Earth's tree cover shrank dramatically last year, a new report reveals, marking the second-worst annual decline on record. The situation is especially dire in tropical climates, which account for more than half of the global loss in tree cover.

Nearly 73 million acres (29.4 million hectares) of tree cover disappeared in 2017, according to data released by the World Resources Institute's Global Forest Watch, just shy of the record 73.4 million acres (29.7 million hectares) lost a year earlier in 2016. That includes some 39 million acres (15.8 million hectares) of lost tree cover in the tropics, an area roughly the size of Bangladesh or the U.S. state of Georgia.

Since that may be hard to picture, Global Forest Watch (GFW) notes that losing 39 million acres is equivalent to losing 40 football fields of trees every minute for an entire year. (Or, if football isn't your sport, it's also like losing enough trees every minute to fill 1,200 tennis courts, 700 basketball courts or 200 hockey rinks.)

'A crisis of existential proportions'

deforestation in Brazil's Western Amazon rainforest, 2017 Brazil suffered more tree-cover loss in 2017 than any other country, according to Global Forest Watch, largely due to fires set by people to clear land for pasture or agriculture. (Photo: Carl de Souza/AFP/Getty Images)

These findings were presented by GFW at the Oslo Tropical Forest Forum, which was held last week in the Norwegian capital. Given the huge ecological and economic importance of forests — which help absorb the carbon emissions that fuel climate change, among many other benefits — this news is drawing widespread concern.

"This is a crisis of existential proportions," said Ola Elvestuen, Norway's minister of climate and environment, as reported by Vox from the Oslo forest forum. "We either deal with it or we leave future generations in ecological collapse."

The annual loss of tropical tree cover has been rising over the past 17 years, according to GFW, despite international efforts to reduce deforestation in the tropics. This trend is partly due to natural disasters like wildfires and tropical storms — "especially as climate change makes them more frequent and severe," the group writes in a blog post — but large-scale declines are still driven mainly by the clearing of forests for farming, livestock grazing and other human activities.

bar graph of tropical tree-cover loss by year This graph shows yearly tree-cover loss in tropical countries from 2001 to 2017. (Image: GFW/WRI)

The numbers in GFW's new report were provided by the University of Maryland's Global Land Analysis and Discovery (GLAD) laboratory, which collects data from U.S. Landsat satellites to measure the complete removal of tree-cover canopy at a resolution of 30 by 30 meters (98 by 98 feet), the size of a single Landsat pixel.

It's worth noting that tree-cover loss is a broader metric than deforestation, and while the two terms often overlap, they don't always mean the same thing. "'Tree cover' can refer to trees in plantations as well as natural forests," GFW explains, "and 'tree cover loss' is the removal of tree canopy due to human or natural causes, including fire." And when a Landsat pixel registers lost tree cover, it means the tree's leaves have died, but it can't tell us whether the entire tree has been killed or removed.

That said, deforestation is a major threat to many of the world's most important tropical ecosystems, and tree-cover data can help reveal its evolution on a global scale. This kind of data may not tell us everything, but given the dangers facing woodlands around the world, we need all the information we can get.

Trouble in the tropics

logging in the Democratic Republic of Congo, DRC The Democratic Republic of Congo is struggling to protect its forests from intensive agriculture, artisanal logging and charcoal production. (Photo: Eduardo Soteras/AFP/Getty Images)

Brazil led all countries for tree-cover loss in 2017, according to the GFW, with a decline totaling more than 11 million acres, or 4.5 million hectares. It's followed in the list by the Democratic Republic of Congo (3.6 million acres), Indonesia (3.2 million acres), Madagascar (1.3 million acres) and Malaysia (1.2 million acres).

Brazil's total is its second-highest on record, down 16 percent from 2016 but still alarmingly high. The country's deforestation rate has improved in recent years, but it's still losing valuable tree cover mainly due to rainforest fires. The Amazon region suffered more fires in 2017 than any year since records began in 1999, according to GFW. And although forests can recover from fire damage — which mainly causes degradation rather than true deforestation — these fires are offsetting Brazil's progress in curbing deforestation-related carbon emissions.

A drought did strike the southern Amazon in 2017, but "almost all fires in the region were set by people to clear land for pasture or agriculture," the GFW notes, activities that allow less chance for recovery than fire damage alone. "Lack of enforcement on prohibitions of fires and deforestation, political and economic uncertainty, and the current administration's roll-back of environmental protections are likely contributors to the high amount of fires and related tree cover loss."

deforestation in Brazil's Western Amazon rainforest, 2017 Dead trees stand in a recently deforested section of the Brazilian Amazon in 2017. (Photo: Mario Tama/Getty Images)

Meanwhile, the Democratic Republic of Congo (DRC) suffered record-high loss of tree cover, up 6 percent from 2016. This is largely due to the growth of intensive farming practices, artisanal logging and charcoal production, the GFW explains.

The report also spotlights Colombia, whose 2017 loss of nearly 1.1 million acres only ranks No. 7, yet represents "one of the most dramatic increases in tree-cover loss of any country." It's up 46 percent from 2016, and is more than double the country's annual loss rate from 2001 to 2015. This shift may be linked to a recent peace agreement between Colombia and the Revolutionary Armed Forces of Colombia (FARC), a rebel group that has controlled swaths of remote forest for decades. The deal has created a power vacuum, the GFW writes, allowing land speculation and illegal land-clearing that Colombian authorities are now working to contain.

On the bright side, however, some countries infamous for deforestation are showing hints of hope. Despite losing 3.2 million acres in 2017, for instance, Indonesia actually experienced a decrease in tree-cover loss, including a 60 percent drop in the loss of primary forest. This might be related to heavier rainfall in the absence of El Niño, although GFW also credits a national peat-drainage ban that took effect in 2016. Primary forest loss in protected peat areas fell 88 percent between 2016 and 2017, reaching the lowest level on record. Other possible factors include educational campaigns and better enforcement of forest laws, but GFW warns that "only time and another El Niño year will reveal how effective these policies really are."

Yes we canopy

forest in Central Java, Indonesia Mist rises from a forest canopy on the island of Java in Indonesia. (Photo: Murrrrr-s/Shutterstock)

Loss of tree cover is not just a tropical problem, but as these data show, it is especially severe in much of the tropics. And that's still relevant for people all over the world, since tropical forests provide benefits far beyond their native countries.

"There's no mystery on the main reason why tropical forests are disappearing," writes Frances Seymour, a senior fellow with the World Resources Institute (WRI), in a blog post about the new findings. "Despite the commitments of hundreds of companies to get deforestation out of their supply chains by 2020, vast areas continue to be cleared for soy, beef, palm oil and other commodities."

Global demand for soy and palm oil, she adds, "is artificially inflated by policies that incentivize using food as a feedstock for biofuels." And once a forest is logged irresponsibly, its chances of a comeback are often limited by the development of roads and by its increased vulnerability to fire.

Fortunately, the solutions aren't very mysterious either. "We actually know how to do this," Seymour writes. "We have a large body of evidence that shows what works."

Brazil already reduced Amazon deforestation by 80 percent from 2004 to 2012, for example, thanks to increased law enforcement, larger protected areas, recognition of indigenous territories and other measures. Policies like those can work, but it helps when they're supported by local populations and encouraged by market forces, such as consumers' growing distaste for products linked to forest loss. "Nature is telling us this is urgent," Seymour writes. "We know what to do. Now we just have to do it."

Russell McLendon ( @russmclendon ) writes about humans and other wildlife.