A recent report indicates that human-generated fossil fuel emissions are pushing the planet towards a critical climate threshold much faster than anticipated.
Rather than breaching the 1.5°C limit by the mid-2030s, as previously estimated, researchers suggest that this threshold may be crossed as early as 2029. The primary contributing factor is identified as the record-breaking average emissions of carbon dioxide observed over the last three years.
In the aftermath of a year marked by unprecedented heat, exemplified by July becoming the hottest month on record, projections for the entirety of 2023 anticipate temperatures hovering around 1.5°C above the pre-industrial level. This baseline corresponds to conditions before widespread use of coal, oil, and gas commenced around 1850.
While this could be considered an isolated incident, scientists express concerns that cumulative greenhouse gas emissions may trap temperatures at this level for an extended period.
Scientists emphasise that escalating levels of carbon dioxide and other greenhouse gases in the atmosphere lead to temperature increases by trapping Earth’s radiation, resulting in a greenhouse effect
. The 1.5°C target is a pivotal component of the commitments made by political leaders when signing the Paris climate agreement in 2015. The agreement aimed to limit the rise in global temperatures to “well below” 2°C, with concerted efforts to stay below a 1.5°C increase this century.
The 1.5°C figure is particularly crucial for developing nations and small island states, as surpassing this threshold could lead to rising sea levels engulfing their homes. To estimate the time required for the world to reach this critical figure, scientists devised a carbon “budget” representing the amount that can still be emitted before breaching the threshold.
Earlier this year, the Intergovernmental Panel on Climate Change (IPCC) projected that the world could emit only another 500 billion tonnes of carbon to have a 50% chance of staying below the 1.5°C target. Given the current annual emissions of around 40 billion tonnes, the IPCC anticipated that this threshold would be permanently breached by the mid-2020s.
However, the new analysis suggests an even more imminent breach of the 1.5°C limit. Researchers noted that the IPCC’s data only extended to 2020, so they adjusted the budget downwards to account for carbon emissions over the last three years. Additionally, they reevaluated the role of non-carbon factors, such as aerosols—sooty particles arising mainly from fossil fuel combustion.
Aerosols contribute significantly to air pollution but paradoxically cool the atmosphere by reflecting sunlight back into space. The latest research reveals that these aerosols have a more substantial cooling impact than previously understood.
As efforts to reduce air pollution and minimise the use of highly polluting fossil fuels progress, the decline in aerosols in the atmosphere accelerates temperature increases beyond prior projections.
The researchers assert that this updated understanding of aerosols removes 100 billion tonnes from the remaining 1.5°C budget. When combined with additional carbon emissions and minor adjustments, this reduces the total remaining budget to 250 billion tonnes.
“The window to avoid 1.5C of warming is shrinking, because we continue to emit and because of our improved understanding of atmospheric physics,” said lead author Dr Robin Lamboll from Imperial College London.
“We now estimate that we can only afford to release about six years worth of current emissions before we are likely to exceed this key Paris agreement reference point.”
Consequently, the researchers argue that to avert crossing the 1.5°C threshold, global carbon dioxide emissions must reach net zero by 2034, considerably earlier than the current expectation of 2050.
“There are no socio-technical scenarios globally available in the scientific literature that would support that that is actually possible, or even describe how that would be possible,” said Prof Joeri Rogelj, also from Imperial College London.
“So that really shows that having a 50% or higher likelihood that we limit warming to 1.5C, irrespective of how much political action and policy action there is, is currently out of the window.”
“That doesn’t mean that we’re spinning out of control to three or four degrees. But it does mean that the best estimates suggest that we will be above 1.5C of global warming.”
Professor Niklas Höhne, Director of the New Climate Institute in Cologne, describes the study as an “emergency mode” call to swiftly reduce emissions.
“It shows that every ton of carbon dioxide saved is all the more important because the budget is so extremely tight. And even if the multi-year average temperature increase exceeds 1.5 degrees, it’s good to have saved as many emissions as possible beforehand, because every ton saved leads to less global temperature increase and therefore less damage,” he said.
The findings underscore the critical need for global cooperation to address climate change promptly and effectively.
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