Weather extremes to increase

Rising sea levels, more localised flooding, storms and droughts are in store for New Zealand unless greenhouse gas emissions are reduced, a Wellington scientist predicts.

Victoria University environmental economist Ralph Chapman says the country will face an increased number of extreme weather events over the next 100 years and beyond.

"It will get worse because of the huge momentum in the emissions, particularly from developing countries," says Chapman.

Many scientists predict a sea-level rise of at least a metre by the end of the century.

Global concentrations of greenhouse gases are gradually increasing and within a decade or so could reach a level which would cause instability in the climate system.

Britain's Hadley Centre for Climate Prediction and Research estimates that an increase of greenhouse gases in the atmosphere from the current 425 parts per million to 450 ppm will be enough to raise the earth's temperature by 2.7C. "It doesn't sound like much, but it's a hell of a lot in terms of global climate change," says Chapman. As the earth gradually heats up, many scientists predict a significant risk of the land-based ice sheets of Greenland and Antarctica melting.

"In broad terms, that means 10 metres of sea-level rise. You're talking about London under water, New York under water, large parts of Wellington under water."

Venice would be gone (it would take less than a metre rise to flood Venice), and most of New Zealand's cities would be partially submerged. Low-lying coastal areas and flood plains would be wiped out.

That sort of devastation would not happen quickly, Chapman says. Because of the lag time in the climate system, as emissions rise and climate is affected, the process goes on for a couple of centuries.

"You can't turn that system off, even if you reduce emissions. You turn on a system that is very powerful, but it doesn't have an immediate impact. By the time it's had an impact, it's too late to do anything about it," Chapman says. "If you reduce emissions very rapidly and very drastically you have a chance of turning that around."

Chapman has studied climate change for the past 20 years and is co-editing a book, Confronting Climate Change: Critical issues for New Zealand, due out next month. Last week he and other scientists gathered in Wellington for a symposium on climate change.

The Hadley Centre, which has been tracking global temperatures since 1861, reports that the 10 warmest years occurred in the past 13 years, including every year since 1997. But scientists here are unwilling to point the finger at global warming when talking about New Zealand's increased level of localised flooding in the past decade.

Climate changes can be caused by El Nino and El Nina variations or by cyclical weather changes. But, they say, an increased level of both major and minor flooding is consistent with the trend of climate change.

The National Institute of Water and Atmospheric Research (Niwa) has been tracking weather patterns and rainfall in recent decades and predicts greater flooding and wet weather on the west coast, with the east coast suffering more droughts.

Niwa climate scientist Georgina Griffiths has analysed New Zealand's daily rainfall between 1950 and 2004. Her study shows a gradual increase in heavy rainfall in western areas and the lower South Island, and a decrease in rainfall in the east and north of the North Island.

Climate scientist David Wratt, leader of Niwa's national climate centre in Wellington, agrees that an increase in floods is expected to happen in the coming decades as part of the climate change.

Areas already at risk from flooding, such as flood plains and low-lying coastal areas, would increasingly be at risk from rising sea levels, storm surges and heavy rain. Niwa is running a climate model on its super-computer, tracking storms and extreme weather changes in the hope of providing more helpful predictions in the future.