Once considered one of Earth's most vital carbon sinks, the Amazon is now showing troubling signs - satellite observations reveal that parts of this vast ecosystem are no longer absorbing carbon dioxide as they once did. In some areas, the forest has even become a net source of carbon emissions.
This emerging transformation underscores a critical need: independent, reliable and continuous monitoring of greenhouse gas emissions across the globe.
As policymakers from nations around the globe gather to assess progress under the Paris Agreement - the international treaty which has set the goal of limiting global warming to 1.5C above pre-industrial levels - they require actionable, science-based information to verify climate action, limit temperature rise and build resilience against unavoidable impacts.
The Earth observation missions developed by the European Space Agency (ESA) are providing precisely this capability - delivering independent, satellite-based evidence that makes climate accountability possible.
Through decades of Earth observation expertise, ESA is providing transparent and reliable data that enables countries to track progress and strengthen national climate action.
Central to this effort is ESA's Climate Change Initiative, which generates long-term satellite-based datasets that satisfy Essential Climate Variables - key aspects of the climate defined by the Global Climate Observing System. These records provide climate researchers worldwide with a solid scientific foundation which can be used to inform effective mitigation and adaptation strategies.
Beyond this, through the Regional Carbon Cycle Assessment and Processes (RECCAP-2) and similar projects, ESA is delivering the research and data needed to support the implementation of the Paris Agreement.
A fundamental metric that informs effective climate action and must be understood is the global carbon budget. It determines the scale and urgency of what must be done. With the Paris Agreement's goal of limiting warming to 1.5C, the remaining carbon budget - the amount of carbon dioxide we can still emit - stands at approximately 235 gigatonnes as of January 2025. At current emission rates, this budget could be exhausted within just six years.
Understanding this budget requires precise knowledge of two key factors: how much carbon is absorbed by natural sinks - primarily oceans and land - and how much is emitted from fossil fuels and land-use change.
While ocean carbon sinks are relatively well understood, accurately quantifying the land sink remains challenging. Small-scale disturbances in tropical forests, typically below two hectares and difficult to detect, exemplify this challenge. Although they only represent 15% of the area affected, they were responsible for 88% of net biomass carbon loss between 1990 and 2020.
The RECCAP-2 project uses satellite data to tackle one of climate science's biggest challenges - understanding how and where carbon is being stored and released across the planet's land surface. By combining satellite observations with ground data and computer models, the project is able to quantify land - atmosphere dynamic carbon exchanges and deliver independent estimates of regional carbon budgets that can be compared with national inventories.
As this ongoing research continues to analyse carbon dynamics across the globe, the findings to date are revealing critical trends that demand urgent attention.
The Amazon Basin, which accounts for 14% of global plant carbon uptake annually, lost 370 million tonnes of carbon between 2010 and 2020, with its south-eastern region particularly affected. The Basin continues to show accelerating carbon losses, raising concerns about potential tipping points.
Satellite data has detected a fundamental shift in the boreal and temperate forests of the northern hemisphere, which account for 41% of the world's forest area. Forests that were once reliable carbon sinks have become carbon sources since 2016, driven by increasing droughts, wildfires and other climate-related stresses.
Across Europe, forests absorbed about 10% of the EU's greenhouse gas emissions between 1990 and 2022. However, carbon uptake by forests is declining due to harvesting, ageing, drought and disease - a trend with significant implications for EU climate neutrality goals by 2050.
While forest recovery offers hope, research shows that secondary and degraded forests regain only about a quarter of the carbon lost from deforestation. This underscores that protecting old-growth forests must remain the priority, as their carbon storage capacity cannot be fully replaced by regrowth.
Perhaps most surprisingly, research has revealed that the majority of land carbon absorption over the past three decades has occurred in non-living reservoirs, such as soil, dead wood and sediments. Between 1992 and 2019, only 6% of the 35 gigatonnes of carbon absorbed by land was stored in living vegetation. This insight highlights carbon pools often underrepresented in national inventories and emphasises the need for comprehensive monitoring systems that capture the full spectrum of land carbon dynamics.
Monitoring these changes requires continuous global observations from space. ESA's expanding suite of Earth observation missions provides the critical climate data needed.
BIOMASS - an ESA Earth Explorer - tracks tropical forest carbon stocks with unprecedented accuracy, providing crucial data on the health of the world's forests.
EarthCARE - an ESA Earth Explorer - addresses cloud-related climate uncertainties that affect our understanding of Earth's energy balance.
HydroGNSS - ESA's first Scout mission - will monitor soil moisture, a critical variable for quantifying land - atmosphere carbon exchange and the functioning of terrestrial ecosystems.
SMOS - an ESA Earth Explorer uses L-band microwave observations to monitor soil moisture and vegetation optical depth. Its data are also used in RECCAP-2 research to track changes in northern forest biomass.
The Copernicus Sentinels provide continuous monitoring of land surfaces, vegetation, oceans, ice sheets and the atmosphere. Sentinel-6B, which is due to launch this month, will continue the crucial sea-level monitoring record. The upcoming Copernicus Anthropogenic Carbon Dioxide Monitoring mission will monitor carbon dioxide and methane emissions, providing independent data to assess the effectiveness of policies aimed at curbing emissions on a national and global scale.
As nearly 200 countries gather in Belem, the stakes could not be higher. The Global Stocktake, which takes place every five years under the Paris Agreement, will assess collective progress toward climate goals.
Novel methods developed by the CCI RECCAP-2 team, which are based on Earth observation and atmospheric modelling, provide a means of comparing greenhouse gas inventories.
Currently, most countries use estimates of sector-based activity to compile their national greenhouse gas reports and to show progress towards delivering on their carbon reduction commitments under the Paris Climate Agreement. However, the Intergovernmental Panel on Climate Change encourages Parties to verify reported emissions against independent measurements, as this promotes transparency and measures progress against empirical records. Satellite observations provide both, equipping countries with data to check net emissions reduction progress so they reflect the real-world.
ESA's Director of Earth Observation Programmes, Simonetta Cheli, noted, "Comparing inversion results with national greenhouse gas inventories can be applied regularly for monitoring the effectiveness of mitigation policy and progress by countries to meet the objectives of their pledges."
Science is clear - climate action is urgent. The tools for monitoring are in place. Thanks to satellites developed by ESA and projects like RECCAP-2 that turn observations into actionable insights, we will know whether climate action is making a difference. What remains is the political will to act - and to act now.
Related Links
European Space Agency
Climate Science News - Modeling, Mitigation Adaptation
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