Contrary to claims made by an Auckland scientist earlier in the week, scientists from around the world and New Zealand are saying the recent Australian heatwave is part of a global trend.
Intergovernmental Panel on Climate Change (IPCC) chairman Rajendra Pachauri has told media the Australia heatwave is part of a warming trend around the world and says more heatwaves are likely.
“We already are getting more frequent and more intense heatwaves, and we are also going to get extreme precipitation events.”
The IPCC, which is currently meeting in Hobart, warned on Tuesday that heatwaves in Australia could become six times more frequent within 30 years.
But earlier this week associate professor of climate and environment science Chris de Freitas of the University of Auckland said there was no evidence to suggest the Australian heatwave was connected to climate change.
“It’s speculation, not fact,” he told 3 News, saying there was no evidence humans were to blame for rising global temperatures.
However James Renwick, a climate scientist at Victoria University of Wellington attending the IPCC conference in Hobart, says although it is difficult to pin one event to climate change, there probably is a connection.
“You can’t ever say a particular heatwave is because of climate change…. [but] there is a connection in the sense that the temperatures over in Australia have gone up over the last century or so, and that means it’s easier for a heatwave to happen.”
Dr Renwick says better evidence of climate change would be seeing repeated heatwaves.
“If we start seeing these more often, that would be better evidence.”
He says a 1degC increase in temperature could double the risk of heatwaves, and expects the frequency of heatwaves in Australia to increase.
“The expectation is we will start seeing these extremes more and more often in the future.”
Dr Renwick says other extremes of weather, like rain and flooding, are also a sign of the earth warming up.
“The amount of moisture in the air is directly proportional to the heat of the air. The chances of getting a heavy rainfall event increases if there is an increase in temperature.
“Generally in a lot of ways the [global] climate is becoming more extreme.”
He is not so sure if New Zealand’s extremes of warm weather in some areas and flooding in others recently are related to climate change.
“That sort of thing has been going on forever. It’s the same story that if you see the occurrence of these very warm conditions and flooding conditions increasing over time.”
Dr Renwick says to really see if climate change is happening, you’ve got to look at trends over a number of years.
He says the decline in the number of frosts in New Zealand is a sign of climate change, and he expects frosts here to disappear by the end of this century.
In his criticism, Dr de Freitas also referred to a leaked draft of the IPCC five-year assessment report which appeared to claim global temperatures have not risen in the past 16 years.
Mr Renwick says this is probably correct.
“That’s right, globally temperatures over the last 10 or 15 years have not risen as fast as you would expect.”
But he says this doesn’t mean climate change is not happening. He says the late 1990s were very warm because of the warm El Nino climate system, but the 2000s have been cooler because of La Nina, which acts to cool the climate.
“Once you take account of that effect, behind that, temperatures are going up and greenhouse gases are going up.
“Fifteen years is still a pretty short period to look at the trend.”