Shub, I recognise that telling it simply has no artistic effect, but 'spewing out... left and right' is rather an exaggeration for one sentence: Net oil imports were 80 million barrels in 2010 implying a cost at current prices of around $8bn. This is net oil imports, not consumption. It dwarfs any green spending, wouldn't you say?

Rhoda,

I assume you are still, after all this time, waiting for your best evidence.

A posting by Marion [ http://bishophill.squarespace.com/blog/2012/7/7/redwood-writes.html#comments Jul 8, 2012 at 12:56 PM Marion ] prompted me to put down my understanding (as a bystander) of "the best evidence". If I've got it wrong, no doubt someone will correct me.

Here is my own understanding of the "evidence". I have the impression that the evidence can be sumarised as follows:

(1) The world has been warming.
(2) Atmospheric CO2 levels have been rising and this is due to fossil fuel use and land use change.
(3) The rising CO2 levels have caused the observed warming.
(4) CO2 levels will continue to cause warming in the future.

(1) is shown by the instrumental record and, prior to the instrumental record, by analysis of proxies such as tree rings.

Marion has listed the issues I was vaguely aware of with the instrumental record.

I had read about issues such as "the original data has been deleted (UEA)", "the homogenisation has been done by undocumented methods", "the quality of many instrument sites is in serious doubt (next to air conditioner outputs etc) - WUWT". To me, even a single one of such issues would mean that the instrumental record would have to be regarded as unfit for purpose. But I have read that studies by climate scientists have shown there is no need to worry about these things.

The use of proxy data (eg tree rings) has its "convergence problem" . It also has the problem that records that don't correlate with the temperature record are, apparently, excluded from the analysis. Climate scientists don't seem to see that as a problem. Who am I to say otherwise?

(2) The rising CO2 levels are shown by Mauna Loa data since around 1960. (Before then, I don't know. Ice records, perhaps?). This has been caused by fossil fuel use and land change use is confirmed by common sense and the close match between annual anthropogenic emissions and the rising atmospheric levels - one is consistently around 45% of the other. Probably by C12/C13 arguments too, though I am ignorant about that.

(3) My understanding of the evidence that the warming to date has been caused by CO2 Is as follows:

- It must have been that because we don't know what else could have caused it.

- Climate models, including the Met Office model, run with CO2 switched off do not show the full warming 'observed'. But, with CO2 switched on, the observed warming is reproduced. That confirms it. This also confirms that the Met Office models can be relied on to predict future climate.

(4) CO2 hangs around a long time - part of it forever, for practical purposes. This is described by the "Bern model" which is referenced by the IPCC. I don't know how the Bern model has been validated.

In carbon cycle modelling, there is discussion on "adjustment time" vs. "residence time" which, from my viewpoint as a bystander, has not yet been resolved and is relevant to calculating future CO2 levels.

In a nutshell, that is my understanding of the "best evidence". I somehow feel you have been waiting for something a bit more convincing than that. Either: (a) It does not exist, (b) I have got it wrong.

rhoda, I've said it before and I'll say it again. The oceans cover over 70% of the planet's surface; clouds over 60%. As climate scientists seem to admit they don't yet much understand how the oceans or clouds affect climate, so it seems to me that any theories about climate might so far be perhaps just a little premature.

Dung

The most helpful thing scientists could do would be to tell politicians "we really do not know enough to understand let alone predict climate and you should adapt as best you can until we understand more."

Why not read Spencer Weart's history of the scientific exploration of AGW? This is the timeline, which hyperlinks to the rest of the content on the site.

This 'we know nothing' meme is blinding you to the actual state of knowledge, which is more than sufficient to be sure that AGW is real, and potentially a very serious problem indeed. Retreating into a comforting blanket of ignorance is only an option for those who do not loudly proclaim that they are 'sceptical' of the science. If you are going to do that, you need to be much more conversant with the science you claim to be 'sceptical' about. Especially since you presume to be in a position to tell scientists what they should be telling policy makers.

BBD

We need to know the sensitivity of the atmosphere to CO2 emissions. To do so needs at least an understanding of how the phenomena of globally ubiquitous cloud formation, precipitation and dissipation can confidently be calculated as they respond to such changes in atmospheric composition as are consequent on increases in the proportions of CO2 not feasibly measurable on any scale coarser than parts per million.

You well understand this problem BBD. So please explain why you are not troubled by this glaring lacuna in our knowledge.

simon abingdon

First, definitions. We need to know the sensitivity of the climate system to increased radiative forcing.

We can ask simple questions like: has the climate system ever been warmer than the present? Obviously we know that it has.

We can infer that whatever global changes occurred in cloud formation as the climate system warmed, they did *not* act as a negative or even neutral feedback or the climate system would not be capable of warming up. Obviously. That's what neutral or negative feedback means.

If clouds represented a neutral or negative feedback to increased RF, known past climate behaviour in response to slight changes in forcing would not - could not - have occurred.

@BBD Jul 11, 2012 at 9:10 PM

Your argument is simplistic as it assumes "other things being equal" on historical timescales and that variables can always be considered in isolation. The ramifications of the multifarious interplays among competing climate effects will continue to defy any attempt at formulating coherent theory.

In science, only one thing really counts and that is the support for a theory provided by observations. The global warming that was earlier predicted with what is now seen as premature confidence has not been realised. Contrary to expectation CO2 increases cannot be shown to correlate with temperature rise after all, so a search has had to be made for convenient straws to clutch (like aerosols) in the hope of rescuing dogmatic theory.

Adequately understanding climate will gradually be accepted as a necessarily Sisyphean task. As the descent into the next ice age begins, AGW will be seen for what it is: an inexplicably hubristic footnote to history.

simon abingdon

Your argument is simplistic as it assumes "other things being equal" on historical timescales and that variables can always be considered in isolation. The ramifications of the multifarious interplays among competing climate effects will continue to defy any attempt at formulating coherent theory.

I'm baffled here. The reasoning I used doesn't have any of the faults you outline. In fact it is distinguished by avoiding them.

If clouds were a negative or neutral feedback, the climate system could not warm under modestly increased forcings (eg Milankovitch; MWP; 1910 - 1940). Climate variability would be smoothed out.

The same holds for the net of all feedbacks, known and unknown. Unless feedbacks net positive, the climate system cannot respond to minor changes in forcing. Everything known about climate behaviour on all time-scales demonstrates that it is sensitive to minor changes in forcing. Therefore feedbacks must net positive.

That's why increased forcing from CO2 will gradually engage positive feedbacks and slowly, discontinuously at first, warm the climate system.

The recent flattening of the warming trend is interesting but beside the point. Consider it a demonstration that the climate system is sensitive enough to be influenced by Increased stratospheric sulphate aerosol loading from Chinese coal and equatorial volcanism, predominantly La Niña conditions, the historically quiet solar cycle 24, heat mixing into the deep oceans and more besides. But if CO2 forcing is maintained, never mind increased, the warming will resume in due course. How can it not?

@BBD Jul 12, 2012 at 10:29 AM You say "How can it not?" I say because the forcing may itself provoke an unanticipated feedback of greater value. There is no law of nature that says this cannot happen. Your final paragraph includes the phrase "and more besides". Indeed so. Who knows what unsuspected cans of worms remain to be opened?

simon abingdon

You say "How can it not?" I say because the forcing may itself provoke an unanticipated feedback of greater value. There is no law of nature that says this cannot happen.

The entire history of known climate behaviour says you are mistaken...

I don't think you have really understood the point I was making above. The entire history of climate behaviour makes a mockery of your position.