New research, led by former Carnegie postdoctoral fellow Summer Praetorius, shows that changes in the heat flow of the northern Pacific Ocean may have a larger effect on the Arctic climate than previously thought. The August 7, 2018, issue of Nature Communications published the findings. The Arctic is experiencing larger and more rapid increases in temperature from global warming more than any other region, with sea ice declining faster than predicted. This effect, known as Arctic amplification, involves many positive feedback mechanisms in polar regions. What has not been well understood is how sea surface temperature patterns and oceanic heat flow from Earth’s different regions, including the temperate latitudes, affect these polar feedbacks. This new research suggests that the importance of changes occurring in the Pacific may have a stronger impact on Arctic climate than previously recognized. Paleoclimate records show that climate change in the Arctic can be very large and can happen rapidly. During the last deglaciation, there were two episodes of accelerated Arctic warming—with temperatures increasing by 15°C in Greenland over the course of decades. The events were accompanied by rapid warming in the midlatitude North Pacific and North Atlantic Oceans. Because of these past changes, the research team* modeled a series of ocean-to-atmosphere heat flow scenarios for the North Pacific and the North Atlantic. They used the National Center for Atmospheric Research’s Community Earth System Model (CESM) to assess the impacts to the Arctic’s surface temperature and climate feedbacks. Praetorius, who was at Carnegie at the time of the research and is now with the U.S. Geological Survey (USGS), explained, “Since there appeared to be coupling between abrupt Arctic temperature changes and sea surface temperature changes in both the North Atlantic and North Pacific in the past, we thought it was important to untangle how each region may affect the Arctic differently in order to provide insight into recent and future Arctic changes.” The researchers found that both cooling and warming anomalies in the North Pacific resulted in greater global and Arctic surface air temperature anomalies than the same perturbations modeled for the North Atlantic. Until now, this sensitivity had been underappreciated. The scientists also found that the strong global and Arctic changes depended on the magnitude of water vapor transfer from the midlatitude oceans to the Arctic. Warm moist air carried poleward towards the Arctic can lead to more low-lying clouds that trap warmth near the surface. The poleward movement of heat and moisture drive the Arctic’s sea ice retreat and low- cloud formation, amplifying Arctic warming. The so-called ice-albedo feedback causes retreating ice and snow, leading to greater warming through increasing absorption of solar energy on darker surfaces. In recent years, the Arctic has experienced an even greater accelerated warming. The unusually warm ocean temperatures in the Northeast Pacific paralleled the uptick in Arctic warming, possibly signaling a stronger link between these regions than generally recognized. “While this is a highly idealized study, our results suggest that changes in the Pacific Ocean may have a larger influence on the climate system than generally recognized,” remarked Carnegie coauthor Ken Caldeira.  This image shows the extent of Arctic sea ice in September 2016. The yellow line shows the average minimum extent of sea ice in the Arctic from 1981 to 2010. Images courtesy Image courtesy NASA COLLABORATORS AND SUPPORT: *Coauthors are Summer Praetorius, U.S. Geological Survey; Maria Rugenstein, Institute for Atmospheric and Climate Science, Zurich; and Geeta Persad and Ken Caldeira of Carnegie’s Department of Global Ecology. Innovative Climate and Energy Research and the Carnegie Institution for Science endowment supported this work. Pacific Ocean’s Effect on Arctic Warming (Above) Former Carnegie postdoctoral fellow Summer Praetorius was lead author on the study. Image courtesy Summer Praetorius 7