New scenarios and greater certainty in IPCC AR6

The Intergovernmental Panel on Climate Change (IPCC) has dramatically increased the certainty of predicted climatic effects under different emissions scenarios in the Working Group 1 contribution to its Sixth Assessment Report (AR6), released yesterday. The report from the global scientific body also introduced two new emission scenarios, one in which 2100 temperatures are kept below 1.5C and another in which emissions continue to increase and roughly double by the end of the century.

A doubling of atmospheric CO2 from pre-industrial levels would result in a “likely” (i.e., 67% chance) increase of 2.5C to 4C in average global temperature, the report shows – a full 50% reduction in uncertainty relative to the 1.5C to 4.5C range given in the 2014 AR5 and earlier reports. The concentration of CO2 in the earth’s atmosphere is already around 50% higher than pre-industrial levels.

Scenario analysis is a key part of climate risk assessment and is based on the physical science of potential emissions pathways and their resulting climatic effects. Guidelines to scenario analysis published by the Taskforce on Climate-related Financial Disclosures (TCFD), Network for Greening the Financial System (NGFS), International Energy Agency (IEA) and other international bodies rely heavily on the IPCC’s scientific assessment, and will incorporate the findings of the AR6 report over time.

However, civil society groups have expressed concern over the assumptions used in the development of climate-related scenarios and warn against reliance on yet-to-be-invented carbon capture and storage (CCS) at scale in order to balance the carbon books. A recent Reclaim Finance assessment of the NGFS’ climate scenarios finds an excessive reliance on CCS and unsustainable biomass energy, and a failure to acknowledge the need to end new fossil fuel investments.

The publication of the IPCC AR6 report was accompanied by the launch of an interactive atlas showing regional climatic projections under different emission pathways, and is intended to assist in climate-related scenario analysis. The new tool offers projections for a range of atmospheric and oceanic variables over both historical and future time scales and using a variety of climate models.

“Climate change is already affecting every region on Earth, in multiple ways, and the changes we experience will increase with additional warming,” said IPCC Working Group I Co-Chair Panmao Zhai in a press release accompanying the AR6 report. “Stabilizing the climate will require strong, rapid, and sustained reductions in greenhouse gas emissions, and reaching net zero CO2 emissions.”

Released during a summer of record-breaking extreme weather events, the AR6 report focuses only on the physical science basis of climate change and is the first of three major working group contributions  to the IPCC AR6 assessment round, the first since 2014. Updated reports on climate impacts and on actions for mitigation will be released next spring along with a synthesis report for policymakers.