A “code red for humanity”?

A “code red for humanity”—that’s how United Nations Secretary-General António Guterres described a climate report issued by an agency of the international body. Inside the full report’s 3,949-pages of facts, figures and references, Intergovernmental Panel on Climate Change officials paint a worrying picture of a world heating up.

“The alarm bells are deafening,” Guterres, a former Portuguese prime minister, said. “The evidence is irrefutable: greenhouse gas emissions from fossil fuel burning and deforestation are choking our planet and putting billions of people at immediate risk.”

The massive climate report, marshalling 234 scientists to review evidence from more than 14,000 journal articles, puts forward an avalanche of evidence of warming. According to the report’s authors, governments around the world must act quickly to reduce greenhouse gas emissions or face dire consequences. But neither the warnings nor the evidence break new ground, and critics contend the IPCC’s doomsday scenarios are very unlikely.

There’s at least one thing most experts agree on: The Earth is warming up. As evidence, the IPCC report’s authors retread several well-worn metrics, including rising sea levels. The authors found a 1.3 millimeters per year rise of the mean global sea level from 1901 to 1971. That rate increased to 1.9 millimeters per year from 1971 to 2006 and 3.7 millimeters per year from 2006 to 2018.

IPCC scientists attribute that rise to melting glaciers and polar ice caps as the Earth’s global surface temperature increases. Comparing the amount of Arctic Sea ice between 1979-1988 to that in 2010-2019, IPCC scientists found a 40 percent reduction in the average September, but just a 10 percent reduction in the average March. Global temperature averages have been 1.09 degrees Celsius warmer in the past decade than between 1850 and 1900, according to the report. “Each of the last four decades has been successively warmer than any decade that preceded it since 1850,” the agency summarized.

IPCC scientists also tried to define humans’ responsibility for any warming. The report described increasing atmospheric concentrations of heat-trapping greenhouse gases linked to human activity. The U.S. National Oceanic and Atmospheric Administration pegged carbon dioxide concentration at 353 parts per million in January 1990, a number that rose steadily in the following decades until it hit 410 parts per million in 2021, according to the IPCC report. That led the authors to say “it is unequivocal” that human activity caused at least some of the temperature change.

Climate scientists have made a global surface temperature change of 1.5 degrees Celsius above pre-industrial temperatures a line of demarcation to prevent the worst consequences of global warming, like intense heatwaves, drought, and flooding. That’s the figure set by signatories to the Paris Agreement, the 2015 international climate change deal.

But climate activists’ calls for drastic action seem likely to be ignored. “If governments are serious about the climate crisis, there can be no new investments in oil, gas and coal, from now—from this year,” Fatih Birol of the Paris-based International Energy Agency told The Guardian in May. “But I see a huge and growing gap between the rhetoric [from governments] and the reality.”

Europe and the United States have actually reduced greenhouse gas emissions over the past decade. But China’s yearly carbon dioxide emissions have surpassed those of the entire developed world, according to a 2019 study by Rhodium Group. The country generates more than half of the world’s coal power capacity and continues to add carbon dioxide–belching coal-powered facilities. In response to criticism, Beijing insisted it was on a course to begin reducing greenhouse gas emissions by 2030.

Most criticism of the IPCC report and its featured studies center on the models climate scientists use to predict future temperature changes. The IPCC’s most cataclysmic scenarios—involving global average temperature increases between roughly 3.5 and 4.5 degrees Celsius by 2100—seem unlikely on their face. The IPCC’s most drastic and headline-generating scenario assumes “an unprecedented fivefold increase in coal use by the end of the century, an amount larger than some estimates of recoverable coal reserves,” according to a pair of authors writing in the journal Nature in 2020. Despite increased usage in China, world coal production peaked in 2013.

The IPCC’s apocalyptic warnings have also drawn criticism from outside the climate science academy. Canadian economist Pierre Lemieux wrote in the Library of Economics and Liberty on Tuesday that this isn’t the first time climate scientists have predicted the end of the world without it coming to pass. “The 1970s were full of predicted catastrophes,” Lemieux wrote, noting warnings about global cooling from decades ago.

Describing himself as a climate agnostic, Lemieux questioned whether an expensive global project to counteract warming was worth the price tag. According to some economists, dealing with floods, heatwaves, and droughts through yet-unknown technological developments or Dutch-style flood controls are a better trade off than crippling future economic growth for generations by adhering to zero-emission policies. “Adaptation to climate change may be much less costly for most people than a quixotic battle to prevent it, especially so if you include the cost in terms of tyranny and lost prosperity for perhaps generations.”