In what is likely its last report before the 2030 target date to align global carbon pollution with 1.5°C climate target, the Intergovernmental Panel on Climate Change (IPCC) details humanity’s “unequivocal” environmental impacts, noting that only immediate, unprecedented climate action can avoid worst-case scenarios.

“It is unequivocal that human influence has warmed the atmosphere, ocean, and land,” the IPCC states in its Summary for Policymakers, warning later in the text of a “rapidly closing window of opportunity to secure a livable and sustainable future for all.”

The changes and impacts from rising temperatures are being observed worldwide, causing widespread damage to nature and people, but these losses are not distributed uniformly. Often, “vulnerable communities who have historically contributed the least to current climate change are disproportionately affected.”

Roughly 3.3 to 3.6 billion people live in circumstances that are highly vulnerable to climate change, with millions exposed to high levels of food, and water insecurity. “Between 2010 and 2020, human mortality from floods, droughts and storms was 15 times higher in highly vulnerable regions, compared to regions with very low vulnerability.”

But despite the high stakes, international efforts to address climate change are not on track to keep rising temperatures within 1.5°C of pre-industrial levels. Global emissions continue to outpace reduction efforts. And despite the ambitions outlined in governments’ nationally determined contributions (NDCs) under the Paris climate agreement, warming will likely exceed 1.5°C this century, and it will become harder to limit warming below 2°C.

Even with progress lagging, governments like the United States and China, among others, continue to advance the fossil fuel development causing the crisis.

The 1.5C° target has been central to climate goals since it was accepted by signatories of the Paris Agreement in 2015. At that time, the world was on track to see 3.5°C of warming, and initial negotiations were to keep warming below a “safe” level of 2°C.

But that target has since been found to be inadequate. “The idea that a safe level of warming could be achieved was subjective,” explained physicist Piers Forster, a professor of physical climate change at the University of Leeds. “Current levels were already unsafe for those on the sharpest end of climate change.”

So 1.5°C has continued to grow in importance, even as lagging climate action has consistently pushed it further from reach—raising questions about whether it is still achievable, and if not, whether it is still a useful policy target. Some experts say many scientists think 1.5 is no longer feasible but are hesitant to say so publicly, for fear of generating a fatalistic response or co misrepresenting the obstacles as scientific, rather than political.

“I think it’s simply a disconnection between what is technically possible but is not politically possible,” Marta Rivera-Ferre, a veterinary scientist with INGENIO, told Scientific American.

“We could achieve 1.5°C if we wanted, it is the political conditions that make this not possible.”

The IPCC report stresses that the most practical pathways to faster, deeper carbon cuts are also the most affordable. In a mid-January post for The Energy Mix, Stephan Singer, senior science and energy advisor at Climate Action Network-International, argued that the barriers to action are political, not technological nor even economic.

The current science outlined by the IPCC indicates that global warming will continue to increase in the near term (now until 2040) because of already accumulated emissions, regardless of what actions are taken next. After that, even low emissions scenarios suggest that the target from the Paris Agreement will be missed, and only a “very low” emissions scenario could narrowly keep warming levels at 1.4°C. Even then, temperature rise is “more likely than not” to increase above 1.5°C.

Some scientists want this reality addressed. “I just think it’s time for us to be grownups,” said climate scientist Peter Kalmus, expressing his own views rather than those of his employer, NASA.

“Basically, we have to look at what’s really happening and respond to it,” Kalmus said. “If we’re not willing to look at what’s really happening, and we just try to not think about it, then we can’t stop it.”

Even though most emissions pathways show global temperatures surpassing 1.5°C, there are still “discernable differences” between each scenario’s temperature trends. The IPCC says every increment of additional global warming will make the impacts of climate extremes worse and more widespread, which means countries should still take every measure they can to keep warming as low as possible—even if their initial goal won’t be achieved.

“The difference between 1.5°C of warming and 2°C might mean that tens of millions more people worldwide experience life-threatening heat waves, water shortages, and coastal flooding,” the New York Times reports. “A 1.5°C world might still have coral reefs and summer Arctic sea ice, while a 2°C world most likely would not.”

Some scenarios do indicate that temperatures can be brought back down after rising above 1.5°C, by pulling enough carbon out of the atmosphere that net emissions are negative. But the IPCC warns that any “adverse impacts that occur during this period of overshoot and cause additional warming via feedback mechanisms, such as increased wildfires, mass mortality of trees, drying of peatlands, and permafrost thawing, weakening natural land carbon sinks, and increasing releases of greenhouse gases would make the return more challenging.”

Bringing temperatures back down would require more carbon dioxide removal than pathways without overshoot, making those pathways less feasible and sustainable, the IPCC warns. More extreme overshoots will naturally require more net-negative emissions to bring temperatures back below the 1.5°C increase before 2100, and cause greater and more widespread impacts to ecosystems and societies. Meanwhile, adaptation options that are feasible and effective today will become less so with increased warming.

The science outlined by the IPCC makes it clear that governments need to make rapid changes to all sectors and systems to reduce emissions as much as possible. The many different strategies include adopting more low- and zero-emission technologies, improving energy efficiency, and substantially slashing the use of fossil fuels, while using carbon capture and storage in all remaining fossil fuel systems.

And regardless of what can be modelled by scientists, the IPCC advises that “effective climate action is enabled by political commitment, well-aligned multilevel governance, institutional frameworks, laws, policies and strategies, and enhanced access to finance and technology.” All levels of government—from local to international—will need to streamline climate action to achieve the deepest emissions cuts possible.

The conclusions of the IPCC “were so clear,” said Katharine Hayhoe, chief scientist at the Nature Conservancy. “They said every bit of warming matters. And if we give up, we are doomed.”