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Climate Change: Polar Regions
Published in Yeqiao Wang, Atmosphere and Climate, 2020
The penultimate interglacial interval, known as the Eemian, peaked at approximately 125,000 years ago (125 ka), with temperatures approximately 1-2°C above those in the twentieth century. Trees grew as far north as northern Norway in what is now arctic tundra. However, the Greenland ice sheet persisted, although it shrank slightly.
Hot summers ahead? Multi-decadal spring season warming precedes sudden summer temperature rise in pre-anthropogenic climate change
Published in GFF, 2019
Margret Steinthorsdottir, Friederike Wagner-Cremer
Our paleo-records indicate an offset between spring and summer warming during natural phases of climate change, where rapid spring warming leads by approximately a century. This divergence in seasonal response to climatic triggers constrains modelled asynchronous responses determined for the warming episodes during the last deglaciation (Buizert 2015). Such temporal and spatial response estimates suggest that over Greenland, intensive winter warming exceeds the ultimate summer and, thus, mean annual temperature shifts (Buziert et al. 2018; Salonen et al. 2018). Asynchronous warming over Greenland is attributed to reorganization of Atlantic meridional overturning circulation, freshwater forcing and atmospheric CO2 dynamics (Buizert 2015; Buziert et al. 2018). Data-constrained simulations of July temperatures over the B–YD time interval show that relatively high summer temperatures prevail during the YD over large parts of the northern hemisphere, where the main temperature change is explained by intensification of continentality and, thus winter to spring cooling (Schenk et al. 2018). Our seasonally resolved temperature reconstructions underpin the relevance of winter and successive spring warming in annual temperature dynamics also during rapid warming phases. Uniquely, we are able to quantify the extremely dynamic seasonal warming outside of Greenland, where ice-core based modelling efforts may exceed their prediction limits. Such records from the terrestrial realm are thus a prerequisite to document the spatio-temporal phase relations of seasonal temperature over the large geographical realm undergoing rapid climate change, after oceanic and/or atmospheric reorganizations. Decoupling of seasonal temperatures during other geological periods which may serve as potential analogues for present climate change, such as the Eemian interglacial, has recently been highlighted by proxy-based temperature reconstructions, where the mixed imprints of insolation and oceanic forcing regulates seasonality expression in the high northern Latitudes (Salonen et al. 2018). The link to potential CO2 forcing during the Eemian, however is low. For the more recent climate episodes studied here, CO2 forcing needs to be considered (Steinthorsdottir et al. 2013, 2014). The CO2 dynamics during past rapid climate change as well as warmer-than-present episodes are related, however, to natural feedback mechanisms whereas ongoing warming is clearly related to the anthropogenic CO2 increase (IPCC 2014) and potentially develops alternative feedbacks. In the context of the ongoing climate change, where close to 40 years of spring warming has already occurred, assuming that the Arctic behaves similarly during the current warming to the two warming transitions we have shown for the late glacial, then we can expect that the rise in summer temperature will occur within 60 years. Given the pace of the present warming however, with at least twice the rate of spring onset advance measured in days/decade, as well as recent documented shifts in mid–low latitudes towards hotter summer temperatures (Hansen & Sato 2016), it is well possible that this threshold will be reached much sooner.