showed how a single physical mechanism could trigger major planet-wide disruptions. It also opened discussions about how rapidly climate might change in the future.

Broecker, who died in 2019, spent his last decades exploring abrupt shifts that are already happening. He worked, for example, with billionaire Gary Comer, who during a yacht trip in 2001 was shocked by the shrinking of Arctic sea ice, to brainstorm new directions for climate research and climate solutions.

Broecker knew more than almost anyone about what might be coming. He often described Earth’s climate system as an angry beast that humans are poking with sticks. And one of his most famous papers was titled “Climatic change: Are we on the brink of a pronounced global warming?”

It was published in 1975. More

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

A small number of “ultra-emitters” of methane from oil and gas production contribute as much as 12 percent of emissions of the greenhouse gas to the atmosphere every year — and now scientists know where many of these sources are.

Analyses of satellite images from 2019 and 2020 reveal that a majority of the 1,800 biggest methane sources come from six major oil- and gas-producing countries: Turkmenistan led the pack, followed by Russia, the United States, Iran, Kazakhstan and Algeria.

Plugging those leaks would not only be a boon to the planet, but also could save those countries billions in U.S. dollars, climate scientist Thomas Lauvaux of the University of Paris-Saclay and colleagues report in the Feb. 4 Science.

Ultra-emitters are sources that spurt at least 25 metric tons of methane per hour into the atmosphere. These occasional massive bursts make up only a fraction — but a sizable one — of the methane shunted into Earth’s atmosphere annually.

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Cleaning up such leaks would be a big first step in reducing overall emissions, says Euan Nisbet, a geochemist at Royal Holloway, University of London in Egham, who was not involved in the study. “If you see somebody badly injured in a road accident, you bandage up the bits that are bleeding hardest.”

Methane has about 80 times the atmosphere-warming potential of carbon dioxide, though it tends to have a much shorter lifetime in the atmosphere — 10 to 20 years or so, compared with hundreds of years. The greenhouse gas can seep into the atmosphere from both natural and human-made sources (SN: 2/19/20).

In oil and gas production, massive methane bursts might be the result of accidents or leaky pipelines or other facilities, Lauvaux says. But these leaks are often the result of routine maintenance practices, the team found. Rather than shut down for days to clear gas from pipelines, for example, managers might open valves on both ends of the line, releasing and burning off the gas quickly. That sort of practice stood out starkly in satellite images as “two giant plumes” along a pipeline track, Lauvaux says.

Stopping such practices and repairing leaky facilities are relatively easy, which is why such changes may be the low-hanging fruit when it comes to addressing greenhouse gas emissions. But identifying the particular sources of those huge methane emissions has been the challenge. Airborne studies can help pinpoint some large sources, such as landfills, dairy farms and oil and gas producers, but such flights are limited by being both regional and of short duration (SN: 11/14/19).

Satellites, such as the European Space Agency’s Tropospheric Monitoring Instrument, or TROPOMI, offer a much bigger window in both space and time. Scientists have previously used TROPOMI to estimate the overall leakiness of oil and gas production in Texas’s massive Permian Basin, finding that the region sends twice as much methane to the atmosphere as previously thought (SN: 4/22/20).

In the new study, the team didn’t include sources in the Permian Basin among the ultra-emitters; the large emissions from that region are the result of numerous tightly clustered but smaller emissions sources. Because TROPOMI doesn’t peer well through clouds, other regions around the globe, such as Canada and the equatorial tropics, also weren’t included.

But that doesn’t mean those regions are off the hook, Lauvaux says. “There’s just no data available.” On the heels of this broad-brush view from TROPOMI, Lauvaux and other scientists are now working to plug those data gaps using other satellites with better resolution and the ability to penetrate clouds.

Stopping all of these big leaks, which amount to an estimated 8 to 12 percent of total annual methane emissions, could save these countries billions of dollars, the researchers say. And the reduction in those emissions would be about as beneficial to the planet as cutting all emissions from Australia since 2005, or removing 20 million vehicles from the roads for a year.

Such a global map can also be helpful to countries in meeting their goals under the Global Methane Pledge launched in November at the United Nations’ annual climate summit, says Daniel Jacob, an atmospheric chemist at Harvard University who was not involved in the study (SN: 1/11/22).

Signatories to the pledge agreed to reduce global emissions of the gas by at least 30 percent relative to 2020 levels by 2030. These new findings, Jacob says, can help achieve that target because it “encourages action rather than despair.”  More

Extremes in rainfall — whether intense drought or flash floods — can catastrophically slow the global economy, researchers report in the Jan. 13 Nature. And those impacts are most felt by wealthy, industrialized nations, the researchers found.

A global analysis showed that episodes of intense drought led to the biggest shocks to economic productivity. But days with intense deluges — such as occurred in July 2021 in Europe — also produced strong shocks to the economic system (SN: 8/23/21). Most surprising, though, was that agricultural economies appeared to be relatively resilient against these types of shocks, says Maximilian Kotz, an environmental economist at the Potsdam Institute for Climate Impact Research in Germany. Instead, two other business sectors — manufacturing and services — were the most hard-hit.

As a result, the nations most affected by rainfall extremes weren’t those that tended to be poorer, with agriculture-dependent societies, but the wealthiest nations, whose economies are tied more heavily to manufacturing and services, such as banking, health care and entertainment.

It’s well established that rising temperatures can take a toll on economic productivity, for example by contributing to days lost at work or doctors’ visits (SN: 11/28/18). Extreme heat also has clear impacts on human behavior (SN: 8/18/21). But what effect climate change–caused shifts in rainfall might have on the global economy hasn’t been so straightforward.

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That’s in part because previous studies looking at a possible connection between rainfall and productivity have focused on changes in yearly precipitation, a timeframe that “is just too coarse to really describe what’s actually happening [in] the economy,” Kotz says. Such studies showed that more rain in a given year was basically beneficial, which makes sense in that having more water available is good for agriculture and other human activities, he adds. “But these findings were mainly focused on agriculturally dependent economies and poorer economies.”

In the new study, Kotz and his colleagues looked at three timescales — annual, monthly and daily rainfall — and examined what happened to economic output for time periods in which the rainfall deviated from average historical values. In particular, Kotz says, they introduced two new measures not considered in previous studies: the amount of rainy days that a region gets in a year and extreme daily rainfall. The team then examined these factors across 1,554 regions around the world — which included many subregions within 77 countries — from 1979 to 2019.

The disparity over which regions are hit hardest is “at odds with the conventional wisdom” — and with some previous studies — that agriculture is vulnerable to extreme rainfall, writes Xin-Zhong Liang, an atmospheric scientist at the University of Maryland in College Park, in a commentary in the same issue of Nature. Researchers may need to incorporate other factors in future assessments, such as growth stages of crops, land drainage or irrigation, in order to really understand how these extremes affect agriculture, Liang writes.

“That was definitely surprising for us as well,” Kotz says. Although the study doesn’t specifically try to answer why manufacturing and services were so affected, it makes intuitive sense, he says. Flooding, for example, can damage infrastructure and disrupt transportation, effects that can then propagate along supply chains. “It’s feasible that these things might be most important in manufacturing, where infrastructure is very important, or in the services sectors, where the human experience is very much dictated by these daily aspects of weather and rainfall.”

Including daily and monthly rainfall extremes in this type of analysis was “an important innovation” because it revealed new economic vulnerabilities, says Tamma Carleton, an environmental economist at the University of California, Santa Barbara, who was not involved in the new work. However, Carleton says, “the findings in the paper are not yet conclusive on who is most vulnerable and why, and instead raise many important questions for future research to unpack.”

Extreme rainfall events, including both drought and deluge, will occur more frequently as global temperatures rise, the United Nations’ Intergovernmental Panel on Climate Change noted in August (SN: 8/9/21). The study’s findings, Kotz says, offer yet another stark warning to the industrialized, wealthy world: Human-caused climate change will have “large economic consequences.” More

What’s in a number? The goals of the 2021 United Nations’ climate summit in Glasgow, Scotland, called for nations to keep a warming limit of 1.5 degrees Celsius “within reach.” But when it comes to communicating climate change to the public, some scientists worry that too much emphasis on a specific number is a poor strategy.

Focusing on one number obscures a more important point, they say: Even if nations don’t meet this goal to curb global climate change, any progress is better than none at all. Maybe it’s time to stop talking so much about one number.

On November 13, the United Nations’ 26th annual climate change meeting, or COP26, ended in a new climate deal, the Glasgow Climate Pact. In that pact, the 197 assembled nations reaffirmed a common “ideal” goal: limiting global warming to no more than 1.5 degrees C by 2100, relative to preindustrial times (SN: 12/17/18).

Holding temperature increases to 1.5 degrees C, researchers have found, would be a significant improvement over limiting warming to 2 degrees C, as agreed upon in the 2015 Paris Agreement (SN: 12/12/15). The more stringent limit would mean fewer global hazards, from extreme weather to the speed of sea level rise to habitat loss for species (SN: 12/17/18).

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The trouble is that current national pledges to reduce greenhouse gas emissions are nowhere near enough to meet either of those goals. Even accounting for the most recent national pledges to cut emissions, the average global temperature by 2100 is likely to be between 2.2 and 2.7 degrees C warmer than it was roughly 150 years ago (SN: 10/26/21).

And that glaring disparity is leading not just to fury and frustration for many, but also to despair and pervasive feelings of doom, says paleoclimatologist Jessica Tierney of the University of Arizona in Tucson.

“It’s something I’ve been thinking about for a while, but I think it was definitely made sort of more front and center with COP,” Tierney says. She describes one news story in the wake of the conference that “mentioned 1.5 degrees C, and then said this is the threshold over which scientists have told us that catastrophic climate change will occur.”

The article reveals a fundamental misunderstanding of what the agreed-upon limit really represents, Tierney explains. “A lot of my students, for example, are really worried about climate change, and they are really worried about passing some kind of boundary. People have this idea that if you pass that boundary, you sort of tip over a cliff.”

The climate system certainly has tipping points — thresholds past which, for example, an ice sheet begins to collapse and it’s not possible to stop or reverse the process. But, Tierney says, “we really should start communicating more about the continuum of climate change. Obviously, less warming is better.” However, “if we do blow by 1.5, we don’t need to panic. It’s okay if we can stop at 1.6 or 1.7.”

Tierney notes that climate communications expert Susan Hassol, director of the Colorado-based nonprofit Climate Communication, has likened the approach to missing an exit while driving on the highway. “If you miss the 1.5 exit, you just slow down and take the next one, or the next one,” Tierney says. “It’s still better than hitting the gas.”

Target numbers do have some uses, notes climate scientist Joeri Rogelj of Imperial College London. After decades of international climate negotiations and wrangling over targets and strategies, the world has now agreed that 1.5 degrees C of warming is a desirable target for many countries, says Rogelj, who was one of the lead authors on the Intergovernmental Panel on Climate Change’s 2018 special report on global warming.

A global temperature limit “is a good proxy for avoiding certain impacts,” he adds. “These numbers are basically how to say this.”

But Rogelj agrees that focusing too much on a particular number may be counterproductive, even misleading. “There is a lot of layered meaning under those numbers,” he says. “The true interests, the true goals of countries are not those numbers, but avoiding the impacts that underlie them.”

And framing goals as where we should be by the end of the century — such as staying below 1.5 degrees C by the year 2100 — can give too much leeway to stall on reducing emissions. For example, such framing implies the planet could blow past the temperature limit by mid-century and rely on still-unproven carbon dioxide removal strategies to bring warming back down in the next few decades, Rogelj and colleagues wrote in 2019 in Nature.

Banking on future technologies that have yet to be developed is worrisome, Rogelj notes. After all, some warming-related extreme events, such as heat waves, are more reversible than others, such as sea level rise (SN: 8/9/21). Heat wave incidence may decrease once carbon is removed from the atmosphere, but the seas will stay high.

Rogelj acknowledges that it’s a challenge to communicate the urgency of taking action to reduce emissions now without spinning off into climate catastrophe or cliff edge narratives. For his part, Rogelj says he’s trying to tackle this challenge by adding a hefty dose of reality in his scientific presentations, particularly those aimed at nonscientists.

He starts with pictures of forest fires and floods in Europe from 2021. “I say, ‘Look, this is today, 1.1 degrees warmer than preindustrial times,’” Rogelj explains. “‘Do you think this is safe? Today is not safe. And so, 1.5 won’t be safer than today; it will be worse than today. But it will be better than 1.6. And 1.6 won’t be the end of the world.’ And that kind of makes people think about it a bit differently.” More