Time may be running out to curb climate change, scientists have warned – as new data reveals that the critical 1.5°C threshold has already been reached.
A new study has found that humans’ contribution to global warming was 1.49°C in 2023 and has now exceeded the limits of the Paris Agreement.
Most measurements for human-caused climate change use the mid-1800s as the benchmark for the ‘pre-industrial’ period.
However, using a novel method looking at gases trapped in ancient ice, researchers from Leeds and Lancaster Universities have pushed the benchmark time back to the 1700s.
Measuring from this period produces estimates for the human contribution to climate change which are 30 per cent higher than standard models.
This method also screens out the natural variations like the El Niño effect, showing exactly how much warming is due to human activity.
Co-author Professor Piers Forster, a climate physicist from the University of Leeds, says: ‘Our study shows that human societies have caused more than 1.5 degrees of long-term global warming.
‘However, this does not necessarily mean that the Paris Agreement’s 1.5 temperature guardrail is breached, as we find that 0.18°C of warming happened before global temperature records began’.
Scientists say that a new method for attributing human-caused climate change shows that the 1.5°C limit laid out in the Paris Agreement has already been passed
This comes after scientists from the Copernicus Climate Change Service (C3S) said that 2024 is now virtually certain to be the hottest year on record and the first year to exceed 1.5°C above the pre-industrial average
Since the global climate system is extremely complex, arriving at an accurate estimate of human’s contribution to climate change is a massive challenge.
However, it is also a vital problem to solve if policymakers are going to know how close they are to reaching climate targets.
Lead author Dr Andrew Jarvis, a climate scientist from Lancaster University, says: ‘Measuring human-caused global warming is a difficult task because it forces us to compare today’s temperature with what it was in pre-industrial times – we call this the pre-industrial baseline.
‘The closest we come to pre-industrial global temperature measurements are from the middle of the 1800’s.’
The Paris Agreement has locked its 1.5°C target to the pre-industrial period defined by the Intergovernmental Panel on Climate Change (IPCC) as 1850–1900.
However, Dr Jarvis explains that this is a relatively poor way of measuring humans’ contribution to warming the climate.
Dr Jarvis says: ‘Unsurprisingly, these data are somewhat patchy and the Industrial Revolution was well underway by then.’
Carbon levels in the atmosphere were already rising well into the period defined as pre-industrial, causing policymakers to underestimate the extent of global warming.
The researchers found that there was a surprisingly linear relationship between atmospheric CO2 and global temperatures. This allows them to calculate the human contribution to climate change (red) from CO2 measurements
To get around this issue, the researchers settled on a surprisingly simple solution.
Looking at gas bubbles trapped in ancient ice cores, the researchers worked out how much CO2 was present in the atmosphere going back to the year 13 AD.
To their shock, atmospheric CO2 and global temperature had a ‘linear’ relationship.
That means if you plotted a graph of global temperatures against the concentration of CO2 in the atmosphere the points would fall on a straight line.
Dr Jarvis told MailOnline: ‘This is about separating the measured warming into its “natural” and “human” components.’
It does this because the linear relation pulls out how much of the increase can be attributed to persistent increases in CO2, leaving behind natural variations.
If you were to look at the average from 10 years of temperature measurements there would be no way to know how much of the change was human-caused and how much was due to natural patterns like volcanic eruptions.
Additionally, since the average would include data from previous years it is likely to suggest that warming has been less severe than it is in reality.
By looking at air bubbles trapped in ancient ice cores the researchers were able to calculate how much CO2 was present in the atmosphere up to 2,000 years ago. Pictured: an ice core taken from the Antarctic
Researchers were able to estimate the CO2 levels in the period between 0 and 1700 AD. Using this period as a pre-industrial baseline produces estimates for human-caused global warming which are 30 per cent higher
Last month was the second hottest October on record, coming in just behind the record-breaking temperatures of 2023 and well beyond the 1.5°C threshold even compared to the 1850-1900 average
But by looking directly at human-caused climate change by measuring CO2 levels, we can now calculate the exact human contribution right up to the current month.
Currently, the IPCC puts human-induced contribution to global warming at 1.31°C, but with an uncertainty range of 1.10 to 1.60°C.
This suggests it isn’t clear whether the 1.5°C limit laid out in the Paris Agreement has been breached.
However, using their new methods, the researchers claim to show that this critical threshold has almost certainly been passed.
They compared the current climate against a pre-industrial baseline online of 1300-1700 when atmospheric CO2 was approximately 280 parts per million.
Through a simple calculation, they were then able to show that human-induced warming likely reached 1.49°C in 2023 and exceeded 1.5°C this year.
Since the Paris Agreement was settled using the 1850-1900 baseline, this does not technically mean that the limit has been surpassed.
However, the authors say their findings suggest passing the Paris Agreement’s targets is almost inevitable.
As world leaders prepare for COP29, the say it will be essential to have reliable and timely estimates for the human contribution to global warming like those provided by this new method
As temperatures rise more than 1.5°C above the pre-industrial average, scientists warn that extreme weather events like the flooding in Valencia will only become more likely. However, the researchers say it is not too late to mitigate the devastating effects of climate change
Professor Forster says: ‘Urgent actions can slow warming rates and push back the time of breaching the Paris 1.5 degree limit.
‘Although breaching the limit is now inevitable, delivering action commensurate with the noble Paris goal is more important than ever.’
Earlier this month, data collected by the Copernicus Climate Change Service (C3S) showed that 2024 was on track to become the first year to exceed 1.5°C above the pre-industrial average.
With the world now so close to passing its self-imposed limits, it is now more important than ever to know exactly where the climate stands in relation to the pre-industrial baseline.
This will be especially relevant as world leaders prepare to meet at COP29 amidst growing evidence that the 1.5-degree target is not feasible.
However, Dr Jarvis insists that their paper does not show that humanity is out of time to act.
Dr Jarvis says: ‘The impacts don’t evaporate simply because you are above a particular level of warming, they have to get progressively worse by definition.
‘So we will never run out of time to do something until we can no longer do anything.’
