WORST-CASE GLOBAL WARMING?

EARTH'S SURFACE will almost certainly not warm up four or five degrees Celsius by 2100, according to a study released Wednesday which-

If correct, voids worst case UN climate change predictions.

A revised calculation of how greenhouse gasses drive up the planet's temperatures reduces the range of possible end-of-century outcomes by-

More than half, researchers said in the report, published in the journal nature.

''Our study all but rules out very low and very high climate sensitivities,'' said lead author Peter Cox, a Professor at the University of Exeter.

How effectively the world slashes CO2 and methane emissions, improves energy efficiency, and develops technologies to remove CO2 from the air-

Will determine whether climate change remains manageable or unleashes a maelstrom of human misery.

But uncertainty about how things will get also stems from the inability of scientists to nail down a very simple question :

By how much will  Earth's average surface temperature go up if the amount of  CO2  in the atmosphere is doubled?

That ''known unknown'' is called equilibrium climate sensitivity  [ECS] and for the last 25 years the  UN's Intergovernmental Change [IPCC] -the ultimate authority on climate science -has settled on a range of-

1.5 C  to  4.5 C  [2.7 to 8.1 degrees Fahrenheit].

Cox and colleagues, using a  new methodology, have come up with a far narrower range -2.2C to 3.4C, with a best estimate of 2.8C  [5F]

If accurate, it precludes the most destructive doomsday scenario.

''These scientists have produced a more accurate estimate of how the planet will respond to increasing  CO2  levels.'' said Piers Forster, director of the  Priestley International Centre for Climate at the University of Leeds.

Gabi Hegeri, a climate scientist at the University of Edinburgh who, like Forster, did not take part in the research, added :

''Having lower probability for very high sensitivity is reassuring.''