In Jan. 2021, Nature Climate Change published a paper titled “Greater committed warming after accounting for the pattern effect”. Associate Prof. C. Zhou and Prof. M. Wang from School of Atmospheric Sciences, Nanjing University are coauthors of this paper.
Our planet’s energy balance is sensitive to spatial inhomogeneities in sea surface temperature (SST) and sea-ice changes. When there is a warming in the tropical subsidence or extratropical regions, the increase in free tropospheric temperature is relatively localized, and the local atmosphere warms less than the surface, leading to a positive lapse rate feedback. Local low cloud cover (LCC) decreases in response to the increase of SST and decrease of estimated inversion strength (EIS), resulting in a positive cloud feedback (Zhou et al. 2017). Conversely, when there is a warming in the tropical ascent regions, the troposphere warms more than the surface due to increased latent heat release, leading to a negative lapse rate feedback. The free-tropospheric temperature increases throughout the tropics, and the tropical mean EIS increases, inducing positive LCC anomalies and negative cloud feedback. The water vapor induced radiation anomalies are positive in response to SST warming all over the world, while the Planck feedback is always negative in response to regional SST warmings, and their magnitude in the tropics is larger than that in extratropics. As a result, the sum of cloud feedback, lapse rate feedback, Planck feedback and water vapor feedback is strongly negative in response to warmings in tropical ascent regions, and less negative or even positive in response to warmings in tropical descent regions and extratropics. The impact of spatial inhomogeneities in SST and sea-ice changes on radiation anomalies is usually defined to be “pattern effect”.
However, this process is typically ignored in climate projections. In Zhou et al. 2021, it is shown that 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 future climate based on 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, 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, though the magnitude is sensitive to SST dataset. Though the pattern effect is important in the closure of Earth’s energy budget and climate prediction, there are uncertainties on its magnitude, so further constraints on the pattern effect are needed to reduce climate projection uncertainty.
1. Zhou, C., M. D. Zelinka, and S. A. Klein (2017), Analyzing the dependence of global cloud feedback on the spatial pattern of sea surface temperature change with a Green's function approach, J. Adv. Model. Earth Syst., 9, doi:10.1002/2017MS001096.
2. Zhou, C., M. D. Zelinka, A. E. Dessler, and M. Wang (2021): Greater committed warming after accounting for the pattern effect. Nature Climate Change, doi: https://doi.org/10.1038/s41558-020-00955-x.