The brutal math of climate change is this: as long as CO2 emissions remain above zero, the world will continue to warm. The medium scenario ends up closer to 3.7C by 2150, while the high scenario ends up more or less matching the warming in the old RCP8.5 scenario despite an assumption of flattening or modestly declining emissions after 2100.
It is also wrong to say that the worst predictions of climate impacts this century can now be ruled out by this revision. High-end temperature projections for the end of the century are reduced compared to earlier IPCC assessments. Yet, the
IPCC WGII report found that risks across the five “reasons for concern” it examines have all risen for a given level of global warming. So, even if the high-end emissions in RCP8.5 won’t materialize, the damages projected in these earlier climate simulations remain very much in play.
A tripling of global CO2 emissions by 2100 may never have been particularly plausible even back in 2011 when RCP8.5 was originally published. But a 21st century of increasing fossil fuel use leading to a doubling of emissions was within the realm of the possible. The fact that we are no longer heading toward that is a sign of progress, rather than somehow undermining the edifice of all of climate science as both President Trump and some overly excited internet pundits claim. And of course, we still have a long way to go to get emissions down to (net) zero and stabilize global temperatures.
After all, as we
wrote back in 2020, “This admission does not make climate action less urgent. The need to limit warming to [well below 2C]
3… does not depend on having a 5C counterpoint.”
