Global Warming Could Stop Relatively Quickly If Emissions Go to Zero, Research Suggests

Parts of the world economy may have been on pause during 2020, dampening greenhouse gas emissions for a while. But that didn’t slow the overall buildup of atmospheric carbon dioxide, which reached its highest level in millions of years.

If anything, research during the year showed global warming is accelerating. Symptoms of the fever include off-the-charts heat waves on land and in the oceans, and a hyperactive and destructive Atlantic hurricane season.

And through November, the last year was on pace to end up as either the hottest, or second-hottest on record for the planet, almost 1 degree Celsius above pre-industrial times, inching closer to the 1.5 degree limit set by the Paris climate agreement.

Here are five aspects of climate change that were new and unexpected in 2020:

Making it Stop

Some scientists are punctuating their alarming warnings with hopeful messages because they know that the worst possible outcome is avoidable.

Recent research shows that stopping greenhouse gas emissions will break the vicious cycle of warming temperatures, melting ice, wildfires and rising sea levels faster than expected just a few years ago.

There is less warming in the pipeline than we thought, said Imperial College (London) climate scientist Joeri Rogelj, a lead author of the next major climate assessment from the Intergovernmental Panel on Climate Change.

“It is our best understanding that, if we bring down CO2 to net zero, the warming will level off. The climate will stabilize within a decade or two,” he said. “There will be very little to no additional warming. Our best estimate is zero.”

The widespread idea that decades, or even centuries, of additional warming are already baked into the system, as suggested by previous IPCC reports, were based on an “unfortunate misunderstanding of experiments done with climate models that never assumed zero emissions.”

Those models assumed that concentrations of greenhouse gases in the atmosphere would remain constant, that it would take centuries before they decline, said Penn State climate scientist Michael Mann, who discussed the shifting consensus last October during a segment of “60 Minutes” on CBS.

The idea that global warming could stop relatively quickly after emissions go to zero was described as a “game-changing new scientific understanding” by Covering Climate Now, a collaboration of news organizations covering climate.

“This really is true,” Mann said. “It’s a dramatic change in the paradigm that has been lost on many who cover this issue, perhaps because it hasn’t been well explained by the scientific community. It’s an important development that is still under appreciated. It’s definitely the scientific consensus now that warming stabilizes quickly, within 10 years, of emissions going to zero,” he said.

The La Niña Effect?

Some scientists noted that the persistent heating came even with the tropical Pacific Ocean tilting toward a cyclical cooling phase that suppresses the global average temperature slightly. November’s warmth across the planet was “stunning, especially considering the ongoing La Niña,” Zack Labe, an atmospheric scientist at Colorado State University, posted on Twitter.

During La Niña, cooler than average sea surface temperatures spread across a large part of the tropical Pacific. During the warm El Niño phase every few years, it’s the opposite, and that’s usually when global temperatures spike to new records, most recently in 2016.

The global climate signal from the cycle usually is strongest about three or four months after the ocean cycle peaks, so the full effect won’t be known until next year, said climate scientist Stefan Rahmstorf, with the Potsdam Institute for Climate Impact Research. He said, “2020 may beat 2016 without the extra push from El Niño.”

This year’s warming is another sign that “heat being trapped by greenhouse gases” is overwhelming the planet’s natural variability, said Jennifer Francis, a climate scientist with the Woodwell Climate Research Center in Massachusetts (formerly the Woods Hole Research Center).

“I hate to think what the global temperature would have been this year if we’d been in an El Niño rather than La Niña,” she said.

The Polar Breakdown

Warming in the Arctic and Antarctic continues to accelerate faster than the global average, scientists reported this year.

In September, NASA Earth wrote on Twitter that, “The Arctic region is warming three times as fast as the rest of the planet, with effects beyond the ocean.” In recent years, the rate of Arctic warming was widely reported at twice the global average.

And in June, a team of scientists tracked a similar rate of warming in Antarctica. Their research, published in Nature, found that, since 1989, the average temperature at the South Pole increased about 0.6 degrees Fahrenheit per decade, also three times as fast as the global average.

The warming of the polar regions disrupts global climate patterns in ways that can cause more extreme droughts, floods and heat waves, and changes in climate-regulating ocean currents.

In a recent letter to the incoming Biden administration, 193 Arctic scientists spelled out their growing concerns, including acidification of the Arctic Ocean that threatens U.S. fisheries, and a loss of sea ice that contributes to “persistent heat waves and cold spells, prolonged stormy periods, and extended droughts that greatly worsen Western wildfires.”

The rapid Arctic warming has also triggered permafrost thaw that is “now releasing carbon at the same scale as many larger nations,” the scientists wrote. “Rising sea levels from melting glaciers and polar ice sheets have accelerated clear-day flooding and storm damage, especially along the U.S. Eastern and Gulf coasts,” they added.

The letter called on President-elect Joe Biden to appoint a U.S. ambassador with a climate mandate to the Arctic Council, as a way of recognizing the “urgency of the threat from a disintegrating Arctic.”

Swamped by the Seas?

As polar ice melts more quickly, sea level rise also accelerates. But sea level is complicated, because it doesn’t rise at the same rate everywhere, at the same time. The global average rate recently increased from about 1.3 inches to about 2 inches per decade.

In the best-case scenario of reaching the Paris target of capping global warming at 3.6 degrees Fahrenheit, sea level will rise between 1 and 2 feet by 2100, the Intergovernmental Panel on Climate Change warned in a 2019 global assessment.

The acceleration could be felt especially strongly along the West Coast, where sea level is starting to rise much faster than in recent years, according to NASA.

In early November, researchers with the agency said a decadeslong lull in sea level rise is ending. Large-scale changes in the Pacific Ocean are accelerating the inundation of beaches and marshes, as well the erosion of the coastal bluffs where millions of people have built homes and businesses.

“We’ve definitely seen an uptick,” said Bill Sweet, a sea level rise expert with the National Oceanic and Atmospheric Administration. “In the next 20 to 30 years, by 2050, sea level will be about a foot higher, compared to 2000. There is going to be more erosion and we’re going to lose beaches,” he said, identifying San Diego and the San Francisco Bay Area as potential trouble spots.

A lot of the Bay Area is built on reclaimed low-lying land that is permeable and vulnerable to incoming saltwater that can cause drainage systems to back up and overflow, and interfere with freshwater supplies.

“You’re going to see more of what we’re already seeing on the East Coast. San Diego is a stand-out spot already. There’s more nuisance flooding these days, and they’re going to see a jump,” Sweet said. At times, the rising ocean will block roads, start to threaten low-lying properties and commerce and increase erosion, collapsing coastal bluffs and overtopping dunes, he added.

Climate Justice and Science are Connected

California, one of the wealthiest parts of the world, may be able to adapt to sea level rise, but it’s a matter of life and death for millions of other people in developing countries with small carbon footprints that contribute little to global warming.

But new research in 2020 showed that researchers have done relatively little to study impacts of global warming extremes in areas where the most people are affected. And this year, climate impacts were compounded by the coronavirus pandemic. Together, they affected at least 50 million people worldwide, mostly in developing countries in Asia and Africa, as well as Central America.

But the impacts have mostly been measured in the developed world by scientists in wealthier nations, raising a fundamental issue of climate justice in science, said University of Oxford climate scientist Fredi Otto, co-author of a recent study that outlines the challenges of understanding climate extremes in lower income countries.

Soon after starting work on the study, she said, “It became very obvious that scientists research what’s in their backyard, but not in Africa, large parts of Asia, or South America.” As climate extremes intensify, the information gaps become “a lot more obvious,” she said.

The reason it’s important is that a lack of accurate information about extreme climate impacts puts more lives at risk, she said. “We don’t know what we need to adapt to and build resilience for … or what should trigger a heat warning,” she added.