CONSTRAIN’s new report on climate sensitivity and its role in climate projections has identified a number of important knowledge gains.
Climate sensitivity indicates how strongly and how quickly the Earth’s temperature responds to rising greenhouse gas concentrations. If the
Earth’s climate sensitivity is high, it means a lot of warming will occur for a given increase in atmospheric CO2 concentration. Calculations of climate sensitivity are therefore central to calculating reliable projections of future climate change.
CONSTRAIN’s insights include narrowing down the uncertainty in climate sensitivity and projected warming by 30-50%. For example, climate sensitivity estimates need to account for the fact that using historical data to derive spatial patterns of warming (the “pattern effect”) probably lead to them being underestimated. Once this is accounted for, “observed” climate sensitivity is in better agreement with other lines of evidence.
The report also discusses how although some of the latest (CMIP6) climate models project very strong warming, they include strong reductions in shallow cloud coverage that are difficult to reconcile with historical data, and so their projections are unlikely.