Fragile ice, fragile credibility

“Climategate” scandals make no difference to the mounting evidence that our planet is warming. [2 February 2010 | Peter Boyer]

TOP: The graph lines, taken from satellite gravity measurements, show that hundreds of billions of tonnes of ice have been lost from the Antarctic ice sheet since 2002—and that the rate of loss is increasing. BOTTOM: The summer melt at Cape Denison, on the edge of the East Antarctic ice sheet.

“Good grief, after climategate and the email scandal we are still talking about carbon and man made climate change?” asked a Mercury website reader last week.

Incredible though it may seem, yes, we are. I’d take great pleasure in abandoning this climate caper if only someone showed conclusively that it was all a bad dream. Getting one’s head around the science and politics can be a real grind. But that hasn’t happened, so I’m still here.

The “email scandal” of last December showed that some scientists, alas, are not above petty manoeuvring and putting down others to advance their own cause. But it produced no evidence of fraud, nor anything else to justify abandoning the generally-held view that human activities are changing climate.

A second “scandal” has blown up: the revelation that the Intergovernmental Panel on Climate Change (IPCC) made an error over the rate of depletion of the Himalayan glaciers. This is more serious, because it suggests that the IPCC’s standards may not be up to scratch.

It all comes down to a statement in the IPCC Fourth Assessment report of 2007 saying that there’s a very high likelihood of the Himalayan glaciers “disappearing by the year 2035 and perhaps sooner” if the current rate of warming continues. In November 2009 a scientific report questioned the statement, but the story didn’t reach global proportions until last month.

The evidence doesn’t support this. Himalayan glaciers are generally receding, but at an average rate no more than that of mountain glaciers elsewhere in the world. The 2035 date apparently came from a typographical error in summarising a much earlier scientific finding that all non-polar glaciers may be gone by 2350, more than 300 years later!

The mistake poses legitimate questions about how the IPCC goes about reviewing scientific papers. The IPCC has already admitted that “clear and well-established standards of evidence, required by the IPCC procedures, were not applied properly”, and is under pressure to review its procedures to ensure it doesn’t happen again.

But we need to put this into context. This is a single error (there may well be others, but none have yet hit the headlines) in a complex, multi-volume report involving input from several thousand scientists and an equal number of representatives from the world’s governments.

What’s more, while the 2035 melting scenario is implausible, there is strong physical evidence that it may not be as far out as the original mistake suggested. Himalayan glacial retreat appears to be accelerating, and Chinese research has revealed a severe loss of ice on the Tibetan plateau, along with a rising snow-line.

The Himalayan glaciers are important because they contribute to the flow of major rivers in China, south-east Asia, India and Pakistan. But in terms of their potential contribution to sea level rise they pale into insignificance against the vast icecaps of Greenland and Antarctica.

Here, the picture is suddenly getting clearer. In 2002, a joint US-German venture put two satellites into orbit that would begin a revolution in the measurement of changes to the Earth’s crust and, crucially, to the Antarctic and Greenland icecaps.

The Gravity Recovery And Climate Experiment (GRACE) measures variations in Earth’s gravity field to register minute changes in Earth’s mass — including changes to the polar icecaps. It is astonishingly precise, detecting shifts over 200 km away as small as a tenth the width of a human hair.

Melting of the big polar ice sheets can have a massive impact on sea levels. GRACE has for some years provided evidence that Greenland’s ice is diminishing at a rate of around 200 billion tonnes a year. It has now produced clear evidence that Antarctica’s much larger ice sheet, containing 90 per cent of the world’s ice, is also losing mass to the surrounding ocean.

In a paper published in a US geophysics journal, Isabella Velicogna of the University of California used monthly gravity measurements from GRACE to determine the ice mass-loss for the Greenland and Antarctic ice sheets from 2002 to early 2009.

The result showed not just that Antarctica as well as Greenland is losing ice, but that loss from both ice sheets is accelerating, and therefore causing the rate of sea level rise to accelerate. The annual loss of Greenland ice more than doubled between 2002 and 2009, from 137 billion tonnes to 286 billion tonnes.

Until recently Antarctica’s ice sheet was thought to be increasing in size, with a net loss in West Antarctica more than made up for by a net gain in the much larger East Antarctica, south of Australia.

The GRACE measurements have shown that to be wrong. Antarctica was losing an average of 104 billion tonnes of ice a year from 2002 to 2006. Over the next three years, it lost 246 billion tonnes a year, contributing almost as much as Greenland to sea level rise.

The acceleration of ice loss in Antarctica is of crucial significance. With about 10 times the ice of Greenland, Antarctica has a much greater long-term capacity to influence sea level.

So yes, we’re still talking about global warming. It would be great if we could wish it all away, but we can’t. Neither the East Anglia email furore nor the IPCC mistake will make the faintest bit of difference to the mounting pile of physical evidence.