'Here is the forecast for 2050'

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An international study of the effects of different policies to curb greenhouse gas emissions has found that real benefits will result, but that they may take decades to become evident.

LONDON, 13 January – The world in under 40 years? Another billion people will have trouble ensuring safe and regular water supplies, and drought will blight an extra three million square kilometres of farmland. More than 330 million people will be at increased risk of flooding in the river valleys and an extra 69 million could be flooded each year along the coasts. More alarmingly, six million square kilometres of farmland will become less productive as global temperatures rise.

All these impacts are based on the assumption that the governments of the world take no action to limit global warming, and average temperatures rise by 4°C. The good news is that swiftly-imposed tough limits of global emissions – to contain warming to an internationally agreed 2°C rise – could reduce or limit the impacts of climate change by between 20 and 65%. The bad news is that there would be no obvious impact until 2030 or after.

The findings, by a team led by the Walker Institute at the University of Reading, and published in Nature Climate Change, are explorations rather than conclusions: attempts to apply some sort of measure to future human actions, in the light of future international decisions.

“There is not a great deal of evidence out there about what dangerous climate change is or what different policies might do for the impacts of climate change,” said Nigel Arnell, director of the institute. “We looked at what would happen if the world managed to hit a particular emissions trajectory; what benefits would there be, what sort of impacts would be avoided.”

“The exercise is a bit like trying to guess how many lives were saved in accidents that did not happen.”

The researchers chose four different hypothetical emissions reductions policies peaking at different years and declining at different rates, and compared the results with two different alternative futures where there are no emissions policies – in which a global “business as usual” response would lead to rises of 4°C or even 6° C.

They then chose 10 ways of measuring impact, ranging from drought and flooding to wheat and soybean yield, changes in heating and air conditioning demand and so on, and tried to forecast possible consequences of each policy.

“We see quite a long lead time before we see any real impacts or benefits of a climate policy. The impacts that you avoid increase over time,” Professor Arnell said. “The earlier and the more rapidly you reduce emissions the greater the impact.”

The results neatly demonstrate the dilemma that faces elected politicians: constraints on energy use are not likely to prove popular, and any pay-off will not be easily measurable in most political lifetimes.

The researchers tried to estimate the consequences of the 2°C ambition – agreed at an international summit in Copenhagen in 2009 – and found that the rewards by 2050 were difficult to quantify. But the guess was that around 50 million people would be spared water shortages, and between 100 and 160 million people would be at a lower risk of flooding because of such action.

The exercise is a bit like trying to guess how many lives were saved in accidents that did not happen.

But the researchers, from the Hadley Centre at the British Met Office, the University of Southampton, the Tyndall Centre for Climate Change Research at the University of Nottingham, the Potsdam Institute in Germany, the University of Aberdeen and the University of East Anglia, are convinced that limits on emissions will nevertheless have a measurable effect by 2050 and a pronounced benefit by 2100.

“Reducing greenhouse gas emissions won’t avoid the impacts of climate change altogether, of course, but our research shows it will buy time to make things like buildings, transport systems and agriculture more resilient to climate change,” said Professor Arnell. – Climate News Network