Leading article: Melting ice in a still-warming world

The record retreat of the ice sheet covering the Arctic Ocean, confirmed by the US National Snow and Ice Data Center, is a dramatically visible marker of the effect of climate change on the planet; indeed, it is the most discernible and convincing sign, currently, of global warming.

The earlier record-shrinking of the ice in September 2007 shocked the entire scientific community – not even the most pessimistic computer models had predicted its suddenness or its extent – and now this retreat has been substantially exceeded.

In the past three years, the dangers of climate change have dropped far down political agendas, for several reasons. The most immediate and obvious one, of course, is the recession: people are preoccupied with the economy and their finances and this is a problem for right now, while global warming, by and large, is a problem for the future. But there are other reasons. The implosion of the international climate negotiating process at Copenhagen in December 2009 was one; even more important, perhaps, is the diminution of popular belief in the importance of the climate threat.

This has partly reflected the efforts of climate sceptics; at base, though, it is because the continuing warming process, the rise year on year in global air temperatures, which was clearly visible in the 1980s and 1990s, appears since the Millennium to have paused. No one really knows why; a good guess is the Chinese sulphur aerosol, the vast cloud of sulphur particles released with the massive increase in Chinese coal burning since the mid-1990s, which will tend to reflect back the sun's heat and hold down observable air temperature rises. But the pause in the warming has meant that the average person is less convinced that the climate is indeed changing, with potentially disastrous consequences.

The Arctic ice melt of 2012 is a salutary reminder that global warming has not gone away, even if we have temporarily turned out backs on it. This same summer, we have witnessed a heatwave so unprecedented in the US that much of its grain harvest, the world's biggest, has withered on the stalk, which will have a very dangerous effect on global food supplies and global food prices. The warming world is very definitely back on the agenda.