The global climate cliff

Paul Rogers , “The global climate cliff,” openDemocracy, 18 July 2013

The events in Uttarakhand closely follow a report from the World Meteorological Organisation (WMO) on weather trends in the first decade of the 21st century, which focuses in part on the increased intensity of severe weather events and their likely link to carbon emissions and climate change. The WMO report – The Global Climate 2001-2010: A Decade of Climate Extremes – is particularly useful because it examine a whole decade and compares it with earlier ones, a process that puts smaller fluctuations in perspective and gives a clearer picture of underlying trends  (see Alex Kirby, “Unprecedented climate extremes marked last decade, says UN”, Guardian Environment Network, 3 July 2013).

A basic finding is that in the century from 1901-10 to 2001-10, average temperature rose by 0.88 degrees Centigrade – but more than half of that rise has occurred in the past thirty years, which confirms many other observations that climate change is accelerating. The WMO also confirms its asymmetry, citing the near-Arctic as a region of rapid warming that is affecting not just sea-ice but also the Greenland ice-cap.

The data on sea-level rise contains a surprise. The overall change since the 1880s is 20 centimetres but here too the process is accelerating; the observed trend in the 20th century was an average rise of 1.6 millimetres per year, but a combination of melting and thermal expansion means that in the past decade this has nearly doubled to 3 mm per year.

The WMO puts great emphasis on extreme weather events, highlighting analysis showing that such events – floods, droughts, hurricanes or other phenomena – are indeed becoming more radical in their scale and effects. The wildfires in Russia and the appalling floods in Pakistan are recent examples of disasters of a kind that may not be more frequent than in the past  but are much more extreme when they do happen. What might once have been seen as a “hundred-year event” is coming to be more like a twenty- or thirty-year one.

The WMO secretary-general Michel Jarraud says: “Rising concentrations of heat-trapping greenhouse gases are changing our climate, with far-reaching implications for our environment and our oceans, which are absorbing carbon dioxide and heat”. This last point is important, because the current role of the oceans as carbon-sponge and heat-sink may be disguising the impact of increases in carbon-dioxide and methane; there is little understanding, though, of how long this might continue. …

The value of the WMO’s work is the way it transcends ordinary timescales. It is easy for climate-change deniers to point to a very warm year like 1998 and argue that since subsequent years were cooler, climate change is a myth. A decade-by-decade approach, and a view that covers the century or more since accurate temperature measurements started, give a much clearer picture of the emerging situation – one, moreover, based on observations not models or predictions. …

Read the full article here.