Climate change is already disrupting human societies and ecosystems across the world, and the window for adapting to food shortages, sea-level rise, wildfires and other impacts is quickly narrowing, the latest report from the United Nations' Intergovernmental Panel on Climate Change said.

For the first time, scientists assessed the impacts of a global temperature rise that temporarily "overshoots" the critical threshold of 1.5 degrees Celsius, concluding that some impacts would be irreversible even if the planet cools again.

But a summary for policymakers also emphasized that urban areas, in particular, offer new opportunities for the development of green buildings and sustainable transportation, solutions that will help societies cope.

To have any chance of keeping global temperatures from rising past 1.5 degrees from preindustrial levels, coal-fired power fleets must be dismantled immediately, United Nations Secretary António Guterres said in a prepared address released with the IPCC report on Feb. 28.

"I've seen many scientific reports in my time, but nothing like this," Guterres said. "Today's IPCC report is an atlas of human suffering. Nearly half of humanity is living in the danger zone, now. Many ecosystems are at the point of no return, now. And unchecked carbon pollution is forcing the world's most vulnerable on a frog march to destruction, now."

Global greenhouse gas emissions are on a trajectory to rise 14% this decade, fueled by energy development and transportation growth. By contrast, scientists say carbon pollution must be reduced by 45% by 2030 to stave off the worst impacts of climate change.

Diversifying and decentralizing power production, while making energy markets more responsive to climate needs, are among the steps nations must take to slow the emissions trajectory and provide more time for adaptation, the IPCC said.

If global average temperatures rise 1.5 degrees from preindustrial times, up to 14% of land-dwelling species will likely face a high risk of extinction, according to the report. At 2 degrees of warming, snowmelt needed for irrigation, hydropower and drinking water could decline by up to 20%, the panel said.

To date, the plant has warmed about 1.1 degrees since the mid-19th century due to human activities, the IPCC previously reported.

US ecosystems under siege

In the U.S., efforts to rein in carbon emissions and prepare communities for more extreme weather events have been delayed "due to misinformation about climate science that has sowed uncertainty and impeded recognition of risk," the lead authors on the North American chapter of the report wrote. At the same time, warming has affected the U.S. in a number of ways over the past 20 years, the scientists noted.

North America and Europe were the only two continents where scientists found that climate change has had a high or very high impact on all facets of ecosystems: Seasons have shifted, the ranges for species have moved and ecosystem system structures have been altered.

For people in North America, such changes translate into reduced agriculture and crop production. Reduced snowpack and earlier runoff have reduced freshwater supplies in the West, in particular, and reduced hydropower resources.

Drought, floods and "harmful algal and pathogen events" have also affected freshwater supplies in other parts of the U.S., along with tourism and other key economic sectors, the report noted. Infectious diseases such as malaria are on the march as the range for mosquitoes or other species that carry the disease has expanded.

The U.S. also has seen indigenous populations and other vulnerable communities being disproportionally affected by the disruption caused by climate change, a pattern the scientists found globally.

In Alaska, for example, the Yup'ik village of Newtok is sinking amid thawing permafrost and erosion and forcing people to relocate. And in Louisiana, residents on the low-lying island of Isle de Jean Charles are uprooting as intruding seawater destroys roads and homes.

Hurricanes, drought and other weather disasters, many of which have already been attributed to climate change, cost the U.S. $145 billion in losses in 2021. By the end of the century, if the global temperatures rise approaches an unsustainable 4 degrees, those losses would be in the hundreds of billions, the IPCC report said.

'Still optimistic'

Worldwide, between 3.3 billion and 3.6 billion people, as much as 45% of the world's population, now live in contexts highly vulnerable to climate change, the report said. Climate risks are now unavoidable, although some risks can be moderated with concerted adaptation measures, the scientists wrote.

Today's efforts are uneven across regions, fragmented and limited in scale. Some adaptation projects are also ineffective: A poorly constructed sea wall, for example, can lull people into a false sense of security, the IPCC authors said.

Even so, Debra Roberts, a co-chair of the IPCC group that produced the report, rejected the idea of planetary doom and gloom, stressing that the world still has opportunities to slow climate change and adapt to the disruption that is already occurring.

"There's a real advantage to reconceptualizing our cities not only as a place for people but a place of nature," Roberts said. "In this report ... we also lay out the solutions to urban areas around the world. I'm still optimistic about the ability to mobilize extensively around this report and then create the kind of societal response we need to see."

Known as the Sixth Assessment Report by IPCC's Working Group II and titled Impacts, Adaptation and Vulnerability, the report was released five months late after the coronavirus pandemic shifted the work online. In all, 270 authors from 67 countries assessed 34,000 scientific findings and 62,480 comments from experts to produce the report.

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