Gulf Stream and the climate

Ocean currents The Berkeley group does depart from the "orthodox" picture of climate science in its depiction of short-term variability in the global temperature. The El Nino Southern Oscillation (ENSO) is generally thought to be the main reason for inter-annual warming or cooling. But by the Berkeley team's analysis, the global temperature correlates more closely with the state of the Atlantic Multidecadal Oscillation (AMO) index - a measure of sea surface temperature in the north Atlantic. There are theories suggesting that the AMO index is in turn driven by fluctuations in the north Atlantic current commonly called the Gulf Stream. The team suggests it is worth investigating whether the long-term AMO cycles, which are thought to last 65-70 years, may play a part in the temperature rise, fall and rise again seen during the 20th Century. But they emphasise that anthropogenic global warming (AGW) driven by greenhouse gas emissions is very much in their picture. "Had we found no global warming, then that would have ruled out AGW," said Prof Muller. "Had we found half as much, it would have suggested that prior estimates [of AGW] were too large; if we had found more warming, it would have raised the question of whether prior estimates were too low. "But we didn't; we found that the prior rise was confirmed. That means that we do not directly affect prior estimates." The team next plans to look at ocean temperatures, in order to construct a truly global dataset. Follow Richard on Twitter