Wrapping up (1)

Unfortunately, it's almost time for this blog to come to an end, so for the last couple of posts I'll try and sum up what I've learned over the course of the past couple of months. At the beginning I posted a few questions that I wanted to answer, so I think these are a good place to start, so I'll use these as a structure for the next couple of posts.

How do we know the sea ice retreat in the past few years is unusual?

The blog started off by looking at this question, firstly by using satellite data. Since satellite data began in 1979, sea ice extent and thickness have been decreasing at an alarming rate. Sea-ice extent during the summer of 2011 (sept) was almost on par with the previous record low during 2007, even without the unusual weather patterns thought responsible for the 2007 low. This strongly suggests that even though sea ice doesn't decrease every winter, overall conditions are worsening for continued survival of permanent sea ice.

A number of proxy records show a sea-ice history going further back than any contemporary records. As part of the blog, I looked at two relatively new methods of constructing these histories; the IP25 biomarker and Quartz records. These, as well as other methods, including documentary and ice-diatom records, show that extent of sea ice has been strongly variable, but also strongly correlated with climate. Sea ice extent is therefore extremely sensitive to temperature changes, meaning if we were experiencing global warming today, we could expect a significant loss of sea ice. Is that what we've been seeing?

Well, the sea-ice is disappearing at a faster rate than any model used by the IPCC has forecast, even the pessimistic 'business as usual' scenarios shown on the graph below. The graph doesn't show the past 5 years, but if it did the trend would be continuing, with 2007 being the minimum.

Sea ice extent output values from 13 IPCC Global climate models with an ensemble mean in thick black.
Actual observations are shown as a thick red line. Direct from Stroeve et al 2007.

Of course, this means a few things could be happening. Firstly, there could be some unknown natural variability that

Arctic Lakes and Zoological Indicators

As we saw in the last post, it is highly likely that climate is indirectly altering Diatom communities in high Arctic lakes through changing levels and patterns of ice cover. Quinlan et al. (2005) used the same cores as the (previously reviewed) Douglas et al. (1994) study and counted the fossil chironomid (non-biting midge) larvae remains down the cores to investigate whether invertebrate communities have also 'shifted', and if they have, how likely it is that the changes are linked to the results from the previous diatom investigations. It's important to note, however, that these results are only taken from three archives (ie lakes and ponds) from Ellesmere island so further study is required to confirm that these findings are widespread.

Chironomidae are a family of flies which are aquatic organisms until their adult stages (see above) and