Thursday, October 24, 2013

John Cook's Climate Change Mythbusters 20

This is part of a series reposting material from John Cook's Skeptical Science website. Although he is a physicist rather than a specialist in climate science, he is a convinced "global warmist" and tries to rebut frequently-raised objections to the theory. However, it is always possible to question the data (e.g. this valuable note about measuring temperature) and the line of argument. Please help advance the debate - with facts and logic.

Are glaciers growing or retreating?

What The Science Says:
Most glaciers are retreating, posing a serious problem for millions who rely on glaciers for water.
Climate Myth: Glaciers are growing
“[R]eports are coming in from all over the world: for the first time in over 250 years, glaciers in Alaska, Canada, New Zealand, Greenland, and now Norway are growing.”(JamulBlog)
Although Glaciologists measure year-to-year changes in glacier activity, it is the long term changes which provide the basis for statements such as "Global Glacier Recession Continues". Some Skeptics confuse these issues by cherry picking individual glaciers or by ignoring long term trends. Diversions such as these do not address the most important question of what is the real state of glaciers globally?

The answer is not only clear but it is definitive and based on the scientific literature. Globally glaciers are losing ice at an extensive rate (Figure 1). There are still situations in which glaciers gain or lose ice more than typical for one region or another but the long term trends are all the same, and about 90% of glaciers are shrinking worldwide (Figure 2).

Figure 1: Long-term changes in glacier volume adapted from Cogley 2009.
Figure 2: Percentage of shrinking and growing glaciers in 2008–2009, from the 2011 WGMS report
It is also very important to understand that glacier changes are not only dictated by air temperature changes but also by precipitation. Therefore, there are scenarios in which warming can lead to increases in precipitation (and thus glacier ice accumulation) such as displayed in part of southwestern Norway during the 1990s (Nesje et al 2008).

The bottom line is that glacier variations can be dependent on localized conditions but that these variations are superimposed on a clear and evident long term global reduction in glacier volume which has accelerated rapidly since the 1970s.

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1 comment:

Graeme said...

I think I will take this with a pinch of salt. According to that well-known climate activist, William Connolley, AR5 is the first IPCC report that is able to say whether the Antarctic ice-cap is increasing or decreasing. In previous reports, the error range was such that it could have been doing either. I imagine that the Antarctic ice cap is the glacier that is studied by more scientists than any other. So, I strongly suspect that the paper on which Cook bases his claims is probably a crock of the proverbial.

As well as this, there have been sporadic headlines in the last n10 or so years such as "global warming means that Mont Blanc is growing" - yes, extra heat leads to more snow on Mont Blanc and thus the glacier is growing.

The fact that reliable long-term measurements exist for essentially none of the key variables fixated upon by activists posing as climate scientists is the key to the debate for me. We are swimming in a sea of uncertainty.

The most reliable measures are probably of surface temperature and yet the UK Met Office seems to think its records are only reliable from 1910 onwards - eg 100 years of measurements of a climatic variable. So how reliable are the temperature records for other countries...such as most of Africa and South America and central Asia? What error ranges do they encompass?