You have heard and read it all over the media in the last several months. An Associated Press article picked up by newspapers and the web (See National Geographic version here) reported that one scientist “speculated that summer sea ice could be gone in five years.” The article warns…
“”The Arctic is screaming,” said Mark Serreze, senior scientist at the government’s snow and ice data center in Boulder, Colorado. “
“The Arctic is often cited as the canary in the coal mine for climate warming,” said Zwally, who as a teenager hauled coal. “Now as a sign of climate warming, the canary has died. It is time to start getting out of the coal mines.”
This week, after reviewing his own new data, NASA climate scientist Jay Zwally said: “At this rate, the Arctic Ocean could be nearly ice-free at the end of summer by 2012, much faster than previous predictions.”
Wow! Where did this ominously close date of 2012 come from? The sea ice extent in the Arctic (and Antarctic) has been monitored by satellite for almost 30 years, since 1979. The extent of the ice rises and falls, as you would expect, as the year cycles through its seasons. It reaches its yearly minimum by late September or early October. On the average, this minimum has been declining for the last 30 years. After October the northern sea ice extent increases until it reaches a maximum in late March or early April each year.
The yearly cycle is huge. Typically, about 60% of the total sea ice extent melts away as is goes from yearly maximum to the yearly minimum. Figure 1, below, shows the northern sea ice extent from 1979 to November 2007. Note the large drop in the yearly minimum sea ice extent by October 2007. This is the canary that Zwally was talking about. The prediction of an ice free arctic summer by 2012 comes by simply extrapolating the change in the minimum ice extent between 2006 and 2007 into the future, as shown.
Figure 1. Northern Hemisphere Sea Ice Extent from 1979 to November 2007. Rapid drop in minimum sea ice extent from 2006 to 2007 is extrapolated to show total loss of ice by 2012. Click on image to enlarge.
Nature, ever the jokester, has had her fun with the climate alarmists since last November. The Arctic has had more than its usual run up of ice this winter. Today’s (3/20/08) version of the Northern Hemisphere Sea Ice Extent shows an unprecedented (Ever heard that word before?) run up of ice in the Arctic in the last five months
Figure 2. Same as figure 1, but updated to March 20th, 2008. The last five months have shown a rapid ice increase in the Northern Hemisphere. Click on image to enlarge.
The 11 million square kilometer gain in sea ice extent is the greatest seasonal ice gain in history (where history, according to alarmist rhetoric, began in 1979 when satellites started tracking the ice extent). You can read about a little bit of “pre-history” here. Take a look at this long list of peer reviewed journal articles showing that the “pre-history” or the Arctic was warmer than the present.
While we are at it, lets not forget about the Southern Hemisphere. After all, they didn’t put the word “global” in “global warming” for nothing. Figure 3, below shows the sea ice extent for the Southern Hemisphere going back to 1979 from the same satellites tracking the northern ice. The peak at the upper right corner of the graph shows that at about the same time that the Arctic ice was at its lowest “historic” extent, the Antarctic ice was at its highest “unprecedented” extent.
Figure 3. Sea ice extent in the Southern Hemisphere. Click on image to enlarge.
I would not predict that the Southern Hemisphere sea ice extent will reach 17 million square kilometers in 2012 by simply extrapolating the increases of the last four years out another four years. The changes are to complex. But that never seems to stop the alarmists.
All the graphs in this post are from the University of Illinois Polar Research Group. They got the data from the National Center for Environmental Prediction/NOAA