The planet is getting greener, with an expansion of vegetation coverage over the last two decades equivalent to the area covered by the Amazon rainforest, according to a new study, covered by BBC News. Surprisingly, much of that global vegetation growth comes from human activities in China and India, emerging economies with the world’s largest populations and some of the highest levels of pollution.

There has been a five percent increase in additional green foliage coverage since the early 2000s, amounting to an additional two million square miles. The foliage helps absorb carbon emissions, limiting climate change.

The study was published last week in the journal Nature Sustainability.

The expansion stems from both intensive agriculture and tree-planting in both countries.

Researchers first observed the greening effect in the mid-90s, but theorized that additional carbon dioxide in the atmosphere was helping to fertilize plants, which were also benefiting from a warmer and wetter climate as a result of climate change. While these factors are indeed playing a role, new observations by US space agency NASA suggest agriculture and forestry changes are contributing as well.

The agency used twenty years of high-resolution data from a system called the Moderate Resolution Imaging Spectroradiometer, or MODIS, which provides images with detail down to the level of 500 meters from the surface. The system has captured up to four shots of every location on Earth, every single day, for the past two decades.

In China, forestry programs including conservation and tree-planting account for about 42 percent of the country’s greening effect. The policies were put in place to fight soil erosion, air pollution, and climate change. An additional 32 percent comes from expanding intensive agriculture from irrigation and fertilizers.

In India, agriculture was responsible for 82 percent of the new vegetation. In both nations, agricultural production of food crops has increased 35 percent since 2000.

“China and India account for one-third of the greening, but contain only 9% of the planet’s land area covered in vegetation – a surprising finding, considering the general notion of land degradation in populous countries from overexploitation,” according the lead author of the new study, Chi Chen of Boston University’s Department of Earth and Environment.

However, new vegetation is enough to offset declining natural vegetation in tropical areas like Brazil and Indonesia, and the expansion may be limited in the future by limits to groundwater irrigation and other factors.

While carbon absorption by plants as factored into predictions by the Intergovernmental Panel on Climate Change (IPCC), it’s considered to be one of the most uncertain variables in climate models.

Earlier this week, a new study was published that showed large-scale replenishment of the world’s forests would be more effective than any other approach to fight climate change. The authors argue that scientists have vastly underestimate the potential of trees to cancel out carbon emissions.

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