An agreement by almost 200 nations to curb greenhouse gas emissions from 2020 will be far more costly than taking action now to tackle climate change, according to research published on Wednesday.

Quick measures to cut emissions would give a far better chance of keeping global warming within an agreed UN limit of 2°C above pre-industrial times to avert more floods, heatwaves, droughts and rising sea levels.

“If you delay action by 10, 20 years, you significantly reduce the chances of meeting the 2°C target,” said Keywan Riahi, one of the authors of the report from the International Institute for Applied Systems Analysis in Laxenburg, Austria.

“It was generally known that costs increase when you delay action. It was not clear how quickly they change,” he said of the findings, which were published in the science journal Nature and were based on 500 computer-generated scenarios.

The study said the timing of cuts in greenhouse gas emissions was more important than other uncertainties about things such as how the climate system works, future energy demand, carbon prices or new energy technologies.

It indicated that an immediate global price of $30 (about R255) a ton on emissions of carbon dioxide (CO2), the main greenhouse gas, would give a roughly 60 percent chance of limiting warming to below 2°C.

Wait until 2020 and the carbon price would have to be about $100 a ton to retain that 60 percent chance, Riahi said.

Delaying action until 2030 might put the 2°C limit – which some of the more pessimistic scientists say is already unattainable – out of reach, whatever the carbon price.

“The window for effective action on climate change is closing quickly,” wrote Steve Hatfield-Dodds of the Commonwealth Scientific and Industrial Research Organisation in Australia in a separate commentary in Nature.

Governments agreed to the 2°C limit in 2010, viewing it as a threshold to avert dangerous climate change.

After the failure of the 2009 summit in Copenhagen to agree on a worldwide accord, almost 200 nations have given themselves until 2015 to work out a global deal that will enter into force in 2020.

Amid an economic slowdown, many countries at the last UN meeting on climate change in Qatar last month expressed reluctance to make quick shifts away from fossil fuels towards cleaner energies such as wind or solar power. Each US citizen, for instance, emits 20 tons of CO2 a year.

There is no global price on carbon, only regional markets. In the EU trading system, for instance, industrial emitters must pay if they exceed their CO2 quotas. EU prices for this year are about $8.83 a ton.

The report also showed that greener policies, such as more efficient public transport or better-insulated buildings, would raise the chances of meeting the 2°C goal.

And fighting climate change would be easier with certain new technologies, such as capturing and burying carbon emissions from power plants and factories. In some scenarios, the 2°C goal could not be met unless carbon capture was adopted. – Alister Doyle from Reuters in Oslo