Re: John Mills' latest letter ‘Can You explain?'(The Weekend Sun, December 13, 2013). As far as tropical rainforests being carbon-neutral goes, it's well known tropical rainforests have shallow topsoil. Yes, that's right, the rain washes the topsoil away.
So all the stuff that goes into the mulch winds up in a swamp or lake or at the bottom of the sea.
I don't know the precise percentage, but it's not minor. John Mills confused two categories: greenhouse effects and the cause of deserts.
The effect of greenhouse gases is global: carbon dioxide re-radiates visible light as heat in all directions, ensuring some remains to heat the earth.
Deserts form as a result of low rainfall along certain latitudes, because of wind circulation preventing those latitudes from getting regular rain.

W Parish, Bellevue.