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THE PENTAGON is hoarding data that could help climatologists to understand
the greenhouse effect and

to predict more precisely the rate of global warming. Peter Wadhams
of the Scott Polar Research Institute at the University of Cambridge said
last week that the US Navy has consistently refused to declassify sonar
readings by American submarines in the Arctic. The data would be invaluable
to researchers investigating how quickly the polar icecaps are melting.

Wadhams announced data last week which show that ice in the Arctic has
thinned substantially over the past decade. In an area north of Greenland,
ice was 6 to 7 metres thick in 1976. In 1987, the same ice had thinned to
between 4 and 5 metres. The findings are alarming, he said, because the
icecaps play a crucial role in helping the oceans to ‘lock up’ airborne
carbon dioxide that would otherwise contribute to global warming. The more
quickly the ice melts, the faster the world will warm up.

Wadhams, director of the institute and an authority on ice physics,
gathers his data from sonar readings taken by British nuclear submarines
as they cruise beneath the icecap. From the readings, Wadhams can calculate
the depth of huge tracts of ice.

He says that the Royal Navy is happy to release its data. He has even
been aboard submarines and recorded data himself. Wadhams says, however,
that the US Navy has classified large amounts of sonar data which would
be invaluable for establishing the pace at which ice is melting. ‘It (the
US Navy) collects data which it neither analyses nor publishes,’ says Wadhams.
‘If we had access to it, it would enable us to fill out the picture substantially,’
he said.

The US Navy confirmed this week that the data in question are classified.
Lieutenant James Wood of the US Navy in Washington DC said that the data
would reveal the tracks of the US’s submarines beneath the Arctic icecap.
‘It’s vitally important for the successful operation of our submarines that
they remain covert,’ he said. He refused to comment on the fact that the
Royal Navy makes sonar data available to scientists.

Wadhams, meanwhile, is now heading for the Antarctic to make similar
measurements aboard a West German research vessel, the Polar Stern. He will
be able to compare the results with measurements that he made when the same
vessel, managed by the Alfred Wegener Institute in Bremerhaven, journeyed
into the Antarctic pack ice in the winter of 1986. Then, Wadhams found that
ice in the Antarctic is much thinner than that in the Arctic. ‘It varies
between 50 and 60 centimetres in depth,’ he says. So global warming could
have more immediate effects in Antarctic waters.

Wadhams explained that the loss of ice would destroy a key process by
which the poles draw carbon dioxide out of the atmosphere. ‘One-half of
the carbon dioxide that dissolves in sea water is lost through deep convection
(in polar regions) into the deep ocean,’ he said.

Ice drives two major mechanisms that subdue the rate of global warming.
One is simple – reflection. ‘Ice and snow reflect 80 per cent of solar radiation
back into space. The open ocean reflects back just 20 per cent,’ Wadhams
explained. Ice will begin to retreat if it continues to thin at the rate
observed. Once this happens, more solar radiation will be trapped in the
oceans.

The other mechanism that mitigates global warming involves the way that
sea water freezes. Brine freezes when the polar winter begins, excluding
salt from the ice. The concentration of salt in water underlying the ice
rises rapidly as water freezes, increasing the density of the water. The
water eventually becomes so dense that it sinks deeper, carrying with it
carbon dioxide absorbed from air.

Elsewhere in the open ocean, there is an equilibrium whereby carbon
dioxide diffuses between the water and the air. This balance exists to a
depth of 100 metres. Waters below that depth, called the thermocline, seldom
mix and exchange with water in the top 100 metres. The deep water that absorbs
carbon dioxide near the poles drifts to other parts of the ocean but never
rises above the thermocline. So the carbon dioxide is there for good, explains
Wadhams. Take away the ice, and the means to ‘bury’ the gas disappears as
well, he says.