Researchers Say the Worst Climate Future is Less Likely. But the Best One is Also Slipping Away

Citing new research, the Associated Press reports that "modest gains in the fight to curb climate change have dialed back the most catastrophic of future heating."
That's the good news. But the same research "also confirmed that there's no chance to limit warming to the international goal set in 2015."

Researchers' new list of seven plausible carbon pollution scenarios for the future are pushing aside two staples of climate policy: the extremes on either end. The extremes have become less probable in the past several years because of how we power our world. Carbon dioxide, released from the burning of gas, oil and coal, is chiefly responsible for warming. Increasing use of green energies, like solar, wind and geothermal, which don't emit carbon dioxide, have lowered top end carbon pollution projections. However, because those changes haven't been fast enough, the bottom end projections have risen.

The Paris climate agreement in 2015 set a goal of limiting warming to 1.5 degrees Celsius (2.7 degrees Fahrenheit) since pre-industrial times, or the mid-1800s, giving rise to the mantra "1.5 to stay alive," but now scientists say that even their best case scenario still shoots past that signature temperature mark. On the other end, those same new scenarios no longer include the coal-heavy future that would lead to 4.5 degrees Celsius (8.1 degrees Fahrenheit) of warming by 2100, a scary scenario that many scientific studies used in their future projections.
The new proposed worst case scenario has an end-of-the-century warming of about 3.5 degrees Celsius (6.3 degrees Fahrenheit), a full degree (1.8 degrees Fahrenheit) less than the old scenario, while the updated best case future is a couple tenths of a degree Celsius (0.36 degrees Fahrenheit) warmer than previously theorized, squeezing past the Paris goal, said climate scientist Detlef Van Vuuren of Utrecht University, lead author of a recent study laying out future scenarios. "There is kind of a narrowing of the futures. It cannot be as bad as we thought, but it cannot be as good as we hoped," said Johan Rockström, director of the Potsdam Institute for Climate Impact Research in Germany.

The scenarios include a "middle" one where by the end of the century the world warms 3 degrees Celsius (5.4 degrees Fahrenheit) above pre-industrial times, which is roughly the path society is currently on, scientists said... Because carbon pollution keeps rising globally and stays in the atmosphere for about century, the best case scenario is for warming to shoot past the 1.5 degree mark, peak at 1.7 degrees Celsius (3.1 degrees Fahrenheit) for maybe as long as 70 years, and eventually somehow come back down below 1.5 degrees if a technology can be designed to remove massive amounts of carbon from the air, said nine of the 10 scientists interviewed for this article. The world is warming at a pace of a tenth of a degree Celsius (nearly 0.2 degrees Fahrenheit) every five years, they said.

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