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.
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.