Earth possibly closer to global warming limit than first thought
Monique Merrill
(CN) — In 2015, world leaders gathered in Paris to establish an international treaty addressing climate change with the goal of capping global warming at 1.5 degrees Celsius as compared to pre-industrial levels. Now, research shows the Earth may be more quickly approaching that limit than previously estimated, depending on the time period considered “pre-industrial.”
In a study published Monday in Nature Geoscience, researchers Andrew Jarvis and Piers Forster established a new approach to assessing human-induced warming. The results indicate a linear relationship between carbon dioxide and temperature increase — when carbon emissions increase, so does the temperature.
Under the Paris Agreement, world leaders agreed to adopt strategies to prevent global temperatures from increasing over 1.5 degrees Celsius, or 34.7 degrees Fahrenheit, compared to global temperature anomaly data from 1850-1900. Although this pre-industrial period was set as the baseline, atmospheric carbon dioxide levels and emissions had already been rising before that period.
Jarvis and Forster decided to expand that analysis by 2,000 years and reassessed the relationship between the Earth’s surface temperatures and atmospheric carbon dioxide trends by using Antarctic ice core records combined with temperature anomaly data. Looking at data from 1850 to 2023, they found a linear relationship between temperature increase and carbon dioxide.
“There is not a precise technical definition for the way you determine the temperature increase within the Paris Agreement,” Forster, a professor at the University of Leeds, said in a press briefing.
Jarvis and Foster argue that, while there are other factors influencing temperature trends since 1850, the linear relationship for the interval is adequate to assess how much humans have impacted global warming.
“This method radically improves the certainty with which can estimate the human-induced warming, which is critical for our climate negotiations,” Jarvis, of Lancaster University, said in a press briefing.
Using the linear relationship, the researchers estimated modern warming against a pre-industrial baseline from 13 to 1700 CE and calculated that, in 2023, human-induced warming reached 1.49 degrees Celsius — just one-hundredth of a degree Celsius below the 1.5-degree Celsius warming limit.
When applying the method and using 1850 to 1900 CE as a baseline, the researchers found that their human-induced warming estimates were up to 30% more certain estimates based on other models, which they attributed to the efficiency of the regression framework. The authors argue that uncertain temperature records and already warming conditions in 1850 to 1900 make it a less productive baseline to measure climate change.
The authors' intent is to have their model widely adopted, and to encourage the scientific community to consider redefining the time period it defines as pre-industrial.
“We know that there’s warming baked into the 1850 to 1900 estimate, simply because that is not the beginning of the Industrial Revolution,” Jarvis said.
Jarvis said he developed the new method based on methods already used to set carbon budgets in an effort to teach people about the fundamentals of climate change so more can understand.
“To do so I needed something that was direct, transparent and could be taught to nonspecialists, really,” Jarvis said.
The resulting method is simple enough that anyone can buy into the process, Jarvis said.
“I’ve sat in the pub, and I’ve been able to draw this on a napkin for farmers, and for accountants and IT consultants and teachers, like myself, and they all nod and pretty much understand these things,” Jarvis said.
Jarvis and Forster acknowledged that though a linear relationship between carbon dioxide and temperature change has been observed to this point, it is possible that may change in the future as additional climate variables intensify.