‘‘What we see today is 100 percent due to human activity,’’ said Tans, a NOAA senior scientist. The burning of fossil fuels, such as coal for electricity and oil for gasoline, has caused the overwhelming bulk of the man-made increase in carbon in the air, scientists say.
The world sent 38.2 billion tons of carbon dioxide into the air in 2011, according international calculations published in a scientific journal in December. China spews 10 billion tons of carbon dioxide into the air per year, leading all countries, and its emissions are growing about 10 percent annually. The U.S. at No. 2 is slowly cutting emissions and is down to 5.9 billion tons per year.
The speed of the change is the big worry, said Pennsylvania State’s Mann. If carbon dioxide levels go up 100 ppm over thousands or millions of years, plants and animals can adapt. But that can’t be done at the speed it is now happening.
‘‘We are a society that has inadvertently chosen the double-black diamond run without having learned to ski first,’’ NASA climate scientist Gavin Schmidt said. ‘‘It will be a bumpy ride.’’
NOAA monitoring at Mauna Loa: http://www.esrl.noaa.gov/gmd/ccgg/trends/weekly.html
Seth Borenstein can be followed at http://twitter.com/borenbears