Two unlikely countries have managed to make the world a greener place, data from the National Aeronautics and Space Administration (NASA) has revealed.
Through ambitious tree-planting programmes and intensive agriculture, China and India account for one-third of the world's greening, lead author of the study from Boston University, Che Chen, said.
The increased greening was first detected using satellite data in the mid-1990s, but it wasn't known whether human activity could be attributed to it.
But 20-year long data collected from a NASA instrument orbiting Earth aboard two satellites was able to show that human activity in China and India dominated the greening of the planet.
"This long-term data lets us dig deeper," Rama Nemani, a research scientist at NASA's Ames Research Center in California, said.
"When the greening of the Earth was first observed, we thought it was due to a warmer, wetter climate and fertilisation from the added carbon dioxide in the atmosphere, leading to more leaf growth in northern forests, for instance."
Now, with the 20-year long data, he said it "lets us understand the phenomenon at really small scales, [and] we see that humans are also contributing".
China has contributed the most to Earth's greening, ahead of India, and then the European Union, Canada, Russia, Australia, the United States and Mexico, respectively.
China's efforts to increase greenery include programmes to conserve and expand forests to reduce the effects of soil erosion and air pollution and climate change, the study noted.
Meanwhile India has contributed to the Earth's greening through intensive cultivation of food crops, where a field is replanted to produce another harvest several times a year.
"In the '70s and '80s in India and China, the situation around vegetation loss wasn't good; in the '90s, people realised it; and today, things have improved."
Now that it's known human influence is a key driver of Earth's greening, Mr Nemani says it needs to be factored into climate models.
"This will help scientists make better predictions about the behaviour of different Earth systems, which will help countries make better decisions about how and when to take action."
The increased greenery in China and India does not offset the intense loss of natural vegetation in tropical regions, such as Brazil and Indonesia, the study noted.
"The consequences for sustainability and biodiversity in those ecosystems remain."