trees and global warming

[miriam_e]

I was just thinking about global warming and letting my mind wander over the various routes that the energy takes to heat up our world if it is prevented from leaving our planet. It hit me that plants must play a direct part in keeping the world cool. Much of the light that we get from the sun is trapped and transformed into food and building materials by plants. That's energy that, if the plants are cleared away, gets re-radiated instead as heat.

The main two concerns usually voiced for keeping plants are aesthetics and controlling CO₂ emissions. Those are valid, of course, but I wonder just how much energy is prevented from being added to that building up in the atmosphere by being absorbed and stored by plants in the first place.

For a long time I've noticed how much hotter cities are than vegetated areas, but had never been able to explain why. Asphalt and concrete receive exactly the same amount of energy from the sun as plants do. Previously I'd vaguely thought the lower temperatures could be explained as evaporative cooling by the plants, but now I realise that can't be the whole story. I'd been neglecting the energy stored by the plants.

I wonder how much radiant energy they take out of the system that way.