Blazing hot

 作者:魏鲶     |      日期:2019-03-08 07:20:02
By Fred Pearce UP TO half the global warming we have experienced over the past 130 years may have been caused by an increase in the Sun’s output of energy. This finding is sure to be seized on by those say that our emissions of greenhouse gases are not the dominant cause of global warming. But Mike Lockwood of the Rutherford Appleton Laboratory in Didcot, Oxfordshire, whose team made the discovery, says the true message is much more disturbing. Taking away the effects of the Sun’s increasing output reveals that, since 1970, greenhouse emissions have had an even more dramatic effect than was thought. “It is a question of balance, and the balance is changing,” he says. “Whatever happened in the past, the greenhouse effect is now the dominant cause of warming.” Lockwood and his colleagues obtained their data from space probes that have been measuring the solar magnetic field, which varies in strength with the amount of energy the Sun emits. By analysing how these variations in solar magnetism affect the Earth’s magnetic field—which has been monitored by scientists in Britain and Australia since 1868—the researchers were able to use historical data to calculate the Sun’s energy output over the entire period. Since the mid-19th century, average global temperatures have risen by around 0.6 °C. Lockwood’s team calculates that solar changes account for about half of this—twice the amount previously accepted by most climatologists. Solar changes may have caused virtually all the warming that occurred between 1860 and 1930, says Lockwood. But since 1970, when the pace of climate change began to accelerate, the Sun has been the source of less than a third of the warming. The build-up of greenhouse gases is to blame for the rest (Nature, vol 399, p 437). One of the prime architects of the scientific consensus on global warming, Tom Wigley of the National Center for Atmospheric Research in Boulder, Colorado, says that Lockwood’s picture of events before 1970 is “quite different” from the view until now. He now intends to look closely at Lockwood’s paper to see whether the consensus needs to shift. Past efforts to estimate historical changes in solar energy have mostly used measures of sunspot activity and the length of the solar cycle, which are thought to correlate with the Sun’s output. “But there isn’t really a strong physical understanding of why the length of the solar cycle should be relevant,” says Lockwood. He argues that the magnetic field method is “more direct and accurate”. But no method that relies on calculating historical events that cannot be measured directly is 100 per cent reliable. “There are still uncertainties,” Lockwood admits. “There may be amplifying effects that we have yet to discover,