Sometimes, the future arrives with alarming speed. In the 1990s, and again in 2000, climate scientists warned that – unless urgent action was taken – the Arctic Ocean could be clear blue water in summer by 2050. This August researchers making a first analysis of data from the European Space Agency's observation satellite CryoSat-2 were startled to find that the loss of sea ice – as measured both by depth, and by area – was far more dramatic than their own forecasts had predicted. The summer Arctic could be an open sea within a decade.

It is the ice cap that keeps the Arctic cold. Sunlight that hits white ice bounces back into space. Dark ocean absorbs light, and therefore warmth, making the next winter's ice pack thinner, and less enduring. The difference between the torrid tropics and the icy Arctic governs weather patterns in the northern hemisphere. The frozen ocean and permafrost at the perimeter prevents ground methane from escaping into the atmosphere and thereby accelerating global warming. The polar seas drive the marine ecosystem and fuel the north Atlantic fish stocks. So the consequences of ice loss could be considerable, although nobody with political authority seems so far to have sufficiently considered them.

Bad news from the far north has just been matched by a bleak warning from the tropics. German, US and Australian scientists report in Nature Climate Change on Mondaythat the double menace of increasing greenhouse gas emissions and rising ocean acidity could spell the end for most of the world's coral reefs. These extraordinary and beautiful structures flourish at the limits of their tolerance. They like it hot, but not too hot. They tend to "bleach" and even die as temperatures rise: during 1998, 16% of all living corals perished in one exceptional tropic summer. Coral reefs deliver coastal protection, tourism and fishing for millions: the reefs are home, habitat and hunting territory for about a quarter of all marine species. The researchers used 19 different climate models to predict the effects of a 2C increase in global average temperatures, and found that by 2030 around 70% of the reefs would suffer what they politely call "long-term degradation".

In fact, pessimists in the climate change community warn that within the next century global mean temperatures could rise by 6C. A fierce, sustained drought in the US, with 170 all-time US heat records broken in June alone, has already hurt world food stocks. The global response to these signals of potential calamity has so far been feeble. Meanwhile Britain's "greenest government ever" has shown what it thinks of scientific evidence, by placing a homeopathic medicine enthusiast in charge of the National Health Service, and a reputed climate sceptic as environment secretary. The outlook is not promising.