Global greening is the name given to a gradual, but large, increase in green vegetation on the planet over the past three decades.
The climate change lobby is keen to ensure that if you hear about it at all, you hear that it is a minor thing, dwarfed by the dangers of global warming. Actually, it could be the other way round: greening is a bigger effect than warming.
It is a story in which I have been both vilified and vindicated. Four years ago, I came across an online video of a lecture given by Ranga Myneni of Boston University in which he presented an ingenious analysis of data from satellites. This proved that much of the vegetated area of the planet was getting greener, and only a little bit was getting browner. In fact, overall in 30 years, the green vegetation on planet Earth had increased by a rather extraordinary 14 per cent. He said this was occurring in all vegetation types — from tropical rainforests to arctic tundra.
What was responsible for this ecological good news? He credited rising carbon dioxide concentrations in the atmosphere for half of the greening — rather than, say, the application of agricultural fertiliser, warmer temperatures or increased rainfall. Carbon dioxide, along with water, is the raw material that plants use to make carbohydrates, with the help of sunlight. So it stands to reason that raising its concentration should help plants grow.
I was startled by Myneni’s data. I knew that there had been thousands of experiments in which carbon dioxide levels had been increased over crops or wild ecosystems to find out whether it boosted their growth (it did). I also knew that commercial greenhouse owners now routinely maintain carbon dioxide levels in their greenhouses at more than double normal levels, because it makes their tomatoes grow faster.