A group of scientists warned Tuesday that world leaders must act more swiftly to slow greenhouse gas emissions or risk “abrupt, unpredictable and potentially irreversible changes” from climate change.

The American Assn. for the Advancement of Science’s blunt report contains no new scientific conclusions. But by speaking in plain, accessible terms it seeks to instill greater urgency in leaders and influence everyday Americans. Scientists said many previous assessments have been long and ponderous, and have failed to shift public opinion on global warming.

The goal “is to move policy forward by making science as clear and straightforward as we possibly can,” association Chief Executive Alan Leshner said. “What we’re trying to do is to move the debate from whether human-induced climate change is reality … to exactly what should you do about it.”

The 18-page report, tiitled “What We Know,” lays out many effects of human-caused climate change already underway. It warns that the consequences are growing more severe the longer governments delay action.


“The sooner we make a concerted effort to curtail the burning of fossil fuels as our primary energy source and releasing the CO2 to the air, the lower our risk and cost will be,” the report says.

Its release marks a new approach by the world’s largest general scientific society, which has more than 120,000 members. A panel of 13 U.S. climate scientists, including oceanographers, ecologists and public health experts, worked with Climate Nexus, a communications nonprofit, to produce the succinct report and a website.

A one-minute online video posted with the report illustrates the problem of climate change and its consequences. Footage shows a mountain biker careening down a bumpy trail and skidding toward the edge of a cliff as a narrator says “the sooner we put the brakes on climate change, the better off we’ll be.”

Though recent polls show many Americans think global warming remains a topic of scientific disagreement, 97% of climate scientists agree that humans are causing climate change — a level of consensus comparable to the science linking smoking to heart and lung disease, the report notes.


“The evidence is overwhelming: levels of greenhouse gases in the atmosphere are rising,” the report says. “Temperatures are going up. Springs are arriving earlier. Ice sheets are melting. Sea level is rising. The patterns of rainfall and drought are changing. Heat waves are getting worse as is extreme precipitation. The oceans are acidifying.”

The planet has warmed by about 1.4 degrees since the late 1800s as carbon dioxide and other heat-trapping gases have built up in the atmosphere from human activity. If emissions keep climbing, temperatures could rise another four to eight degrees over the century, the report says, pushing the climate beyond the range experienced in millions of years and increasing the odds of irreversible damage.

The scientists did not prescribe specific solutions, “but we believe that the full suite of innovative instruments, whether it’s technologies or markets or policies, should be brought to bear on this problem,” said James McCarthy, a professor of biological oceanography at Harvard University who co-chaired the panel.

A report last month by the National Academy of Sciences and Britain’s Royal Society struck a similar tone, distilling the latest climate science into an easy-to-read series of 20 questions and answers.


The United Nations’ body of climate scientists, the Intergovernmental Panel on Climate Change, will meet in Yokohama, Japan, next week to complete its latest assessment. That report will focus on the effect of climate change on nature and society, including the risks warming poses to the world economy, food, water supplies and security.

tony.barboza@latimes.com