Governments should treat climate change as seriously as threats to national security or public health, partly by focusing more on the worst scenarios of rising temperatures, an international report said on Monday.
Crop failures, extreme heat waves or high rates of sea level rise could be so harmful that governments should examine even small chances of the most severe impacts, according to the study by about 60 experts from 11 nations.
"The risks of climate change should be assessed in the same way as risks to national security or public health," according to the experts from countries that included Britain, the United States, China, Russia and India.
Almost 200 governments will meet in Paris in December to try to work out a global deal to slow climate change.
The study said U.N. reports about climate change focused mainly on moderate warming and rarely mentioned the impacts of five degrees Celsius (9 Fahrenheit) or more, which are far less likely but would be far more damaging.
The Greenland ice sheet, Arctic ecosystems and tropical coral reefs are systems vulnerable to big rises in temperatures.
Governments have long been at odds about how to present the risks of climate change, partly because some voters doubt scientific findings that warming is man-made. Spending on national security or health is less controversial.
The report said the world was not on track to limit greenhouse gas emissions to keep temperatures within a U.N. goal of two degrees Celsius (3.6 F) above pre-industrial times.
"It is very likely that the world will continue to follow a medium to high emissions pathway for the next few decades," the authors wrote.