Fasting Season Length Sets Temporal Limits for Global Polar Bear Persistence. Polar bears (Ursus maritimus) require sea ice for capturing seals and are expected to decline range-wide as global warming and sea-ice loss continue1,2. Estimating when different subpopulations will likely begin to decline has not been possible to date because data linking ice availability to demographic performance are unavailable for most subpopulations2 and unobtainable a priori for the projected but yet-to-be-observed low ice extremes3. Here, we establish the likely nature, timing and order of future demographic impacts by estimating the threshold numbers of days that polar bears can fast before cub recruitment and/or adult survival are impacted and decline rapidly. Intersecting these fasting impact thresholds with projected numbers of ice-free days, estimated from a large ensemble of an Earth system model4, reveals when demographic impacts will likely occur in different subpopulations across the Arctic. Our model captures demographic trends observed during 1979-2016, showing that recruitment and survival impact thresholds may already have been exceeded in some subpopulations. It also suggests that, with high greenhouse gas emissions, steeply declining reproduction and survival will jeopardize the persistence of all but a few high-Arctic subpopulations by 2100. Moderate emissions mitigation prolongs persistence but is unlikely to prevent some subpopulation extirpations within this century. Nature

 

Arctic Sea Ice is in a Downward Spiral, and May Break a Record in 2020. If one were to design a weather pattern that's most efficient at ridding the Arctic of its increasingly fragile ice cover during the region's summer melt season, it would look like what occurred earlier in the month - clear skies, above-average air temperatures, a high-pressure system across the Central Arctic, and an ongoing heat wave and wildfires in Siberia. A recent study concluded that the unusual warmth in Siberia could not have happened in the absence of human-caused global warming. The Washington Post

EU Reflects on the Future of Arctic Policy. The European Commission and the European External Action Service jointly launched on July 20 a public consultation on the way forward for the European Union's Arctic policy. The consultation will enable a broad reflection on the EU's Arctic policy in the face of new challenges and opportunities, including the EU's ambitions under the European Green Deal. "The Arctic is a rapidly evolving frontier in international relations," High Representative/Vice-President Josep Borrell said, adding that climate change is dramatically transforming the region, and increasing its geopolitical importance, with a number of players seeing new strategic and economic opportunities in the High North. "We must ensure that the Arctic remains a zone of low tension and peaceful cooperation, where issues are solved through constructive dialogue. The European Union must be fully equipped to manage the new dynamics effectively, in line with our interests and values," Borrell said. New Europe

 

Carbon Loss From Northern Circumpolar Permafrost Soils Amplified by Rhizosphere Priming. As global temperatures continue to rise, a key uncertainty of climate projections is the microbial decomposition of vast organic carbon stocks in thawing permafrost soils. Decomposition rates can accelerate up to fourfold in the presence of plant roots, and this mechanism-termed the rhizosphere priming effect-may be especially relevant to thawing permafrost soils as rising temperatures also stimulate plant productivity in the Arctic. However, priming is currently not explicitly included in any model projections of future carbon losses from the permafrost area. Here, we combine high-resolution spatial and depth-resolved datasets of key plant and permafrost properties with empirical relationships of priming effects from living plants on microbial respiration. We show that rhizosphere priming amplifies overall soil respiration in permafrost-affected ecosystems by ~12%, which translates to a priming-induced absolute loss of ~40 Pg soil carbon from the northern permafrost area area by 2100. Our findings highlight the need to include fine-scale ecological interactions in order to accurately predict large-scale greenhouse gas emissions, and suggest even tighter restrictions on the estimated 200 Pg anthropogenic carbon emission budget to keep global warming below 1.5°C.  Nature