New method finds human-caused warming is about to reach the limit set by the Paris climate agreement.
Human-induced global warming may be approaching a critical climate threshold more rapidly than previously estimated. A recent study of Antarctic ice cores indicates that, as of 2023, the increase in temperature attributed to human activities has reached 1.49 °C above pre-industrial levels.
In 2015, nearly all nations committed to the Paris climate agreement, a legally binding accord aimed at limiting global temperature rise to below 1.5 °C above pre-industrial levels in order to mitigate the effects of climate change.
The Intergovernmental Panel on Climate Change (IPCC) currently estimates that human-induced warming is approximately 1.31 °C. However, the IPCC does not monitor annual temperature changes; rather, it assesses temperature averages over several decades, which results in its figures lagging behind actual current temperatures. The organization uses the average temperature from 1850 to 1900 as its reference point for ‘pre-industrial’ levels.
It is important to note that carbon dioxide concentrations and temperatures began to rise well before 1850, indicating that the conventional 1850–1900 baseline may not provide a comprehensive view. This raises concerns that existing methods for estimating global temperature changes, which depend on climate models and statistical analyses, may be underestimating the extent of human-induced warming, according to Andrew Jarvis, a climate scientist at Lancaster University, UK, and co-author of the study.
Global warming : – Frozen record
To tackle this issue, Jarvis and his colleague Piers Forster, a climate scientist at the University of Leeds, UK, utilized Antarctic ice-core data that document atmospheric CO2 levels over the last 2,000 years. This data enabled the researchers to establish a pre-industrial baseline from AD 13 to 1700, a timeframe during which CO2 levels remained approximately 280 parts per million and exhibited relative stability. They integrated this information with global temperature data spanning from 1850 to 2023 to determine the extent of warming from the baseline in each year of the twenty-first century.
Their findings revealed that by 2023, CO2 levels had risen by 142 parts per million above the pre-1700 baseline, signifying that human-induced warming had reached 1.49 °C. When Jarvis and Forster adjusted their baseline to the conventional 1850–1900 period, they calculated a temperature increase of 1.31 °C. This indicates that the more recent baseline does not adequately reflect the pre-industrial warming that was already in progress prior to 1850. Alternative methods for assessing global temperature change, such as those involving long-lived marine sponges, suggest that warming may have exceeded 1.50 °C.
Additionally, they discovered that temperature-change estimates derived from their pre-1700s baseline were approximately 30% more reliable than those obtained through standard methodologies.
This approach is deemed “important and useful” as it provides a relatively swift and straightforward means to calculate near-real-time estimates of human-induced warming without depending on models or statistical techniques that may introduce uncertainties, according to Richard Betts, a climate scientist at the University of Exeter, UK. “We need immediate information to inform urgent responses,” he asserts.
