One of my aunts, a sharp lady I love dearly, is skeptical of climate change.  A few months ago, I sent her links to the IGBP Climate Change Index and an EPA slideshow describing some of the climate change indicators in the US.  This sparked a conversation on climate change that I’m making public because I think my aunt shares her questions and concerns with many Americans.  This is part five in a series.  If you’re new to this blog, you might want to catch up here.

This post is going to focus on disappearing glaciers.  My aunt observes that for Arctic sea ice (slide 17),

The ice coverage photos for 1979 and 2007 are both noted to be September (and they are dramatic).

Then points out a potential problem with the comparison of Muir Glacier in 1941 and 2004 (slide 18):

Even more dramatic are the Muir Glacier photos but no mention if they are from the same month?

From the EPA slideshow on climate change indicators

This is a sensible question.  It’s colder in winter, so we expect the glacier to be bigger in winter than in summer.  The slide doesn’t specify what month the pictures were taken in – what if the 2004 photo is from August and the 1941 photo is from February?

Let’s do some digging and find out.  First I checked the additional information linked from the slide.  It didn’t say what month the photos were from, but it did give a citation, which led me to the National Snow and Ice Data Center Glacier Photograph Collection.  It turns out both the photos are from August.

But two photos do not a dataset make!  To actually claim that glaciers are shrinking over time we need to show two things 1) that 1941 or 2004 aren’t “outliers” – that there is a consistent shrinking trend through time and 2) that the trend is widespread – glaciers around the world are shrinking.

The additional information linked from the EPA slideshow does both in one simple graph:

So glaciers around the world are shrinking, as we’d expect with climate change.

My aunt’s question did get me wondering just how much of Muir Glacier has disappeared. It’s hard to get a sense of scale from the photographs.  Between 1941 and 2004 the glacier got 7 miles shorter and almost 900 yards thinner.  That’s a lot more ice melt than you’d expect from one hot summer!

If you want more info on disappearing glaciers, I really enjoyed the USGS’s repeat photography of Alaskan glaciers.