The great floods across parts of southern England may have abated, but questions over their linkage to climate change are among the most powerful residues. For scientists, experts and citizens the evidence may be compelling, but many parliamentarians and some cabinet ministers in the governing Conservative Party remain unyielding members of the climate-change-denial community (see "A flooded future: Essex to the world", 20 February 2014).

In the weekly knockabout that is prime minister’s question-time, the Labour opposition leader Ed Miliband pressed David Cameron to admit to this tendency at the heart of his own party. Cameron refused, but when Miliband pressed him on the whole climate-change issue, the prime minister agreed that the phenomenon was of huge significance and a serious threat to the UK.

On its own, this is not a big deal. The UK is neither the world’s leading carbon-emitter nor a very important player on the climate scene, yet Cameron’s statement counts. It carries the assessment that climate change has risen up the political agenda sufficiently far that he (and his party) must avoid being tarred by the "denial" label.

Between science and politics

What adds to the piquancy of this moment in the political sphere is that it coincides with a breakthrough in the scientific one: namely, findings on the rapid retreat of glaciers in the high-altitude tropics, notably the Andes. For many years, glaciologists have reported on glaciers’ rate of decline, and many have connected this to a warming of the atmosphere. There has, though, been a lack of scientific consensus over the cause.

There are two main possibilities. The long-term record from ice-core studies could indicate that the retreat is due to atmospheric warming, or else to changes in precipitation (which itself could be a result of climate change). There has been no ranting by either “side” in the matter, rather genuine differences of interpretation of the data. The political relevance here is that the denial community has been forced to concede that tropical glaciers are retreating – but clings to the notion that this has no connection to atmospheric warming.

Now, however, meticulous decade-long research of the largest tropical ice-cap – Quelccaya in the Peruvian Andes – shows that changes in snowfall and ice-accumulation do not correlate with glacier behaviour (see Justin Gillis, “Unwinding a climate mystery”, New York Times, 26 February 2014).

The extended evidence is in the detailed work of a group of researchers at Dartmouth College, published in the journal Geology (see Justin S Stroup, Meredith A Kelly, Thomas V Lowell, Patrick J Applegate, & Jennifer A Howley, "Late Holocene fluctuations of Qori Kalis outlet glacier, Quelccaya Ice Cap, Peruvian Andes", Geology, 25 February 2014). They use a range of techniques to track changes in the volume of the ice-sheet over a 500-year period, and compare it with measurements of ice-accumulation obtained by deep boring undertaken by Lonnie Thompson of Ohio State University. 

In broad terms, the results show that ice-declines at Quelccaya have not coincided with decreases in the rate of accumulation due to precipitation (snow), the implication being that temperature changes have been more influential. Moreover, the rate of loss there is staggering – what has taken 1,600 years to accumulate appears to have been lost in just twenty-five years.

The Peruvian site’s very scale makes this work of vital concern. True, the study is not absolutely conclusive, as it applies to just one example of tropical ice. But similar rates of decline are recorded elsewhere in the tropics, most notably Africa’s highest mountain, Kilimanjaro in northern Tanzania. In that case, it is not possible to use the same techniques as in the Peruvian study, and arguments continue over whether changes in precipitation are the cause. Meredith A Kelly is now studying the Rwenzori (the fabled "mountains of the moon") in western Uganda, which does permit the methods applied in Peru.

Most glaciologists working in the tropics agree that the ice-caps and glaciers are melting at a remarkable rate, and that climate change is responsible. The Peruvian research points to temperature change, but even if changes in precipitation are the cause, the most probable explanation for that too is…climate change.

Whatever the results of current and future climate research, however convincing – they will have zero impact on the denialists. This is why an important scientific finding may be less effective, in political terms, than David Cameron’s acknowledgment that climate change is a reality. A party leader facing an election in a year, with a resolute contingent of deniers in his midst, has made his own breakthrough. That may prove more momentous than he realises.

Photo credit: Wikipedia/Edubucher