Scientists scotch ‘tenuous’ 2C climate goal

THE pause in average surface temperature rise made the case to limit climate change to 2 degrees C “tenuous”, scientists say.

THE 16-year pause in global average surface temperature rise made the scientific case to limit climate change to 2C “tenuous”, a widely promoted article in Nature says.

As a result, a new set of indi­cators or “vital signs” was needed to gauge the stresses that humans were placing on the climate system, joint authors David Victor and Charles Kennel from University of California said.

The suggested new measures include the level of CO2 in the atmosphere, ocean heat content and high latitude temperatures.

The Nature article confronts head-on the dilemma of the pause in global surface temperatures that climate scientists have long argued did not exist. Strong debate remains as to whether or not the pause is an “existential” issue for climate change as a major ­concern.

A recent peer-reviewed paper said the earth’s climate was less sensitive to rising levels of CO2 than had previously been claimed.

At the least, the lack of surface warming has highlighted gaps in scientific understanding of natural variability. US climate scientist ­Judith Curry said: “I do regard the emerging realisation of the importance of natural variability to be an existential threat to the mainstream theory of climate variations on decadal to century timescales.”

The Victor and Kennel article said the fact the planet’s average temperature had barely risen in the past 16 years made the scientific basis for the 2C goal set by the Intergovernmental Panel on Climate Change tenuous.

“But other measures show that radiative forcing — the amount by which accumulating greenhouse gases in the atmosphere are perturbing the planet’s energy balance — is accelerating,” they said.

“How could human stresses on the climate be rising faster even as global surface temperatures stay flat?” they asked. “The answer almost certainly lies in the oceans.

“The oceans are taking up 93 per cent of the extra energy being added to the climate system, which is stoking sea-level rise and other climate impacts.”

Limiting global warming to 2C has been the aim of nearly every policy to reduce carbon emissions.

Professor Victor and Professor Kennel said “politically and scientifically the 2 goal is wrongheaded. Politically, it has allowed some governments to pretend that they are taking serious action to mitigate global warming when in ­reality they have achieved almost nothing,” they said.

“Scientifically, there are better ways to measure the stress humans are placing on the climate system than the growth of average global surface temperature, which has stalled since 1998 and is poorly coupled to entities that governments and companies can control directly.”