Four key decades

main greenhouse gas is continuing to increase in the atmosphere at an alarming rate. The level of the gas at the Zeppelin research station in Svalbard peaked at more than 397 ppm, an increase of more than 2.5 ppm on 2008. Carbon dioxide levels at Svalbard tend to be higher than the global average, but scientists said the carbon dioxide level they had measured was unprecedented, even for that location. At Mauna Loa Observatory in Hawaii, the main monitoring station for the National Oceanic and Atmospheric Administration (NOAA), the May figure was 390.18 ppm and they note that only rarely has a level dropped in a current month compared to the same month in the previous year in their more than 50-year records. Before the industrial revolution the carbon dioxide level was about 280 ppm. And it is at high latitudes that the effects of warming are already most apparent. Arctic summer sea ice is declining. Beyond a certain point there will not be enough to allow polar bears to hunt, pushing this iconic species towards extinction. Pimm in his review (pages R595–R601) has looked at some terms coined in discussions of global warming. He finds 'tipping point' largely unhelpful, but with regard to polar bears it has some resonance and, after the bears are gone, predictions suggest the ice might completely disappear, and it would be very difficult to get it back. The reflective power of the ice would be lost and the open sea would absorb radiation providing a positive feedback. But alarm bells are also ringing at lower latitudes. Corals seem particularly vulnerable to both increasing atmospheric carbon dioxide levels but also rising sea surface temperatures. As Brierley and Kingsford (pages R602–R614) point out, increasing acidification of seawater has seen calcification of Great Barrier Reef corals decline by 14.2 per cent since 1990. On present trends they believe corals will become increasingly rare beyond 2050. Also, when temperatures exceed 31ºC the zooanthellae algae are ejected and coral bleaching occurs. It is the difficult job of the International Panel on Climate Change, a group of climate scientists to assess the data and models to come up with policy This year marks the fortieth anniversary of the successful Apollo mission to land men on the moon. While that achievement was remarkable there was another outcome: the startling image of the earth rising above the moon's horizon. The image was …