Global warming is happening, but not getting worse statistically, new study finds

Given the record number of heatwaves around the world in recent years, an international team of researchers, including a statistician from Lancaster University, investigated whether the rate of global warming has increased significantly, or “increased.” , over the last half century. statistically detectable rates.

The new study, published October 14 in the journal Earth and Environment Communicationsand led by scientists at UC Santa Cruz in the United States, confirms the broad consensus that the planet is warming, but at a statistically constant rate – not at a sufficiently accelerated rate that could be statistically defined as a surge.

Recent years have seen record temperatures and heatwaves globally: data shows that 2023 was the hottest year since global records began in 1850 – by far – and that the 10 The hottest years in history have all occurred within the last decade (2014-2023).

Global average surface temperature, by NOAA

These record temperatures have sparked discussion and debate about whether the pace of global warming has accelerated, with some saying it has accelerated over the past 15 years. However, the team’s results demonstrate a lack of statistical evidence of an increase in the rate of warming that could be defined as a surge.

“We’ve had record-breaking temperatures recently. But that’s not necessarily inconsistent with ever-increasing global warming,” said lead author Claudie Beaulieu, a professor of ocean sciences at UC Santa Cruz.

“Of course, it is always possible that an acceleration of global warming is occurring. But we found that the magnitude of the acceleration is either statistically too small or there is not yet enough data to detect it robustly.”

The research team conducted a rigorous analysis of sets of global surface temperature averages from the four major agencies that track Earth’s average surface temperature, including NASA and the National Oceanic and Atmospheric Association (NOAA). , dating back to 1850. Since that year, Earth’s temperature has increased by 0.11 degrees Fahrenheit per decade, according to NOAA.

Specifically, the study analyzed “global mean surface temperature” (GMST), which is widely studied to monitor climate change, but also presents some challenges: GMST tends to increase over time due to climate pressures. human origin, and it fluctuates around this duration. long-term trend due to natural phenomena, such as major volcanic eruptions and the El Niño Southern Oscillation, which affect global temperatures. So distinguishing between this natural variability and true underlying changes in the rate of warming poses a statistical challenge, the team acknowledged.

Their analysis estimated that an increased warming burst was statistically detectable if it exceeded and sustained a level above these temporary fluctuations over a long period of time. Imagine temperature records plotted on a graph: a small change in slope would require more time to be detected as significant, whereas a large change would be evident more quickly.

After accounting for short-term average temperature fluctuations – which can mask long-term trends and create the appearance of slowdowns and accelerations in warming – and using a series of statistical methods, the team determined the level of increased warming that would be necessary for faster global warming. given number of years in order to detect overvoltages.

For example, they identified that, for the year 2012, the rate of warming would have had to increase by at least 55% before its trajectory could be statistically detectable in 2024 – and therefore qualify as a “surge”. In another example, they show that a change in the rate of warming of around 35% in 2010 would become statistically detectable around 2035.

The team applied this threshold in their statistical analysis of more recent records dating back to the 1970s to see if temperature trends exceeded this threshold, and found that none did.

“Our concern with the current debate over whether there is a ‘surge’ is that there has not been a rigorous statistical treatment or evidence,” said Rebecca Killick, professor of statistics at Lancaster University and co-author of the study. “We decided to tackle this problem head-on, using all commonly used statistical approaches and comparing their results.”

Their study also provides the minimum percentages of statistical detectability in the coming years, until 2040.

“In addition to our results, we give scientists a benchmark, a minimum threshold that must be exceeded before a change can be detectable,” explained Professor Killick. “We hope this helps add rigor to future discussions about possible increases or disruptions.”

Although their findings show no statistical evidence that we are in the midst of a warming wave, Beaulieu stressed that they do not refute the reality of climate change.

“The Earth has never been warmer since instrumental records began due to human activities – and to be clear, our analysis demonstrates continued warming,” Professor Beaulieu said. “However, if there is an acceleration of global warming, we cannot yet detect it statistically.”