Climate Sensitivity

Research by NASA climatologist Drew Shindell published in Nature Climate Change estimates that doubling the concentration of carbon dioxide in the atmosphere produces 1.7 degrees Celsius of warming and is unlikely to be less than 1.3 degrees.  This contrasts with an estimate used by IPCC of 1.0 degree Celsius. Despite the so-called pause in atmospheric warming, future warming is likely to be on the high side of current projections.

Update (March 20):  Michael Mann calculates that the 2 degree Celsius warming threshold could be reached as soon as 2036 with a climate sensitivity of 3 degrees Celsius under a "business as usual" emissions scenario.  I'm finding out that there's a difference between transient climate sensitivity (reported above) versus equilibrium climate sensitivity (used by Mann).  IPCC uses a range of 1.5 to 4.5 degrees Celsius for ECS.