Lauren Fuge
The European Space Agency (ESA) has released nearly two decades worth of satellite data that will help us understand how forests shape our climate.
This long-term record, which stretches from 2007 to 2022, contains global information about “above ground biomass”: the carbon-rich, woody parts of vegetation like trunks, branches and stems.
Measuring total forest biomass is a proxy for carbon storage, which means this dataset provides the clearest picture yet of how forest ecosystems – and the carbon within them – have changed over time.
The data is available for free online.
“The new dataset provides a much more accurate representation of global forest biomass, particularly in regions where earlier versions underestimated high-density forests,” says Richard Lucas of Aberystwyth University in Wales, who leads ESA’s Climate Change Initiative Biomass Project.
Forests store enormous amounts of carbon. As trees grow, they take in carbon from the atmosphere and store it in their trunks and branches as biomass. Forests therefore play a vital role in the global carbon cycle – every year, they absorb up to 8 billion tonnes of carbon dioxide (CO2 emissions are estimated at 36 billion tonnes a year).
But when forests are lost through deforestation or fire, this carbon is released back into the atmosphere, driving up the concentration of carbon dioxide and influencing global climate change.
Deforestation hotspots include northern South America, sub-Saharan Africa, south-east Asia and the Pacific, where forests are cleared not just for timber, but also to produce beef, soya, coffee, cacao, and more.
A challenge for scientists and policymakers alike is the deficit of accurate data on how much carbon forests store and where, how stable that storage is, and whether those carbon levels are changing.
ESA’s Frank Martin Seifert says that this new long-term dataset is “a pivotal moment for climate science as it provides an unprecedented level of consistency and timeliness in the provision of above-ground biomass estimates globally”.
“This empowers researchers and policymakers alike to track carbon dynamics with the temporal precision necessary for meaningful climate action.”
ESA says the data will be used in climate and carbon modelling, in forest management, and in national greenhouse-gas reporting under the Paris Agreement.
Carbon storage
To look at above-ground biomass across the planet, the new dataset merges observations from multiple satellites including ESA’s Envisat and Europe’s Copernicus Sentinel-1, Japan’s ALOS PALSAR, and NASA’s ICESat and GEDI lidar missions.
The observations were taken at resolutions between 100m and 50km. The researchers say that the dataset remains most accurate up to 400 tonnes of biomass per hectare.
But it still remains tricky to measure extremely dense forests.
“Detecting biomass densities above 400 tonnes per hectare is considerably more difficult,” says Lucas, “because the relatively short wavelengths of current radar sensors don’t fully penetrate or interact with the larger woody components of dense tropical forests.”
But since these are often also the most carbon-rich ecosystems, they are important to capture accurately in the dataset.
Luckily, a new player is now in the forest-mapping game.
The forest space age
The dataset was released just days after the launch of a new ESA satellite called Biomass. This 1.25-tonne satellite will spend 5 years in orbit creating the most detailed 3D maps ever of our planet’s densest, darkest, remotest forests.
Biomass will be 600km above these forests, yet will be able to peer right through to their leafy floors, scanning trees from tips to roots to estimate how much carbon the forest is storing.
This will be achieved using a special instrument: a P-band synthetic aperture radar, with a long wavelength capable of penetrating thick forest canopies. This is the first time a P-band radar has been sent to space, and it may help dramatically reducing uncertainties in biomass measurements – especially in places like the Amazon, Central Africa and Southeast Asia.
“We hope and anticipate that data from the Biomass mission, once available, will be able to extend the record of biomass stored in the world’s forests, with this reducing uncertainties in the global carbon cycle and its contribution to climate change,” says Lucas.
Work remains on the ground
But while Biomass will become ESA’s new eye in the sky, there is much work still to be done on the ground
Ground-truthing – including taking tree-by-tree measurements – is still vital to verify satellite data, especially in tropical forests which contain immense amounts of biodiversity.
“Even the most advanced satellite can’t tell a mahogany from a Brazil nut tree without help from the ground, and there are more than ten thousand tree species in the Amazon alone,” says Oliver Phillips from the University of Leeds.
Phillips is part of a global network of forest scientists called GEO-TREES, which aims to complement the work done by Biomass and help fund and support the scientists working on the ground.
“GEO-TREES will implement rigorous ground-validation protocols and push for major investments in the people behind the data – particularly in the Global South, where much of the world’s biodiversity resides,” says ESA’s Biomass Mission Manager, Klaus Scipal.
“Satellites, such as our Biomass, offer a wealth of information to understand our changing world, but we must not forget those working tirelessly on the ground taking in situ measurements, often in difficult conditions, who allow us to have confidence in the data returned from space.”