The Earth has been warmed by 1.5°C due to human activity since 1700

Humankind has already caused around 1.5 degrees Celsius of warming since the start of the industrial revolution, according to new estimates based on temperature data collected from air bubbles trapped in ice.

Measuring anthropogenic global warming typically uses the period from 1850 to 1900 as a pre-industrial baseline. This is because this is the time when temperature records began. 2024 is almost certain to be the first year in which average temperatures rise by more than 1.5 degrees Celsius above this baseline. This single-year data is influenced by naturally occurring factors such as the strong El Niño event, which has pushed up global temperatures.

When you remove this natural variation, scientists believe humans alone have caused 1.31°C of warming since the Industrial Revolution. But by 1850, the Industrial Revolution was already underway, and fossil fuel-powered engines were in use around the world.

Andrew Jarvis Lancaster University and Piers Foster Researchers at the University of Leeds, both in the UK, set out to establish a new pre-industrial baseline using data taken from Antarctic ice core samples. The pair analyzed the composition of air bubbles trapped in ice cores to establish atmospheric carbon dioxide concentrations from 13 AD to 1700, before humans significantly influenced atmospheric temperatures. This CO2 data was then used to establish the average global temperature over the same period, assuming a linear relationship between CO2 and temperature increases.

Using this new pre-1700 baseline, humanity has caused 1.49°C of warming by 2023, meaning the 1.5°C level has been “effectively reached,” the researchers say in their findings. It is written in the paper to be reported. “We have provided a new, scientifically defensible way to derive a pre-industrial baseline for measuring global warming,” Jarvis told reporters at a press conference.

Jarvis said the new method would also help reduce the uncertainty in temperature estimates based on the current 1850-1900 baseline used by the Intergovernmental Panel on Climate Change. Using ice core data to establish a baseline between 1850 and 1900, the researchers say humans caused 1.31°C of warming. This is consistent with existing median estimates, but the range of uncertainty is significantly reduced, the researchers note.

“The problem with just looking at surface temperature observations is that the further back in time you go, the more uncertain those observations become,” Forster says. “We are now much more confident than before that the current temperature is around 1.3°C.”

Jarvis and Forster hope their new method will be adopted by scientists and policymakers as the primary way to judge humanity's progress against global climate goals. “I think there is still room in the policy and scientific communities to rethink the pre-industrial baseline,” Jarvis said. “We know that the estimates for 1850 to 1900 incorporate warming, simply because that was not the beginning of the industrial revolution. We provide a way to operate from a secure baseline.”

However, new methods may not be future-proof. The linear relationship between CO2 concentrations and global temperatures is likely to break down as the climate changes. For example, if a so-called tipping point is triggered in the Earth system that triggers a series of warming events.

The new methods won't change the effects of climate change that are felt on the ground, Forster said. “The impact on human life from Spain and the hurricanes we are experiencing today is exactly the same whether you call it 1.3°C above pre-industrial levels or 1.5°C above pre-industrial levels. is” . Influence is influence. ”

Richard Betts The Met Office, the UK's meteorological agency, said the new method “provides a clear and easy way to provide an up-to-date estimate of the current level of anthropogenic global warming”. Part of the reason is that it can produce “real-time” estimates of human-induced warming, rather than relying on 10-year moving averages as current estimates do.

He said the approach could help provide policymakers with a more up-to-date picture of current levels of warming, but changing the baseline used in the assessment would be an “objective” for climate action. It warned that it could be considered as “moving.'' “Even without changing the baseline, it is clear that current warming is much closer to 1.5°C than expected using older 10-year averages,” he says .