The new van Vuuren et al 2026 paper formally retired RCP8.5/SSP5-8.5 from the upcoming IPCC AR7. Cue celebration from skeptics (including Donald Trump: "WRONG! WRONG! WRONG!") and pushback from folks who say nothing has actually changed gmd.copernicus.org/artic…
When RCP8.5 was published in 2011, global emissions had just grown 30% in a decade, clean energy was expensive, and EVs barely existed. Even then, RCP8.5 was chosen to represent the ~90th percentile of baseline scenarios. It was always the high end, not the central case.
But due to a breakdown in communication between energy modelers and climate scientists, RCP8.5 got widely (mis)labeled as "business as usual." That framing stuck, and led to inaccurate portrayals of likely futures in a lot of impact research over the past 15 years.
Methane and other short-lived GHGs have an outsized climate impact but a short lifetime. In a new preprint with Ella Holme, Randy Spock, and Chris van Arsdale, we explore how these can be combined with durable carbon removal to make credible neutralization claims: cdrxiv.org/prepr…
Claiming to neutralize CO2 emissions with methane (or other SLCP) mitigation is problematic. It trades off short-term cooling for long-term warming in a way that is inconsistent with our targets of long-term stabilization global surface temperatures:
However, if SLCP mitigation is paired with delayed durable carbon removal purchasing, it can effectively result in the same climate impacts as CO2 mitigation. We propose a "Warming Neutralization" approach that combines the two:
The underlying math is complex and relies on running climate model simulations, but we distill it into simple heuristics including the latest year of replacement with durable CDR and the amount of SLCP mitigation needed per ton of CO2 emitted.
First, I've incorporated the ECMWF 46-day forecast (and its ensemble uncertainty) into the global mean surface temperature anomaly figure, so you can see both historical and forecast near-term temperatures.
Second, I've added a daily-updated tracker of the likely annual rank for the current year (2026) in ERA5 based on both the year-to-date temperatures and the ENSO forecast, accounting for uncertainties.
The next week is looking like it might be toasty for global temperatures in the latest model runs. If this holds it would put us well into record territory for this time of year: karstenhaustein.com/clima…
