Attribution science, the branch of climate research that assigns observed changes to specific causes, has matured rapidly over the past decade. Earlier studies established methods for attributing a share of historical warming to individual companies, building on the Carbon Majors database, a comprehensive accounting of the emissions associated with the largest fossil fuel and cement producers in the world. Those efforts focused largely on the past and the present. Frierson and Henrie extended the approach forward in time, asking not only how much warming these entities have already caused, but how their historical emissions will continue to shape the climate system across coming centuries under different assumptions about humanity’s collective future.

To do this, the researchers turned to the Finite Amplitude Impulse Response model, or FaIR, a widely used reduced-complexity climate model that simulates the interactions between greenhouse gas emissions, atmospheric concentrations, radiative forcing, and global temperature. FaIR captures the essential physics of the carbon cycle and the atmospheric chemistry of methane and other greenhouse agents while remaining computationally efficient enough to run many simulations. The team ran the model out to the year 2500, an unusually long horizon for attribution work, and performed counterfactual experiments: simulations in which the emissions associated with the Carbon Majors were removed from the historical record, with the difference between the factual and counterfactual worlds representing the perturbation attributable to those entities.

The counterfactual technique is the analytical heart of the study. By comparing a simulated world that includes the emissions of the top 178 producers with an otherwise identical world that excludes them, the researchers isolated the corporate contribution to atmospheric carbon dioxide, methane, ozone, stratospheric water vapor, and ultimately global mean temperature. They repeated this comparison across several different future emissions scenarios, ranging from futures in which global emissions fall rapidly to futures in which they continue to climb. This design allowed them to test a question that has received little attention: does the warming legacy of past emissions look different depending on what the rest of the world does next?

The answer, perhaps unexpectedly, is yes—and in two opposing directions. For atmospheric carbon dioxide, the anomaly attributable to a company’s historical emissions is smaller, and carries less uncertainty across the model ensemble, in a low-emissions future than in a high-emissions one. The reason lies in carbon cycle feedbacks. In a high-emissions world, warming itself weakens the ability of oceans and land ecosystems to absorb carbon, so an initial pulse of carbon dioxide produces a larger and more variable atmospheric anomaly. In a cooler, lower-emissions world, those feedbacks are muted, and the extra carbon dioxide from historical emissions is drawn down more efficiently and more predictably.

Yet when the researchers translated those carbon dioxide anomalies into temperature, the picture reversed. The temperature change attributable to past emissions turned out to be larger in a lower-emissions future, even though the atmospheric carbon dioxide anomaly was smaller. The explanation is the logarithmic relationship between carbon dioxide concentration and radiative forcing: each additional part per million of carbon dioxide traps less additional heat than the part per million before it. In a high-emissions future, the background concentration is already so elevated that the corporate contribution sits on the flat, less sensitive portion of the forcing curve. In a low-emissions future, where concentrations are brought down substantially, the same corporate contribution occupies a steeper portion of the curve and therefore exerts a proportionally larger influence on temperature. In other words, the more successfully the world decarbonizes, the more visible the fingerprint of historical emitters becomes in the remaining warming.

Methane added a further twist. The simulations showed that after roughly 2080, the methane concentration anomaly attributable to the Carbon Majors turns negative, meaning the counterfactual world without their emissions actually contains more methane than the factual one. This counterintuitive result stems from atmospheric chemistry: methane’s lifetime in the atmosphere depends on temperature, and a warmer climate shortens the chemical lifetime of methane by accelerating its removal. The historical warming caused by corporate emissions therefore acts as a small negative feedback on methane concentrations in later centuries, partially offsetting—but nowhere near fully compensating for—the positive forcing from carbon dioxide.

Across every scenario the researchers examined, the net effect of the Carbon Majors’ historical emissions remained a warming one. The perturbations propagate through many linked components of the climate system: carbon dioxide in the atmosphere and in other reservoirs of the carbon cycle, methane, ozone, and stratospheric water vapor, the latter two arising as chemical byproducts of methane oxidation. When all of these contributions to radiative forcing are summed, the total stays positive throughout the simulations running to 2500, and positive forcing translates directly into positive temperature perturbations. There is no scenario in the study in which the corporate legacy simply cancels itself out.

The implications extend well beyond academic attribution. Courts, legislatures, and communities increasingly ask not just who caused climate change, but who bears responsibility for damages that have not yet occurred. This study demonstrates that such future damages are, in principle, calculable on timescales of centuries. Because the temperature perturbation attributable to each entity can be tracked through a physically consistent model under any given emissions pathway, the framework could in theory be coupled with damage functions and sea level projections to quantify ongoing liabilities. The researchers emphasize that the attributable warming is not a fixed historical quantity but a pathway-dependent one, which means that choices made in the coming decades will shape how the responsibility of past emitters is expressed in the climate of the future.

The study also carries a sobering message for the general public: the climate consequences of emissions already released are effectively locked in for many generations, regardless of how quickly the world now decarbonizes. Even in optimistic scenarios, the simulations show the Carbon Majors’ historical emissions continuing to raise global temperatures for centuries, interacting with carbon cycle feedbacks, atmospheric chemistry, and the logarithmic physics of radiative forcing in ways that keep their influence positive and quantifiable. As Frierson and Henrie conclude, in addition to the damages that have already occurred, these entities can be expected to be responsible for calculable climate damages for many centuries to come—a legacy written into the physics of the atmosphere itself.

Subject of Research: Attribution of centuries-long global warming to major fossil fuel and cement producers under future emissions scenarios

Article Title: Centuries of global heating from Carbon Majors: Dependence on future emissions pathways

Article References: Centuries of global heating from Carbon Majors: Dependence on future emissions pathways. (n.d.). https://doi.org/10.1371/journal.pclm.0001036

Image Credits: AI Generated

DOI: 10.1371/journal.pclm.0001036

Keywords: climate attribution, Carbon Majors, FaIR model, fossil fuel emissions, carbon cycle feedbacks, radiative forcing, methane lifetime, counterfactual simulations, PLOS Climate, global warming, emissions scenarios, climate damages