Global temperatures
for 2008 will be slightly cooler than last year as a result of the cold
La Nina current in the Pacific, UN meteorologists have said.
The World Meteorological Organization's secretary-general, Michel
Jarraud, told the BBC it was likely that La Nina would continue into
the summer.
But this year's temperatures would still be way above the average - and
we would soon exceed the record year of 1998 because of global warming
induced by greenhouse gases.
The WMO points out that the decade from 1998 to 2007 was the warmest on
record. Since the beginning of the 20th Century, the global average
surface temperature has risen by 0.74C.
While Nasa, the US space agency, cites 2005 as the warmest year, the
UK's Hadley Centre lists it as second to 1998.
Researchers say the uncertainty in the observed value for any
particular year is larger than these small temperature differences.
What matters, they say, is the long-term upward trend.
Rises 'stalled'
La Nina and El Nino are two great natural Pacific currents whose
effects are so huge they resonate round the world.
El Nino warms the planet when it happens; La Nina cools it. This year,
the Pacific is in the grip of a powerful La Nina.
It has contributed to torrential rains in Australia and to some of the
coldest temperatures in memory in snow-bound parts of China.
Mr Jarraud told the BBC that the effect was likely to continue into the
summer, depressing temperatures globally by a fraction of a degree.
This would mean that temperatures have not risen globally since 1998
when El Nino warmed the world.
Watching trends
A minority of scientists question whether this means global warming has
peaked and argue the Earth has proved more resilient to greenhouse
gases than predicted.
Animation of El Nino and La Nina effects
But Mr Jarraud insisted this was not the case and noted that 2008
temperatures would still be well above average for the century.
"When you look at climate change you should not look at any particular
year," he said. "You should look at trends over a pretty long period
and the trend of temperature globally is still very much indicative of
warming.
"La Nina is part of what we call 'variability'. There has always been
and there will always be cooler and warmer years, but what is important
for climate change is that the trend is up; the climate on average is
warming even if there is a temporary cooling because of La Nina."
China suffered from heavy snow in January
Adam Scaife, lead scientist for Modelling Climate Variability at the
Hadley Centre in Exeter, UK, said their best estimate for 2008 was
about 0.4C above the 1961-1990 average, and higher than this if you
compared it with further back in the 20th Century.
Mr Scaife told the BBC: "What's happened now is that La Nina has come
along and depressed temperatures slightly but these changes are very
small compared to the long-term climate change signal, and in a few
years time we are confident that the current record temperature of 1998
will be beaten when the La Nina has ended."
http://news.bbc.co.uk/1/hi/sci/tech/7329799.stm
