Highlighting a remote sensing inquiry
Key Points & Overview
- In cold areas, plants are generally greener during a warmer year, whereas in dry areas, plants are generally greener during either cooler or wetter years.
- The influence of plants on the climate are dependent both on the rainfall and the temperature of a particular location.
We set out to discover if plants grown in different climates respond to changes in their environment in different ways. People studying plants in the field have measured whether there is more growth during warmer years, or wetter years — but doing this by hand limits how many climates in the world you can visit, and on what scale you can measure these behaviors. Instead of going to the field, we used satellites that can measure the greenness of plants, and combined this with measurements of rainfall and near surface temperature to measure these responses from space. Critically these satellites have been up longer than a decade, which allows us to look at the correlation between greenness and climate. With these observations, we could essentially go across the whole world, and its myriad of climates, asking “do plants get greener during a warmer year? Or a wetter year?” Then we combined this with information about the climate the plant is growing in (hot, cold, wet, dry etc.) to quantify broad patterns of how plant behavior changes depending on the climate in which they grow.
Some of our results follow our intuition from people measuring plants in the field, or even from gardening in the back yard. In cold areas, such as Canada, plants are generally greener during a warmer year, and in dry areas, such as Southern California, plants are generally greener during either cooler or wetter years. However, we didn’t know at what climate (mean annual rainfall and temperature) the plant behavior changes. What we find is that the changes are dependent on both rainfall and temperature of a place, so that plants in a cool/dry climate behave similarly to those in a hot/wet climate.
Our analysis takes years of satellite measurements of both plants and climate. Only over the last few decades have the satellites, observing specific bands of light and radiowaves, been available to delve into plant-climate interactions at this scale. Concurrently, the Earth system models we use to predict future climate change have developed representations of the carbon cycle, which is a critical element in understanding whether the biosphere will absorb more and more of our emissions into the future, or become a source of emissions itself and exacerbate climate change. We imagine using our research to improve the function of our Earth system models, and create better predictions of how plants, and the carbon cycle, will change as temperatures rise, and patterns of rainfall shift under climate change.