Global temperatures may have already passed a critical climate threshold and are set to exceed another by the end of the decade, scientists suggested Monday, a finding experts say is a stark warning to take urgent action to curb carbon emissions, address the climate crisis and stave off even greater temperature increases.
Global temperatures have already climbed past the threshold of 1.5C above pre-industrial levels, scientists from universities in Australia, the U.S. and Puerto Rico said in a paper published in Nature Climate Change.
The 1.5C threshold is an important political and scientific benchmark to mitigate the damage of climate change that countries agreed to strive for as part of the 2015 Paris Agreement and previous estimates suggest the limit has not yet been breached.
However, the researchers argued the baseline used to assess the level of warming since the start of the industrial era is flawed and doesn’t consider historical changes to ocean temperature, which is lacking in comparison to measurements of temperature on land.
Sea sponges—which have a calcium carbonate skeleton that acts as a natural archive of ocean temperature—offer a more accurate account of global temperatures and heating, the researchers argue, and data going back 300 years suggests human-driven warming began in the 1860s, decades earlier than baseline measurements used for pre-industrial times.
The new baseline means global warming was already at around 1.7C above pre-industrial levels by 2020, the researchers said, 0.5C higher than many of the most respected estimates and decades before scientists thought the 1.5C limit would be crossed.
The findings illustrate that “the opportunity to limit global warming to no more than 1.5C by emission reductions alone has now passed” and underscore the “even more urgent need” to halve emissions by the end of the decade in order to limit further temperature increases, the scientists said.
What To Watch For
The Paris Agreement also saw countries pledge to keep global warming “well below” 2C above pre-industrial levels. This is a level at which climatic changes will be much more profound and much deadlier, experts warn. This new baseline assessment of global warming suggests meeting this target is going to be a “much greater challenge,” the researchers said. At current rates of warming, this 2C threshold will be breached within a few years, they said, before the start of the 2030s. A much more serious level of warming, 2.5C above pre-industrial levels, could be reached by about 2035, they warn. At this level, the Earth risks toppling over devastating tipping points and triggering catastrophic climate breakdown.
Scientists have asked whether it is reasonable to use this to question how we see the hard-won goals of the Paris Agreement. It “is quite a stretch,” said Joeri Rogelj, a climate researcher at Imperial College London’s Grantham Institute. Countries use these temperature limits “as a proxy for climate impacts” they aim to avoid, Rogelj explained. “Relabelling the warming that has occurred until today by using a different starting point does not change the impacts we are seeing today, or the impacts we are aiming to avoid.” Robin Lamboll, also of Imperial’s Grantham Institute, concurred and said the results are “interesting” but have no “legal ramifications for the Paris Agreement” whatsoever. Gabi Hegerl, a climate scientist at the University of Edinburgh, said the study is a “nice new record” of the Caribbean, where the sponges were collected, but is no substitute for global data. “The interpretation in terms of global warming goals overstretches is,” Hegerl said.
“The way these findings have been communicated is flawed, and has the potential to add unnecessary confusion to public debate on climate change,” said Yadvinder Malhi, a professor of ecosystem science at the University of Cambridge. “Despite the headline, the results of this paper do not show that we have already exceeded the Paris climate targets.” The findings, “if real,” are probably not even the result of human actions, Malhi said, pointing to the small level of emissions at the time (“a mere 2.5% of our cumulative emissions by 2021”). “It is the date of the reference period that matters rather than whether it is labeled pre-industrial or not.”
Sea sponges offer lifeline to women in Zanzibar (BBC)
New Zealand sea sponge populations ‘dying by the millions’ due to climate change (CNN)