46. Plant a Tree in the Tropics

It seems like simple arithmetic: a tree can absorb up to a ton of carbon dioxide over its lifetime, so planting one should be an easy way to mitigate climate change. Turns out it's not so simple. Recent studies have shown that trees in temperate latitudes—including most of the U.S.—actually have a net warming effect on the climate. The heat that dark leaves absorb outweighs the carbon they soak up.