Hemispheric albedo equivalence as a new constraint for climate models
Jim Haywood
The amount of sunlight reflected from the northern and southern hemispheres is the same (owing to
greater cloud cover in the southern hemisphere. The equivalence is unlikely to be by chance but
reasons are open to debate. Here we show that equilibrating hemispheric albedos by various idealised
methods in HadGEM2-ES leads to significant improvements in what have been considered
longstanding and apparently intractable model biases. Monsoon precipitation biases almost vanish over
all continental land areas, the penetration of monsoon rainfall across the Sahel and the west African
monsoon “jump” become well represented, and indicators of hurricane frequency are significantly
improved. Mechanistically, our analysis suggests that equilibrating hemispheric albedos improves the
atmospheric cross-equatorial energy transport and increases the supply of tropical atmospheric
moisture to the Hadley cell. Thus hemispheric albedo equivalence may provide a fundamental
constraint for climate models that must be satisfied if model tropical performance is to be improved.