As we near the end of summer in the northern hemisphere, the annual melting of the free-floating sea ice is reaching its maximum extent. Soon the temperatures will fall, the ice will re-form, and another winter freeze will commence. The annual melting has been the subject of satellite observation for more than 30 years and there is no doubt that the extent of the summer melting is increasing.
The data from the US National Snow and Ice Data Centre indicate that this year will probably see the greatest extent of summer melting ever seen since humans evolved as a separate species around one million years ago. Compared to 1979, this summer has witnessed the melting of an additional 2 million square kilometres of sea ice. Just to repeat that: two MILLION square kilometres! This is an area of roughly one thousand miles by one thousand miles. It is colossal.
As a specialist in temperature measurement, I am familiar with the use of ‘temperature fixed-points’ for calibrating thermometers. Even when heated, a mixture of ice and water does not increase in temperature, but instead maintains a stable temperature close to 0 ºC until all the ice has melted. In this sense, the arctic ocean in summer forms a gigantic, planetary-scale fixed point. But when all the ice has melted, heating the liquid causes a temperature rise. And climatalogically, should the summer ever see the complete melting of arctic sea ice – in perhaps as little as 50 to 100 years according to current trends – we can expect the temperature of the region to begin to rise: no longer will an ice-water mixture stabilise the regional temperature.
The gob-smacking magnitude of ‘ice events’ – even on a smaller scale – is evident in this BBC story about the area left by the Peterman Glacier when it broke off from Greenland last year. It is still a major hazard to shipping around Newfoundland with a web page tracking it constantly and this video gives some idea of the scale of just one of the iceberg fragments.
And is all this due to anthropogenic global warming? Well I don’t know, and neither does anyone else. But it is a distinct possibility that we have played a part.