Unraveling the impacts of North Pacific and North Atlantic Ocean warming on Arctic climate

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This article is part of the Spring 2019 issue of the Earth Science Matters Newsletter.

The Arctic is one of the world’s most sensitive regions to climate change, where temperatures typically change three times more than the global average in response to a given (radiative) climate forcing (an effect known as Arctic amplification). This makes the Arctic particularly susceptible to rapid perturbations in both physical and ecological systems. In recent years, the Arctic has experienced record-breaking warming and sea-ice retreat that have exceeded climate model predictions, making it essential to unravel the mechanisms underpinning this acceleration.

Paleoclimate records preserved in deep-sea sediments and ice cores show that abrupt temperature changes in the Arctic occurred at the same time as rapid changes in sea surface temperature in the high-latitude North Pacific and North Atlantic, hinting at strong links between subpolar ocean change and rapid Arctic climate change. However, these observations alone do not provide a way to parse the distinct contributions of regional ocean warming on Arctic change.

Previous research has largely focused on the role of North Atlantic Ocean circulation changes in abrupt Arctic climate fluctuations with the assumption that a stronger deep-water formation in the North Atlantic was responsible for rapid warming events in the Arctic. However, unprecedented warming of the North Pacific between 2014-2016 was accompanied by recordbreaking Arctic warming, despite a weakening of North Atlantic circulation and relatively ‘cool’ sea surface temperature in the subpolar North Atlantic (Figure 1). This highlights uncertainty in how sea surface temperature in the North Pacific and North Atlantic may affect Arctic climate processes differently.

map of arctic surface air temperature anomalies

Figure 1. Surface air temperature anomaly (oC) between 2014-2016 relative to 1890-1970. Record-breaking warming in the Arctic occured in conjunction with anomalous warming in the Northeast Pacific, despite anomalously cool sea surface temperatures in the North Atlantic. Continents are outlined in white. Data were accessed from NASA GISS Surface Temperature Analysis (GISTEMP). Source for historical temperature data: NOAA/NCEI's Extended Reconstructed Sea Surface Temperature (ERSST) v.5 and GLobal Historical Climatology Network (GHCN) v.3. (From Figure 1 in Praetorius et al., 2018).

(Credit: From Figure 1 in Praetorius et al., 2018. Public domain.)

Researchers from the USGS and the Carnegie Institution for Science set out to investigate whether remote temperature changes in the North Pacific and North Atlantic impact the Arctic in distinct ways. They used a global climate model (the Community Earth System Model from the National Center for Atmospheric Research) to modify the ocean-to-atmosphere heat transfer in regions of the North Atlantic and North Pacific Oceans to see how warming and cooling in each region affects Northern Hemisphere climate.

The resulting simulations showed that the Arctic was more sensitive to changes in ocean heat flux from the North Pacific than from the same latitude in the North Atlantic. This effect was primarily linked to a larger net moisture transfer (and accompanying latent heat flux) into the Arctic region in response to North Pacific warming. The larger moisture flux was associated with an increase in the formation of low-altitude clouds in the Arctic, which act as insulation to trap surface warmth and keep it from dissipating. The surface warming effect of these low-clouds thus accelerates the loss of sea-ice and amplifies ice-albedo feedback. This feedback causes retreating sea ice to further enhance surface warming through increased solar radiation absorption as highly reflective ice (high albedo) is replaced with darker (lower albedo) waters. Both processes act in concert to magnify the Arctic amplification effect.

These results highlight the central role that moisture flux into the Arctic plays in the feedbacks involved in Arctic amplification and casts new light on links between Pacific Ocean variability and Arctic change, providing insight into mechanisms that may accelerate Arctic warming in the future. Analysis of recent Arctic variability appears to corroborate the link between moisture intrusions (storms), enhanced low clouds, and accelerated sea-ice retreat.

While this study provides a first step in describing broad-scale differences in North Pacific and North Atlantic warming, further work is needed to understand how more complex modes of oceanic variability (such as the El Nino Southern Oscillation) manifest in the Arctic.

The paper, “Global and Arctic climate sensitivity enhanced by changes in North Pacific heat flux” was published in Nature Communications and is available here: https://www.nature.com/articles/s41467-018-05337-8

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