Climate 101 is a Mashable series that answers provoking and salient questions about Earth’s warming climate.
We aren't yet doomed.
Climate research published on Nov. 12 in the journal Scientific Reports claims Earth "is alreadypast a point-of-no-return for global warming," which provoked the ire of many climate scientists. The research has glaring flaws (detailed later), ultimately making the dubious case that the planet's frozen soil, or permafrost, will inevitably "melt" (soil actually thaws), leading to a cycle of more warming as heat-trapping greenhouse gases leach from the carbon-rich soil.
Though the scientific world is filled with quality, carefully vetted climate research, from time to time a "point of no return" study makes its way into a mainstream research journal and, unfortunately, might get amplified or misinterpreted by some news outlets. When you see these doomist-type headlines, it's crucial to remember that humanity still has great swayover how much we disrupt the climate in the coming decades. We haven't tipped the global climate, in terms of warming, past a "point of no return," according to climate scientists.
"We have a significant amount of influence over how much warmer it gets," said Zeke Hausfather, a climate scientist and the director of climate and energy at the Breakthrough Institute, an environmental research center. Hausfather had no involvement with the Scientific Reports study.
The climate — an intricate nexus of the expansive oceans, diverse lands, the frozen polar regions, and a wildly chaotic atmosphere — is difficult to flip into an abrupt "tipping point," like a switch. Yet the continued heating of the globe brings the adverse consequences of surging wildfires, melting ice sheets, destabilized glaciers, major droughts, historic heat waves, and beyond. More warming exacerbates these impacts. "It's a progressively worse problem," emphasized Hausfather.
(It is, of course, already possible for localized or regional places to shift into a new environmental paradigm that can't be reversed for thousands of years or longer, like the disappearance of glaciers, loss of Arctic sea ice, or potentially the irreversible drying of large swathes of the Amazon rainforest.)
"We are making tomorrow's climate today."
There isn't a specific, known tipping point that would drive unstoppable warming in the near future, though such tipping points might exist. But limiting carbon emissions today inherently reduces the possibility of triggering such an exceptional event.
"We are making tomorrow's climate today," said Sarah Green, an environmental chemist at Michigan Technological University who had no role in the study. "In the long term, we should be worried about tipping points and work to understand the risks. However, if a tipping point is in our future, we still have some control over when it occurs. The faster we decrease our emissions the farther into the future any tipping points will be."
Humanity has already stoked significant climate change. Nineteen of the last 20 years are the warmest on record, and Earth's levels of atmospheric carbon dioxide are the highest they've been in at least800,000 years, but more likely millions of years. That's why extreme deluges are increasing, and long-held heat records are breaking.
"We’re already experiencing the dangerous effects of climate change," said Bob Kopp, a climate scientist and director of the Institute of Earth, Ocean, and Atmospheric Sciences at Rutgers University. Kopp had no role in the Scientific Reports study.
What comes next is still largely up to us, no matter what a doomist headline claims. It's relatively simple. Greenhouse gases, particularly carbon dioxide and methane, trap heat on Earth. (As far back as 1896, the Swedish scientist Svante Arrhenius had establishedthe fundamental relationship between rising CO2 and a changing climate). So emitting less carbon will reduce the severity of climate change.
"Every bit we emit causes more damage," said Kopp. "The sooner we stop emitting, the less damage we’ll cause."
Though projections into the future (of any sort) come with some uncertainty, climate scientists have a good handle on where the climate is broadly headed, based on different carbon emission scenarios (projections of how much carbon society might emit this century). On supercomputers, climate researchers run complex simulations of how the oceans, atmosphere, and lands will react to different levels of greenhouse gases in the atmosphere. Higher emissions mean a hotter future with increasingly adverse climate impacts. "Our best knowledge continues to suggest that we have a clear and still large say in how our future looks," said Flavio Lehner, a climate scientist at Cornell University who researches climate change projections. Lehner had no involvement with the Scientific Reports study.
Right now, the carbon emissions path we're on, commonly called "business as usual," will lead to some 3 degrees Celsius, or some 5.4 degrees Fahrenheit, above pre-Industrial Revolution temperatures by the century's end, according to an analysis by Hausfather (though the warming could be more or less than 3C, depending on how Earth responds to increased greenhouse gases). This 3C path, which would have extreme if not catastrophic effects, implies no new climate policies by world governments (beyond those in place today) to curb carbon emissions.
But with robust efforts from the world's nations, particularly major emitters like China, the U.S., the EU, and India, civilization might stabilize the climate at around 2C, or 3.6F, above pre-industrial levels. In 2015, global nations agreed to try and limit warming "to well below 2C above pre-industrial levels." This would be hugely significant, though also hugely ambitious (because prodigious carbon emissions continue to saturate the atmosphere).
As future projections go, a common refrain or idea that persists in the climate conversation is we only have around a decade to avoid climate catastrophe, which references a 2030 tipping point deadline, popularized in media stories in 2018. But this sort of threshold or tipping point, based on an interpretation of a UN Intergovernmental Panel on Climate Change report about limiting warming to 1.5 C, is misleading.
"The message is not 'the world ends in 2030,'" explained Kopp. Rather, it's that if we hope to eventually stabilize the planet's warming at an extremely ambitious 1.5C above pre-Industrial levels by mid-century, CO2 emission levels in 2030 have to be substantially lower than they are today. (Emissions would have to start dropping sharply, and promptly, eventually by some 45 percent by 2030.) Critically, if emissions don't drop so dramatically by 2030 — and they may not — catastrophe isn't imminent.
Tweet may have been deleted
Tweet may have been deleted
1.5C and 2C targets aren't tipping points or "points of no return," though they may appear like absolute cutoffs from misleading headlines. "People treat them as thresholds," said Hausfather, noting the targets are the results of political negotiations, not scientifically proven thresholds. "It's not like 1.9C is completely safe and 2C is extremely unsafe," he said.
There's no need to accept doom if a climate target is missed. That might lend itself to defeatism or inaction. "The need to limit warming to below 2C doesn't require an apocalyptic counterfactual," said Hausfather.
The recent "point of no return" study likely won't be the last.
In this case, the two authors use an oversimplified climate model (ESCIMO) that doesn't capture complicated earth systems, explained Hausfather. They conclude that the warming of frozen soil (permafrost) will result in a runaway release of carbon, in combination with other factors like the disappearance of snow and ice. "Certainly, I would not trust such a simplified model to predict tipping points, which are by definition non-linear, highly uncertain responses to a complex system," said Michigan Technological University's Green. To boot, it appears the authors are somewhat unfamiliar with permafrost, as they note it will "melt," though ice melts and the ground thaws. (In an updated press release from Scientific Reports, the journal now emphasizes the climate model used is of "reduced complexity" and "The authors encourage other researchers to explore their results using alternative models.")
Importantly, permafrost is warmingas the Arctic heats up, and it could become a significant source of carbon emissions. Already, thawed permafrost could be releasing some 300 to 600 million tons of carbon into the atmosphere each year (equating to about 5 to 10 percent of annual greenhouse gas emissions from the U.S.). It's an area of active and salient research, as Arctic areas could potentially unleash hundreds of billions of tons of carbon into the atmosphere in the coming centuries. But, critically, climate researchers haven't observed permafrost regions reaching a purported "point of no return," noted Kopp.
The looming impacts of climate change, however, remain serious. The oceans are projected to rise by around one to two feet by the century's end. Though with more human-caused warming, the seas could potentially rise by some three feet, or significantly more. This is all the reason not to accept doom or helplessness.
Tweet may have been deleted
"The worst impacts of climate change happen with the most warming," said Hausfather.
When you see a sensationalist "point of no return" headline in the future, here are some tips:
Look if the story includes the perspective of outside experts not involved in the research. If the story makes big claims but lacks outside scrutiny, be wary of a headline that advertises momentous, irreversible impacts.
Climate change is largely a progressive problem. It gets worse as human activities make it progressively worse.
Sometime this century, however, we may become aware that we've passed some type of tipping point, perhaps in a critical region on Earth. Civilization, having already destabilized Antarctica's Florida-sized Thwaites Glacier, which is capable of unleashing many feetof sea level rise, might watch Thwaites purge an unstoppable barrage of ice into the ocean. Such an event would likely redraw coastal maps around the world. Even if that happens, it would still be critical to curb carbon emissions, for all is not lost: An ever-warming climate will still exacerbate a plethora of other impacts like wildfires, deluges, and droughts.
"If we stop putting greenhouse gases into the atmosphere, climate change will stop getting worse," emphasized Kopp.
相关文章：
相关推荐：