Breaching 1.5 °C: Give me the odds

This paper develops a probability framework to convey the uncertainty surrounding predictions of when the temperature thresholds established by the Paris Agreement will be breached. The motivation for reporting probabilities is that they enable policymakers to make timely and informed decisions. The method can be summarised as predicting future temperatures under different scenarios and calculating the proportion of predicted outcomes that exceed the specified limits. These probabilities can be computed for different time horizons and updated as new data become available. We illustrate our method using two forecasting mechanisms. The first model links temperature anomalies to effective radiative forcings, enabling the assessment of how emissions scenarios affect breaching probabilities. The second model relies solely on the time series dynamics of observed temperatures and does not require additional inputs for forecasting. Our methodology is simple to implement and can be readily adapted to more complex climate models. We encourage climate model developers to include probabilities of breaching these limits in their reports.