Current global climate commitments are insufficient to keep the 2015 Paris Agreement target firmly within reach. Global warming is likely to exceed the 1.5 degree Celsius limit. We will overtake.
But countries can limit the time spent in a warmer world by adopting more ambitious climate pledges and decarbonizing faster, according to new research from scientists at the Department of Energy’s Pacific Northwest National Laboratory, University of Maryland and the United States Environmental Protection Agency. This, they warn, is the only way to minimize overshoot.
Although overshooting the 1.5 degree limit seems inevitable, the researchers chart several potential trajectories in which the overshoot period is shortened, in some cases by decades. The study published today in the journal Natural climate changeduring the 2022 United Nations Climate Change Conference, also known as COP27, held in Sharm el-Sheikh, Egypt.
“Let’s face it. We will break through the 1.5 degree limit in the next two decades,” said Haewon McJeon, corresponding author and PNNL scientist. “That means we’ll go up to 1.6 or 1.7 degrees or more, and we’ll have to get it down to 1.5. But how fast we can get it down is key.”
Every shaved second of overshoot translates into less time courting the worst consequences of global warming, from extreme weather to rising sea levels. Forgoing or delaying more ambitious goals could have “irreversible and harmful to 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.
“Acting quickly means reaching net zero commitments sooner, decarbonizing faster and meeting more ambitious emissions targets,” Iyer said. “Every little bit helps, and you need a combination of it all. But our results show that the most important thing is to do it early. Do it now, really.”
At COP26 in 2021, the same research team found that the then-updated pledges could significantly increase the odds of limiting warming to 2 degrees Celsius above pre-industrial levels. In their new paper, the authors go a step further by answering the question of how to move the needle 2 to 1.5 degrees.
“The promises for 2021 do not come close to 1.5 degrees – we are forced to focus on overshooting,” said PNNL scientist Yang Ou, who co-led the study. “Here we are trying to provide scientific support to help answer the question: what kind of ratchet mechanism would get us back below 1.5 degrees? That is the motivation behind this article.”
The authors model scenarios – 27 emissions pathways in total, each varying in ambition – to explore what degree of warming would likely follow which course of action. At the baseline, the authors assume that countries will meet their emissions commitments and long-term strategies on time.
In more ambitious scenarios, the authors model how limited warming is when countries decarbonize faster and bring forward the dates of their net zero pledges. Their findings underscore the importance of “increasing near-term ambition”, which involves rapid reductions in carbon dioxide emissions from all sectors of the energy system, immediately and through 2030.
If countries maintain their nationally determined contributions until 2030 and follow a minimum decarbonization rate of 2%, for example, global carbon dioxide levels would not reach net zero in this century.
Taking the most ambitious path described, however, could bring net carbon dioxide emissions to zero by 2057. Such a path, the authors write, is marked by “rapid transformations across the entire global energy system” and the scaling up of “low carbon technologies”. such as renewable energy, nuclear energy, and carbon capture and storage.”
“Technologies that help us get to zero emissions include renewables, hydrogen, electric cars, etc. Of course, those are big players,” Iyer said. “Another important piece of the puzzle involves technologies that can remove carbon dioxide from the atmosphere, such as direct air capture or nature-based solutions.”
The most ambitious scenarios sketched out in their work are intended to illustrate the paths proposed. But the central takeaway remains clear in all the scenarios modeled: if 1.5 degrees is to be reached sooner after we have passed it, more ambitious climate commitments must come.
This work was supported by the United States Environmental Protection Agency.