What's causing Arctic amplification?
https://www.skepticalscience.com/print.php?r=67The warming trend in the Arctic is almost twice as large as the global average in recent decades. This is known as Arctic amplification. What's the cause? Changes in cloud cover, increases in atmospheric water vapour, more atmospheric heat transport from lower latitudes and declining sea ice have all been suggested as contributing factors. A new paper The central role of diminishing sea ice in recent Arctic temperature amplification (Screen & Simmonds 2010) (here's the full paper
https://www.researchgate.net/publication/43352154_The_Central_Role_of_Diminishing_Sea_Ice_in_Recent_Arctic_Temperature_Amplification) examines this question. The title is a bit of a give-away - the decline in sea ice is the major driver of Arctic amplification.
The vertical profile of Arctic warming (i.e. - how much warming occurs at different altitudes) gives us insight into the underlying cause. If atmospheric heat transported from lower latitudes was the major driver, more warming would be expected at greater heights. On the other hand, if retreating snow and sea ice cover was the major cause, maximum warming would be expected at the surface. Figure 1 shows the simulated warming expected in each season if declining sea ice was the major cause of warming.
Figure 1: Temperature trends linked to changes in sea ice. Temperature trends over the 1989–2008 period averaged around circles of latitude for winter (a), spring (b), summer (c) and autumn (d). The trends are derived from projections of the temperature field on the sea ice time series.
Using higher resolution temperature data supplemented with updated satellite measurements, Screen 2010 analyse the observe warming trend in each season. What they find is maximum Arctic warming at the surface and that warming lessens with height in all seasons except summer. This vertical structure suggests that changes at the surface, such as decreases in sea ice and snow cover, are the primary causes of recent Arctic amplification.
Figure 2: Observation of temperature trends, 1989–2008. Temperature trends averaged around circles of latitude for winter (December–February; a), spring (March–May; b), summer (June–August; c) and autumn (September–November; d). Red shading indicates that the lower atmosphere has warmed faster than the atmospheric column as whole. Blue shading indicates that the lower atmosphere has warmed slower than the atmospheric column as a whole.
The central role of diminishing sea ice in recent Arctic temperature amplification
James A. Screen & Ian Simmonds
Nature volume 464, pages1334–1337(2010)Cite this article
956 Citations
Abstract
The rise in Arctic near-surface air temperatures has been almost twice as large as the global average in recent decades1,2,3—a feature known as ‘Arctic amplification’. Increased concentrations of atmospheric greenhouse gases have driven Arctic and global average warming1,4; however, the underlying causes of Arctic amplification remain uncertain. The roles of reductions in snow and sea ice cover5,6,7 and changes in atmospheric and oceanic circulation8,9,10, cloud cover and water vapour11,12 are still matters of debate. A better understanding of the processes responsible for the recent amplified warming is essential for assessing the likelihood, and impacts, of future rapid Arctic warming and sea ice loss13,14. Here we show that the Arctic warming is strongest at the surface during most of the year and is primarily consistent with reductions in sea ice cover. Changes in cloud cover, in contrast, have not contributed strongly to recent warming. Increases in atmospheric water vapour content, partly in response to reduced sea ice cover, may have enhanced warming in the lower part of the atmosphere during summer and early autumn. We conclude that diminishing sea ice has had a leading role in recent Arctic temperature amplification. The findings reinforce suggestions that strong positive ice–temperature feedbacks have emerged in the Arctic15, increasing the chances of further rapid warming and sea ice loss, and will probably affect polar ecosystems, ice-sheet mass balance and human activities in the Arctic2.