The Arctic and Tibetan Plateau—the Two Poles—have warmed 2–3 times faster than the global warming rate since the late twentieth century. The challenges and opportunities are two sides of the same coin. On the challenging side, the two emerging heat engines drive waves in the midlatitude westerly jet streams and could lead to more persistent extreme weather events over Eurasia. In terms of opportunities, two-pole interactions are likely an untapped source of climate predictability, conveying memory from the slowly evolving boundary conditions (i.e., sea ice, snow, or sea surface temperature) to the atmosphere by modulating midlatitude teleconnections.
The COMBINED project sets out to better understand interactions between the rapid warming of the Arctic and Tibetan Plateau, as well as other remote and regional feedback processes. These complex interactions are poorly understood but potentially have profound climate impacts. In addition, COMBINED will exploit the benefits of the Arctic sea ice initialisation and Tibetan Plateau land-surface initialization to improve the prediction of Eurasian climate from weeks, seasons, to a decade in advance.
The COMBINED project will make extensive use of available observed datasets and international multi-model databases, as well as perform targeted “pacemaker” experiments to disentangle two-pole interactions and the remote influences on them. The COMBINED will conduct new experiments to assess the potential to improve climate prediction. For this we will use two national prediction systems from Norway (the Norwegian Climate Prediction Model) and China (the Beijing Climate Center Climate System Model) with refined initialisation methods of the Arctic and Tibetan Plateau cryosphere.
Finally, COMBINED aims to strength international collaboration between China and Norway on climate research.
The Arctic and Tibetan Plateau (TP) have warmed 2–3 times faster than the global warming rate since the late twentieth century. They act as two emerging heat engines, driving large-scale atmospheric circulation anomalies. COMBINED addresses two key open questions: What are the roles of internal and external climate variability and various physical processes in driving synchronous and asynchronous climate variations at the two poles, on sub-seasonal and longer timescales? What is the combined and likely non-linear impact of the warming of these two poles on Eurasian and global climate?
In COMBINED we will take an important step to distinguish the causes of the synchronous accelerated Arctic and TP warming and departures from it on S2S, S2D, and longer timescales. We will disentangle the global impacts of TP amplification and how it acts in concert with that of the Arctic to nonlinearly influence Eurasian climate; and we will assess how these impacts are modulated by interactions with the ocean and land-surface boundary conditions via midlatitude teleconnections. We will finally assess the emerging sources of predictability from the Arctic and TP for Eurasian climate on S2S and S2D timescales. To this end, in addition to advanced statistical approaches, we will perform a suite of pacemaker experiments where conditions over the Arctic, TP, and over the Pacific and Atlantic Oceans are constrained to follow historical observations. Through these we will quantify the relative roles of the various factors in driving TP and Arctic changes, and their combined effects. Parallel S2S-S2D predictions using two national prediction systems (NorCPM and BCC_CSM) with the same accurate initialisation methods for the Arctic and TP cryosphere will be conducted to provide deep insight into the mechanisms and predictability associated with the two-pole interactions.