LONDON A widely agreed international target to avoid dangerous global warming must take account of local impacts and may need to change, said the chief scientist at the MetOffice Hadley Center, Britain's biggest climate research center.
Julia Slingo said the target of limiting global temperature rise to 2 degrees Celsius (2C) may need adjusting to take into account research into local and regional effects, particularly on rainfall patterns, as climate science advances.
More than 120 nations agreed to the U.N.'s Copenhagen Accord last December which aimed to limit average global warming to less than 2C, in one of the main outcomes of a fractious summit.
But hopes are low for agreement on a global climate deal, to succeed the Kyoto Protocol on curbing greenhouse gas emissions after 2012, at a follow-up U.N. conference in Cancun, Mexico later this month.
Slingo said the world should keep the 2C target for now to aid negotiations, but that it should be kept under review.
She said better local and regional data would "enable individual countries to enter negotiations in a more informed, engaged way because it doesn't seem like an arbitrary target that's just been set at a global level."
Slingo added: "Temperature change in many respects is not the most dangerous part of climate change. The most dangerous part is arguably around the shift of regional rainfall patterns.
"It would be wrong to suggest in any way that the target is inappropriate, but in parallel we want to start to put some more substance on it."
The over-riding goal of the 1992 U.N. climate convention is to avert "dangerous" climate change -- many scientists say 2C is the maximum safe limit. Temperatures have already risen about 0.7 degrees C since the Industrial Revolution.
But small island states, fearing sea level rise, favor a ceiling of 1.5 Celsius.
Some experts say global warming beyond 2C poses a 50 percent chance or more that the Greenland ice sheet will melt, over centuries, raising global sea levels by about 7 meters.
A global trend toward living in cities and near coasts means the world was already more vulnerable to natural, extreme weather, Slingo said.
She said new data also showed that manmade greenhouse gas emissions implied irreversible climate change.
"The greater understanding we have now ... is that a fraction of the carbon we put in the atmosphere will stay there forever, all else being equal.
"There's an irreversible nature to temperature, carbon dioxide and sea level rise which goes on for several centuries. That has to enter into our consideration of what's dangerous."
(Additional reporting by Alister Doyle in Oslo; Editing by Janet Lawrence)