‘Human-induced global warming increasing at unprecedented rate’
DELHI: Human-induced warming has been increasing at a rate that is unprecedented in the instrumental record, reaching 0.26 degree C per decade over 2014–2023, a pre-print paper by a diverse group of climate scientists has said.
It has also flagged on Wednesday that the 1.5°C compatible carbon budget is very small and shrinking faster than earlier understood, due to continuing high global CO2 emissions.
The instrumental record is the period for which there is data on temperatures available from direct records (and not from reconstructions), and, at the global level, it is widely accepted to start in 1850.
The paper has compared how key climate indicators have changed since Intergovernmental Panel on Climate Change’s (IPCC) AR6 Working Group 1 report published in 2021, which used data up to 2019.
The indicators show that, for the 2014-2023 decade, observed warming (global mean temperature) was 1.19 degrees C on average of which nearly all of it was human-induced. In comparison, human-induced warming as per IPCC AR6 report was 1.09 degrees C of which 1.07 degree C was human induced.
For a single year average, human-induced warming reached 1.31°C in 2023 relative to 1850–1900. This is below the 2023 observed global mean temperature record of 1.43°C, indicating a substantial contribution of internal variability in the 2023 record. “Human-induced warming has been increasing at rate that is unprecedented in the instrumental record, reaching 0.26 degree C per decade over 2014–2023. This high rate of warming is caused by a combination of greenhouse gas emissions being at an all-time high of around 54 GtCO2e per year over the last decade, as well as reductions in the strength of aerosol cooling,” the paper, to be published in Earth System Science Data (ESSD), a Copernicus publication, concluded.
The authors clarified that there is evidence that the rate of increase in CO2 emissions over the last decade has slowed compared to the 2000s. The paper has been put together by scientists from Priestley Centre, University of Leeds; Environmental Change Institute, University of Oxford, UK; Centre for Environmental Policy, Imperial College London, UK; European Centre for Medium-Range Weather Forecasts, Bonn, Germany; NASA, Langley Research Center among 57 authors and is available on the ESSD website.
Most importantly, the paper has flagged that the remaining carbon budget for meeting Paris Agreement’s 1.5 degrees C goal, with a 50% likelihood, has reduced from 500 GtCO2 at the end of 2020 to 150 GtCO2 at the start of 2024 due to continuing high CO2 emissions globally.
“Note that the 50 % RCB is expected to be exhausted a few years before the 1.5 °C global warming level is reached due to the way it factors future warming from non-CO2 emissions into its estimate,” the paper said.
The IPCC AR6 provided an assessment of human influence on key indicators of the state of climate based on data up to year 2019. But the next IPCC AR7 report is due towards the end of the decade, around 2028.
“Given the speed of recent change, and the need for updated climate knowledge to inform evidence-based decision-making, the Indicators of Global Climate Change was initiated to provide policymakers with annual updates of the latest scientific understanding on the state of selected critical indicators of the climate system and of human influence,” the paper said. The team had released an assessment last year also based on data up to 2022.
“This is a critical decade: human-induced global warming rates are at their highest historical level, and 1.5 °C global warming might be expected to be reached or exceeded within the next 10 years in the absence of cooling from major volcanic eruptions. Yet this is also the decade that global greenhouse gas emissions could be expected to peak and begin to substantially decline,” the paper added.
“The paper clearly says the rate at which temperatures are increasing is unprecedented and alarming. Most importantly most of the warming is due to human influences. Natural variability has little role to play. In my feeling things are going out of control. We need to accelerate our climate action and prepare solid road map. We cannot continue to sit in isolation and blame each other,” said M Rajeevan, climate scientist and former secretary, ministry of earth sciences.