How Strange are the 2023-2024 Global Mean Temperatures?An Analysis Using Simple Models

2023 was the hottest year in the modern era of instrumental data. 2024 is likely to break that record. It has been suggested that this is, at least in part, the result of a supposed doubling of the earth’s energy imbalance. In the present work we address two questions:

Are the global mean temperatures for 2023 and 2024 out of line with what we should have expected?

and

Is the putative doubling of the earth’s energy imbalance since the first decade of this century consistent with the global mean temperatures since then?

Using the well-known logarithmic dependence of the temperature anomaly on CO2 concentration one can fit the data for the global temperature anomaly in terms of two parameters: the climate sensitivity and a reference CO2 level that depends on the baseline period for the temperature anomaly dataset. Subtracting this from the temperature anomaly time series yields residuals representing the impact of internal and external variability. We discuss the statistical properties of this distribution; 2023 is consistent with earlier fluctuations.

One can relate the earth’s energy imbalance to the temperature anomaly by introducing an effective heat capacity for the earth’s climate system. The results do not appear to support claims that a putative doubling in the earth’s energy imbalance is significantly impacting our recent temperatures.