What effects are global warming feedbacks likely to have?
One of the easiest to estimate is the “ice-albedo” feedback. As the world warms, ice caps will melt, to be replaced by water or land. Ice is very efficient at reflecting solar radiation, whereas water and land are less so. Therefore, the Earth’s surface will trap more heat, increasing warming – a positive feedback. Less clear-cut is the impact of the extra water vapour likely to enter the atmosphere because of higher evaporation rates. This added water vapour itself contributes to the greenhouse effect, another positive feedback. But it may also increase cloud cover, shrouding and cooling the Earth – a negative feedback. Disputes about how water vapour and clouds will influence global warming are at the heart of disputes between mainstream scientists and the handful of greenhouse sceptics. Most believe that positive feedbacks could amplify the warming effect by between two and five times. But some sceptics believe the feedback effect could be neutral or negative.
