Summer comes, weather warms – Arctic melts away?

  • 02 Jun 2011, 16:00
  • Christian

Climate skeptics are often quoted in the media suggesting that the polar regions are not melting. Telegraph columnist Christopher Booker has described projections that the Arctic could be ice-free within 30 years as "laughable" and "propaganda of the silliest kind".

In April 2010 David Whitehouse of skeptic think-tank the Global Warming Policy Foundation was quoted in both the Daily Telegraph saying:

"It does seem that the sea ice is returning to 'average' after the record lows of 2007 and 2008. There has been a definite recovery trend since then, so far from being a progression towards ice free summers it seems that it was a temporary dip. The recent observations do make the 2007 projections that the region would be ice free by 2013 look very unrealistic. Given what is happening only the foolish would look many years into the future and predict ice free summers now [our emphasis]."

However, the science tells a different story altogether. Dr Whitehouse made this statement for the GWPF in April 2010 - very soon after the height of the Arctic winter, when the Arctic sea ice reaches its greatest extent. At the time the extent of sea ice did not differ greatly from the average for 1979-2000.

However a glance at the graph below, showing the change in the extent of Arctic sea ice over the last three decades, gives a fuller picture.  The upper data points show the winter maxima in March and the lower data points the summer minima in September for the extent of Arctic sea ice from 1979 to 2010.

They can both be compared to the average sea ice extent over the whole period (the dotted line). It is clear from this graph that the overall trend is downwards, particularly in the summer.

Arctic _sea _ice

The change in Arctic sea ice extent, 1979-2010. The graph shows the ice extent in March and September, as compared to the average sea ice extent for the whole period (the grey dotted line). Source: US National Oceanic and Atmospheric Administration (NOAA)

As can be seen, sea ice extent reached a record low in the summer of 2007 and then recovered marginally in the following two years. It makes little sense scientifically however to argue that there was a "recovery trend" between September 2007 and April 2010 as it is impossible to detect any trend of that sort based on only two and a half years of data.

In its FAQ, the National Snow and Ice Data Centre says that:

"Although the 2009 sea ice minimum was larger than the past two years, the rate of decline since 1979 increased to -11.2 percent per decade … sea ice in the Arctic is in decline in all months and the decline is greater and the rate faster than natural causes could account for."

The 2007 IPCC report projected that Arctic sea ice would decrease over the next century, with a worst-case scenario projecting ice-free summer seas by the end of the 21st century. In 2009, however, the authors of the Copenhagen Diagnosis concluded:

"The observed summer-time melting of Arctic sea-ice has far exceeded the worst-case projections from climate models of IPCC AR4…The warming commitment associated with existing atmospheric greenhouse gas levels means it is very likely that in the coming decades the summer Arctic Ocean will become ice-free, although the precise timing of this remains uncertain."

The record melt of 2007 prompted suggestions that Arctic sea ice had gone beyond a ' tipping point', and was now trapped in a ' death spiral' from which it would not recover. More recent research subsequently suggested however that loss of ice from the Arctic in the summer is reversible - in other words it will not lead inevitably to a loss of ice the following year.

In 2011, National Snow and Ice Data Center's director Mark Serreze summed up this debate (pdf). His article referred to the view the "mainstream view" that

"a seasonally ice-free Arctic ocean is inevitable if greenhouse gas concentrations continue to rise"

and concluded that

"….although the tipping-point argument can perhaps be laid to rest, we may nevertheless be looking at ice-free summers only a few decades from now."

In this context, it is clearly inaccurate to claim that "only the foolish" would predict ice-free summers in the future.

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