Overlooked Evidence - Global Warming May Proceed Faster than Expected

It’s known as “single study syndrome”.  When a new scientific paper is published suggesting that the climate is relatively insensitive to the increased greenhouse effect, potentially modestly downgrading the associated climate change threats, that sort of paper will generally receive disproportionate media attention.  Because of that media attention, people will tend to remember the results of that single paper, and neglect the many recent studies that have arrived at very different conclusions.

Clouds Point to a Sensitive Climate
For example, there have been several recent studies finding that the global climate models that most accurately simulate observed changes in clouds and humidity over the past 10–15 years also happen to be the ones that are the most sensitive to the increased greenhouse effect.  For example, a 2012 paper by Kevin Trenberth and John Fasullo concluded,

These results suggest a systematic deficiency in the drying effect of either subsident circulations or spurious mixing of moister air into the region in low-sensitivity models that directly relate to their projected changes in cloud amount and albedo … the results strongly suggest that the more sensitive models perform better, and indeed the less sensitive models are not adequate in replicating vital aspects of today’s climate.

A 2014 paper led by Steven Sherwood took a similar approach with similar results. The paper concluded,

The mixing inferred from observations appears to be sufficiently strong to imply a climate sensitivity of more than 3 degrees for a doubling of carbon dioxide.  This is significantly higher than the currently accepted lower bound of 1.5 degrees, thereby constraining model projections towards relatively severe future warming.

Another 2014 paper published by scientists from CalTech and UCLA arrived at a similar conclusion, as lead author Hui Su explains,

This study used an index that represents how models capture the observed spatial structure of the Hadley Circulation and associated humidity and cloud distributions.  We showed that the inter-model spread in climate sensitivity and cloud feedback is closely related to models’ Hadley Circulation change and present-day circulation strength varies systematically with models’ climate sensitivity (Figure 9).  The stronger Hadley Circulation in the models, the higher climate sensitivity the models have (Figure 10).  The observed circulation strength is on the high end of the modeled ones.

Those who argue that the Earth’s climate is relatively insensitive to the increased greenhouse effect need a big negative feedback to offset those factors we know amplify global warming. Clouds represent the only such plausible mechanism, because we don’t have a very good grasp on how different types of clouds will change in a hotter world.
...
Not only have the aforementioned studies found that changes in humidity and clouds are consistent with simulations from more sensitive climate models, but previous research led by Andrew Dessler and more recently by Kevin Trenberth and colleagues has shown that observed changes in water vapor amplifying global warming as expected, and that clouds are thus far acting to weakly amplify global warming.  These observations are inconsistent with the strong cloud dampening effect contrarians need to justify arguments for low climate sensitivity.

Read more at Overlooked Evidence - Global Warming May Proceed Faster than Expected