Scientists at Lawrence Livermore National Laboratory in collaboration with colleagues from Nanjing University and Texas A&M University have re-evaluated how much future global warming is in the pipeline if atmospheric greenhouse gas concentrations were to remain fixed at present-day levels, a quantity known as committed warming. Their new analysis accounts for the fact that surface warming to date has been large in certain regions but small in others, which has temporarily allowed Earth to shed heat more efficiently. Ignoring this “pattern effect”, as has been done in previous studies, gives the false impression that Earth’s energy budget is nearly balanced and implies that committed warming is only about 1.3°C (2.3°F) above pre-industrial levels. The team’s updated estimate is substantially larger, with a most likely value of 2.3°C (4.1°F). 

Our planet’s energy balance is sensitive to spatial inhomogeneities in sea surface temperature and sea ice changes, but this is typically ignored in climate projections. Here, we show the energy budget during recent decades can be closed by combining changes in effective radiative forcing, linear radiative damping and this pattern effect. The pattern effect is of comparable magnitude but opposite sign to Earth’s net energy imbalance in the 2000s, indicating its importance when predicting the future climate on the basis of observations. After the pattern effect is accounted for, the best-estimate value of committed global warming at present-day forcing rises from 1.31 K (0.99–2.33 K, 5th–95th percentile) to over 2 K, and committed warming in 2100 with constant long-lived forcing increases from 1.32 K (0.94–2.03 K) to over 1.5 K, although the magnitude is sensitive to sea surface temperature dataset. Further constraints on the pattern effect are needed to reduce climate projection uncertainty.

The widespread idea that decades, or even centuries, of additional warming are already baked into the system, as suggested by previous IPCC reports, were based on an “unfortunate misunderstanding of experiments done with climate models that never assumed zero emissions.” 

Ein Gastbeitrag von Stefan Rahmstorf Dramatisch übertriebene Berichte über Forschungsergebnisse können Resignation auslösen. Ein aktuelles Beispiel machte wieder Schlagzeilen – dabei war die Methode wenig aussagekräftig.

The severity of damaging human-induced climate change depends not only on the magnitude of the change but also on the potential for irreversibility.

The Zero Emissions Commitment (ZEC) is the change in global mean temperature expected to occur following the cessation of net CO2 emissions and as such is a critical parameter for calculating the remaining carbon budget. The Zero Emissions Commitment Model Intercomparison Project (ZECMIP) was established to gain a better understanding of the potential magnitude and sign of ZEC, in addition to the processes that underlie this metric. A total of 18 Earth system models of both full and intermediate complexity participated in ZECMIP. All models conducted an experiment where atmospheric CO2 concentration increases exponent