Global Warming Rate Nearly Doubles: Paris Agreement Limit at Risk Sooner

A new study published in Geophysical Research Letters reports a significant acceleration in the rate of human-caused global warming over the past decade. Researchers found that after accounting for natural climate variations, the planet's warming rate has nearly doubled since 2015, potentially leading to the breach of the Paris Agreement's 1.5 degrees Celsius limit before 2030.

Study Findings

The study indicates that the planet's warming rate has accelerated significantly over the past decade, reaching approximately 0.35°C to 0.4°C per decade since 2015. This contrasts with an average warming rate of just under 0.2°C per decade observed between 1970 and 2015. This recent rate is reported as the highest decadal warming rate recorded since instrumental records began in 1880.

Study authors Stefan Rahmstorf and Grant Foster, from institutions including the Potsdam Institute for Climate Impact Research, noted:

"This paper is considered the first to demonstrate a 'statistically significant acceleration' in the underlying human-driven warming trend."

Supporting observations, such as rising ocean heat content and an increasing Earth’s energy imbalance, are also highlighted by the study authors.

Methodology

Researchers utilized a statistical technique to remove the influence of natural factors, including the El Niño-Southern Oscillation (ENSO), volcanic activity, and solar variation, from five established global average surface temperature datasets (NASA, NOAA, HadCRUT5, Berkeley Earth, and Copernicus ERA5). This approach aimed to isolate the long-term human-driven warming signal.

Removing natural variability made recent years appear slightly cooler but confirmed 2023 and 2024 as the two warmest years on record.

Two statistical approaches—a quadratic trend analysis and identifying change points—were applied to test for a statistically significant acceleration. Both tests confirmed a warming acceleration with over 98% confidence across all five datasets after natural variability was accounted for. The study's method for removing natural variability is described as empirically based, approximate, and imperfect.

Implications for Climate Targets

If the accelerated warming rate observed in the study persists, the Paris Agreement's 1.5°C threshold is projected to be breached between 2026 and 2029. Current projections, without accounting for this acceleration, typically estimate the limit to be surpassed in the 2030s.

Study co-author Stefan Rahmstorf stated:

"If the warming rate of the past 10 years continues, it would lead to a long-term exceedance of the 1.5°C limit before 2030."

The World Meteorological Organization has confirmed that the past three years constitute the hottest three-year period on record. Human-induced carbon pollution has heated the planet by approximately 1.4°C since preindustrial levels. Scientists suggest that 1.5°C-2°C of global heating could potentially trigger "tipping points" over decades and centuries, with increased catastrophe chances at higher warming levels. The rate of future warming will ultimately depend on the pace at which global CO₂ emissions from fossil fuels are reduced to zero.

Potential Contributing Factors

While the study focused on the statistical acceleration rather than its specific causes, a probable explanation suggested by some researchers involves stricter regulations on shipping emissions implemented since 2020. Ocean-going vessels release pollutants that, while harmful to human health, also contribute to the formation of clouds that reflect sunlight, providing a cooling effect. The reduction in these emissions may have contributed to the observed increase in warming. If this hypothesis is accurate, the current elevated warming rate might be temporary, as no similar significant reduction in atmospheric aerosols is widely anticipated in the near future.

Expert Perspectives

Katharine Hayhoe, an atmospheric scientist at Texas Tech University not involved in the research, described the study's methodology as "careful and meticulous."

Claudie Beaulieu, an ocean and Earth sciences assistant professor at the University of California, Santa Cruz, noted that all five datasets showed an acceleration, supporting the study's accuracy. She also emphasized the importance of continued monitoring to determine if this is a lasting shift or a transient feature of natural variability.

Zeke Hausfather, a climate scientist not involved in the study, acknowledged widespread agreement on a detectable acceleration in warming in recent years. He noted that the extent to which additional warming over the past decade is a forced response versus unforced variability remains unclear. A previous study co-authored by Hausfather also identified an acceleration, reporting a slightly slower rate of 0.27°C per decade.

Conversely, Michael Mann, a professor of Earth and environmental science at the University of Pennsylvania, expressed a differing view, stating there is no evidence of accelerated warming over the past decade. Mann attributes increasing warming since the 1970s to reduced aerosol pollution and recent heat spikes to El Niño events, maintaining that the planet is warming at a roughly constant rate. Study authors noted that their work provides statistical proof of acceleration, distinguishing it from other analyses. Another study in 2024, which did not remove natural drivers, found that a recent surge in warming was not yet statistically detectable.