Separating Greenhouse-Gas Driven Forcing from Natural Fluctuations in the Time Series for Global Mean Temperatures

The year 2024 was the hottest in the modern era, followed by 2023. Do these temperatures signal unexpected changes in the climate system? Writing the global annual mean temperature as the sum of two terms, greenhouse-gas driven climate change and fluctuations due to internal and external variability, we model the first term by extending the logarithmic dependance of the temperature anomaly to non-equilibrium conditions. We validate the method using the illustrative scenarios considered by the IPCC. Fitting the data, we find that the residuals for 2023 and 2024 are consistent with past fluctuations. We comment on how putative changes in the climate regime will manifest themselves in coming years.