Climate sensitivity higher than was thought

Note acceleration in the temperature rise after 2010, from 0.2°C/decade to 0.3°C/decade/

From Climate News Network:

Teams in six countries, using new climate models, say the warming potential of CO2 has been underestimated for years. The new models will be used in revised UN temperature projections next year. If they are accurate, the Paris targets of keeping temperature rise below 2°C − or preferably 1.5°C − will belong to a fantasy world.

Vastly more data and computing power has become available since the current Intergovernmental Panel on Climate Change (IPCC) projections were finalised in 2013. “We have better models now,” Olivier Boucher, head of the Institut Pierre Simon Laplace Climate Modelling Centre in Paris, told the French news agency AFP, and they “represent current climate trends more accurately”.

Projections from government-backed teams using the models in the US, UK, France and Canada suggest a much warmer future unless the world acts fast: CO2 concentrations which have till now been expected to produce a world only 3°C warmer than pre-industrial levels would more probably heat the Earth’s surface by 4 or 5°C.

Scientists want to establish how much the Earth’s surface will warm over time if the amount of CO2 in the atmosphere doubles. The resulting temperature increase, known as Earth’s climate sensitivity, is a key indicator of the probable future climate. The part played in it by clouds is crucial.

“How clouds evolve in a warmer climate and whether they will exert a tempering or amplifying effect has long been a major source of uncertainty,” said Imperial College London researcher Joeri Rogelj, the lead author for the Intergovernmental Panel on Climate Change (IPCC) on the global carbon budget − the amount of greenhouse gases that can be emitted without exceeding a given temperature cap. The new models reflect a better understanding of cloud dynamics that reinforce the warming impact of CO2.

For most of the last 10,000 years the concentration of CO2 in the atmosphere was a nearly constant 280 parts per million (ppm). But at the start of the 19th century and of the industrial revolution, fuelled by oil, gas and coal, the number of CO2 molecules in the air rose sharply. Today the concentration stands at 412 ppm, a 45% rise − half of it in the last three decades.

[Read more here]


This is very, very bad news.  This means that even if CO2 emissions peak, the rise in global temperatures by 2100 will be much higher than 3°C.  And so far, emissions are not peaking.  We face a climate catastrophe unless we act aggressively, now.   Every country in the world needs to aim for a minimum cut in emissions of 3% per year.