We know that our way of living introduces increased green house forcings to our planetary system. Uncertain is: "How much will that warming be?" And this is an essential question for policy-makers (who don't like uncertainties), and it is directly tied to this one number, whether we like it or not.

Models and measurements are the only two methodologies climate scientists have got for understanding the earth's sensitivity. And it is so focused on CO2 since other forcings are converted to CO2 equivalents. There is nothing dangerous to this choice, it is one of practicality - for as far I understand the matter. Understanding the sensitivity for CO2, should enable correlation to other forcings and reach a total sensitivity for the earth. It is true that the role of particulates, soot, clouds may play a significant influence, and they too remain relatively large unknowns. Perhaps a correlation to atmospheric temperatures may turn out to be a foolish exercise altogether, and are we better off with oceanic warming. I can't say. This is why this topic is such a battleground.

Even when sensitivity calculations are fraught with uncertainties, this does not reduce the importance of understanding CO2 sensitivity - because it largely determines the severity and rate of anthropogenic climate change, and hence its understanding underpins political solutions in response to a warming planet.

On the focus on CO2, we are in agreement. I've long argued at ET that CO2 as the main greenhouse bogeyman is a too narrowed and too limited approach of the issue at stake. As there are plenty articles in the science literature mapping out other important forcings and influences, this implies that our approach to anthropogenic climate change should also be multifaceted, and not strictly limited to the mitigation of greenhouse gases.

A positive corollary of this is that our world's fate is not decided purely by rising atmospheric CO2 concentration. Neither should it trivialize the role it does play.

I find the Lyman et al (2010) paper eurogreen cited and the included graph shown below to be particularly concerning. If this is a reasonable sample of the top 700 meters of the ocean it would seem something is likely happening. After all, the oceans are the biggest source of thermal inertia in the entire weather system and more ocean heat leads to greater energy in the atmospheric system. Is there any basis for making an argument that this sort of change is cyclical over a few decades or less?

And what about the rate of loss of Arctic sea ice:

From the discussion at the first link:

In this case, the match is not very good, and possibly getting worse, but unfortunately it appears that the models are not sensitive enough.

"It is not necessary to have hope in order to persevere."