The world’s forests continue to disappear at an alarming rate, threatening a resource that scientists say is a crucial “natural solution” for controlling climate change on an urgently short timescale.

Last year, the planet saw its fourth-highest level of tropical tree loss since the early 2000s—about 30 million acres, according to a new analysis published Thursday.

Those losses have continued even as more corporations and countries made commitments to preserve forests, and as scientists emphasized that maintaining forests must be a global priority—as crucial to staving off the worst risks of climate change as cutting fossil fuel use.

Forests absorb roughly a quarter of the carbon dioxide emitted by human activity each year. Destroying all of the world’s forests would release the same amount of stored carbon as burning all the planet’s readily extractable fossil fuel deposits, a group of prominent scientists wrote.

“Continued tropical forest loss pulls the rug out from under efforts to stabilize the global climate,” said Frances Seymour, a senior fellow with the World Resources Institute (WRI), which publishes the annual forest assessment. “For every hectare of forest lost, we’re one step closer to the scary scenario of runaway climate change, because forests not only store carbon, they continue to absorb it as they grow.”

The tree loss report, produced by the University of Maryland and published by WRI’s Global Forest Watch, is based on a global analysis of satellite images, using cloud computing and artificial intelligence.

The 2018 global figures were an improvement over 2016 and 2017, but those years saw huge spikes in tree loss because of widespread fires. The overall trend in forest loss has climbed since the early 2000s, when the analyses began.

The researchers also determined that critically important “old growth” tropical forest ecosystems, which hold more carbon than younger forests and have an important cooling effect, declined by nearly 9 million acres, an area larger than Belgium. “That’s mature, humid forest, which represents some of the most biodiverse and carbon-rich areas, and therefore some of the most important loss we’re seeing,” said Liz Goldman, a researcher with Global Forest Watch. 

The Global Forest Watch analysis uses the terms “forest loss” and “tree loss” rather than deforestation, which defines a permanent conversion of forest into another use, like agriculture or oil production. That’s because satellite data can’t fully capture how the trees are disappearing and whether they’ll be replanted. The new analysis captures other types of loss, including those that could be natural or temporary. (For an explanation of types of tree loss and drivers, read this study.)

Progress in Indonesia, Backsliding in Brazil

The analysis found that the “frontiers of loss” are shifting.

In recent decades, Brazil and Indonesia made up the largest percentage of tropical old-growth forest loss, accounting for nearly two-thirds of all declines globally. Now the Democratic Republic of the Congo, Colombia and Bolivia, combined with Brazil and Indonesia, account for that same percentage.

Deforestation in the Brazilian Amazon dropped by 70 percent, beginning in 2005, but spiked in 2016 and 2017 due to large-scale burning, largely to clear forests for agriculture, mining or infrastructure projects. The 2018 figures, while lower than those years, suggest deforestation is on the rise again. The country still accounts for the greatest loss in tropical rainforest acreage overall.

Those rates will likely go up under the leadership of newly elected President Jair Bolsonaro—known as the Trump of the Tropics—who has threatened to undo regulations protecting the rainforest.

Indonesia, which has experienced massive tropical forest loss, largely for palm oil plantations, appears to be making progress, with lower levels of forest loss in 2018 than in any year since 2004. The report notes, however, that the past two years have been wetter, with fewer fires. The authors are waiting to see if newly enacted government programs and enforcement are having a meaningful effect. 

Rates of forest loss shot up dramatically in 2018 in Ghana and Cote D’Ivoire, by 60 and 26 percent respectively, which researchers attribute to the expansion of small-scale cocoa farming amid a global surge in cocoa demand.

Forests Rise on International Climate Agenda

The Intergovernmental Panel on Climate Change (IPCC), in a landmark report published last October, said that preventing forest loss and planting new forests represent critical steps in the all-out effort required to keep global temperatures within a 1.5 degree Celsius increase compared to pre-industrial times. To stay within that limit, the report’s authors said, carbon emissions would need to be cut 45 percent by 2030 and reach net-zero emissions by the middle of the century.

Under the 2015 Paris climate agreement—which laid out a target of keeping global warming under 2°C and urged the more ambitious 1.5°C target—developing countries can participate in the REDD+ program, which compensates them for conserving forests.

The REDD+ program relies on international funding, which has only recently started to come through. Last month, the United Nations Green Climate Fund approved the first payment to a country when the fund’s board authorized money for Brazil.

“The international institutional architecture that we’ve put into place is just starting to bear fruit,” Seymour said. “This is all just beginning to get traction.”

So far, roughly one-third of the countries that have signed on to the Paris Agreement have included REDD+ in their national emissions reduction plans.

Seymour says that forests must be a major topic in the next round of international climate meetings, which include a UN Climate Action Summit in September and the 25th Conference of the Parties of the UN’s Framework Convention on Climate Change in December.

“The IPCC reports are clear,” Seymour said. “We can’t do this without forests.”