claim: Worst-case global heating scenarios may need to be revised upwards in light of a better understanding of the role of clouds, scientists have said.
evidence: Climate model projections summarized in the report indicated that during the 21st century the global surface temperature is likely to rise a further 0.3 to 1.7 °C ( 0.5 to 3.1 °F ) in a moderate scenario, or as much as 2.6 to 4.8 °C ( 4.7 to 8.6 °F ) in an extreme scenario, depending on the rate of future greenhouse gas emissions and on climate feedback effects.