The World Could Exceed 1.5°C of Global Warming as Early as 2026
By: Sean Youra
Tags: Paris Agreement, Climate Action, Global Warming, Science, Climate Change

The World Could Exceed 1.5°C of Global Warming as Early as 2026

Photo by Marcin Jozwiak on Unsplash

Article 2 of the Paris Agreement signed in 2016 stated as one of its objectives: “Holding the increase in the global average temperature to well below 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5°C above pre-industrial levels, recognizing that this would significantly reduce the risks and impacts of climate change.”

However, the world is currently not on track to avoid 1.5°C of global warming, or 2°C for that matter. In fact, we are currently on track for 3°C of warming by 2100 compared to pre-industrial levels. This is still lower than what’s usually referred to as the business as usual scenario, in which 5°C of warming could occur, but it’s certainly not great either as the climate impacts of 3°C of warming would be disastrous.

The Climate Action Tracker video below provides a nice summary of countries’ commitments and actions to do their part to hold the global temperature rise below 1.5°C. They similarly state that the world is on track for about 3°C of warming by 2100 based on current inadequate targets and policies.

The state of the climate crisis. Source: TED

A detailed analysis conducted by Zeke Hausfather, climate scientist and Director of Climate and Energy at the Breakthrough Institute, used the latest Coupled Model Intercomparison Project version 6 (CMIP6) climate models to provide a range of estimates for when the 1.5°C and 2°C targets might be exceeded. These are the same models that will be used in the forthcoming IPCC’s Sixth Assessment Report (AR6) for next year.

Although there are some issues that Hausfather discusses regarding what year marks the end of the “pre-industrial era,” which data records are used, and when the 1.5°C and 2°C temperature targets should be considered “exceeded”, the analysis that he ran avoided these issues by using observational records up to 2020 and then the CMIP6 models post-2020.

A range of possible years when the 1.5°C and 2°C targets are exceeded is provided based on combinations of both Representative Concentration Pathways (RCPs) and Shared Socioeconomic Pathways (SSPs). For in-depth explanations on RCPs and SSPs, check out these articles from Carbon Brief and Skeptical Science. Hausfather summarizes both by saying, “The RCPs set pathways for greenhouse gas concentrations and, effectively, the amount of warming that could occur by the end of the century. Whereas the SSPs set the stage on which reductions in emissions will — or will not — be achieved.”

For all scenarios that were analyzed, the earliest the 1.5°C target could be exceeded occurs in 2026. In the highest emissions scenario (i.e., SSP5–8.5), there is a greater probability of exceeding the 1.5°C target by 2026 compared to the lowest emissions scenario (i.e., SSP1–2.6) based on a greater confluence of model estimates around 2026 being the “exceedance date.” Importantly though, the median exceedance date is between 2030 and 2033 in all scenarios, meaning that there is a greater confluence of model estimates around 2030 to 2033 depending on the scenario.

A similar analysis was conducted for the 2°C target, with the earliest exceedance date being 2034 for the SSP5–8.5 scenario. Median estimates for all scenarios ranged from 2043 to 2052. The ranges of model estimates for the exceedance date were greater for the 2°C target as there is a larger gap between current observed global warming and the target that introduces more variability into the modeling process.

It’s important to keep in mind that because the global temperature is a noisy signal that is subject to some natural variability in addition to anthropogenic global warming, the global temperature might exceed the 1.5°C or 2°C targets one year and then drop back down the next year. For example, when 390 ppm CO₂ was exceeded in 2011, the average global temperature anomaly reached 0.9°C, then dropped below 0.9°C and went back up. In addition, there is a time lag of a decade or more between a pulse of emissions and the maximum global warming caused by those emissions.

This is why using a multi-year average for determining when a particular target is exceeded is important. If we see that over the course of 5 years, the average global temperature anomaly is above 1.5°C, then it’d probably be safe to say the target has been exceeded. However, there is still no agreed-upon approach for determining this multi-year average.

Averaged global temperature anomalies and annual CO₂ concentrations; Source: Climate Central.

As noted in IPCC’s Special Report: Global Warming of 1.5°C, the climate risks associated with 1.5°C and 2°C of warming are significant. For example, global sea level is expected to be 0.1 meters (3.9 inches) lower by 2100 for warming of 1.5°C compared to 2°C, which may not seem like much but has important implications for coastal cities in terms of climate adaptation.

Yet, we are not on track to keep global warming below either of these targets meaning the climate risks of continued inaction and inadequate policies are even greater than the ones noted in the IPCC report. Hausfather’s analysis now provides us with a range of potential exceedance dates for these two targets — and the fact that 1.5°C could be exceeded in six years (although unlikely) should be cause for concern.

The longer we continue to treat climate change as a long-term threat, the more it’ll sneak up on us with devastating consequences. If we want to have any chance of a sustainable future, then the time to act is now.