After years of severely underestimating the number of trees on Earth, scientists are now calculating that a massive, global reforestation effort could offset at least 10 years of greenhouse gas emissions produced by human activity.
Yet a separate study reported just days later concludes humanity is unlikely to hit its targets to get greenhouse gas emissions under control, at a time when deforestation is still on the rise.
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In the first of the two studies, a team led by British ecologist Dr. Thomas Crowther combined data from ground surveys and satellites to conclude that there are an estimated three trillion trees on the planet—seven times more than the previous NASA estimate—plus space for 1.2 trillion more.
Crowther and colleagues concluded that “undervaluing trees means scientists have also been massively underestimating the potential for forests to combat climate change,” The Independent reports. “The same approach, using machine learning and AI to analyse the enormous data set, allowed the researchers to predict the number of trees that could feasibly be planted in empty patches around the world.”
“There’s 400 gigatons [of carbon sequestration] now, in the three trillion trees, and if you were to scale that up by another trillion trees that’s in the order of hundreds of gigatons captured from the atmosphere—at least 10 years of anthropogenic emissions completely wiped out,” Crowther said. While precise numbers are still under development, that magnitude makes reforestation “our most powerful weapon in the fight against climate change,” he told a recent meeting of the American Association for the Advancement of Science in Washington, DC.
“We are not targeting urban or agricultural areas, just degraded or abandoned lands, and it has the potential to tackle the two greatest challenges of our time—climate change and biodiversity loss,” he added. “It’s a beautiful thing because everyone can get involved. Trees literally just make people happier in urban environments, they improve air quality, water quality, food quality, ecosystem services. It’s such an easy, tangible thing.”
While “full restoration of all sites identified is clearly unrealistic,” The Independent adds, “tree planting is increasingly being recognized as a critical activity to preserve life on Earth.” The United Nations, whose Billion Tree Campaign has already seen 17 billion planted in different parts of the world, renamed the program the Trillion Tree Campaign in light of Crowther’s findings.
But according to a mid-February paper in the journal Nature Climate Change, those efforts aren’t out of the woods yet.
When the Paris Agreement was adopted in 2015, “nearly 100 countries pledged to make their use of land less damaging to the climate, mainly by limiting deforestation rates and boosting forest restocking,” the U.S. Cable News Network (CNN) reports . “But those commitments were unrealistic and need to be stepped up dramatically, according to researchers at the Karlsruhe Institute of Technology and the University of Edinburgh, who pointed to inaction by richer countries and a rise in deforestation in several countries since the treaty was signed.”
The continuing increase in deforestation, coupled with the delays in hitting land use targets, may make it impossible to meet the Paris goals, the study team concluded.
“In most cases, little progress has been made, [and] often, the situation has actually worsened in the last three years,” said lead author and Karlsruhe Institute researcher Calum Brown. “Many of the plans for mitigation in the land system were unrealistic in the first place and now threaten to make the Paris target itself unachievable.”
Brown summarized the research in his own detailed post  for Carbon Brief.
Brazil saw deforestation increase 29% between 2015 and 2016 after a decade of progress, CNN notes—and before seeing an extreme new government  take office with plans to accelerate forest exploitation. “Palm oil cultivation in Indonesia and Peru has also scuppered deforestation efforts and led to increased emissions rates.”
(In Canada, meanwhile, CBC is raising tough questions  about plans to change national accounting practices for forest carbon in a way that would set aside the more than 400 million tonnes of net forest emissions produced by one province, British Columbia, over a two-year span.)
“The commitments were never sufficient, which is bad enough, but also the commitments that have been made are not realistic given the political support they have in general,” said co-author and University of Edinburgh food security specialist Peter Alexander. “We need to find rapid but realistic ways of changing human land use if we are to meet our climate change targets,” but “richer countries have not been leading the way, either in reducing their own emissions or in reducing the pressure on developing nations.”
“Ongoing destruction of tropical forests in Brazil, the Democratic Republic of the Congo, and Indonesia is particularly concerning, because these forests store huge quantities of carbon, as well as containing high levels of biodiversity,” added co-author and Karlsruhe Institute professor of land use change Mark Rounsevell. “Attempts to protect these forests have had limited success, and laws against felling have recently been rolled back.”