Being green is not good for Earth
...as it show that all leaves are not equally valuable and CO2 absorbed by crops is quickly released back into the atmosphere
It seems obvious that ‘greening’ of the planet would be good for reducing atmospheric carbon, but a closer look shows that not all leaves are equally valuable. Chi Chen, a Boston University graduate researcher, and Ranga Myneni, professor of Earth and environment, are lead and senior authors of the paper in Nature Sustainability.
Here, they explain their work: Looking at remote sensing data from NASA’s satellites, we have discovered that over the last two decades, the Earth has increased its green leaf area by a total of 5 percent, which is roughly five and a half million square kilometers— an increase equivalent to the size of the entire Amazon rain forest. Each year, about 10 to 11 billion tons of CO2 is emitted into the atmosphere from carbon sources, such as burning fossil fuels and tropical deforestation.
About half of those emissions are stored temporarily in equal parts in the oceans, soils, and land plants—our Earth’s so-called carbon sinks. Green leaves produce sugars using energy from the sunlight to mix CO2 absorbed from the surrounding air with water and nutrients soaked up from the ground. These sugars, whose production helps eliminate CO2 from the atmosphere, are the source of food, fiber, and fuel for life on Earth.
Here’s the catch. Not all land plants are created equally. China and India each have about two million square kilometers of croplands, which has not changed much since the early 2000s. In contrast, total food production of grains, vegetables, and fruits has increased greatly, about 35-40 percent, in that time. Rama Nemani, a scientist from NASA’s Ames Research Center and one of our paper’s coauthors, says that the increase in food production is due to the planting of multiple crop rotations each year and by heavy fertilizer and irrigation use.
Although China’s Green Great Wall tree-planting efforts—similar to sustainable forestry practices in Western Europe and tree regrowth on abandoned lands in Eastern Europe—enhance our planet’s ability to absorb atmospheric carbon, greening achieved through intensive agriculture does not have the same effect, says Victor Brovkin of the Max Planck Institute for Meteorology, another coauthor of our paper. Instead, carbon absorbed by crops is quickly released back into the atmosphere.