The best current science predicts that greater than 1.5° C (2.7° F) would cause catastrophic, irreversible climate change; therefore, many institutions have set goals to align with a <1.5° C pathway.
This benchmark was created in the Paris Agreement, a global climate pact signed by 195 countries, to define a reasonable target that would help the world avoid the worst outcomes of climate change. At present, though, the world is falling well short of what it needs to remain below 1.5°. Few countries are on track to meet their Paris pledges, and even if every country met every one of their pledges, emissions would still surpass 1.5° levels by over 19 Gigatonnes –the equivalent annual emissions of nine of the top ten emitting countries in the world in 2023.[1] If every country met their goals, we would still expect to see 2.9° C warming by 2100.
The current path would see us surpass 4.4° C (7.9° F) by 2100. Scientists warn that these seemingly small differences between 1.5 and 2, or 3 and 4, have major implications. It can be hard to predict exactly what each degree of warming means, but we know that risk grows geometrically (meaning a 1% change in temperature causes a >1% change in risks, and that those differences add up for each small change in temperature). Looking back over the Earth’s history, we find that a shift of 11° C is the difference between an ice age and having palm trees growing in the Arctic Circle. Taken at the scale of human-caused global warming, the 0.5° C (0.9° F) between 1.5° C and 2° C could mean the difference between losing 75% of coral reefs and 99%; at 2° C warming we expect to see heatwaves that occurred once per decade before climate change happen roughly every other year, but at 4° C they would happen almost every year. 4.4° C (7.9° F) warming would fundamentally change the way that humans have to live as certain areas become uninhabitable for parts of the year, once-in-a-century storms happen regularly, and diseases spread to new regions. It is imperative that we start reducing emissions now or else future cuts will have to be even more severe to avoid the worst possible impacts. Otherwise, we will have to adapt to a new world of our own creation.
[1] The best science suggests that we need to reduce emissions by 43% relative to 2019 levels by 2030 to keep global warming below 1.5° C. Meanwhile, all the existing targets would only yield a 5.3% reduction. Based on total emissions in 2019 (52.4 Gigatons), this leaves a 19.75 Gigaton gap between goals and needs.
