A New Zealand scientist who contributed to the latest UN report on climate change says it's becoming increasingly unlikely the world will avoid the worst-case scenarios of melting ice caps and rising sea levels.
Victoria University professor Timothy Naish says the evidence that humans are contributing to rising temperatures is clearer than ever, despite the report's official stance leaving room for doubt at "95 percent" sure.
But this is up from 2007, when the UN's Intergovernmental Panel on Climate Change said it was ony "90 percent" certain.
"The IPCC is inherently conservative – I think it has to be that way," Prof Naish said on Firstline this morning.
"I think it's always an easier situation to increase your certainty than to be overly certain and then have to come back."
Rather than present new scenarios of what may unfold over the next century of rising temperatures, this latest report narrows down the range of possibilities.
"The significant point here is we've got a number of scenarios, and they depend on how we essentially limit our emissions of greenhouse gases," says Prof Naish. "Three or four of those scenarios tell us we're going to be warmer than 1.5degC, and one of them says well, you can keep the temperature under 2degC, but that would require widespread extraction of carbon dioxide out of the atmosphere. "
Unfortunately, particularly for those living in vulnerable parts of the world such as low-lying Pacific islands, Prof Naish says it will be "extremely difficult" now to keep the world's average temperature less than 2degC above pre-industrial levels.
"Above 2degC and getting up to 4degC is when we see the irreversible meltdown of the Greenland ice sheet, we parts of the Antarctic ice sheet go, we see sea level rise greater than one metre, we see the increase in the intensity of storms, the big rainfall events, all those sort of worst, extreme things we expect with climate change."
The best-case scenario offered in the report is that temperatures rise only about 1degC by 2100.