The latest UN report on climate says reducing deforestation is crucial to slowing global warming. But researchers must first reconcile two contradictory sets of statistics on tree loss in order to determine whether promises made by nations to protect and restore forests are on target.
The world is losing trees faster than ever. An area the size of Italy disappeared last year. Or did it? New research suggests three-quarters of those lost forests may already be regrowing. That hardly means we are out of the woods. Fighting climate change and protecting biodiversity still needs a global campaign to reforest the planet. But it does suggest that, given the chance, nature will do much of the work.
This week, a special report of the UN’s Intergovernmental Panel on Climate Change (IPCC) confirmed the vital role that ending deforestation can play in holding global warming to 1.5 degrees Celsius. To underline the point, the UN’s environment, development, and agriculture chiefs issued a joint statement declaring that “forests are a major, requisite front of action in the global fight against catastrophic climate change – thanks to their unparalleled capacity to absorb and store carbon. Stopping deforestation and restoring damaged forests could provide up to 30 percent of the climate solution.”
But behind the challenging words lies a yawning data gap. For we still know remarkably little for sure about the true extent of deforestation and its contribution to carbon emissions and climate change. As Peter Holmgren, then director-general of the Center for International Forestry Research in Indonesia, put it last year, the existing deforestation data is of “low quality,” relying either on satellite imaging that is “shallow, ambiguous, and generally incomparable” or on government data that may “under-report deforestation for political reasons.”
Researchers say we urgently need a way out of the statistical quagmire. And this year the first tentative steps at resolving the data crisis have been taken.
There are two main data sources for tree loss, and they are increasingly contradictory. One, the Global Forest Watch (GFW), is compiled from satellite images by the World Resources Institute, a Washington think tank. It paints a gloomy picture, putting the decline in tree cover last year at 72.6 million acres, almost 50 percent more than in 2015. That analysis is supported by on-the-ground observations, especially in Southeast Asia, where forest continues to be converted to oil palm.
The other main source for deforestation data, the Global Forest Resources Assessment (FRA), which is compiled from government inventories by the Rome-based UN Food and Agriculture Organization, is less bleak. It estimates the annual net loss, once forest regrowth is taken into account, at barely a tenth as much: just 8.2 million acres. And it says deforestation rates have declined by more than 50 percent in the past decade.
The drastic difference extends to data from individual countries. In the United States, China, Australia, Canada, Russia and several other countries, the FRA shows forests gains while the GFW shows big losses, says Holmgren.
The two datasets were more or less in agreement 20 years ago, but have been diverging ever since. So how have such huge differences arisen? And which, if either, is right?
On the face of it, the satellite-based GFW is more rigorous. It asks a simple question of the Landsat images it analyzes: What area of tree cover has disappeared since last year? It does not ask how or why, just how much. The FRA data, on the other hand, is largely a measure of registered land use rather than actual tree cover. For instance, its definition of a forest includes areas that may be treeless as a result of logging, but where governments still classify the land as productive forest that is expected to regrow and be logged again…
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