If a traveler on Continental Airlines pays an optional $5 surcharge to plant a tree as a “carbon offset” how much difference will it make to the planet? Traveling Americans are paying millions of dollars to plant hundreds of thousands of additional trees. Many of these new trees are being planted in the tropics; where tree-planting does the most good in cooling the earth.
It seems a well-intended, way to spend the cost of a McDonald’s hamburger. But is it the best way to make a difference? The World Agroforestry Centre has just discovered that the earth has billions more trees then we knew about—so how much good will it do for the Americans to finance the planting of a few million more?
The Agroforestry Center used detailed satellite imagery to survey a billion hectares of the farmlands around the world—about half the cropland total. To their surprise, they found that about half the farmland surveyed contained at least 10 percent tree cover. Since a hectare is about the size of two football fields, the “end zones of a billion football fields” are sustaining many billions of trees.
This tree-rich farmland is fabulous news for the planet: the trees not only prevent soil erosion and fertilize the fields with extra nitrogen, but their harvests offer the farmers fruits, nuts, fodder for livestock, timber, fuelwood, medicines and such cash crops as coffee, rubber, nuts, gums and resins.
However, trees don’t do nearly as much to combat global warming as most of us think. Trees planted north of Florida won’t cool the earth. Above the Canadian border they absorb enough extra heat to warm the planet. Ditto for trees planted south of the Amazon rain forest. Tropical trees supposedly cool the earth by about 0.7 degree C. But the trees in the Amazon are already cooling that region, which in any case is the most-forested part of the earth. Sub-Saharan Africa and Southeast Asia are tree-rich too.
The tree-denuded parts of the earth are North Africa and West Asia and those are also the driest, toughest places to grow trees. In Libya, Morocco, Turkey or Iraq, the trees must be carefully tended and protected by their owners or their harvests will be stolen—or the trees themselves stolen for charcoal or firewood.
Fortunately, says World Agroforestry Center, trees have so many benefits that the farmers continue to plant and protect them. The message from the satellites is that they’re doing far more of this than we’ve realized.
Will farmers plant still more trees into the future? As long as the householders must walk miles a day gathering firewood, they’ll have an incentive to plant more trees if they have private land on which to plant them. Kenya has been nearly denuded of trees on public land for charcoal. Tree cutting at the base of Mt. Kilimanjaro is a big reason why that mountain’s glacier is melting. Outside money might make a difference by reserving more land for trees, though the pressure for cropland in Kenya continues to grow as its population increases and farmer’s yields are constrained by the lack of modern farming methods.
One of the best ways to protect forests, however, comes when rural populations are able to burn kerosene instead of charcoal. Burning kerosene allows villagers to cook and heat their homes without cutting trees. It also has huge health benefits for the householders in terms of avoiding smoke inhalation and lung disease.
But the Western world is hell-bent on getting rid of fossil fuels. If we take away the billions of liters of kerosene the poor countries are burning now, where will the extra firewood come from? How long will the forests last? Will the trees lost to banning kerosene overcome all re-planting efforts?
DENNIS T. AVERY, a CFACT advisor, is an environmental economist, and a senior fellow for the Hudson Institute in Washington, DC.