Plants and other photosynthetic organisms (algae, cyanobacteria, etc.) play an essential role in our global climate system. Through the process of photosynthesis, plants take up carbon dioxide and water and turn it into glucose and oxygen. In fact, humans rely on plants in many more ways than one. The production of oxygen through photosynthesis promoted the development of the ozone layer and allowed for the development of life on earth. Plants provide our food, our textiles, building materials, and so much more. Additionally, the absorption of carbon dioxide from the atmosphere through the process of photosynthesis means that currently plants are a gigantic sink for atmospheric carbon.

However, despite decades of research, scientists still aren’t sure if plants on land, also known as the terrestrial biosphere, will become a source or a sink of carbon in future climate change projections^[1]. On the one hand, increased carbon, forest regrowth, high latitude warming, and longer growing seasons could all amplify the terrestrial biosphere as a carbon sink. On the other, drought, conversion of forests to agriculture, and nutrient limitations could all lead the biosphere to become a carbon source. Part of this uncertainty arises from the ongoing challenge of extrapolating local relationships to a global scale.

One way of doing this is with remote sensing – in other words, collecting information about something without making physical contact with it. Remote sensing has a tremendous number of applications and you’re probably even more familiar with it than you realize. Google earth, sonar navigation, and even a phone camera are all examples of remote sensing. Check out this organization if you would like to help scientists by contributing your own remote sensing data using just a camera. Using remote sensing, we can track vegetation dynamics on a global scale.

Previously, scientists used a measure of ‘greeness’ to determine plant health and distribution from space. You can read more about it here. This greenness measure has undoubtedly led to many great discoveries, particularly in how vegetation distribution impacts the carbon balance and species habitats. However, this method can be an unreliable measure of photosynthesis and carbon uptake itself. This is particularly evident in evergreen ecosystems, such as needle leaf forests and rainforests, where changes in photosynthesis occur without a subsequent change in color. In this regard, the use of chlorophyll fluorescence poses a huge advantage because it emanates directly from the photosynthetic machinery of a plant.

The first documentation of fluorescence from chlorophyll dates all the way back to 1834 when Sir David Brewster, a British inventor, observed a red light emitted when sunlight struck a solution of leaves and alcohol. Nearly 100 years later, Kautsky and Hirsch connected this mysterious red light to photosynthesis and carbon exchange. Since then, scientists have used chlorophyll fluorescence to understand photosynthesis locally including coral bleaching, crop responses to pollutants, and plants resistance to heat stress, among many others.

In 2009, scientists made the first spaceborne measurements of chlorophyll fluorescence, a major breakthrough. Measuring chlorophyll fluorescence from space provides valuable information on plant productivity on a global scale and can help us infer how ecosystems will change in a changing climate. Check out this video to watch the earth ‘breathe’ using chlorophyll fluorescence data from NASA and this video to learn about future plans for measuring photosynthesis from space.

The measurement of chlorophyll fluorescence from space prompted a boom in the number of studies and scientists using chlorophyll fluorescence to understand plants and plant productivity in various ecosystems around the world – including the educator behind this video Zoe Pierrat. You can learn more about her research here.