As we approach the recommended limits of global warming set by the Paris Agreement, with warming already at 1.3°C above Pre-Industrial, our study asks: At what level of global warming do fires affect the world's forests and carbon sinks? Fires are long known for their role in shaping ecosystems and are increasingly seen as a critical factor that could influence the global carbon balance. So, we want to know what these fire impacts suggest for the Paris Agreement’s ambition to avoid the worst impacts of climate change.
We find that fire will affect the ability of ecosystems to absorb carbon, even at relatively modest levels of warming—between 0.8-1.3°C above pre-industrial levels. The study reveals that fires are increasingly transforming forests, grasslands, and other landscapes at lower temperatures than previously thought. Many of these ecosystems may be pushed towards carbon sources, impacting the global carbon cycle.
What makes this particularly important is that this study suggests these changes are happening now, not just in the distant future. As we approach the 1.5°C threshold, which many associate with critical climate impacts, fire is already contributing to shifts in ecosystem behaviour. This highlights the need to act swiftly, as every fraction of a degree of warming can have a noticeable impact on the Earth’s ecosystems, their capacity to store carbon, and even their ability to recover at all.
Modelling Fire’s Impact on Ecosystems
Predicting fire’s impact on global ecosystems is complex and requires a model - a numerical tool - capable of representing the complexities of the land surface, which requires not only fire but also vegetation, soils and hydrology and how all of these interact with climate. We used the JULES-INFERNO Land and Vegetation Model to represent how plants grow, how carbon cycles through ecosystems and soils, and how these systems interact with climate. We use this model in two setups: one that explicitly includes how fire processes are changing with climate and the environment and another that doesn’t so that we can isolate the role of fire in the world. The model accounts for how fires occur under specific weather conditions and fuel availability and how it affects vegetation and carbon emissions. We can contrast this to a hypothetical world where fire impacts are not included. Using data from four different climate models lets us explore a range of possible future climate projections and isolate the specific effects of fire on carbon storage and ecosystem shifts.
Fire’s Role in Weakening Carbon Sinks
The study provides new evidence that fires are weakening natural carbon sinks. Normally, ecosystems like forests act as buffers, absorbing carbon from the atmosphere and helping to moderate climate change. But when fires occur, they release large amounts of carbon back into the air, which weakens the overall capacity of these ecosystems to mitigate climate impacts.
By looking at fire’s role in reducing carbon storage, the research suggests that we may need to adjust our assumptions about carbon budgets. It’s not only about reducing emissions but also about ensuring that ecosystems can continue to play their vital role in capturing carbon. If fires continue to reduce the effectiveness of these sinks, we could face a more challenging pathway to limiting global warming.
Regional Variation: Why Every 0.1°C Counts
Limiting global warming to 1.5°C is widely seen as an effective guardrail for avoiding the worst impacts of climate change and defining action on mitigation. However, this research shows that fire impacts vary considerably, emerging at different times depending on the region. Some areas, like the Northern Boreal forests and tropical South America, are already showing signs of stress earlier than expected. In contrast, other regions may not experience the worst impacts until closer to 2°C of warming.
This regional variation underscores why every 0.1°C matters. Small differences in global temperature could mean the difference between ecosystems continuing to store carbon or releasing it. These findings emphasise the need for both global and region-specific strategies to mitigate fire impacts.
Brazil as a Lens for Understanding Global Patterns
Although this study takes a global view, the fires currently burning in Brazil offer a timely example of fire’s effects on carbon sinks. The Amazon rainforest, one of the planet’s largest carbon stores, Pantanal and the Cerrado biomes are experiencing fires that not only threaten biodiversity but also its ability to sequester carbon. This is a reminder of the complex ways in which fire interacts with climate and ecosystems.
In addition, Brazil's fires highlight the value of international scientific collaboration. Partnerships between Brazilian and UK researchers, including those involved in this study, are leading to new insights into how fire regimes are changing and how best to manage these risks. The JULES-INFERNO fire model, which was central to this study, is a prime example. Other standout achievements include the fire probability seasonal forecast, predicting fire-prone periods to inform planning and response efforts, and the FLAME driver attribution framework, which pinpoints the causes of fire events. Together, these tools underscore how coordinated global efforts can tackle shared challenges and inform more effective fire management strategies. As fire is a global issue, the Brazil-UK collaboration serves as a model for how countries can work together to confront these shared challenges.
Rethinking Mitigation and Adaptation Strategies
One of the paper’s critical contributions is its call for a rethink of the relationship between mitigation and adaptation. Traditionally, these two approaches have been seen as separate: mitigation reduces emissions, and adaptation helps us cope with the impacts that are already happening. But fire shows how closely linked they are. Reducing emissions can lessen future fire risks, while adapting fire management strategies can help ecosystems remain resilient in the face of changing fire regimes.
This research suggests that more integrated approaches are needed to address the dual challenge of fire and climate change. As fires alter the carbon cycle, they also change the global carbon budget, meaning that mitigation strategies need to consider these feedbacks. Adaptation, meanwhile, must incorporate more forward-looking fire management plans and fire-free agricultural policies and investments that account for the growing influence of fire in different ecosystems.
Focusing on Impact Avoidance
The findings of this study point towards a broader shift in climate policy: prioritizing impact avoidance alongside temperature targets. While temperature limits like 1.5°C are important, it’s equally critical to focus on minimizing the specific impacts we’re already starting to see—such as fires reducing carbon storage capacity.
The research suggests that human actions can still influence future fire regimes, and the more we do now to limit warming, the better our chances of protecting vulnerable ecosystems. This approach could help steer the conversation away from just temperature thresholds and towards a more comprehensive view of how we can avoid the most severe impacts of climate change.
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