The world must adopt more ambitious climate pledges and decarbonise faster, if it is to have any chance to curb global warming.
A study by scientists at the Department of Energy’s Pacific Northwest National Laboratory, the University of Maryland and the U.S. Environmental Protection Agency has concluded the world’s current climate pledges are insufficient to keep the goal of the 2015 Paris Agreement firmly within grasp. Global warming will likely surpass the 1.5-degree Celsius limit.
While exceeding the 1.5-degree limit appears inevitable, the researchers chart several potential courses in which the overshoot period is shortened, in some cases by decades.
“Let’s face it. We are going to breach the 1.5 degrees limit in the next couple of decades,” said corresponding author and PNNL scientist Haewon McJeon. “That means we’ll go up to 1.6 or 1.7 degrees or above, and we’ll need to bring it back down to 1.5. But how fast we can bring it down is key.”
The team said every second shaved off the overshoot translates to less time courting the most harmful consequences of global warming, from extreme weather to rising sea levels.
Forgoing or delaying more ambitious goals could lead to “irreversible and adverse consequences for human and natural systems,” said lead author Gokul Iyer, a scientist alongside McJeon at the Joint Global Change Research Institute, a partnership between PNNL and the University of Maryland.
“Moving fast means hitting net-zero pledges sooner, decarbonizing faster, and striking more ambitious emissions targets,” said Iyer. “Every little bit helps, and you need a combination of all of it. But our results show that the most important thing is doing it early. Doing it now, really.”
During COP26 in 2021, the same research team found that the then updated pledges could substantially increase the chance of limiting warming to 2 degrees Celsius over pre-industrial levels. In their new paper, the authors take an additional step in answering the question of how to move the needle from 2 to 1.5 degrees.
“The 2021 pledges don’t add up to anywhere near 1.5 degrees, we are forced to focus on the overshoot,” said PNNL scientist Yang Ou, who co-led the study. “Here, we’re trying to provide scientific support to help answer the question: What type of ratcheting mechanism would get us back down and below 1.5 degrees? That’s the motivation behind this paper.”
The authors model scenarios, 27 emissions pathways in total, each ranging in ambition, to explore what degree of warming would likely follow which course of action. At a base level, the authors assume that countries will meet their emissions pledges and long-term strategies on schedule.
In more ambitious scenarios, the authors modelled how much warming is limited when countries decarbonize faster and advance the dates of their net-zero pledges. Their results underscore the significance of “ratcheting near-term ambition,” which entails rapid reductions in carbon dioxide emissions from all sectors of the energy system, immediately and through 2030.
If countries uphold their nationally determined contributions through 2030 and follow a two percent minimum decarbonisation rate, for example, global carbon dioxide levels would not reach net zero this century.
Taking the most ambitious path outlined, however, could bring net-zero carbon dioxide emissions by 2057. Such a path, the authors write, is marked by “rapid transformations throughout the global energy system” and the scaling up of “low-carbon technologies like renewables, nuclear energy, as well as carbon capture and storage.”
“The technologies that help us get to zero emissions include renewables, hydrogen, electric cars, and so on. Of course those are important players,” said Iyer. “Another important piece of the puzzle is the technologies that can remove carbon dioxide from the atmosphere, like direct air capture or nature-based solutions.”