Oceans are blue and likely to get bluer in the era of climate change – and that’s not necessarily a good thing, according to new research. In a similar way, the Earth is getting greener too, and while that’s widely considered a positive development coming from some unexpected corners of the globe, the new findings published in Nature Sustainability warn that not all of that “green” plant life is created equal.
In raw numbers, the Earth has increased its green leaf coverage by a total of 5 percent, which is about 5.5 million square kilometers. That’s equivalent to the size of the entire Amazon rain forest, according to Ranga Myneni, a professor of earth and environment at Boston University in the United States. Myneni and graduate research student Chi Chen, lead authors of the paper, measured all that green using two decades’ worth of data recorded by instruments on NASA’s Terra and Aqua satellites.
“The two countries that have been most responsible for the global greening came as a surprise to us,” said Myneni and Chen. “We found that China and India, the world’s first and second most populous and still-developing countries, are leading the world in greening due to widespread crop farming.”
At least 25 percent of global green gains are attributed to China, and that’s in many ways welcome news. Each year some 10 to 11 billion tons of carbon dioxide (CO2) emissions are pumped into the atmosphere and land plants, along with ocean and soils, play a key role in carbon sequestration. The role of plant leaves in photosynthesis, removing CO2 and producing food, also seems a clear benefit.
“Here’s the catch. Not all land plants are created equally,” the Boston scientists said. That’s because, as co-author Victor Brovkin of the Max Planck Institute for Meteorology notes, agricultural plants that uptake carbon quickly release it back into the atmosphere. Their short lives are not the same thing as the Amazon, or forestry projects like China’s “Great Green Wall” and similar efforts in Africa or Europe that offset carbon emissions.
The good news is that China’s renewed commitment to forest conservation accounts for about 42 percent of its greening contribution; for example, China expects by 2050 to reduce desertification with a swath of forests that’s 4,800 kilometers long and in some places nearly 1,500 kilometers wide. Yet a full third of China’s “greening” comes from intensive agriculture, and that number jumps to 82 percent in the greener India.
Rama Nemani, a NASA scientist and paper co-author, evaluated data that points to a 35 or 40 percent increase in food production in China and India on crop lands that haven’t changed much since the early 2000s. What has changed are the intensive practices of irrigation, fertilizer use and crop rotations, and while that’s clearly needed to feed massive populations, the “green” it’s creating isn’t necessarily good.
Besides the fact that agricultural plants aren’t managing the CO2 in the same way, irrigation practices place pressure on groundwater sources, and raise concern over impacts on insect populations and other consequences of pesticides. Above all, the different kinds of “green” aren’t accounted for well, and the Asian agricultural increase does not offset the loss of carbon sequestration and biodiversity elsewhere.
“Now that we know direct human influence is a key driver of the greening Earth, we need to factor this into our climate models,” Nemani said. “This will help scientists make better predictions about the behavior of different Earth systems, which will help countries make better decisions about how and when to take action.”
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