The world is facing a critical moment in the fight against climate change, and the eyes of the global community are on Belém, Brazil, where the United Nations COP30 climate change conference is taking place. This conference is a pivotal gathering, as it brings together policymakers from around the globe to assess the progress made under the Paris Agreement, an international treaty aiming to limit global warming to 1.5°C above pre-industrial levels.
But here's where it gets controversial: the Amazon rainforest, once a mighty carbon sink, is now showing worrying signs of transformation. Satellite observations reveal that parts of this vast ecosystem are no longer absorbing carbon dioxide as they once did, and in some areas, the forest has even become a net emitter of carbon. This emerging reality underscores the urgent need for independent, reliable, and continuous monitoring of greenhouse gas emissions worldwide.
Enter the European Space Agency (ESA) and its Earth observation missions. These missions provide an invaluable capability: independent, satellite-based evidence that holds nations accountable for their climate actions. Through its Climate Change Initiative, ESA generates long-term satellite datasets that meet the Essential Climate Variables defined by the Global Climate Observing System. These records offer a solid scientific foundation for climate researchers worldwide, enabling them to develop effective mitigation and adaptation strategies.
And this is the part most people miss: ESA's efforts extend beyond data collection. Through projects like Regional Carbon Cycle Assessment and Processes (RECCAP-2), ESA delivers the research and data needed to support the implementation of the Paris Agreement. By quantifying the global carbon budget, we gain a fundamental understanding of the scale and urgency of the actions required. As of January 2025, the remaining carbon budget stands at approximately 235 gigatonnes, and at current emission rates, we could exhaust this budget within just six years.
Understanding this budget requires precise knowledge of carbon absorption by natural sinks, primarily oceans and land, as well as emissions from fossil fuels and land-use change. While ocean carbon sinks are relatively well-understood, accurately quantifying the land sink remains a challenge. Small-scale disturbances in tropical forests, typically below two hectares and difficult to detect, exemplify this challenge. Despite representing only 15% of the affected area, they were responsible for 88% of net biomass carbon loss between 1990 and 2020.
The RECCAP-2 project uses satellite data to tackle this challenge, combining satellite observations with ground data and computer models to quantify land-atmosphere dynamic carbon exchanges. By doing so, it delivers independent estimates of regional carbon budgets that can be compared with national inventories. The findings to date reveal critical trends that demand immediate 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. This accelerating loss of carbon raises concerns about potential tipping points. Similarly, boreal and temperate forests in the northern hemisphere, which account for 41% of the world's forest area, have shifted from being reliable carbon sinks to becoming 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, but carbon uptake is declining due to harvesting, aging, drought, and disease, posing significant challenges to EU climate neutrality goals by 2050.
Research also highlights the irreplaceable value of primary forests. While forest recovery offers hope, secondary and degraded forests regain only about a quarter of the carbon lost from deforestation. This underscores the critical importance of protecting old-growth forests, as their carbon storage capacity cannot be fully replaced by regrowth. Furthermore, research has revealed the hidden importance of non-living carbon reservoirs, such as soil, dead wood, and sediments, which have absorbed the majority of land carbon over the past three decades. Only 6% of the 35 gigatonnes of carbon absorbed by land between 1992 and 2019 was stored in living vegetation, highlighting the need for comprehensive monitoring systems that capture the full spectrum of land carbon dynamics.
ESA's Earth observation missions, such as BIOMASS, EarthCARE, HydroGNSS, SMOS, and the Copernicus Sentinels, provide the critical climate data needed to monitor these changes. These missions track tropical forest carbon stocks, address cloud-related climate uncertainties, monitor soil moisture, and provide continuous monitoring of land surfaces, vegetation, oceans, ice sheets, and the atmosphere. The upcoming Copernicus Anthropogenic Carbon Dioxide Monitoring mission will specifically monitor carbon dioxide and methane emissions, offering independent data to assess the effectiveness of emission-curbing policies on a national and global scale.
As nearly 200 countries gather in Belém, the stakes are incredibly high. The Global Stocktake, which occurs every five years under the Paris Agreement, will assess collective progress toward climate goals. Novel methods developed by the CCI RECCAP-2 team, based on Earth observation and atmospheric modeling, provide a means of comparing greenhouse gas inventories. Most countries currently use estimates of sector-based activity to compile their national reports, but the Intergovernmental Panel on Climate Change encourages the verification of reported emissions against independent measurements to promote transparency and measure progress against empirical records. Satellite observations provide this verification, equipping countries with data to check their net emissions reduction progress and reflect the real-world situation.
ESA's Director of Earth Observation Programs, Simonetta Cheli, emphasizes the importance of regular comparisons between inversion results and national greenhouse gas inventories for monitoring the effectiveness of mitigation policies and countries' progress towards their pledges. The science is clear: climate action is urgent, and the tools for monitoring are in place. Thanks to ESA's satellites and projects like RECCAP-2, we will have the data to determine whether our climate actions are making a difference. What remains is the political will to act, and to act decisively.
