Seeing Leaves in a New Light



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As anyone who has tended a garden knows, even relatively minor changes in climate and temperature can have a pronounced effect on plant life. Less understood, perhaps, is that en masse plants can in turn have a sizable impact on the climate. Regionally, an increase in plant growth can cool surface temperatures and give rise to more rain and cloud cover. On a global scale, a rise in plant growth can lower the amount of atmospheric carbon dioxide, which is one of the most abundant of the greenhouse gases, and potentially cool the atmosphere.


Photographs of Leaves


For many years biologists and Earth scientists have known of these interactions, but they have never been able to assess to what degree plants influence climate. The problem has always been how to observe this influence. In order to understand the interaction of vegetation with the climate, researchers must have long-term, worldwide measurements of plant growth. So far scientists have met with limited success. While they have obtained qualitative records of relative plant density across the world using satellite imagery, they still cannot quantitatively assess the degree to which vegetation changes from one month to the next. For years, labs around the world have been working towards this goal.


Although it’s obvious that climate determines what types of plants live in a given area, plants themselves have an effect on climate. Lush vegetation absorbs sunlight, cools the Earth’s surface and increases humidity. Current climate models don’t always account for these effects, so scientists are developing new datasets based on satellite data to use in improved models. (Photographs courtesy Philip Greenspun)


Map of spring greening based on Leaf Area Index


Remote sensing specialists at the University of Boston and NASA may now be onto a solution. Using a measurement known as Leaf Area Index, they have found a way to quantify plant growth on a global scale with satellite imagery. Their method can pinpoint when leaves begin to grow in a region, when they fall off, and how dense they become at peak growing season. With the aid of instruments such as MODIS aboard NASA’s Terra satellite and the AVHRR instrument aboard NOAA’s polar satellites, the researchers may soon be able to forecast the ways in which plants impact our weather and global climate.

next How Plants Can Change Our Climate

The data used in this study are available in one or more of NASA's Earth Science Data Centers.

  The two images above show the changes in Leaf Area Index (LAI) that occured during the spring of 2002 in Switzerland and eastern France. White corresponds to an LAI of 0, while green, dark green, and blue represents increasingly dense vegetation. Topographic shading emphasizes the barren peaks of the Alps. (Data provided by Boston University Climate and Vegetation Research Group. Images by Robert Simmon)