Humanity has already caused an increase in global temperature of 1.5°C, according to a new study published in the journal Nature Geoscience. The estimate evaluates the impact of man from a time before the pre-industrial era and before the beginning of large-scale carbon emissions.
The project was led by Andrew Jarvis, a PhD at Lancaster University, and Piers Forster, a professor at the University of Leeds. It is based on a new methodology that uses the period before the year 1700 as a reference. The authors concluded that the human contribution to the long-term increase in temperatures was 1.49°C in 2023 over the proposed interval, with a margin of error of ±0.11°C. The calculation reveals a variation of almost 0.2°C compared to what was believed until now.
The work explains that the 1.5°C threshold established in the Paris Agreement has become the criterion to measure the progress of climate change. The limit was established considering the variations in temperature documented between 1850 and 1900 (the pre-industrial era). Under these standards, it has been defined that human-caused warming is currently 1.3°C, with a margin of uncertainty between 1.1 and 1.6°C, according to the Intergovernmental Panel on Climate Change (IPCC). .
The evaluation technique proposed by Jarvis and Forster implemented on the IPCC canons reduces the range of imprecision by half. The report notes that this shows that global warming caused by humanity is now below the limit set in the global environmental treaty, but could be surpassed in less than a decade if contemporary trends continue.
“Our study shows that human societies have caused more than 1.5°C of long-term global warming. However, it does not necessarily mean that the Paris Agreement limit has been violated. We found that there was an increase in temperatures of 0.18 °C before that would not have been taken into account in the international convention,” explains Forster.
The challenge of measuring global warming
Researchers recognize that measuring the historical increase in the planet’s temperatures is a difficult task because the first accurate data date back to the mid-19th century. Making projections on this basis “not only ignores the warming that was already underway, but also introduces significant uncertainty into estimates of the phenomenon,” says Jarvis.
The new work’s criteria use records of carbon dioxide (CO2) trapped in air bubbles within the cores of ice sheets. In this way, it was possible to establish a temperature baseline prior to the 17th century and counteract the deficiency.
“If you compare global temperatures with the concentration of CO2 in the atmosphere, both indicators show up on a remarkably straight line, much straighter than current theory would predict. The above indicates not only how much the Earth has warmed since pre-industrial times, but also how much of that warming can be attributed to human activity,” the authors emphasize.
The researchers are confident in the strength of their methodology. They reiterate that it allows the problems to be addressed to establish a solid reference period older and before industrialization. They claim that it has the potential to deliver estimates “at least 30% safer than current procedures.” They add that climate change assessments can be more immediate. “It is feasible to generate assessments as soon as the CO2 data and temperature variations are available,” they say.
Specialists believe that their proposal can become a methodological tool that responds to the criteria established in the Paris Agreement. They warn that it is not entirely effective in making a forecast about the progress of the crisis, since CO2 emissions are not the only indicator of human impact on global temperature.
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