Nature and Biodiversity

Why we need to weigh, not count, trees from space

Seeing the wood and the trees … measuring the tree weight for large areas delivers new insights on forest-related projects.

Seeing the wood and the trees … measuring the tree weight for large areas delivers new insights on forest-related projects. Image: Unsplash/Yulian Alexeyev

Florian Reber
Head of Partnerships, Chloris Geospatial Inc.
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Climate and Nature

This article is part of: Centre for Nature and Climate
  • Quantifying trees by weight, rather than their number or forest area extent, allows more accurate assessment of their carbon impact.
  • Remote sensing technology can now analyze tree weight from space, allowing forest carbon monitoring and accounting at scale.
  • Through this approach, forest-related carbon projects can be precisely assessed for whether they are net sinks or net emitters.

There is an old Yiddish proverb that says that “words should be weighed, not counted”. The same is true for trees. It is the weight of trees, not their number, that really matters. Specifically, it’s the weight gains and losses of trees that matter.

This is because the changes in the weight of the trees in an area (i.e. their biomass gains and losses) tell us how much carbon is drawn down from the atmosphere as they grow, and how much is emitted as an area is deforested or degraded. Tracking those tree weight dynamics over large areas delivers new insights on the climate impact achieved by forest conservation and restoration projects, be it at the farm, project or jurisdictional level.

Have you read?

But how to best estimate the weight of a tree without felling it? For a long time, the only way to attempt it was by working with field sample-based biomass estimates. Today, cutting-edge remote-sensing technology weighs trees from space directly. It has a number of advantages over traditional in-situ and remote-sensing approaches. For example:

  • Scalability: Advanced algorithms generate “spatially explicit” forest carbon data – direct carbon estimates for every pixel, at operational resolution – with scalability from small farms to entire continents. By analyzing large amounts of space agency data over long time series, they increase the robustness of estimates, with the cost effectiveness and speed that software unlocks. This combination of accurate, scalable and cost-effective carbon data production is critical to support the scaling of nature-based solutions.
  • Consistent data quality: To ensure comparability across projects, data consistency in space and time is as important as data scalability. Direct biomass measurements deliver that data consistency by deploying the same methodology globally, and by neither relying on greatly varying forest definitions nor generic emission factors (which plague standard approaches for forest carbon estimation).
  • Auditable results: Last but not least, such algorithmic data comes with quantified uncertainty at the pixel level and can be audited across scales. While today, carbon projects are primarily undergoing process audits, with this new data, the actual carbon observations can be audited. This unlocks new possibilities to assess the carbon integrity of projects.

At Chloris, we are proud to be a champion of this new approach and demonstrate its transformative power for accurate forest carbon accounting and monitoring at scale. In less than 12 months, we have monitored from space how the weight of an estimated 100 billion trees has changed annually since the year 2000.

Measuring forest carbon projects

The new approach has wider implications for carbon markets. In the discussion on avoided deforestation and degradation activities, the focus today is often on the “baseline”, or the counterfactual: What would have happened in the absence of the project. But from an atmospheric CO2 concentration point of view, a key question is: How much carbon does woody vegetation actually absorb as a consequence of its growth, and how much does it emit, because it is lost or degraded? And, in sum, is a carbon project involving those processes a net sink or a net source of emissions?

This is a perspective that our approach for direct biomass stock and change measurement provides. It is a different and complementary view to what voluntary carbon markets and other carbon accounting methodologies currently do and ask for. To illustrate what carbon insights can be gained with the approach, we take a look at the controversial – and now stalled – Kariba REDD+ project in Zimbabwe.

Kariba REDD+ Project is Zimbabwe is net carbon sink over time.
Kariba REDD+ Project in Zimbabwe, a net carbon sink, over time. Image: Chloris

Our data shows that the area of the Kariba REDD+ Project – a project designed to fund the prevention of expected deforestation and hence maintain carbon stock, rather than increasing it – has increased its carbon stock over time and hence is a net carbon sink. From the project’s start date in 2011 to 2022, the area has drawn down a total of 16.5 million tons of CO2e, and emitted 15 million tons of CO2e.

The result is a positive net carbon impact of 1.52 million tons of CO2e since the project started. Our 23-year series also shows what happened in the area since the year 2000. In total, from 2000 to 2022, trees and shrubs located in the Kariba project area sequestered a total of 35.4 million tonnes of CO2e and emitted 31.4 million tons of CO2e, resulting in a net positive carbon impact of 4 million tonnes of CO2e, according to our data.

To gain more insights into the Kariba carbon and forest dynamics, you can have a look at our analysis of the project. We hope that it can stimulate further dialogue on data innovation for a trustworthy, impactful and scalable carbon market. Beyond the Kariba example, our customers can also access our insights on forest carbon projects from around the world, including spatially explicit insights on biomass change, forest area growth, forest area losses and degradation.

True carbon monitoring and accounting

It is time to measure what the atmosphere shows – not just globally, but also at the level of individual projects – and embrace spatially explicit biomass change time series. What if carbon finance rewarded the actual net carbon impact over time, resulting from the growth and loss of trees and forests? What if it embraced spatially explicit biomass maps, delivering spatially explicit emission factors for deforestation and degradation events? And what if it embraced the fact that the boundaries between natural and human drivers of biomass gains and losses cannot always be clearly defined?


What’s the World Economic Forum doing about deforestation?

Standard-setting bodies and reporting protocols in the voluntary carbon market are crucial in accelerating credible, trustworthy and scalable climate action (the same holds for corporate carbon accounting protocols). Technology will always be ahead of reporting protocols. To avoid slowing down corporate climate action, protocols should avoid locking in outdated accounting and monitoring technologies in their provisions.

Instead, they can adopt guidance that invites market participants to embrace science-based, cutting-edge accounting and monitoring technologies that are fit for purpose: technologies that deliver trustworthy carbon removals and emissions data with the speed, scale and cost-effectiveness that the climate and nature crises require.

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