Case Study: How is Arctic Ocean Sea Ice Changing?
Arcitic Ocean temperatures have increased over the years and the extent of sea ice has decreased. The example below looks at one region north of Alaska to understand the extent of these changes.
Part 1: Information from Cryosphere Today:
As shown in the figure below, the areal extent of Arctic Ocean Ice has changed dramatically over the past 30 years. These images show the extent of ice in September, which is the annual minimum. As shown in the circles, ice loss has been most dramatic in the region north of Alaska and Siberia. Ice loss in northern Canada has resulted in the opening of a navigable passageway.
Scientific analysis of the extreme ice loss in 2007 shows that the air temperature north of the Alaska/western Siberia region and in the islands of northern Canada to be well above normal (+4°C) in the summer months, and even further above normal (+6-12°C) in September and October. These extremely high temperatures contributed
Part 2: Quantitative assessment of changes
Analysis from the MS Excel workbook included an assessment of changing ocean air temperatures in September from -154° to +154° longitudes at 80° latitude. It was expected that a significant increase in temperatures in this region would be correlated to the changing sea ice extent since that is one of the areas close to the most substantial losses in September sea ice.
As shown in the graph below, the ice extent decreased by approximately 2 million km2 over the period for which we have data (1994-2008). The rate of loss was determined from the linear regression ~ -0.15 million km2 lost per year.
The ocean air temperatures increased substantially over this same period ~10°C. This is a huge amount given an overall surface air temperature increase over the last century of less than 1°C. The ocean temperatures are changing at ~0.45°C per year.
Another way to look at these trends is to plot the ice area as the dependent variable and the ocean air temperature as the independent variable:
The graph shows that the Arctic region loses ~0.22 million km2 ice for every degree (°C) rise in ocean air temperature in the region -154° to +154° longitude at 80° latitude.
Part 3: Predicted future temperature changes
The IPCC DDC maps tool was used to look at projections of 20 year temperature anomalies for the region 78-82° latitude and -154 - +154° longitude. The temperature anomalies are relative to the 20th century average. IPCC DDC selections included:
- 4th assessment report
- Scenario SR A2
- 20 year average temperature anomalies (September 2080-2099)
- NASA's GISS-ER model
The results show that the September average air temperature at the end of this century is expected to be ~5°C higher than the 20th century average. This is much higher than the 2°C goal set in the Copenhagen accord. The continue rise in temperatures are expected to bring further loss in the September sea ice. Based on the graph above, a 5°C increase should result in an additional loss of 1.1 million km2 (0.22 x 5 = 1.1) of sea ice by the end of the century. Actual predictions, however, suggest that the rate of sea ice loss will be even faster. The change in albedo and positive feedback loop that that contributes to ocean warming is not adequately captured in our linear regression and extrapolation analysis.
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