>A doubling of the Sun's coronal magnetic field during the past 100
>years by M. Lockwood, R. Stamper, and M.N. Wild
>5 June 1999
> 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
> Since the mid-19th century, average global temperatures have
>risen by around 0.6 =B0C. 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, which could
>change the calculations again."
>Donald L. Anderson
>Climate Change Specialist
>Maine DEP (Bureau of Air Quality)
>Augusta, ME 04333-0017
>(207) 287-2437 (207) 287-7641 (fax)
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