For decades scientists have struggled to determine how much the Earth will warm up for a given amount of carbon dioxide in the atmosphere. The term for this is Equilibrium Climate Sensitivity (ECS). The classic way of framing it is to ask what happens if we double the amount of carbon dioxide in the atmosphere compared to the level prior to the Industrial Revolution, which was 280 parts per million (ppm). (Today it is 415 ppm.)
Historically the ECS has been estimated at 1.5 to 4.5 degrees Celsius, but in July 2020, a team of 25 scientists from around the world recalculated the ECS using more data than was previously available. They determined that the ECS is actually between 2.6 and 3.9 degrees Celsius. This is a tighter range than before, and the low end is 1.1 degrees higher. This means that, without serious mitigation efforts, the Earth will heat faster than has been predicted.
Based on current energy consumption trends, and allowing for the growth of renewables, some estimates predict that carbon dioxide concentration will reach 560 ppm (a doubling of 280) by 2050. If we conservatively take the low end of the ECS range, that means that by mid-century, the average global surface temperature will be at a minimum 2.6 degrees higher than the pre industrial level. The International Panel on Climate Change (IPCC), representing the studies of climate scientists from across the world, has stated that at 2.0 degrees increase, the climate impact would be catastrophic with severe consequences for the global civilization.
Editor’s note: Dan Lennon distilled this piece from Umair Irfan’s piece on Vox.com: Scientists have backed away from the worst-case climate scenario — and the best one too