YOKOHAMA, Japan -- If the world doesn't cut pollution of heat-trapping gases, the already noticeable harms of global warming could spiral "out of control," the head of a United Nations scientific panel warned Monday.
And he's not alone. The Obama White House says it is taking this new report as a call for action, with Secretary of State John Kerry saying "the costs of inaction are catastrophic."
Rajendra Pachauri, chairman of the Intergovernmental Panel on Climate Change that issued the 32-volume, 2,610-page report here early Monday, said, "It is a call for action." Without reductions in emissions, he said, impacts from warming "could get out of control."
One of the study's authors, Maarten van Aalst, a top official at the International Federation of the Red Cross and Red Crescent Societies, said: "If we don't reduce greenhouse gases soon, risks will get out of hand. And the risks have already risen."
Twenty-first century disasters such as killer heat waves in Europe, wildfires in the United States, droughts in Australia, and deadly flooding in Mozambique, Thailand and Pakistan highlight how vulnerable humanity is to extreme weather, according to the report from the Nobel Prize-winning group of scientists. The dangers are going to worsen as the climate changes even more, the report's authors said.
"We're now in an era where climate change isn't some kind of future hypothetical," said the report's overall lead author, Chris Field of the Carnegie Institution for Science in California. "We live in an area where impacts from climate change are already widespread and consequential."
Nobody is immune, Mr. Pachauri and other scientists said. "We're all sitting ducks," said Princeton University professor Michael Oppenheimer, one of the report's main authors.
After several days of late-night wrangling, more than 100 governments unanimously approved the scientist-written 49-page summary, which is aimed at world political leaders. The summary mentions the word "risk" an average of about 51/2 times per page. "Changes are occurring rapidly, and they are sort of building up that risk," Mr. Field said.
These risks are both big and small, the report said. They are now and in the future. They hit farmers and big cities. Some places will have too much water; some, not enough -- including drinking water. Other risks the report cites involve the price and availability of food and, to a lesser and more qualified extent, some diseases, financial costs and even threats to world peace.
"Things are worse than we had predicted" in 2007, when the group of scientists last issued this type of report, said co-author Saleemul Huq, director of the International Centre for Climate Change and Development at Bangladesh's Independent University. "We are going to see more and more impacts, faster and sooner than we had anticipated."
The report predicts that the highest level of risk would first hit plants and animals, both on land and in acidifying oceans. Climate change will worsen woes society already has, such as poverty, sickness, violence and refugees, the report said. At the same time, such change will act as a brake slowing down benefits of a modernizing society, such as regular economic growth and more efficient crop production, it said.
"In recent decades, changes in climate have caused impacts on natural and human systems on all continents and across the oceans," the report said. And if society doesn't change, the future looks even worse, it said: "Increasing magnitudes of warming increase the likelihood of severe, pervasive and irreversible impacts."
While the problems from global warming will hit everyone in some way, the magnitude of the harm won't be equal, coming down harder on people who can least afford it, the report said. It will increase the gaps between the rich and poor, healthy and sick, young and old, and men and women, Mr. van Aalst said.
But the report's authors say this is not a modern-day version of the Four Horsemen of the Apocalypse. Much of what they warn about are more nuanced troubles that grow by degrees and worsen other societal ills. The report also concedes that there are uncertainties in understanding and predicting future climate risks.
The report, the fifth on warming's impacts, includes risks to the Earth's ecosystems, including a thawing Arctic, but it is far more oriented to what it means to people than past versions were.
Unlike in past reports, where the scientists tried to limit examples of extremes to disasters that computer simulations can attribute partly to man-made warming, this version broadens what it looks at because it includes the larger issues of risk and vulnerability, Mr. van Aalst said.
Freaky storms such as 2013's Typhoon Haiyan, 2012's Superstorm Sandy and 2008's ultra-deadly Cyclone Nargis may not have been caused by warming, but their fatal storm surges were augmented by climate change's ever-rising seas, he said.
Part of the report discusses what can be done: reducing carbon pollution and adapting to and preparing for changing climates with smarter development.
There is still time to adapt to some coming changes and reduce heat-trapping emissions, so it's not all bad, said study co-author Patricia Romero-Lankao of the National Center for Atmospheric Research in Colorado. "We have a closing window of opportunity," she said. "We do have choices. We need to act now."