Nature Climate Change, a professional academic journal under Springer Nature, recently published two papers assessing the impact of 2024 temperatures on the goals of the Paris Agreement. The results show that a temperature rise of more than 1.5°C in 2024 may indicate that the world has entered a period of several decades with an average temperature rise of 1.5°C, and strict climate mitigation measures are needed to achieve the goals of the Paris Agreement.
The two papers explore the potential possibility of the Paris Agreement to limit warming to 1.5°C above pre-industrial temperatures. According to reports, in 2015, the Paris Agreement set a goal to limit human-induced global warming to 1.5°C above the pre-industrial baseline. The temperature target of the Paris Agreement is understood to refer to the average temperature over a 20-30 year period in order to eliminate the impact of short-term natural changes (such as El Niño) on the climate system.
Current simulations show that this 20-year warming threshold will be exceeded in the late 2020s or early 2030s. Recently, it was announced that 2024 will be the first year that temperatures exceed 1.5°C relative to pre-industrial levels, but how this will affect the long-term goals of the Paris Agreement remains unclear.
To explore the relationship between a single warm year and a longer-term warming trend, Emanuele Bevacqua, first author and corresponding author of the first paper, and collaborators at the Helmholtz Centre for Environmental Research in Germany, combined climate observations with simulations from the Coupled Model Intercomparison Project 6 (CMIP6), focusing on models that represent the warming trend from 1981 to 2014.
Looking back at historical warming trends, they believe that the first single year in which temperatures exceed different warming thresholds in the range of 0.6°C to 1°C above pre-industrial temperatures also falls into the first 20-year period in which the annual average temperature exceeds these different thresholds. This pattern suggests that with the 1.5°C warming in 2024, the Earth may have entered a 20-year warming period. When the study simulated various climate scenarios, 2024 fell within the first 20-year period of reaching the 1.5°C target, ranging from likely (66% or greater) to almost certain (99% or greater), depending on the specific climate scenario.
In the Shared Socioeconomic Pathway (SSP) 2-4.5 scenario, which best reflects current climate policy scenarios, all models showed that the first year of breaking 1.5°C fell within the 20-year warming period, the authors said. They cautioned that the start of the 20-year period of 1.5°C warming should not be mistaken for the time when the warming level itself is reached, as the latter is likely to occur at the midpoint of the 20-year period.
The second paper's sole author, Alex J. Cannon of Environment and Climate Change Canada, used simulated data from CMIP6 to find that June 2024 was the 12th consecutive month that the temperature rose above 1.5°C. Based on existing models, he analyzed how this would affect the Paris Agreement target and believed that the forecast of a temperature rise of 1.5°C for 12 consecutive months was more likely to occur when long-term (i.e., 20-year average) warming had already occurred. It was calculated that the probability of this happening was 76% under the SSP2-4.5 scenario and 56% under the SSP1-2.6 scenario.
The authors of the paper pointed out that based on this simulation, if the temperature rise reaches 1.5°C or more for 18 consecutive months, then under SSP2-4.5, the Paris Agreement would almost certainly be broken.
The two papers used different methodologies and time periods to explain some of the differences in their respective results. However, both papers pointed out that rapid and tough mitigation measures can still reduce the possibility of breaking the Paris Agreement temperature target in the next few years to a decade.
