The Science is Settled, CO2 is a Greenhouse Gas, But Our Atmosphere's Sensitivity to it is Uncertain

In 1992 Al Gore famously and infamously stood before the US Congress and declared, "the science is settled",  in his usual style of sensationalistic, oversimplified, headline hunting hyperbole. And the with those words our climate war began. Al was of course right that back in 1862 John Tyndall described the key to climate change. He had discovered [and many have repeated his experiments since then] in his laboratory that certain gases, including water vapor and carbon dioxide (CO2), are opaque to heat rays. He understood that such gases high in the air help keep our planet warm by interfering with escaping radiation, the Greenhouse Effect..

What Al neglected to mention, perhaps because it clouded his hunt for the perfect headline, was that our planet's atmospheric sensitivity to those gases and all the other complex interactions from a wide range of confounding factors make climate science a study in uncertainty. Consequently, climate sensitivity is the term scientists use to describe the way our climate reacts to changes in carbon-dioxide levels.

Climate sensitivity is one of the key parameters that the various computer programs we call climate models use to output future climate prognostications from an alphabet soup of parameters all of whose values are a function of other derivatives. In reality, climate sensitivity itself is function of hotly debated parameters derived from things like the looking backward at the historic records of temperature and CO2 concentrations which are themselves debatable. Simply put [for now] they strongly correlate over time but because there's no way to know 'the chicken or the egg' answer, this correlation is no proof of causation.

In the next few days The Mud Report will try to navigate the switchbacks of climate sensitivity and some of the uncertainties embedded in it from proponent, opponent and heretical perspectives. Columbia University has an excellent one page non-technical primer called 'The Carbon Cycle and Earth's Climate'. It explains that, "Carbon dioxide is an atmospheric constituent that plays several vital roles in the environment. It is a greenhouse gas that traps infrared radiation heat in the atmosphere. It plays a crucial role in the weathering of rocks. It is the carbon source for plants. It is stored in biomass, organic matter in sediments, and in carbonate rocks like limestone."

As PhD Physicist Joel Shore said in an email response recently:
"It seems to me that “the science is settled” is a phrase that is probably used more often by [Anthropocentric Greenhouse Warming - ed.] AGW skeptics (clearly, not approvingly) than it is by AGW proponents. It is of course true that in science, all knowledge is tentative…And, yet people don’t argue that one should make policy decisions under the assumption that the Law of Gravity could still theoretically be overturned by new knowledge (which may sound ridiculous, but if you consider the issues of Dark Energy and of the fact that nobody has ever successfully married quantum mechanics and gravity, there truly are some unsettled issues).

The fact is that various aspects of climate science are known to various degrees of certainty. The value of climate sensitivity…and particularly the feedback from clouds is clearly much more uncertain, as are some of the consequences of climate change on sea level, flora, fauna, and society. However, that does not mean that nothing is known about them.

To the extent that AGW proponents do say things to the effect that “the science is settled,” what is often meant is that the weight of the evidence is sufficiently clear that it is unwise to act as if we are not facing a serious problem and that continuing to burn through all of the likely reserves of fossil fuels is probably going to cause significant disruptions. Depending on just how large the climate sensitivity turns out to be and how large the impacts from climate change turns out to be, we probably face significant disruptions if we don’t move to drastically curtail our emissions." 

Shore obviously believes in 'The Precautionary Principle' not because he's certain, but because he's not...