Tropical Decadal Variability and the Rate of Arctic Sea Ice Retreat

The Interdecadal Pacific Oscillation (IPO) transitioned from positive to negative around 2000, and the tropical Atlantic was warming, while the trend for cold season (NDJF) decreases in Arctic sea ice extent from 2000-2014 was about a factor of two larger than the 1979-2000 trend, and the warm season (JJAS) trend was about a factor of three larger. This suggests a possible contribution from decadal timescale forcing from the tropics to Arctic sea ice decrease. Sensitivity experiments with an atmospheric model show that a negative convective heating anomaly in the tropical Pacific, associated with the negative IPO phase after 2000, produces an atmospheric teleconnection pattern over the Arctic comparable to the observations in NDJF but not JJAS. Meanwhile, a positive convective heating anomaly over the tropical Atlantic, associated with warming SSTs there in the 2000-2014 period, produces an atmospheric teleconnection pattern over the Arctic comparable to the observations in JJAS but not NDJF. The model results demonstrate that the observed anomalously strong Arctic surface winds and sea ice drifts after 2000, which produced accelerated decreases in sea ice extent and consequent changes in net surface heat flux and surface temperature, likely had contributions from decadal variability of tropical SSTs in the Pacific and Atlantic.