The potential of seasonal-to-decadal-scale inter-regional linkages to advance climate predictions

Global warming is enhanced in the Arctic, where surface air temperature has increased at twice the rate of the global average in recent decades - a feature called Arctic amplification. The rapid reduction in Arctic sea ice is the most visible indicator of global warming. In contrast to global warming, northern continents have experienced severe cold winters. The linkage between the warm Arctic and cold continents has drawn much attention. However, no consensus has been reached. On the other hand, both the Pacific and Atlantic Oceans have clear multi-decadal variability. Furthermore, individual studies also suggest both Oceans influence Arctic climate. Thus, there is a need to better understand the linkages between the rapid change in Arctic climate and the climate over lower latitude regions and how these Oceans regulate the linkage. We used satellite-derived sea ice and sea surface temperature to run coordinated hindcast experiments with five different atmospheric general circulation models. The ensemble means of multi-model mean suggest that Arctic sea ice loss is not responsible for the observed cooling trend over Eurasia. By performing further analysis on each individual simulation by each model, we found that the cooling over Eurasia is more closely linked to the Arctic tropospheric warming, not surface warming (sea ice loss).

The project results suggest that the Pacific is a potential source region to predict the decadal-scale warming over the Arctic. This can benefit the Arctic society to prepare the adaption measures in response of climate change. The sea ice change in the Barents Sea and the upper troposphere warming can likely serve another potential source for sub-seasonal to seasonal prediction of winter climate over Eurasia which can benefit the society in mid-latitude countries.

Globally averaged surface air temperature (SAT) during the 20th and 21st centuries displays a gradual warming and superimposed year-to-year and decadal-scale fluctuations. The upward trend contains the climate response to an anthropogenic increase of heat trapping atmospheric greenhouse gases. The temperature ups and downs around the trend - that are particularly pronounced in the Arctic - mostly reflect natural variability. Natural climate variations are of two types, internal and external. The former is produced by the climate system itself, e.g., due to variations in ocean circulation. An example of the later is solar-induced climate variability. Decadal-scale variability is of large social relevance. It is observed, for example, in Atlantic hurricane activity, Sahel rainfall, Indian and East Asian Monsoons, Eurasian winter coldness and in the Actic SAT and sea ice. The understanding and skillful prediction of decadal-scale climate variability that modulates the regional occurrence of extreme weather events will be of enormous societal and economic benefit. InterDec is an international initiative aiming at understanding the origin of decadal-sacle climate variability in different regions of the world and the linkages between them by using observational data sets and through coordinated multi-model experiments. How can a decadal-scale climate anomaly in one region influence very distant areas of the planet? This can happen through atmospheric or oceanic teleconnections. Fast signal communication between different latitudinal belts within days or weeks is possible through atmospheric teleconnection, whereas communication through oceanic pathways is much slower requiring years to decades or even longer. Understanding these processes will enhance decadal climate prediction of both mean climate variations and associated trends in regional extreme events.