Leeds University’s Dr Alan Grainger was in a meeting of the United Nations Food and Agriculture Organisation in November 2015, watching the initial results of a survey of the world’s forest land which he and a team of 239 researchers from 15 different institutions dotted around the world had begun to work on. The images, beamed up on the screen, showed a map of the world.
In his head, Alan held one map: of the world’s known forests, collated by a collection of satellite images called Landsat, which have been collected since 1972, but weren’t mapped and published until 2012. In front of his eyes, he saw the second map: a more detailed image – using satellite sensors 30 times more precise, and collected from the images that, stitched together, present our world on Google Earth. It was the map the researchers had been working on. Alan knew the Landsat map very well, and as the image in his mind’s eye switched to the one he could see in front of him, he noticed differences.
‘There were very large areas that we had discovered that weren’t on the Landsat map,’ he explains. ‘That was one of those Eureka moments. That’s what scientists labour for for many years. They don’t happen very often.’
It was vindication for the academic, who had been calling for a better survey of the world’s forestlands since 1984. He’s been particularly focused on drylands, the supposedly barren scrubs of the world that are meant to be little more than sand – but which have now been proven to have plenty of wood. This dryland covers around 40 percent of the planet, and contains some of the world’s most threatened ecosystems, and was the modern-day equivalent of the old ‘terra incognita’ (unknown territory) that used to be marked on maps. People knew it was there; they just didn’t know what was in it.
Dry forest was overlooked for various reasons, reckons Alan. Firstly, money talks. ‘Dryland doesn’t contain as much commercial timber,’ he says, and it’s also more difficult to map technologically than closed forest. Governments are meant to keep a check on the amount of woodland within their borders, but focus on the lush, green land that is commercially beneficial, rather than all woodland. They also rarely monitor more often than every 20 or 30 years. ‘Even our estimates of the total area of forestation in the world aren’t reliable because they’re based on piecing together the numbers in different countries in different years,’ says Alan.
The study that Alan helped drive through provided a more accurate estimate for the world’s woodland, both dry forest and the more verdant areas. The mammoth team of analysts counted how many trees there were in a more accurate way. They did that by analysing a stratified sample of more than 210,000 sample plots throughout the world. Each university was allocated a different parcel of the planet to analyse: the team at Leeds were allocated an area around south west Asia, covering countries including Afghanistan, Iran and Pakistan. Taking hyper-detailed satellite images of the land that had a resolution of one metre or less via a piece of software called Collect Earth, developed by the United Nations Food and Agriculture Organisation, the 22 student team at Leeds University sifted through 1,000 plots over the course of 10 days, checking them and marking whether the images included wooded land. ‘It was hard work,’ Alan admits, ‘because we’re not able to map these high-resolution images in an automated way. We rely on people.’ It may have been hard work, but he was astounded by the results which showed that there was nine percent more forest cover of all types across the globe than was previously thought. In all, 467 million hectares of new woodland – an area roughly the combined size of Mexico and Argentina – was discovered.
The global coverage of dryland, which had inspired Alan to take up the cudgels of increasing forest awareness, increased by 40 percent from previous estimates. It meant that the estimated size of the globe’s dryland was similar to the size of the more traditional rainforests found in the Amazon, Borneo and the Congo basin.
‘I think it’s a tremendous achievement that we’ve solved one of these puzzles about our world,’ says Alan. But it’s not simply the fact that this area of woodland has been discovered that is so astounding: it’s the knock-on effect that this density of forestation has on the rest of our atmosphere (and our understanding of it) which is so impressive.
Finding almost 10 percent more forest cover across the planet means that the science behind carbon levels and climate change needs to be rewritten. ‘If you want to estimate how much carbon there is on land, you’ve got to start with the exact area of forest,’ explains Alan. ‘If you’ve got your basic forest number incorrect, your estimate of how much carbon there is is incorrect too.’ He’s succinct in what’s happened: ‘All of our previous estimates of how much carbon there was in the world’s forests are based on inaccurate numbers of the global forest area.’
At a simplistic level, forests sequester carbon from the atmosphere as part of their existence, sucking in carbon, reducing the level of harmful greenhouse gases in our atmosphere, and breathing out oxygen, keeping our air cleaner. The fact that there’s now two countries’ worth of woodland doing that which scientists previously didn’t think was there, means their sums need to be recalculated.
They may not need to wipe the whole blackboard of equations, though. The discovery of the new forest land goes some way to explaining a quibble that had irked scientists for years, which they called the carbon sink. When scientists add up all the known emissions of carbon, and net that off against the known uptakers of carbon (the world’s trees, sucking it in and spitting out oxygen), they found a gap between the two. ‘The fact that we’ve found nine percent more forest land helps to explain this carbon sink,’ Alan explains.
It’s a momentous occasion, and not just because of the sheer numbers involved. We’re literally reshaping how we view our planet and its environment.
‘The dry forests were one of the great areas of uncertainty in global forest cover,’ says Alan. ‘The fact that we’ve got a more reliable area for the dry forest means we’re on the way to working out how much forest there is in the world.’
You may notice that Alan said ‘on the way’. The work isn’t over yet, he believes. If you can discover another nine percent of forest simply by looking a little harder, who’s to say that there aren’t more surprises lurking around the corner? ‘We are just at the start of an exciting revolution in planetary measurement. The thing to take away from this is that we need to keep on measuring,’ says Alan. ‘If we do, there's much more to discover.’