The ‘other’ Arctic sea ice melt


Reports focus on the possibility a record minimum for Arctic sea ice in September, but a major loss during the early summer months is climatologically more important

From the Guardian Environment Network, Dirk Notz, Friday 9 September 2011

Clear skies allowed a largely unobstructed view of the Arctic in early July 2011

Clear skies allowed a largely unobstructed view of the Arctic in early July 2011. Photograph: MODIS/Terra/NASA

“Well, it’s not really good timing to write about global warming when the summer feels cold and rainy,” a journalist told me last week. Hence, at least here in Germany, there hasn’t been much reporting about the recent evolution of Arctic sea ice – despite the fact that Arctic sea ice extent in July, for example, was the lowest ever recorded for that month throughout the entire satellite record. Sea-ice extent in August was also extremely low, second only to August 2007 (Fig. 1). Whether or not we’re in for a new September record, the next weeks will show.

Figure 1: Evolution of Arctic sea-ice extent in July and August from 1979 until 2011. (NSIDC)

Figure 1: Evolution of Arctic sea-ice extent in July and August from 1979 until 2011. (NSIDC)

A rainy summer might be one reason for an apparent lack of public attention with respect to the ongoing sea-ice loss. Another reason, however, is possibly the fact that we scientists have failed to make sufficiently clear that a major loss of sea ice during the early summer months is climatologically more important than a record minimum in September. This importance of sea-ice evolution during the early summer months is directly related to the role of sea ice as an efficient cooling machine: Because of its high albedo (reflectivity), sea ice reflects most of the incoming sunlight and helps to keep the Arctic cold throughout summer. The relative importance of this cooling is largest when days are long and the input of solar radiation is at its maximum, which happens at the beginning of summer.

If, like this year, sea-ice extent becomes very low already at that time, solar radiation is efficiently absorbed throughout all summer by the unusually large areas of open water within the Arctic Ocean. Hence, rather than being reflected by the sea ice that used to cover these areas, the solar radiation warms the ocean there and thus provides a heat source that can efficiently melt the remaining sea ice from below. In turn, additional areas of open water are formed that lead to even more absorption of solar radiation. This feedback loop, which is often referred to as the ice-albedo feedback, also delays the formation of new sea ice in autumn because of the accompanying surplus in oceanic heat storage.

More (Click Here)

The following three graphs are from my own calulations. Figure 5 shows the daily extent, Figure 6 shows the daily change in extent (averaged over the prior week) and Figure 7 compares the recent extents as a percentage of the 2003 – 2010 extent for the same day of the year. The data for this analysis were downloaded from “IJIS” (the IARC-JAXA Information System) reporting the AMSR-E sea ice extent on a daily basis since 2002.

Ice Fig. 5. Measured Extent

Ice Fig. 5. Measured Extent

Ice Fig. 6. Average Daily Change

Ice Fig. 6. Average Daily Change

Ice Fig. 7. Extent as a Percent of the Average Since 2003

Ice Fig. 7. Extent as a Percent of the Average Since 2003

About these ads
This entry was posted in Uncategorized and tagged , , , , , , , , , . Bookmark the permalink.

3 Responses to The ‘other’ Arctic sea ice melt

  1. Pingback: The ‘other’ Arctic Sea Ice Melt | ikners.com

  2. Pingback: More on Arctic ice melt | ikners.com

  3. Pingback: The Arctic’s near-record sea ice low – big picture | ClimateInsight

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s