Worst-case global warming scenarios not credible: study

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 gases drive up the planet's temperature reduces the range of possible end-of-century outcomes by more than half, researchers said in the report, published in the journal Nature.How effectively the world slashes CO2 and methane emissions, improves energy efficiency,