Friday, February 10, 2012
The Arctic Ocean continues to warm up...July 2011 had a record sea ice minimum
The amount of the Arctic Ocean covered by sea ice is the lowest on record for the month of July, according to The National Snow and Ice Data Center http://nsidc.org/arcticseaicenews/, located at the University of Colorado, Boulder.
This new sea ice minimum for the month of July exceeds even the previous record set in 2007, but toward the end of July the rate of sea ice melt slowed allowing the minimum from 2007 to once again surpass it. If you look at the graph below (courtesy of the NSIDC.org) you can see the curves for 2007, the year with the standing record minimum sea ice for the year (dotted line) and the sea ice remaining for 2011 (the blue curve). The sea ice amount for 2011 was less than in 2007 or any other previous year for which we have satellite data. The rate of sea ice melt slowed at the end of July 2011, but during the past few days the rate of sea ice melt has picked up again. Don't be surprised if we see a new sea ice minimum this September, but only weather conditions between now and then will determine that.
This map shows the 1979-2000 average sea ice for this time of year (pink lines) and the current amount of sea ice cover shown in white (also courtesy of NSIDC.org). If you notice, sea ice melt is progressing particularly rapidly along the Russian and western Canadian and Alaskan shorelines. It makes me wonder how long it will be this year before the NW passage will be ice free again this year.
This graph (courtesy of NSIDC.org) shows the sea ice extent for July 2011 compared to all previous years since 1979. It shows clearly that it was a record low sea ice total for the month. It's interesting that there are some people who look at data like these and say, for example, what happened in 2008!? 2009!? Those were above the descending trend line? And they conclude, based on one year's data that global warming is not happening. In fact, years like 2008 and 2009 are to be expected. We are, after all, looking at a natural trend, and there is always variability around any natural trend. It's the overall trend of many years worth of data that need to be considered before a conclusion can be made. In this case, the data all support the conclusion that we are looking at a trend of decreasing sea ice as the years pass.
In addition, climatologists have also been monitoring the age and thickness of sea ice, in addition to sea ice cover. This graph shows the percent of sea ice cover on the left-hand image, and the age of ice on the right-hand image. Scientists have discovered that there is less old (>2-3 year old ice) in the Arctic Ocean than in years past. What this means is that younger, and therefore thinner ice melts faster than older, thicker ice. And, since the NSIDC uses a 15% ice cover as a threshold for their measurements for their graphs, etc., this graph is particularly telling when it comes to assessing the status of ice cover in the Arctic Ocean.
If you look at the left-hand map, you will see that only a very small percentage of the Arctic Ocean still has 100% ice cover, and a significant area has only 15% or slightly more. The prevailing winds and currents tend to cause ice to stack up along the north coasts of Greenland, Baffin Island, and other Canadian Arctic islands, so that is why the ice is thicker and older there.
I, for one, would not be a bit surprised if we saw a record or near record maximum sea ice melt this summer.
Interestingly, sea ice melt has no direct affect on sea levels. When sea ice melts, it's just like ice cubes in your drink melting. If you marked the level of fluid containing ice cubes in a glass, you will notice that there is no difference before the ice cubes melt and after they melt, because the total amount of water present in the glass does not change. What we need to consider when it comes to sea level rise are two things, well, at least these two things: land ice/glacier melt (e.g., the Greenland ice cap), and thermal expansion of water. As the world's oceans warm, the water becomes slightly less dense, and total volume increases. We will also see increased evaporation, but the vast majority of evaporated sea water falls directly back on the ocean, so that's probably a negligible effect.
So...so what!? It's still warming up in the Arctic.
(Originally posted 8-9-2011)