Global warming is depleting fresh water and crops, destroying coral reefs and melting the Arctic, the United Nations said Monday in a report that concludes the world is ill-prepared to face many new threats.

Climate change has brought “key risks” that endanger lives and health worldwide, including storm surges and coastal flooding worsened by rising sea levels; infrastructure destruction and the disruption of power networks, communications and health services by extreme weather, and the depletion of crop production due to droughts and floods, the UN Intergovernmental Panel on Climate Change said.

“If you look around the world today, people, cities, businesses and nations aren’t prepared for the climate-related risk we face now,” Chris Field, the U.S. professor who co- chaired the 309 scientists drafting Monday’s report, said in a phone interview from Yokohama, Japan. “The climate changes that have already occurred have been widespread and have really had consequences. It’s not the case that climate change is a thing of the future.”

The report is designed to guide global lawmakers as they devise policies to reduce heat-trapping emissions and make their infrastructure, agriculture and people more resilient to a warmer world. It aims to influence climate treaty talks among 194 nations that are working to devise an agreement next year to rein in global warming.

Global Impact

The researchers documented how climate change affects everything from retreating glaciers in East Africa, the Alps, the Rockies and the Andes to the bleaching of corals in the Caribbean Sea and Australia’s Great Barrier Reef. Mussel-beds and migratory patterns for salmon are changing off the U.S. West Coast, grapes are maturing faster in Australasia and birds are flying to Europe earlier in the year.

Today’s 49-page study, dealing with “impacts, adaptation and vulnerability” of climate change is the second of three “Summaries for Policymakers” that the panel is preparing in its most comprehensive assessment of climate science, an exercise it last carried out in 2007.

The evidence of impacts is strongest for natural systems, and there are early warning signs that damage to coral reefs and the retreat of the Arctic Sea ice may become “irreversible,” while a “large fraction” of land and freshwater species face a growing risk of extinction, they said. Some impacts on cities and societies are also attributable to climate change.

‘Under Threat’

“It is not just polar bears, coral reefs, and rainforests that are under threat: it is us,” Kaisa Kosonen, political adviser to the environmental group Greenpeace International, told reporters in Yokohama, where the report is being published today. The word “risk” appears more than 5,000 times in the wider underlying report that spans thousands of pages, she said.

“The choices we make now will affect the risks we face for the rest of the century,” the authors wrote, while warning that the uncertainty surrounding future vulnerability is large. The scientists “reformulated the challenge of managing climate change into a challenge of managing risks,” said Field, a professor of environmental earth science at the Carnegie Institution for Science in Stanford, California.

One of the panel’s starkest findings concerns water availability and food production. Where seven years ago, researchers were less certain about the potential damage to staple crops, in today’s study, they said global wheat and maize production are already being negatively impacted by warmer temperatures, with yields of wheat declining by about 2 percent per decade and those of maize by 1 percent. Total soy and rice yields are largely unchanged.

Food Prices

Since 2007, “several periods of rapid food and cereal price increases following climate extremes in key producing regions indicate a sensitivity of current markets to climate extremes,” the panel wrote. Fisheries in the tropics will suffer as species migrate towards the poles, they said. Under all warming scenarios, the global stock of fish is projected to decline by 2100.

“This shows climate change is not a distant future threat to food,” Tim Gore, a climate campaigner at the development charity Oxfam International told reporters in Yokohama. “It is a clear and present danger.”

Shrinking glaciers are affecting water resources, and rising greenhouse gas emissions will raise the fraction of the global population facing water scarcity this century, the researchers wrote. Changes in food and water availability “disproportionately” affect the welfare of the rural poor.

Wars

Projected changes could trigger the displacement of people, help instigate wars and threaten the physical integrity of low- lying countries because of the encroachment of rising seas, the researchers found.

Impacts on human health include injury, illness and death due to more intense heat waves, wildfires, increased under- nutrition due to lower availability, and food- and water-borne diseases.

While the poorest people in countries of Africa, Latin America and Asia are those most at risk from climate change, richer nations aren’t immune to its effects and also have to adapt, according to Field.

“Vulnerability is not just concentrated in poor pockets or coastal areas,” he said. “There’s vulnerability throughout the world: from the tropics to the poles and the deserts to the rainforests. You just have to look at something like the impacts of Hurricane Sandy on New York to see that even a very wealthy area can be vulnerable to an extreme weather event.

Unprepared

“Vulnerability in rich countries is usually experienced as economic losses while in poor countries it’s often existential – you get huge amounts of deaths,” Field said. “It’s not like we’re prepared anywhere.”

Global economic losses stemming from further warming of about 2 degrees Celsius (3.6 degrees Fahrenheit) range from 0.2 percent of income to 2 percent, and losses are “more likely than not to be greater rather than smaller than this range,” the researchers wrote, citing “incomplete” estimates.

“The true cost of climate change cannot be represented just in monetary terms,” said Sandeep Chamling Rai, delegation head for the environmental group WWF in Yokohama. “There can be no cost put to losing a husband, a mother, a son, or a daughter and loved ones. There can be no cost to losing the home where, often, our previous generations settled hundreds of years ago. This is the true cost of inaction on climate change.”

Greenhouse Emissions

Field said the rising trajectory of greenhouse emissions is projected to lead to more than 3 degrees Celsius of additional warming this century. That’s on top of the 0.85 degrees of warming already observed since 1880. UN treaty negotiators aim to limit the total rise to 2 degrees.

Economic losses accelerate with greater levels of warming, the researchers wrote, warning that little analysis has been done for levels of warming of 3 degrees Celsius more than present. That amount of additional warming would lead to “extensive biodiversity loss,” they said.

Richard Tol, a professor of economics at the University of Sussex in England and the Vrije University in Amsterdam, asked for his name to be removed from the summary document because it concentrated too much on the negative effects of climate change, he said. Tol is still a convening lead author of chapter 10.

“Subsequent drafts of the summary for policymakers further and further drifted towards alarmism,” Tol said. “It underplays the opportunities. It does not sufficiently emphasize that with adaptation and development these risks are manageable.”

Mandate

Tol’s views are “very mainstream on some issues and not very mainstream on some others,” said Field. “The 300 scientists’ mandate is to represent the complete range of scientific positions on the issues we address, and we go out there and we try and get authors who represent the full range. I think every author thinks we did a bad job of representing his or her exact perspectives.”

The report does mention some positive impacts of climate change, including improved crop yields in southeastern South America and declining deaths connected to extreme cold. At the same time, it refers to “future risks and more limited potential benefits.”

The report was revised line-by-line by government envoys in a meeting last week. It follows the IPCC’s first installment, on the physical observations of climate change in September. A third study in April will examine the tools available to reduce emissions, and a final report will tie the three together in October.

“Governments own this report,” said Greenpeace’s Kosonen. “They have now gone through it line-by-line. Now we expect them to take it home and act on it, speeding up the transition to clean and safe renewable energy for all.”