The roughest storms are set to get rougher under climate change predictions that already have two decades of proven reliability.

It was possible events such as the floods in Nelson and Golden Bay last December could become more common, said New Zealand Climate Change Research Institute director David Frame.

Professor Frame is co-author of a report published in the latest edition of Nature Climate Change.

Along with Daithi Stone, from the Lawrence Berkeley National Laboratory in California, Prof Frame has compared predictions from the first Intergovernmental Panel on Climate Change (IPCC) assessment report in 1990 with actual data from the past 20 years.

The comparison showed global climate change was happening as predicted in 1990. "Things are changing pretty much the way we thought - surprisingly so," Prof Frame said.

Since 1990 the average global surface temperature rose by between 0.35 degrees Celsius and 0.39C, in line with 1990 predictions. This was in spite of unforeseen climate-altering events, such as the eruption of Mt Pinatubo in 1991, the collapse of Soviet bloc industries in the 1990s, and the recent fossil fuel-intensive growth in economies such as Asia.

"What we've found is that these early predictions seem pretty good, and this is likely due to the climate responding to concentrations of greenhouse gases in the Earth's atmosphere at a rate broadly in line with what scientists in 1990 expected."

The 1990 predictions looked ahead as far as 2030, and forecast that average temperatures would continue to rise by about 0.2C a decade.

As temperatures rose, the air was able to hold more water, meaning that, when it rained, more water would come down.

The Manawatu floods of 2004, and last year's flooding in Nelson and Golden Bay, were "explosive summer events" that may be shown to be linked to global warming and examples of what the future may hold.

However, further predictions for what rising temperatures could mean for New Zealand were difficult to make, because global warming worked on a large scale. "We can be right about the globe, but wrong about Eketahuna," Prof Frame said.

But Bryan Leyland, from the New Zealand Climate Science Coalition, said science had shown global temperatures had not risen in 16 years and the world was more likely to get cooler.

THE 20-YEAR FORECAST

Sea levels will rise, though it is hard to say by how much.

Continents will have warmer winters. Heatwaves will increase.

The warming will be greatest over land areas at the highest northern latitudes, and least over the Southern Ocean and parts of the North Atlantic.

Sea ice and snow cover will decrease in many places.

- © Fairfax NZ News

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