Nova’s Analogy

Nova’s Rerouting Analogy.

Jo Nova’s “pipes and dams” analogy fails in its purpose and highlights the flaws in this rerouting thinking.

http://joannenova.com.au/2015/10/new-science-11-an-alternative-modeling-strategy/

Nova’s Analogy.

Nova doesn’t understand her analogy.

An analogy is used without the realisation that an analogy cannot be expected to account for all the features that it is supposed to represent.

The obvious.

When greenhouse gases are added to the atmosphere it doesn’t stop radiation escaping to space when equilibrium is reached. If it did the Earth would not stop getting hotter and hotter. Conventional thinking with vast amounts of research and evidence are dismissed by this rerouting proposal.

The myth presented by the rerouting idea is based on the simplistic thinking that if the energy is just eventually all radiated to space by whatever means then the surface can’t get warmer. It also then assumes that if water vapour plays a part in this then it must be a negative feedback. This confuses the part that water vapour plays in the Planck response with the positive feedback due to water vapour.

The Explanation.

When equilibrium is reached in her very large “bath tub” the outgoing flow will still equal the ingoing flow. This is still true even as the pipes are partially blocked. David Archer I recall made some very good analogies using bath tubs for educational purposes. David Archer was well aware of how the analogy worked and its limitations.

It should have been obvious to Nova that if the level in the reservoir did not rise then the flow to the other pipes would not increase. As Nova herself should have realised... how would the other pipes know or even “think” that ....unless the reservoir level rose and added extra pressure to make these other flows increase?

This of course IS the Planck response. It is sometimes referred to as a negative feedback but what it really means is that the Earth’s surface and atmosphere heats up to a new level increasing the outgoing long wave radiation to what is was prior to the addition of the extra greenhouse gases.

When greenhouse gases are added to the atmosphere the initial outgoing LW radiation is reduced. The Earth responds by getting warmer until the outgoing radiation at the top of the atmosphere again is in balance with the incoming solar energy. The bath tub level raises until the total outgoing flows equal the incoming flows to the reservoir.

The analogy is limited.

The greenhouse effect works by greenhouse gases absorbing and emitting longwave radiation. When more GHG are added to the atmosphere more back radiation heats the surface which in turn increases the outgoing LW radiation and eventually (at equilibrium) the outgoing radiation will equal that of the incoming radiation.

Since CO2 raises the temperature of the atmosphere then the amount of water vapour will increase making the greenhouse effect larger. Thus water vapour will increase the amount of radiation to space but also the radiation back to the surface. This is a positive feedback and not a negative feedback.

Genuine research.

This rerouting  proposal  reminds me of a genuine scientific investigation by Lacis et al using GCM’s whereby different gases could be added to the atmosphere or removed from the atmosphere and the effects observed.

http://pubs.giss.nasa.gov/docs/2013/2013_Lacis_etal_1.pdf

By comparing the top of the atmosphere outgoing radiation with the surface radiation, a global average greenhouse effect, GHE, is experimentally observed on Earth to be about 152W/m². This can be verified using the GCM’s whereby all GHG are removed as seen in the short term. (Greater surface cooling is observed if these GHG are removed over longer terms because the ice albedo positive feedback kicks in). If CO2 is singly added to the GHG depleted atmosphere it creates about 40W/m2 immediately to the GHE. This value is larger than its contribution today because it overlaps with wavelengths that would be absorbed by water vapour, WV, mainly but also by other GHG. This overlap can be quantified by another experiment. If CO2 alone is removed from an otherwise complete GHG compliment then it reduces the GHE by 24W/m2. In this case the other GHG’s absorb wavelengths that would be absorbed by CO2. Lacis et al calculate a normalised GHE due to CO2 in our present atmosphere of 31W/m2 or about 20% of the GHE. Similarly it can be shown that WV contributes about 75% of the GHE. However, importantly, they also look at the response of a WV only depleted atmosphere and notice that within days the WV is returned due mainly to the influence on temperature from the presence of the other GHG’s and in particular CO2. (In fact they estimate that about 80% of the WV is returned due to GHG from similar experiments by finding out how much WV would exist without any of the other non-condensing GHG). This of course is a measure of the WV feedback.

Nova has crudely attempted to look at these overlaps, ignore the positive WV feedback and instead has confused the role of water vapour’s contribution to the Planck response as a negative feedback.