Saturday, July 9, 2011

Warming Arctic air temperatures causing less snow, more rain, faster ice melt

Arctic air temperatures are warming faster than anywhere else on Earth. Although the level of precipitation is remaining unchanged, there is reduced snowfall in summer which is being replaced by increasing rain. The loss of summer snow and increase in rain is resulting in a positive feedback mechanism increasing warming and melting of the Arctic ice.

We are already witnessing an increase in the Albedo feedback mechanism - loss of reflectivity in the arctic leading to more warming and greater ice melt. Research published early in 2011 revealed Loss of reflectivity in the Arctic is double the estimate used in climate models. With the change in precipitation we have a further feedback mechanism contributing to Arctic warming and melting of snow and sea ice.


The research on this new polar global warming feedback mechanism was presented by Dr James Screen from the University of Melbourne at the XXV International Union of Geodesy and Geophysics General Assembly in Melbourne on 2 July 2011.

“As a result of this temperature shift, we estimate that there has been a 40 percent decrease in summer snowfall over the last 20 years.” said Dr Screen, who was lead author for this research.

“The reductions in snowfall in the summer months (when there is still typically significant snow in Arctic regions) have knock-on effects for the sea ice - the ice floating on top of the Arctic Ocean,” he said.

“Snow is highly reflective and bounces up to 85 percent of the incoming sunlight back into space. Snow on top of ice effectively acts as a sunscreen protecting the ice from the power of the sun rays.”

“As the snow cover has decreased, more sea ice has become exposed to the sunlight, increasing the melting of the ice. Measurements show that the sea ice has been getting thinner and less extensive,” he said

The study was conducted with Professor Ian Simmonds of Melbourne University’s School of Earth Sciences and was published in the prestigious international journal Climate Dynamics.

The article - Declining summer snowfall in the Arctic: causes, impacts and feedbacks was published in Climate Dynamics on June 10. The abstract for the article concludes:

"We perform a series of sensitivity experiments in which inter-annual changes in snow-covered ice are either unaccounted for, or are parameterized. In the parameterized case, the loss of snow-on-ice results in a substantial decrease in the surface albedo over the Arctic Ocean, that is of comparable magnitude to the decrease in albedo due to the decline in sea ice cover. Accordingly, the solar input to the Arctic Ocean is increased, causing additional surface ice melt. We conclude that the decline in summer snowfall has likely contributed to the thinning of sea ice over recent decades. The results presented provide support for the existence of a positive feedback in association with warming-induced reductions in summer snowfall."

Background

A comprehensive study published in 2004 conducted by 300 scientists and elders from native communities in the arctic found that the Arctic ice cap is melting at an unprecedented rate due to human induced global warming. A review of scientific literature reported in 2007 that Arctic Sea Ice heading for Rapid Disintegration: Greenland Ice Sheet melting.

An Arctic climate change report card produced by the National Oceanic and Atmospheric Administration (NOAA) in 2010 found that Arctic climate warming at unprecedented rate due to Global Warming. Other research found that Greenland sets a new melt record in 2010 - sea levels to rise. (See also Record summer melting in Greenland 2010)

Scientists have also discovered the albedo climate feedback mechanism - Loss of reflectivity in the Arctic - is double the estimate used in current state-of-art climate models. We are also seeing signs of Arctic Permafrost thawing raising CO2 levels. The 2011 winter sea ice maximum has continued the strong decline trend.


Source:

* University of Melbourne, July 2, 2011 - More rain, less snow leads to faster Arctic ice melt
* James A. Screen, Ian Simmonds. Declining summer snowfall in the Arctic: causes, impacts and feedbacks. Climate Dynamics, 2011; DOI: 10.1007/s00382-011-1105-2