Detection and Attribution of Anthropogenic Global Warming Using Northern Hemisphere Sea Ice Extent

Surface and satellite-based observations show decrease in Northern Hemisphere sea ice extent during the past 25 years. We compare these observed trends to control and transient (forced by observed CO₂ and sulfate aerosols) runs from the Geophysical Fluid Dynamics Laboratory and Hadley Centre climate models. The estimates of natural variability are based on the control integrations. The observed decrease is far larger than would be expected by natural climate variations. The decrease agrees with a statistically significant retreat in sea ice extent during the second half of the century, mostly during the last 25 years, predicted by the forced integrations of both models. Therefore, we conclude that the observed sea ice decrease could be a fingerprint of anthropogenic global warming. Both models predict continued sea ice decreases in the next century.