GREAT uncertainty remains about how much of an impact climate change will have on future extreme weather events, the world’s leading climate scientists have found.
While there has been an increase in warm days and a decrease in cold nights, the likely impact on future weather events would not be evident for decades because of natural variability, the scientists say in a key review prepared for the UN’s Intergovernmental Panel on Climate Change.
The review of the global climate change literature, prepared as a prelude to the year’s biggest climate change conference to be held in Durban in South Africa, says the rising global temperatures can be expected to have an impact.
But it adds: “Projected changes in climate extremes under different emissions scenarios generally do not strongly diverge in the coming two to three decades, but these signals are relatively small compared with natural climate variability over this timeframe.
“Even the sign of projected changes in some climate extremes over this timeframe is uncertain.”
Releasing a summary of the review last night in Kampala, the Ugandan capital, lead author Thomas Stocker said extreme weather events were some of the most complex phenomena in nature to understand, simulate and predict.
The IPCC report expressed the level of uncertainty attached to future scenarios, Dr Stocker said. But for many phenomena, the picture was very clear and the physical relationship was well understood.
“A changing climate leads to changes in intensity and frequency, spatial extent, duration and timing of extreme weather and climate events, and can result in extreme weather and climate events,” Dr Stocker said.
“An increase in the frequency and magnitude of warm daily temperature extremes will occur in the 21st century on a global scale. For high-emission scenarios of greenhouse gases, the incidence of hottest days will increase by a factor of four within the next 30 to 40 years and by a factor of 10 by the end of the 21st century.”
IPCC chairman Rajendra Pachauri said it was “very likely” there had been an overall decrease in cold days and nights and an increase in warm days and nights. He said there had clearly been “statistically significant” trends in heavy rain events in some regions.
However, Dr Pachauri said there had been “strong variations to the trend”.
Dr Pachauri described the extreme weather report as “robust and balanced”.
Global Warming Policy Foundation director Benny Peiser said the overall message was “there was not a strong empirical link between anthropogenic climate change and weather events”.
“It is unlikely there will be one for 20 to 30 years,” he said.
He said any suggestion that recent weather events could be directly linked to climate change went directly against the general scientific consensus.
Kathy McInnes, lead author of chapter three – Changes in Climate Extremes and their Impacts on the Natural Physical Environment – said a lot of uncertainty remained.