IPCC climate report: six things we’ve learned

Scientists are more certain than ever that humanity is to blame for rising temperatures. The head of the UnitedNations‘ World Meteorological Organisation, Michel Jarraud, said “it is extremely likely that changes in our climate system in the past half century are due to human influence.

” The report says: “Human influence on the climate system is clear. This is evident from the increasing greenhouse gas concentrations in the atmosphere, positive radiative forcing, observed warming, and understanding of the climate system.”

Concentrations of CO2 and other greenhouse gases in the atmosphere have increased to levels that are unprecedented in at least 800,000 years. The burning of fossil fuels is the main reason behind a 40% increase in CO2 concentrations since the industrial revolution.

We’re likely to surpass rises of 2C by 2100, the threshold of warming that governments have pledged to hold temperatures to, and beyond which dangerous consequences including drought, floods and storms are expected.

“What is very clear is we are not” on the path to keeping temperatures below 2C, said Thomas Stocker, one of the co-chairs of today’s report. Global temperatures are likely to rise by 0.3C to 4.8C by the end of the century, the report said.

Sea level rises are coming. “Global mean sea level will continue to rise during the 21st century,” says today’s report, by a further 26-82cm by 2100, but Stocker said “there is no consensus in the scientific community over very high sea level rises”.

Scientists said claims that the rate of temperature rises in the last 15 years has slowed did not affect the big picture, and temperatures are going up in the long-term. Climate trends “should not be calculated for periods of less than 30 years,” said Stocker

The amount of carbon the world can burn without heading for dangerous levels of warming is far less than the amount of fossil fuels left in the ground.

“The IPCC carbon budget to stay below 2C is 800-880 gigatonnes of carbon (GTC). 531 GTC had already been emitted by 2011. So we have 350 GTC left, which is much less than the carbon stored in fossil fuel reserves,” notes our correspondent Fiona Harvey.

The guardian