The world is at growing risk of "abrupt, unpredictable and potentially irreversible changes" because of a warming climate, America's premier scientific society warned on Tuesday.
In a rare intervention into a policy debate, the American Association for the Advancement of Science urged Americans to act swiftly to reduce greenhouse gas emissions – and lower the risks of leaving a climate catastrophe for future generations.
"As scientists, it is not our role to tell people what they should do," the AAAS said in a new report, What we know.
"But we consider it our responsibility as professionals to ensure, to the best of our ability, that people understand what we know: human-caused climate change is happening, we face risks of abrupt, unpredictable and potentially irreversible changes, and responding now will lower the risks and costs of taking action."
The United Nations' climate science panel, the IPCC, will gather in Yokohama, Japan next week to release the second in a series of blockbuster reports, this time outlining how a changing climate is affecting rainfall and heat waves, sea level and the oceans, fisheries and food security.
But the AAAS scientists said they were releasing their own assessment ahead of time because they were concerned that Americans still failed to appreciate the gravity of climate change.
Despite "overwhelming evidence", the AAAS said Americans had failed to appreciate the seriousness of the risks posed by climate change, and had yet to mobilise at a pace and scale needed to avoid a climate catastrophe.
The scientists said they were hoping to persuade Americans to look at climate change as an issue of risk management. The society said it plans to send out scientists on speaking tours to try to begin a debate on managing those risks.
The report noted the climate is warming at almost unprecedented pace.
"The rate of climate change now may be as fast as any extended warming period over the past 65 million years, and it is projected to accelerate in the coming decades,"
An 8F rise – among the most likely scenarios could make once rare extreme weather events – 100-year floods, droughts and heat waves – almost annual occurrences, the scientists said.
Other sudden systemic changes could lie ahead – such as large scale collapse of the Antarctic and Greenland ice sheets, collapse of part of the Gulf Stream, loss of the Amazon rain forest, die-off of coral reefs, and mass extinctions.
"There is a risk of abrupt, unpredictable and potentially irreversible changes in the earth's climate system with massively disruptive impacts," the report said.
The risks of such catastrophes would only grow over time – unless there was action to cut emissions, the scientists said.
"The sooner we make a concerted effort to curtail the burning of fossil fuels as our primary energy source and releasing the C02 to the air, the lower our risk and cost will be."