Forced Changes in the Arctic Freshwater Budget Emerge in the Early 21st Century

Abstract:

Arctic liquid freshwater (FW) storage has shown a large increase over the past decades, posing the question: Is the Arctic FW budget already showing clear signs of anthropogenic climate change, or are the observed changes the result of multi-decadal variability? We show that the observed change in liquid and solid Arctic FW storage is likely already driven by the changing climate, based on ensemble simulations from a state-of-the-art climate model. Generally, the emergence of forced changes in Arctic FW fluxes occurs earlier for oceanic fluxes than for atmospheric or land fluxes. Nares Strait liquid FW flux is the first to show emergence outside the range of background variability, with this change potentially already occurring, followed by Davis Strait. Other FW fluxes have likely started to shift but have not yet emerged into a completely different regime. By re-sampling the model simulations, we find that the already changing nature of many FW budget terms over the observational period can delay detection of shift and emergence from observations. Future emissions reductions have the potential to avoid the emergence of some FW fluxes beyond the background variability, in particular for runoff and Fram Strait solid FW export. However, under both low and high warming scenarios, all FW fluxes show changes, just not always completely outside the background variability.