PLEA Network

30 July 2015, New Scientist, Earth now halfway to UN global warming limit – Earth now halfway to UN global warming limit: IT’S the outcome the world wants to avoid, but we are already halfway there. All but one of the main trackers of global surface temperature are now passing more than 1 °C of warming relative to the second half of the 19th century, according to an exclusive analysis done for New Scientist. We could also be seeing the end of the much-discussed slowdown in surface warming since 1998, meaning this is just the start of a period of rapid warming. “There’s a good chance the hiatus is over,” says Kevin Trenberth of the National Center for Atmospheric Research in Boulder, Colorado. “The slowdown in warming since 1998 was partly due to oceans taking up more heat. That could be over”. Last year was the hottest since records began, but only just. With an El Niño now under way – meaning warm surface waters in the Pacific are releasing heat into the atmosphere – and predicted to intensify, it looks as if the global average surface temperature could jump by around 0.1 °C in just one year. “2015 is shaping up to smash the old record,” says Trenberth. The UN negotiations on climate change aim to limit warming to 2 °C above pre-industrial temperatures. There is, however, no agreement on how to define pre-industrial temperature, says Ed Hawkins of the University of Reading, UK. Because some global temperature records only begin in 1880, the period 1880 to 1899 is the easiest “pre-industrial” baseline for measuring warming. It is somewhat misleading, though, because the 1880s were particularly cold after the eruption of the Krakatoa volcano. The period 1850 to 1899 is a better baseline, says Hawkins. What’s more, there are several long-term records of global annual average surface temperatures. All differ slightly because they use slightly different data sets and have their own ways of adjusting for relocations of weather stations and changes in instrumentation over time. Read More here