The inevitable rise in global temperatures beyond the Paris climate agreement threshold has raised concerns, according to a recent UN report. It emphasizes that our current choices still have a substantial impact on the extent of temperature rise, the duration of this rise, and the possibility of reversing it in the future.
Nearly a decade has been committed to limiting global warming below 1.5C. However, a first-ever conclusion by the UN Environment Programme (UNEP) suggests that this limit will likely be surpassed within the next few years. The report clarifies that surpassing this limit does not necessitate that temperatures remain above it, nor does it render future efforts to limit warming useless.
The UNEP’s “Limiting Overshoot” report explains an “overshoot, peak and decline” pathway. It describes a situation where temperatures exceed 1.5C, peak as greenhouse gas emissions approach net zero, and then begin to decline. This decline can only occur if more carbon dioxide is removed from the atmosphere than is released into it.
UNEP’s most ambitious scenario predicts that warming would peak at approximately 1.8C by the mid-century. In contrast, if current policies stay in place, the world is headed for about 2.6C of warming by 2100. That’s why it’s crucial to avoid even fractional degrees of warming, as each reduction lessens the potential harm.
Climate scientists insist that the 1.5C limit is not a definitive boundary between a safe world and one where further action becomes pointless. The risks increase with rising temperatures, so a world that reaches 1.6C is safer than one that reaches 1.7C. Also, spending less time above 1.5C significantly reduces the damage compared to staying there for decades.
“The 1.5 limit is not ‘some magical climate cliff’ where it’s just game over,” said Andrew Weaver, a climate scientist. “Every tenth of a degree we avoid still means less damage.”
In 2024, global temperatures exceeded 1.5C above pre-industrial levels for the first time. The Paris agreement threshold is evaluated over a longer period rather than a single unusually hot year. With sustained warming estimated at around 1.4C, it’s believed that we’ve not formally crossed the threshold yet. However, UNEP predicts it’s likely to happen within the next few years.
The report advises keeping any temperature overshoot as low and brief as possible, instead of simply giving up on the original goal once the limit is breached. “Decisions, science, and most importantly, mindsets need to shift to seeing 1.5C as a goal we’ll be approaching from above rather than below,” said Mirey Atallah, chief of UNEP’s adaptation and resilience branch.
Reversing temperatures below 1.5C would still require deep and sustained reductions in fossil fuel emissions followed by a period of net-negative emissions. This process involves removing and storing carbon dioxide through forests, natural approaches, and technologies yet to be implemented on a large scale. UNEP emphasizes that carbon removal cannot substitute for cutting emissions. Some damage caused during an overshoot could be irreversible, and even if temperatures fall later, rising seas, lost species, and other changes can’t simply be reversed.
The report changes the understanding of crossing the 1.5C threshold. The ultimate peak, the length of time the world spends above 1.5C, and whether temperatures can eventually be brought down again heavily depend on the speed and scale of emissions cuts made in the future.
“It’s a reality check. We have to live with this warmer world. But there’s still a lot we can do to limit warming,” expresses report co-author Richard Betts, a climate scientist.
