It is very difficult to attribute any single event to climate change, however, new research from the Climate Change Research Centre (CCRC) at UNSW shows that extreme rainfall experienced in Queensland during the summer of 2010/2011 was enhanced by background ocean warming.
It is well known that La Nina events, in Australia, lead to above average rainfall across much of eastern Australia. In fact, recent La Nina events have been responsible for our recent cool and wet summer we experienced in Canberra this year.
While it’s always tempting to explain anything that doesn’t fit our idea of what the weather should be as a manifestation of climate change, we need to remember that our weather is naturally variable, and we need to be careful in attributing individual events to climate change, without having a proper understanding of the natural background conditions.
A recent paper published in Geophysical Research Letters goes about quantifying the effects of background ocean warming on the 2010/2011 flooding event in Queensland. The authors use a regional climate model to try to recreate the recorded rainfall totals using the observed climate conditions at the time, particularly, observed warm sea surface temperatures (SST). This model run was then repeated, using the average SST experienced during La Nina events in this region, over the past 30 years. This allowed the authors to determine how much of the observed rainfall was directly caused by the warmer than normal ocean temperatures at the time.
It turns out, that the natural La Nina-related rainfall was enhanced by 25%, due to these very warm SST.
“Between December 23 and 28 many places experienced up to 400 millimetres of rain in a few days. That [means] 100 millimetres of rain was attributable to sea surface temperatures,” said Dr Evans, a future fellow at the University of NSW’s Climate Change Research Centre.
Head of the CCRC, Matt England suggests that this warming trend is likely attributable to background climate change.
“While the La Nina event played a big role in this record ocean warmth, so too did the long-term warming trend over the past 50 years,” Professor England, the co-director of the UNSW Climate Change Research Centre, said.
Another hypothesis for the observed background warming trend, is a shift to the negative phase of the IPO. Check out Kelly’s post from a few weeks ago for more details.