One person who is concerned with Earth's rapidly changing wardrobe is Gordon Bonan from the US National Center for Atmospheric Research (NCAR) in Boulder, Colorado. He is using experiments and coupled ecosystem–climate models to study the impact that changes to Earth's surface have on climate.

Forests are one of Earth's most sophisticated garments. In recent years there has been much talk of reforestation, afforestation and avoiding deforestation, as a mitigation strategy for anthropogenic climate change. The theory is that forests store carbon, thereby reducing the accumulation of carbon dioxide in the atmosphere and diminishing global warming. However, Bonan's work shows that this view may be too simplified.

The impact of forests on climate depends strongly on their location. Projections suggest that Arctic regions will become much warmer over the coming years, meaning that ice will melt and trees are likely to march north. Unfortunately the cooling effect of these trees (from storing extra carbon) is likely to be outweighed by their low albedo (reflectivity), which will soak up far more heat than bright reflective snow and ice, and their enhanced transpiration. "Forests evaporate a considerable amount of water," says Bonan. Water vapour is a powerful greenhouse gas.

Recently Bonan and his colleagues modelled the effect of adding deciduous trees to bare ground at high latitudes, and showed that enhanced transpiration could create a radiative imbalance 1.5 times larger than the forcing because of albedo change. "Furthermore, greenhouse warming by additional water vapour melts sea ice and triggers a positive feedback through changes in ocean albedo and evaporation," explains Bonan.

Another major consideration for Bonan is the interactions between the carbon and nitrogen cycles. Traditional ecosystem models indicate that rising carbon dioxide will stimulate plant activity but that this effect will be countered by carbon storage in plants and soils becoming less efficient as temperatures rise. However, these models only consider the carbon cycle. When Bonan and his colleagues included the nitrogen cycle too, they found a more complex picture. "We simulate less carbon storage from carbon dioxide fertilization but also increased plant productivity with soil warming because of greater rates of decomposition and nitrogen mineralization," Bonan told environmentalresearchweb.

As well as looking at natural ecosystems, Bonan is also interested in the effect of urban environment on climate change. "Urban 'ecosystems' are where most people live," he says. "I want to be able to simulate the temperature in cities so that we can examine climate-change mitigation strategies."

In a recent study Bonan and his colleagues showed that if every roof were painted white, the urban-heat island effect could be reduced by one third. This would cool the world's cities by an average of 0.4 °C. Furthermore, their model showed that some cities would benefit more than others from such an intervention. New York, for example would experience an average summer-afternoon cooling of 1.1 °C if its roofs were painted white.

Using experimental data and their modelling techniques Bonan and his colleagues aim to explore the implications of changing the Earth's clothes. From a white sun-hat for New York, to a woodland scarf around the Arctic region's neck, Bonan and his team are keeping up to date with Earth's trends and they are trying to help us to avoid a major fashion mistake.