Decadal Predictions of the Probability of Occurrence for Warm Summer Temperature Extremes

Abstract

We use a decadal prediction system with the Coupled Model Intercomparison Project Phase 6 version of the coupled Max Planck Institute Earth System Model to predict the probability of occurrence for extremely warm summers in the Northern Hemisphere. An assimilation run with Max Planck Institute Earth System Model shows a robust response of summer temperature extremes in northern Europe and northeast Asia to North Atlantic sea surface temperature via a circumglobal Rossby wavetrain. When the North Atlantic is warm, warm summer temperature extremes occur with a probability of 20% and 24% in northern Europe and northeast Asia, respectively. In a cold North Atlantic phase, these probabilities are 0% and 8%. A similar difference in probability of occurrence is found in the initialized climate predictions. Consequently, the likelihood of a warm summer temperature extreme occurring in the examined regions in the next 10 years can be inferred from predictions of North Atlantic temperature. Plain Language Summary Extremely warm summers can have a substantial impact onsociety. Trustworthy predictions of such events several years ahead could help in anticipating the extremes and managing their impacts. In this study, we show that the probability with which a warm summer temperature extreme occurs in northern Europe and northeast Asia can be linked to the surface temperature of the North Atlantic ocean. We further show that North Atlantic ocean surface temperature and the connection between ocean temperature and extreme summer temperature can be predicted. As a result, the probability for extremely warm summers to occur in northern Europe and northeast Asia in the next 10 years can be predicted.

Summary of a workshop on extreme weather events in a warming world organized by the Royal Swedish Academy of Sciences

“…These results stand in contrast to modelling studies e.g. from CMIP6 suggesting a 0 to 8% probability for heat waves following cold surface temperatures (Borchert et al, 2019) or single-event attributions which show a small or no surface temperature control (Wehrli et al, 2019).…”

“…There is currently no consensus on the mechanisms causing the sudden increase in major European heat waves in recent decades. One possible mechanism, although its robustness is yet uncertain (Borchert et al, 2019), suggested that most major heat waves/droughts during this period appear to be linked with unusually cold North Atlantic sea-surface temperatures (e.g. Duchez et al, 2016) possibly due to a slowdown of the Atlantic Meridional Overturning Circulation (e.g.…”

On the risk of abrupt changes in the North Atlantic subpolar gyre in CMIP6 models

“…3A), which might influence heat wave occurrence over Europe, as suggested recently for the 2015 cooling event in the SPG, 28,29 although this remains under debate. 30 Figure 4 depicts the three-model ensemble mean response to cooling events in terms of precipitation. It shows a relatively clear southward shift of the Intertropical Convergence Zone (ITCZ) over the Atlantic sector for both summer and winter seasons.…”

North Atlantic climate far more predictable than models imply

“…We present results for the combination of 4 lagged forecasts, but find similar levels of skill for other combinations (NAO ACC = 0.71 and 0.78 for combining 3 and 5 lagged forecasts respectively). A similar technique relying on persistence of the predictor recently proved to strongly reduce the noise in decadal predictions of summer temperature extremes over land 62 .…”