STOCKHOLM – Top scientists have a better idea of how global warming will shape the 21st century. In a new report, they predict sea levels will be much higher than previously thought, and they pinpoint how dangerously hot it’s likely to get.
In its most strongly worded report yet, an international climate panel said it was more confident than ever that global warming is a man-made problem and likely to get worse.
The report was welcomed by the Obama administration and environmental advocates who said it made a strong and urgent case for government action, while skeptics scoffed at it.
“There is something in this report to worry everyone,” said Chris Field, a Carnegie Institution scientist who is a leader of the Intergovernmental Panel on Climate Change but wasn’t involved in the report released Friday.
Without any substantial changes, he said the world is now on track for summers at the end of the century that are hotter than current records, sea levels that are much higher, deluges that are stronger and more severe droughts.
The Nobel Prize-winning panel’s report called the warming of the planet since 1950 “unequivocal” and “unprecedented” and blamed increases in heat-trapping greenhouse gases such as carbon dioxide from the burning of coal, oil and gas.
The United Nations created the panel of climate researchers in 1990 to tell world leaders what science is saying about global warming and how bad it will get. This is the group’s fifth major state-of-the-science report, approved by nearly 200 nations at the end of a weeklong meeting in Stockholm.
In its last massive report in 2007, the panel said it was “very likely,” or 90 percent certain, that global warming was due to human activity, particularly carbon dioxide from sources like coal-burning power plants and car exhaust. The new report raises that to 95 percent or “extremely likely.”
The panel also fine-tuned its predictions for temperature changes and sea levels by the end of this century. Their worst case scenario previously put sea level increase at just shy of 2 feet by 2100; now they put it at slightly more than 3 feet. They cite better understanding of how much glaciers and ice sheets are melting and how water expands as it warms.
Unless the world drastically cuts emissions – an event scientists called highly unlikely to happen – the panel said Earth will warm by at least 2 more degrees Fahrenheit this century in all but one of the four scenarios they outline.
That 2-degree threshold is “where the risks start piling up,” including food crises in developing countries, people forced to move from coastal cities because of rising seas and more extinctions, said Princeton University climate scientist Michael Oppenheimer, a co-author of an upcoming IPCC report on impacts of climate change. “This is a point where any sensible person would look and say the risks are just getting too high.”
One of those IPCC emission scenarios – the one that scientists say is closest to what is now happening and has no projected reduction in pollution – has Earth hitting the 2 degree mark by mid-century.