Quantifying two-way influences between the Arctic and mid-latitudes through regionally increased CO2 concentrations in coupled climate simulations

Abstract

In which direction is the influence larger: from the Arctic to the mid-latitudes or vice versa? To answer this question, CO 2 concentrations have been regionally increased in different latitudinal belts, namely in the Arctic, in the northern mid-latitudes, everywhere outside of the Arctic and globally, in a series of 150 year coupled model experiments with the AWI Climate Model. This method is applied to allow a decomposition of the response to increasing CO 2 concentrations in different regions. It turns out that CO 2 increase applied in the Arctic only is very efficient in heating the Arctic and that the energy largely remains in the Arctic. In the first 30 years after switching on the CO 2 forcing some robust atmospheric circulation changes, which are associated with the surface temperature anomalies including local cooling of up to 1 °C in parts of North America, are simulated. The synoptic activity is decreased in the mid-latitudes. Further into the simulation, surface temperature and atmospheric circulation anomalies become less robust. When quadrupling the CO 2 concentration south of 60° N, the March Arctic sea ice volume is reduced by about two thirds in the 150 years of simulation time. When quadrupling the CO 2 concentration between 30 and 60° N, the March Arctic sea ice volume is reduced by around one third, the same amount as if quadrupling CO 2 north of 60° N. Both atmospheric and oceanic northward energy transport across 60° N are enhanced by up to 0.1 PW and 0.03 PW, respectively, and winter synoptic activity is increased over the Greenland, Norwegian, Iceland (GIN) seas. To a lesser extent the same happens when the CO 2 concentration between 30 and 60° N is only increased to 1.65 times the reference value in order to consider the different size of the forcing areas. The increased northward energy transport, leads to Arctic sea ice reduction, and consequently Arctic amplification is present without Arctic CO 2 forcing in all seasons but summer, independent of where the forcing is applied south of 60° N. South of the forcing area, both in the Arctic and northern mid-latitude forcing simulations, the warming is generally limited to less than 0.5 °C. In contrast, north of the forcing area in the northern mid-latitude forcing experiments, the warming amounts to generally more than 1 °C close to the surface, except for summer. This is a strong indication that the influence of warming outside of the Arctic on the Arctic is substantial, while forcing applied only in the Arctic mainly materializes in a warming Arctic, with relatively small implications for non-Arctic regions.

Process Drivers, Inter-Model Spread, and the Path Forward: A Review of Amplified Arctic Warming

“…Since 2010, studies have focused on using observations and coupled models synergistically to understand polar amplification, including a reemergence of idealized model set-ups (e.g., Chung and Räisänen, 2011;Feldl et al, 2017a;Yoshimori et al, 2017;Park et al, 2018;Shaw and Tan, 2018;Stuecker et al, 2018;Previdi et al, 2020;Semmler et al, 2020). New satellite data sets (Winker et al, 2010;Boisvert et al, 2013;Kato et al, 2018;Loeb et al, 2018;Duncan et al, 2020) and more sophisticated meteorological reanalyses have been enabling factors (Screen and Simmonds, 2010;Boisvert and Stroeve 2015).…”

“…GCM experiments have been performed to gauge the remote impact on Arctic warming. Some used a direct extra energy term added to the SEB ("ghost forcing", Alexeev et al, 2005;Park et al, 2018), some used latitudinally confined CO 2 increases (Chung and Räisänen, 2011;Shaw and Tan, 2018;Stuecker et al, 2018;Semmler et al, 2020) while others specified SST increases at lower latitudes (Yoshimori et al, 2017). Common to these approaches is that any Arctic warming that occurs, does so due to the indirect effects of the remote warming.…”

Process drivers, inter-model spread, and the path forward: A review of amplified Arctic warming

“…Since 2010, studies have focused on using observations and coupled models synergistically to understand polar amplification, including a reemergence of idealized model set-ups (e.g., Chung and Räisänen, 2011;Feldl et al, 2017;Yoshimori et al, 2017;Park et al, 2018;Shaw and Tan, 2018;Stuecker et al, 2018;Semmler et al, 2020). New satellite data sets (Loeb et al 2018;Kato et al 2018;Boisvert et al 2013;Winker et al 2010;Duncan et al 2020) and more sophisticated meteorological reanalysis are enabling factors (Screen and Simmonds 2010;Boisvert and Stroeve 2015).…”

“…GCM experiments have been performed to gauge the remote impact on Arctic warming. Some used a direct extra energy term added to the SEB ("ghost forcing", Alexeev et al, 2005;, some used latitudinally confined CO 2 increases (Chung and Räisänen, 2011;Shaw and Tan, 2018;Stuecker et al, 2018;Semmler et al, 2020) while others specified SST increases at lower latitudes (Yoshimori et al, 2017). Common to these approaches is that any Arctic warming that occurs, does so due to the indirect effects of the remote warming.…”

“…Common to these approaches is that any Arctic warming that occurs, does so due to the indirect effects of the remote warming. Chung and Räisänen (2011) attribute 60-85% of Arctic warming to non-local drivers, Yoshimori et al (2017) AA therefore arises in part due to an asymmetry between low-to-high and high-to-low latitude impacts: low-latitude warming is efficiently communicated poleward while high-latitude warming is less efficiently communicated equatorward (Alexeev et al, 2005;Chung and Räisänen, 2011;Shaw and Tan, 2018;Park et al, 2018;Stuecker et al, 2018, Semmler et al, 2020. Non-Arctic…”