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The world’s carbon budget is rapidly diminishing. A new assessment revealed that 50 per cent of the remaining carbon budget will likely be exhausted in just over three years if the global carbon dioxide (CO2) emissions persist at 2024 levels.
The remaining carbon budget is the net amount of carbon dioxide humans can still emit without exceeding a 1.5-degree Celsius global warming limit.
The remaining carbon budget for 1.5°C, 1.6°C, 1.7°C and 2°C is 130 gigatonnes of carbon dioxide (Gt CO2), 310 Gt CO2, 490 Gt CO2 and 1050 Gt CO2, respectively.
These findings are a part of the Indicators of Global Climate Change (IGCC), which provides policymakers with annual updates on the latest scientific understanding of the state of selected critical indicators of the climate system.
The study also estimated that human-induced warming for 2024 reached 1.36°C. The rate of warming has been particularly high, with a 0.27°C increase per decade between 2015 and 2024. This suggests that continued emissions at current levels could lead to human-induced global warming reaching 1.5°C in around five years.
The high rate of warming, according to the analysis, is driven by two factors. The first is a combination of greenhouse gas emissions, which reached an all-time high of 53.6 Gt CO2e per year over the last decade (2014–2023).
The second is the reduction in strength of aerosol cooling. Aerosols are small particles that can cool the atmosphere. When fossil fuel is burned, they release sulphate particles and sulphur dioxide, which can reflect sunlight and make the atmosphere cooler. However, Europe’s air pollutant regulations have led to a decrease in atmospheric aerosols, thereby diminishing their cooling effect.
The analysis highlighted that the average decadal greenhouse gas emissions have increased steadily since the 1970s, driven primarily by increasing CO2 emissions from fossil fuel and industry, but also rising emissions of methane and nitrous oxide.
The analysis “shows that global greenhouse gas emissions are at a long-term high, yet there are signs that their rate of increase has slowed,” the paper read.
Also since the 1970s, there has been a persistent imbalance in the Earth energy system or Earth energy imbalance (EEI), a global warming indicator that provides a measure of accumulated surplus energy (heating) in the climate system.
The EEI value during 1975–1994 was estimated to be 0.43 watts per square metre (W / m2), which is more than doubled to 0.89 W / m2 during 2005–2024.
Oceans are bearing the brunt of this imbalance, as they absorb more than 90 per cent of anthropogenic heat. The study highlighted a robust increase in ocean warming, particularly at depths of 700–2000 metres below the surface, observed since the 1990s.
This change in global energy inventory drives global mean sea level rise through two mechanisms: The thermal expansion of water as it warms and the increased addition of water from land-based ice reservoirs like glaciers and ice sheets.
The global mean sea level has risen by 26.1 millimetres (mm) between 2019 and 2024. The total global mean sea-level rise is estimated to be 228 mm for the period 1901–2024, averaging an annual rise of 1.85 mm.
“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 in around five years in the absence of cooling from major volcanic eruptions,” the researchers wrote in the analysis.