Global warming has accelerated significantly over the past decade, with Earth’s temperature rising faster than at any time since modern records began in 1880. A study by the Potsdam Institute for Climate Impact Research (PIK) provides the first statistically significant evidence that the rate of warming has increased since around 2015, even after accounting for natural factors that can temporarily raise or lower global temperatures.
Evidence of an accelerating warming trend
The researchers found that Earth has warmed by about 0.35°C per decade over the past 10 years, although the precise estimate varies among temperature datasets. That rate is almost twice the average increase of just under 0.2°C per decade recorded between 1970 and 2015.
The findings indicate that global temperatures are not merely continuing to rise; the rate of increase has also accelerated.
“We are now able to demonstrate that global warming has been accelerating statistically significantly since about 2015,” said Grant Foster, a US statistician and co-author of the study published in Geophysical Research Letters.
Detecting a change in the underlying pace of global warming is more difficult than simply comparing annual temperatures. Natural climate patterns can temporarily make Earth warmer or cooler, obscuring longer-term trends.
For example, El Niño can temporarily increase global temperatures by releasing heat from the tropical Pacific Ocean into the atmosphere. Volcanic eruptions can have the opposite effect, as particles released into the atmosphere reflect sunlight back into space. Changes in solar activity can also alter the amount of energy Earth receives from the Sun.
These influences create fluctuations in the temperature record, making it difficult to determine whether the underlying warming trend is accelerating.
Adjusting for natural climate influences
To address this problem, the researchers mathematically adjusted temperature observations to account for these known effects. This allowed them to examine long-term warming trends more clearly, without short-term fluctuations masking changes in the rate of warming.
“By removing known natural influences from observational data, we reduce the ‘noise’ and make the underlying long-term warming signal more visible,” Foster said.
The team analyzed five major global temperature datasets: NASA, NOAA, HadCRUT, Berkeley Earth and ERA5. These widely used records combine observational data, and in some cases additional atmospheric data, to track changes in Earth’s temperature.
The results were consistent across the datasets. Regardless of the dataset or statistical method used, the researchers found strong evidence that global warming is accelerating.
“The adjusted data show an acceleration in global warming since 2015 with over 98 percent statistical certainty, are consistent across all datasets examined and are independent of the analysis method chosen,” said Stefan Rahmstorf, a researcher at PIK and the study’s lead author.
In statistical terms, this means the evidence for a change in the warming trend is strong enough to distinguish it from normal fluctuations in the temperature record with more than 98 percent confidence.
2023 and 2024 remain the hottest years after adjustment
One key question was whether the exceptionally high temperatures recorded in 2023 and 2024 made the recent warming trend appear steeper than it actually was.
Both years were unusually hot, partly because of natural influences including El Niño and an increase in solar activity known as solar maximum. During solar maximum, the Sun reaches the most active phase of its approximately 11-year cycle.
After accounting for these effects, the researchers found that adjusted temperatures for 2023 and 2024 were slightly lower than the original observations. Nevertheless, both years remained the warmest since instrumental temperature records began.
The analysis also found signs of accelerated warming as early as 2013 or 2014 in all five datasets. This suggests that the result was not simply caused by unusually high temperatures in the most recent years.
Two statistical methods support the finding
To determine whether the rate of warming had changed since the 1970s, the researchers used two statistical methods.
The first, quadratic trend analysis, looks for curved patterns in the temperature record that indicate warming is accelerating rather than continuing at a constant rate.
The second, a piecewise linear model, compares warming trends over different periods and identifies when the rate of warming appears to have changed. Unlike methods that assume acceleration began in a particular year, this approach estimates the most likely timing of the shift from the data.
Both methods supported the conclusion that global warming is accelerating significantly.
What is driving the acceleration?
Although the study provides strong statistical evidence that global warming is accelerating, it was not designed to determine precisely why the acceleration is occurring.
The researchers emphasize that detecting a change in the rate of warming is different from identifying the physical processes responsible for it.
However, the observed acceleration is consistent with what current climate models can produce. These models use established physical principles to simulate how Earth’s atmosphere, oceans, ice and land respond to changes in the climate system.
The findings therefore do not suggest that climate models are fundamentally unable to represent the recent increase in warming. Instead, they provide additional observational evidence that the pace of climate change can vary substantially over time.
Implications for the Paris Agreement
The acceleration has important implications for international efforts to limit global warming.
Under the Paris Agreement, countries agreed to pursue measures to limit the long-term increase in global temperatures to 1.5°C above pre-industrial levels. This threshold refers to sustained global warming, rather than a single unusually hot year.
Researchers have warned that if the warming rate measured over the past decade continues, the planet could exceed that threshold sooner and for a longer period than previously expected.
“If the rate of warming of the past decade continues, we will exceed the long-term limit of 1.5 degrees Celsius under the Paris Agreement by 2030,” Rahmstorf said.
He added that “how quickly the planet continues to warm will ultimately depend on how quickly we can reduce global carbon dioxide emissions to zero.”
The study highlights that Earth’s temperature is not only rising but has been rising substantially faster in recent years than in previous decades. Whether this rapid pace continues will have a major effect on how quickly the world reaches critical climate thresholds.
Source: www.sciencedaily.com