White paint as climate saviour?

With the US finally climbing onto the global warming bandwagon at last weeks G-8 meeting, India and China will come under pressure to curb their energy use and carbon emissions. China will overtake the US as the biggest carbon emitter by 2008, and India will follow in two decades.

India and China currently resist curbs on energy use, saying they are poor countries needing more energy to develop. They emit a tiny fraction of US emissions in per capita terms. But that will not let them off the hook: global warming is caused by total emissions, not per capita emissions.

I regard catastrophic global warming as a plausible hypothesis, not a proven fact. But Western popular pressure for immediate action to check warming is enormous, and probably irresistible. Moral pressure on India and China will soon be buttressed by economic pressure, maybe even sanctions.

Is there a low-cost way to respond to this looming threat? Yes indeed. India should learn from research by Dr Govindasamy Bala and his colleagues at Lawrence Livermore National Laboratory, California. Most climate models calculate the impact of different gas concentrations on global temperature. But Bala’s model goes further, including the impact of photosynthesis (by which grass and plants grow, extracting carbon dioxide from the atmosphere).

Trees are dark in colour, and so absorb sunlight, causing warming. But trees also absorb water from the ground and send it into the atmosphere through their leaves (transpiration). This aids cloud formation, diminishing warming. On balance, tropical trees cool the world.

The opposite is true in cold forests at high latitudes. Tree growth and transpiration there are slow. If temperate forests are cut, much more snow will be exposed in winter, and this snow will reflect back sunlight instead of absorbing it. This produces cooling through reflection the so-called albedo effect.

Now, if all the world’s trees are cut, Bala’s model shows that the concentration of carbon dioxide in the atmosphere will double by 2100. A disaster, you might think. Yet, the model shows that global temperature will actually fall by 0.3 degrees Celsius.

How can the world get colder despite double the carbon emissions? The model shows that deforestation will heat up the tropics, but the albedo effect of snow reflection in high latitudes will produce a huge cooling effect. On balance, the cooling albedo effect will exceed the warming effect of doubling carbon in the atmosphere.

Bala and his colleagues conclude that tree growth needs to be promoted in the tropics rather than temperate latitudes. But a more important implication is that the world should seek to increase the albedo effect, not just aim for carbon reductions.

We can increase the albedo effect in many ways. The most obvious is to convert vast man-made surfaces across the world from dark colours to white, reflecting more sunlight.

The albedo effect of painting every roof in the world white will be substantial (though the roof area will be less than that of all temperate forests). White roof tiles will be more expensive but more durable than white paint. Broken white china could cheaply be used in India’s flat cement roofs. The resultant cooling will reduce the use of fans and air-conditioners.

We use millions of vehicles of all sorts. The albedo impact of painting white If all cars, trucks, railway carriages and ships and painted white, they will reflect a lot of sunlight.

Asphalt used in roads and airports is black, and absorbs sunlight. Cement is somewhat less dark. Why not mix white colour (chalk might suffice) in all asphalt and cement used in external surfaces?

White is not the only colour that reflects sunlight. Silver paint could be as effective, and maybe some metallic colours. But white will be the cheapest.Some imaginative folk want to float huge arrays of white planks on the oceans to reflect sunlight. Others suggest launching massive white parasols, the size of several football fields, into outer space, to block sunlight. We must study possible undesirable side-effects of such ideas. Some day, such ideas may prove both cost-effective and safe. But for starters, white paint is the simplest, cheapest way for India to do its bit to check warming. It is obviously a very partial solution. If global warning is a real threat, it needs to be tackled by a dozen strategies, ranging from energy conservation and biofuels to solar energy and carbon capture. But increasing the albedo effect should be one such strategy, much simpler and cheaper than capping carbon emissions.

The government could mandate mixing white colour in asphalt/cement in public works, and white roofs in building standards. And it could offer subsidies to paint existing houses and vehicles white. This will not cost much if it qualifies for carbon credits under the Kyoto Agreement.

I foresee opposition from ideologues for whom carbon reduction has become an end in itself, and from industrial lobbies seeking profits from carbon reductions. Remind them of Bala’s research finding in California: even if carbon in the atmosphere doubles, the albedo effect can actually reduce global temperatures

What do you think?