Global warming is already on the verge of crossing the 1.5°C threshold
The planet is likely to warm up by two degrees Celsius by 2050, even under a low-emission scenario, suggesting that we may fail to uphold the Paris Agreement, according to a new study.
The world has recorded a 1.1°C rise in temperature compared with the average in 1850-1900. The Paris Agreement aims to limit the rise to below 2°C while pursuing efforts to limit the increase to 1.5°C.
The findings of the research, published in Proceedings of the National Academy of Sciences on January 30, 2023, contradicted projections from the Intergovernmental Panel on Climate Change (IPCC). IPCC predicted that the world will likely warm up by 2°C by 2050 only under a high-emission scenario.
The researchers from Stanford University and Colorado State University wrote:
While our main analysis suggests a higher likelihood that 2°C will be reached under the low scenario compared with the IPCC AR6 (Sixth Assessment Report) synthesis assessment, it does not rule out the possibility of avoiding 2°C if the low scenario is achieved.
These thresholds, according to them, are relevant for a broad range of climate risks — such as impacts on human health, economic growth, crop yields, coastal and small island communities, terrestrial and marine ecosystems, as well as the frequency, intensity and cost of extreme climate events.
For example, limiting warming to 1.5°C would reduce the number of people frequently exposed to extreme heatwaves by about 420 million.
It could also reduce the probability of drought and risks related to water availability, according to the US National Aeronautics and Space Administration (NASA).
The researchers used artificial intelligence called artificial neural networks (ANN) to predict the time for reaching the 1.5 °C and 2°C thresholds.
The team trained the ANN using climate model simulations. Then, they provided historical temperature observations as input to the ANN to make future predictions. Their findings showed that the world will likely reach the 1.5°C threshold between 2033 and 2035.
This is consistent with previous assessments. The IPCC estimated that the 1.5°C threshold could be attained as early as the 2030s under all emission scenarios.
“The fact that our central estimate for the time until 1.5°C lies between 2033 and 2035 in the high, intermediate and low forcing scenarios confirms that global warming is already on the verge of crossing the 1.5°C threshold, even if the climate forcing pathway is substantially reduced in the near term,” the researchers wrote in their study.
A 2021 report warned that the probability of temporarily exceeding the 1.5°C threshold has increased by nearly 50 per cent from 2022-2026.
The new findings projected that the world could touch 2°C by 2050 under the high-emission scenario, 2049 and 2054 in the intermediate and low-emission scenarios, respectively.
In contrast, the IPCC estimated the likelihood of touching 2°C of global warming during the mid-21st century is high under a high-emission scenario.
But low and extremely low warming scenarios are “unlikely and extremely unlikely to cause 2°C of warming by the end of the 21st century,” the IPCC projections read.
“Even with substantial greenhouse gas mitigation, there is still a possibility of failing to achieve the UN-mandated Paris goal of holding global warming well below the 2°C threshold,” the study read.
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