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Our world is 1.2 degrees Celsius (2.2 degrees Fahrenheit) hotter than it was at the dawn of the second Industrial Revolution. And without a rapid decrease in greenhouse gas emissions, the odds of exceeding the critical 1.5 degrees Celsius (2.7 degrees
Fahrenheit) threshold within the next five years are roughly 50/50.
A new study suggests that the consequences of crossing those limits could be more severe than previously thought — including the irreversible
breakdown of foundational Earth systems, Henry Fountain reported for The New York Times.
The study’s authors, including Johan Rockström, Conservation International’s chief scientist, assessed the risk of 16 different climate “tipping points” — events that, if triggered, could set in motion a self-perpetuating
cycle of environmental collapse. Their research, published in Science, identified three such tipping points that become likely at 1.5
degrees Celsius (2.7 degrees Fahrenheit) of warming.
First, enormous ice sheets in Greenland and West Antarctica could collapse. As these structures lose mass to melting, they also lose height, which means the surface is exposed to warmer, lower-lying air. Shrinking, in essence, begets more shrinking. Losing
this much ice would translate to multi-foot sea-level rise around the world.
Second, Arctic permafrost would rapidly thaw. These frozen soils and sediments store more than 1,000 gigatons of carbon — equivalent to a century
of human emissions at current levels. Thawing would release this gas back into the atmosphere, accelerating atmospheric warming. Moreover, the loss of reflective ice would increase the amount of solar radiation absorbed by Arctic landmasses, further hastening melting.
Third, coral reefs, which support a quarter of the world’s marine species,
could face mass bleaching. When corals are exposed to sufficiently warm waters, they expel the symbiotic microbes that keep them alive. The loss of coral cover would have disastrous effects on marine food webs, potentially jeopardizing hundreds of millions of people around the world who depend on them for food, livelihoods and storm protection.
Authors identified even greater risks at 2 degrees Celsius (3.6 degrees Fahrenheit), including the rapid loss of mountain glaciers that feed into freshwater rivers, as well as the collapse of deep-sea systems in the North Atlantic that regulate weather in Europe. These tipping points, if triggered, would be catastrophic for climate, biodiversity and human well-being. Researchers
could not rule out the possibility that some of these processes are already underway.
“Every tenth of a degree counts,” Rockström told The New York Times.
When the Paris Agreement was adopted in 2015, 196 countries committed to limiting global warming to “well below” 2 degrees Celsius (3.6 degrees Fahrenheit), and “preferably” lower. To achieve those targets, Rockström found that humanity must cut fossil fuel emissions in half every decade. Presently, few countries are on track to achieve this, and estimates suggest that existing climate policies could result in net warming of 2.6 degrees Celsius (4.7 degrees Fahrenheit) by 2100.
In November, world leaders will gather in Egypt for the United Nations climate conference, known as COP27. Last year, negotiators overcame years of stalemate to agree on rules for international carbon trading. Delegates will now turn to implementation of the Paris Agreement —
and experts expect negotiations will be complicated by ongoing
energy shortages, even as the effects of climate change become increasingly visible.
“This report by Johan Rockström and colleagues is a sobering reminder that +1.5 degrees Celsius is not a prescription, it is a threshold — the point at which the fabric of life starts to come apart at the seams,” wrote Conservation International CEO M. Sanjayan. “We cannot afford gridlock at COP27: It’s time to fully deliver on the Paris Agreement.”
Read the full article here.