By Alister Doyle, Environment Correspondent
The report, by scientists in the Netherlands and Germany, indicated that initial investments needed to be high to have any impact in slowing temperature rises. Beyond a certain threshold, however, extra spending would have clear returns on warming.
Until now, most governments have worried that costs may start low and then soar -- suggesting that ambitious targets will become too expensive for tackling threats such as extinctions, droughts, floods and rising seas.
"It gets easier once the world gets going ... ," said Michiel Schaeffer of Wageningen University in the Netherlands and lead author of the study in Tuesday's edition of the journal Proceedings of the National Academy of Science.
"In a sense ... our paper is bad news: doing a bit is hardly effective," he told Reuters. "On the other hand it's good news, because the return on the really 'painful' investments later on, of which the world is so afraid, gives you much better returns."
More than 190 governments have agreed to work out a new U.N. climate treaty by the end of 2009. Global economic slowdown is making many wary of setting too strict goals.
The article suggested there was a 90 percent chance of limiting global warming to 2 Celsius (3.6 Fahrenheit) above 19th century levels with average annual global investments of 2 percent of gross domestic product (GDP) from 2005-2100.
That is roughly comparable to the percentage of GDP the European Union spends on environmental policies, Schaeffer said.
But early investments would have little impact. Spending 0.5 percent of world GDP would give a 10 percent chance of achieving the 2 Celsius goal while an investment of one percent of GDP would give a 40 percent chance.
Two Celsius is a goal adopted by the EU, some other nations and many environmental groups as a threshold for "dangerous" climate change.
The study focused on setting a ceiling for temperature rises, rather than on more normal goals of stabilizing concentrations of greenhouse gases in the atmosphere, mainly from burning fossil fuels in cars, factories and power plants.
The scientists said that shift gave a better perspective and toned down worries about exponential rises in costs.
"This viewpoint is more relevant for real-life climate impacts," Schaeffer said. "Concentrations don't tell you that much about what happens in terms of rainfall ... or to society."
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