Tuesday, March 13th 2012, 2:20 PM EDT
COOLER weather in Australia in the past two years due to the rain-inducing La Nina weather pattern does not undermine the collective evidence of climate change, the nation's peak scientific and weather organisations say.
In their second State of the Climate report released today, the CSIRO and Bureau of Meteorology say evidence shows global warming continued and human activities were mainly responsible.
The report says natural climate variability had affected the global mean temperature and sea levels during the past century but much less than greenhouse gases, which continued to rise.
"It is clear that increasing greenhouse gas concentrations will result in significant further global warming," the report says.
Uncertainties remained regarding future levels of greenhouse gas concentrations, and the timing and magnitude of changes, particularly at regional scales.
There were further uncertainties relating to tipping points in the climate system, such as the break-up of ice sheets, which could lead to rapid climate change, the report says. "Unless greenhouse gas emissions decrease, we expect to see the temperature of the atmosphere and the oceans continue to warm and sea levels continue to rise at current or even higher rates," the report says.
Australian average temperatures were projected to rise by 1-5C by 2070 when compared with the climate of recent decades.
Bureau of Meteorology climate monitoring manager Karl Braganza said the scientific community found it difficult to communicate the climate change message because of the long timeframes involved.
"People want to see the things projected for the next 20 to 30 years happening now and if they don't see it, their acceptance of the science is ameliorated by that," Dr Braganza said.
"That is a hard thing to get around."
He said there were a number of factors that had made near-term warming forecasts difficult.
"We are probably at a period where solar forcing (the sun's energy) has been lower than recent decades," he said.
There was an influence from China's rapid economic development, which was causing more particles to be put into the atmosphere that reflect sunlight. "I think all of those things are affecting the climate system but the dominant, real standout influence is the increase in greenhouse gases, mostly CO2," Dr Braganza said.
The report says the concentration of CO2 in the atmosphere last year was 390 parts per million, higher than at any time for the past 800,000 years.
The State of the Climate report provides a summary of observations of Australia's climate and analysis of the factors that influence it.
It is broken into chapters dealing with temperature, rainfall, sea levels, greenhouse gases and future predictions.
Despite 2010 and last year being the coolest years recorded in Australia since 2001, the report says the long-term warming trend has not changed, with each decade warmer than the previous decade since the 1950s.
The report says Australian annual-average daily mean temperatures showed little change from 1910 to 1950 but have progressively warmed since, increasing by 0.9C from 1910 to last year.
Global-average surface temperatures were the warmest on record in 2010 and the world's 13 warmest years on record have all occurred in the past 15 years.
The summary says the very strong La Nina event in 2010 followed by another last year produced the highest two-year Australian-average rainfall total on record.
Sea level rises since 1993 ranged from 11mm a year in northwest Australia to less than 2mm on the central east coast.
CSIRO: warming up to five degrees by 2070
- By Richard Chirgwin - The Register
Image source: The Australian