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Humans are already causing long-term global warming of 1.5°C, according to new estimates

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New research published today in Nature Geoscience by Dr Andrew Jarvis of Lancaster University and Professor Piers Forster of the University of Leeds shows that humans have already contributed to global warming of 1.5°C, measured since the period just before the industrial revolution and the 2000s. This indicates that it may be causing the The beginning of large-scale carbon emissions.

The 2016 Paris Climate Agreement sets a long-term temperature goal of “limiting the rise in global temperatures to below 2°C, while continuing efforts to limit the rise to 1.5°C.” Since then, a global warming of 1.5°C has become the standard for determining whether climate change is progressing or not.

According to the Intergovernmental Panel on Climate Change (IPCC) recommended methodology, the anthropogenic contribution to global warming is currently estimated at 1.31°C, with uncertainties ranging from 1.10 to 1.60°C. This means that it is unclear from the estimates adopted by the IPCC whether the 1.5°C boundary has been breached.

Importantly, the method recommended by the IPCC uses temperature records from 1850 to 1900 as a “pre-industrial” baseline for calculations. They do so because this is when the first temperature records were taken, even though the exact way to measure global temperature rise has not been defined in climate change negotiations.

Using this same 1850-1900 baseline, Dr. Jarvis and Prof. Forster’s method reduces the uncertainty in current anthropogenic warming estimates by more than half, and when measured in this way, anthropogenic global warming This indicates that global warming will currently remain below 1.5°C. According to this indicator, at the current rate of warming, Paris’ 1.5°C guardrail will be exceeded within 10 years.

But Dr. Jarvis and Professor Forster go further. Their method moves the reference period for measuring global temperature changes back to before 1700 to more accurately estimate the true long-term contribution of humans to global warming.

The authors found that, when measured based on an earlier, more precise pre-industrial definition, the long-term human contribution to warming was 1.49°C ± 0.11°C in 2023; We found it to be over 1.5°C. This reveals almost 0.2°C of warming within the 1850-1900 baseline currently used to define warming.

Dr Jarvis, lead author of the study, said: “Measuring anthropogenic global warming is a difficult task because it requires comparing today’s temperatures to pre-industrial temperatures. The closest we can get to pre-industrial Earth temperature measurements are from the mid-1800s, but of course, these data are somewhat spotty; The Industrial Revolution was well underway.

“Thus, using these early temperature data as a baseline, as in traditional methods, not only ignores the warming that was already occurring, but also builds significant uncertainty into the warming estimates. ”

The new study instead uses CO2 records from air bubbles trapped in ice cores to establish a baseline of temperatures before 1700. These records date back thousands of years, long before the industrial revolution and the effects of anthropogenic carbon emissions. Scientists can use carbon dioxide records to anchor estimates of global warming. The reason is that they claim there is an overlooked relationship between carbon dioxide and carbon dioxide.

Humans are already causing long-term global warming of 1.5°C, according to new estimates

Estimated HIW. Credit: Nature Geoscience (2024). DOI: 10.1038/s41561-024-01580-5

“When you plot global temperature against atmospheric carbon dioxide concentration, both are surprisingly linear, much more linear than current theory predicts,” Dr Jarvis said. “This sentence shows not only how much the Earth has warmed since before the Industrial Revolution, but also how much of that warming is due to human activity.

“Climate is so unimaginably complex that it may not be so surprising that such a direct way to accurately measure the warming that humans are responsible for has been overlooked,” Jarvis said. the doctor added.

The scientists believe their new method is a strong candidate for measuring progress against the Paris 1.5° and 2.0° standards.

“Our method has many strengths. First, it directly addresses the question of how to establish a robust baseline for the pre-industrial era, but not for the period 1850-1900,” Dr. Jarvis said. The baseline also performs equally well. Second, it produces estimates of “anthropogenic warming that are at least 30% more reliable than current methods.”

“Finally, it is easy and quick to apply, meaning we can generate warming estimates as soon as CO2 and temperature data are available, without having to rerun complex climate models. This also means that the results are transparent, making it much easier to communicate with non-experts.

Professor Forster, a co-author of the study, said: “Our research shows that human society is causing global warming of more than 1.5 degrees Celsius over the long term. However, this does not necessarily mean that the Paris Agreement temperature “It doesn’t mean we’re breaking through the 1.5 degree guardrail.” Because it turns out that 0.18°C of warming had occurred before global temperature records began, and this baked-in warming would not have been factored into the Paris Agreement.

“Policymakers set the Paris temperature target to limit the devastating climate impacts that many around the world are already experiencing. It is clear that we need to do more. Rather, each country was not commensurate with its efforts.

“Urgent action could slow the rate of warming and delay the timing of breaking the Paris 1.5°C limit. Breaking the limit is no longer inevitable, but action must be taken to meet the noble Paris goal. is more important than ever,” he added.

Although useful for measuring the current level of human-induced global warming, researchers caution against using this method to predict future warming.

Dr Jarvis said: “Atmospheric CO2 has so far been responsible for most of the anthropogenic warming, but it is not the only cause, especially in the face of climate change. We know that these factors are likely to become increasingly important in the future.” This means we need to keep an eye on our analysis, but fortunately any deviation from the current linear regime can be a valuable warning against such changes. ”

Further information: Andrew Jarvis et al. Estimating anthropogenic warming from linear temperature and atmospheric CO2 relationships, Nature Geoscience (2024). DOI: 10.1038/s41561-024-01580-5. www.nature.com/articles/s41561-024-01580-5

Provided by Lancaster University

Citation: New estimates (November 11, 2024) obtained from https://phys.org/news/2024-11-humans-15c-term- show that humans have already causing long-term global warming of 1.5°C. global.html

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