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

Den globale oppvarmingen er sterkere i Arktis, hvor lufttemperaturen har økt dobbelt så mye som det globale gjennomsnittet i løpet av de siste tiårene. Dette kalles Arctic amplification, eller arktisk forsterkning på norsk. Det raske tapet av sjøis i Arktis er den mest synlige faktoren på global oppvarming. I kontrast med den globale oppvarmingen har de nordlige kontinentene opplevd svært kalde vintre. Sammenhengen mellom det varme Arktis og de kalde kontinentene har fått mye oppmerksomhet, men det er ikke oppnådd en felles forståelse for denne sammenhengen. På den andre siden, så har både Stillehavet og Atlanterhavet tydelig multi-dekadisk variabilitet, og individuelle studier foreslår at begge havene påvirker Arktisk klima. Det er derfor behov for en bedre forståelse av sammenhengene mellom de raske klimaendringene i Arktis og klimaet over lavere breddegrader, samt hvordan havene kontrollerer denne sammenhengen. Vi har brukt sjøis og havoverflatetemperatur fra satellittdata for å lage varsler tilbake i tid med fem forskjellige sirkulasjonsmodeller for atmosfæren. Gjennomsnittet av modellene indikerer at sjøistapet i Arktis ikke er ansvarlig for nedkjølingen over Eurasia. Ved å gjøre videre analyser for hvert enkelt eksperiment for hver modell finner vi at nedkjølingen over Eurasia henger nært sammen med oppvarmingen i troposfæren i Arktis, og ikke oppvarming ved havoverflaten (på grunn av sjøistap).

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.