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20 years on, climate change projections have come true

The climate may vary from year to year but the overall trend is toward a much hotter planet, scientists say.

Climate change predictions made 20 years ago have so far proved accurate, suggesting that the world is indeed on track to a radical climate shift, according to a new paper published today.

In 1990, the Intergovernmental Panel on Climate Change (IPCC) – a group of the world’s top climate scientists – released its First Assessment Report, predicting global warming of about 1.1 degrees celsius between 1990 and 2030.

In today’s edition of Nature Climate Change, climate scientists David Frame and Dáithí A. Stone argue that, halfway through that projection period, the predictions made in 1990 are proving mostly accurate.

The 1990 report’s “best estimate” was that the world would warm by about 1.1 degrees celsius between 1990 and 2030, meaning that the halfway prediction would be about 0.55 degrees celsius by 2010.

In fact, the world has now warmed by about 0.39 degrees celsius, coming very close to the prediction despite several unforeseen historical events, such as the collapse of the Soviet Union, the Mt Pinatubo volcanic eruption and the rise of China.

“As is always the case in science, we cannot know for certain that the 1990 prediction was accurate for the right reasons but, given the apparent absence of any credible alternative theories and the robustness of the prediction, this evaluation strongly supports the contention that the climate is responding to enhanced levels of GHGs (greenhouse gases) in accordance with historical expectations,” the authors wrote.

The paper also said that climate policies enacted between now and 2030 would “will only very gradually manifest themselves in the climate signal.”

Penny Whetton, Senior Principal Research Scientist at the CSIRO and a lead author for the Third Assessment Report of the (IPCC), said the paper confirmed that “projections that climate scientists have been making have been accurate.”

“There are implications for the wider community for how they accept the IPCC conclusions. This is good evidence to show that what the IPCC has been saying for a while is coming true,” she said, adding that the discrepancy between the 0.55 degree projected rise and the 0.39 actual rise was explained by variability in estimates due to natural fluctuations.

“Once you allow for that, this paper demonstrates that the warming we are seeing is consistent with the projections made by the IPCC,” said Dr Whetton.

“What we do in our emissions now could be the difference between a two degree rise and a four degree or five degree rise later in the century.”

Steve Sherwood, Co-Director, Climate Change Research Centre at the University of New South Wales said the paper showed “that if you take natural year-to-year variability into account in any reasonable way, the predictions are as close as one could reasonably expect.”

“Those who have been claiming ad nauseum that the climate models have been proved wrong, should read this paper, even though for most of us it is not very surprising,” said Dr Sherwood, who was not involved in the Nature Climate Change paper.

“Though there is no contrarian analogue to the IPCC, individual contrarians have made predictions over a similar time frame that the warming would stop or reverse. The data since then have probably falsified many of those predictions (which the deniers continue to make today).”

Stuart Corney, a Climate Systems Modeller at the Antarctic Climate and Ecosystems CRC at the University of Tasmania, pointed out that social and economic factors make it hard to predict future emissions but that, even so, the 1990 projections had turned out to be very close.

“Twenty years after the 1990 prediction, we see it’s not perfectly accurate – it’s about a 0.4 degree rise instead of a 0.55 degree rise – but it’s still statistically significantly above zero,” he said.

“Climate models can’t predict year to year variations but the long term trends are clear. The take home message is that the climate models we are using now should be accurate in years to come.”

Dr Corney said the trend showed showed the benefit of acting quickly.

“We are locked in now for a certain amount of climate change between now and 2030. No matter what we do now it will have little effect between now and 2030,” he said.

“But what we do now will have a stark effect on what happens in 50 years time or 100 years time.”

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