Author: MATT CAWOOD
Via: Farm Weekly – online
NASA’s Goddard Institute for Space Studies (GISS) has placed 2009 as the warmest year in the Southern Hemisphere since records began 130 years ago, and the past decade as the warmest globally.
The decade from January 2000 to December 2009 was clearly the warmest since modern instrumentation was introduced in 1880.
“There’s substantial year-to-year variability of global temperature caused by the tropical El Nino-La Nina cycle”, said GISS director James Hansen.
“But when we average temperature over five or ten years to minimize that variability, we find that global warming is continuing unabated.”
Over the past three decades, according to the GISS analysis, the global average temperature has increased 0.2 degrees Celsius a decade.
The Australian Bureau of Meterology (BoM) is waiting on the results of a similar analysis by the UK Met Office’s Hadley Centre, which BoM has traditionally used as a guide to global temperature trends.
The Hadley Centre analysis tends to be more conservative than GISS, according to BoM senior climatologist Dr Karl Braganza, because Hadley scientists leave out areas of the Arctic and Antarctic where climate monitoring stations are scarce.
GISS extrapolates data for these areas from the nearest monitoring stations in an attempt to deliver a fuller climate picture.
In the Hadley analysis, polar areas without monitoring stations are assumed to be warming at the same rate as the global average. GISS incorporates sea ice data from satellites that indicates the Arctic is warming faster than the rest of the planet.
Dr Braganza said while the two methods produce slightly different results – although often within a tenth or a hundredth of a degree – both show the same global warming trend.
A key driver of natural climate variability is the El Nino-La Nina cycle, which stems from the cyclic warming and cooling of the Pacific Ocean.
GISS and BoM climatologists believe the El Nino of late 2009 combined with greenhouse gas-driven warming to produce an unusually warm year in 2009.
“The unusual thing about this El Nino when it got going around mid-2009 was that Pacific ocean temperatures were already very warm, which was likely a continuation of the greenhouse warming effect,” Dr Braganza said.
That warmth across the Pacific generated rain, which counteracted the usual El Nino drying effect on eastern Australia for several months. But as the year went on, across eastern Australia as a whole it was very dry.
“Tasmania got some good rainfall, and Victoria had two or three rainfall events, but they were just weather events. Typically during an El Nino we get less of them.
“When you are talking about climate, you’re talking about what history can tell you might happen over a particular stretch of time–but during an El Nino, you can still get a good rainall event coming through with the normal weather that gives a bit of relief.”
The global warming trend, which is reflected in the warming of the Australian temperature record, appears to be continuing despite the deepest recorded solar minimum.
During solar maximums, high sunspot activity is generally correlated with higher surface temperatures on Earth. Solar minimums, or low sunspot activity, are generally related to cooler temperatures, but this is not the case during the current minimum.
Aerosols, particularly sulfate aerosols produced by volcanoes, are also known to cool global temperature by reflecting sunlight, but aerosols appear not to have played a significant role during 2009.