It’s pretty simple to tell when deciduous trees are photosynthesizing—their leaves are green. When that process is over for the year, the foliage shrivels up, turns brown, and falls off, an event so widespread it can be tracked by satellites in space. But tracking when evergreen trees crank up their chloroplasts and begin turning sunlight and CO2 into energy is much more difficult since, as their name implies, they stay green year-round (the trees actually stop photosynthesizing in the autumn but use a green pigment as a type of sunblock, keeping them green year-round). That has been a problem when it comes to climate modeling, which currently relies on estimates to determine how much CO2 evergreen forests pull out of the atmosphere. But a new study suggests there’s another way to keep tabs on photosynthesis in evergreen forests: watching their fluorescent glow from space. | 
