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Wednesday, 16 September 2009

This is my model. If you don't like it, I have others.

About a year ago, I spent many weeks trying to get to the bottom of the man-made global warming debate. I diligently wrote notes and performed rough calculations to understand the physics and broader arguments from both sides. I had a good grasp of the basic physics, of planets surrounded by gases blasted by solar rays, of Boltzmann and black body radiation, eletromagnetc absorption and the rest, but I must confess a lot of the climate models seemed to me to be overly complex (to the extent that I understood them) to be reliable.

The problem I had was that whenever I tried to do a back of the envelope calculation I could never come up with the same level of temperature increase. My simplistic approach would be, for example, to take recorded atmospheric CO2 levels and known average surface temperatures, and extrapolate from there using forecast figures for hydrocarbon consumption/CO2 production reduced by previous annual rates of natural absorption of manmade atmospheric CO2, to give a guess of average world temperatures.

The approach was probably naive, but I reasoned that whatever processes were involved in future global warming were already at work, so what could be simpler than making a prediction by extrapolating from historic data? The trouble was that whereas my worst case was a temperature rise of about 1 degree, climate scientists and their models were coming up with numbers between 3 and 6 degrees.

Now, this never made sense, and because I neither understood nor trusted these models, I left it at that, but deep down I always had a gut feeling that these results were wrong. Why? Well because going back to the basic physics, a 6 degree rise in temperature (2% in degrees Kelvin) would imply an 8% increase in blackbody radiation (there is a 4-th power relationship between energy radiation and abolute temperature), and the effect of extra CO2 in the atmosphere didn't seem like something that would stop 8% of heat loss.

Whatever was going on in these models seemed to rely on secondary effects, tipping points, etc, and whilst there were many explanations, they defied common sense. Why, if temperatures varied widely over seasons, or even over the course of a day, were these effects not currently active, or were these tipping points not reached in extreme conditions?

Moreover, there is a gut instinct that says that if a natural system has reached some sort of equilibrium over time, then when the system is shifted away from that equilibrium point, various processes may well come into play to return it towards the equilibrium point that it had reached. For example, more CO2 in the atmosphere might encourage CO2 consuming processes such as plant growth, perhaps not as quickly as the CO2 was being produced, but common sense (not always right I will admit) tells me that this sort of secondary process would predominate rather than a positive feedback reaction, simply because the earth has been in a high CO2/high temperature before and yet it naturally cooled to the state it is in today.

And thirdly, I am naturally sceptical about any physical system which seems to accumulate energy rather than dissipate it. An analogy to the solar radiation hitting the earth might be water flowing into a bucket with many holes. As the bucket fills with water it eventually reaches a point where water is flowing in to the bucket at the same rate that it empties through the holes. If some of the holes are filled, the water level will rise (analagous to the temperture) and the higher pressure at the remaining holes will force the water out faster through those holes.

But that is not necessarily the only way the bucket will empty. Perhaps the extra pressure will cause the holes to stretch, or the water will rise to a level where it leaks through higher holes, or it even rise to the top of the bucket where it flows over the edge (but it doesn't rise any higher than the rim of the bucket). To my mind similar processes would apply to the heating of the earth, and my gut feeling would have to be that any global warming from CO2 would not be a process that continues indefinitely.

So I took a great interest when I heard that Mojib Latif of the Leibniz Institute of Marine Sciences at Kiel University said earlier this month that we might be about to enter one or even two decades during which temperatures cool.

"I am not one of the sceptics," he told more than 1500 of the world's top climate scientists gathering in Geneva at the UN's World Climate Conference "However, we have to ask the nasty questions ourselves or other people will do it."

Latif is an author for the Intergovernmental Panel on Climate Change. He predicts that in the next few years a natural cooling trend would dominate over warming caused by humans. The cooling would be down to cyclical changes to ocean currents and temperatures in the North Atlantic, a feature known as the North Atlantic Oscillation (NAO). He added that NAO cycles were probably responsible for some of the strong global warming seen in the past three decades.

Latif says NAO cycles also explained the recent recovery of the Sahel region of Africa from the droughts of the 1970s and 1980s. James Murphy, head of climate prediction at the Met Office, agreed and linked the NAO to Indian monsoons, Atlantic hurricanes and sea ice in the Arctic. "The oceans are key to decadal natural variability," he said.

Now that has me really confused. On the one hand, climate scientists are saying that there are natural processes that will dominate the effects of global warming. Secondly, they are also saying that those effects are also responsible for historic observed warming, so any calculations I may have made in the past about correlations between CO2 levels and temperature rises may have overstated the link, and so even my 1% forecasts may be overstated. So where do these 6% increases come from?

It strikes me that Airfix enthusiasts aren't the only modellers getting high on banned substances.

Oh, and its bad news for the Maldives then, because by my reckoning, lower surface sea temperatures means less evaporation, so a smaller depression in the earth's geoid in the Indian Ocean than the current 100m, hence higher sea levels.


harmonyfuture said...

You may be playing with fire here Alex. I too have always been ready to accept a certain amount of 'robustness' within our ecosystem but must now acknowledge the vast scale of humankinds ability to throw a spanner in the works. Doing back of the envelope calculations on population growth versus resource depletion, consumption rates and availability of basics (food & water) show that we shall be placing ever greater demands upon the planet. As such, the AGW movement may well be just a metaphor for the recognition of the industrial abuse of this planet and its possible, if not likely, consequences.

Alex said...

Well as I see it there are 3 ways we can mess up the world:
(a) biological - we make or propagate a virus or bacterium that destroys life forms,
(b) chemical - we fill the planet with pollutants that destroy the ecostem, or
(c) physical - we do something that changes the physical state of the planet.

But because of the sheer size of the place I find (c) by far the most implausible. Global warming is about sticking a spanner in the works of the process whereby we are heated by the sun and dissipate heat into space. If we wanted to heat the world, I think it would be hard to achieve.

harmonyfuture said...

D'accord, just got to avoid the other two.

I are wun said...

Good try, but too much 'gut feeling' for comfort

The CO2 greenhouse effect is surprisingly uncontentious. Each doubling of CO2 requires roughly 1C rise to restore radiation balance, other things equal

The dispute is over those other things. The models amplify each 1C up to 6C - positive feedback. Why?

There are good reasons to believe that negative feedback prevails, the 1C becoming only 1/3C - i.e negative feedback and stabilisation

If the models are right, we must be receiving excess heat (because the temperature has not yet increased to cause extra re-radiation). That heat has to go somewhere - it cannot be hidden or 'masked'. The planet's dominant heat sink (80%) is the top 750m of the oceans. These are well monitored.

There is no evidence of increasing ocean temperatures.

Therefore the models are faulty. QED. (latin for 'no gut required')

This is easy - economics is scary


Alex said...

Thanks Engineer

I think your version is a slight improvement on my own version of extrapolation from prior results.

Another way of looking at the issue is that if a doubling of CO2 -> 1 deg temp rise -> feedback effects -> 6 deg temp rise, shouldn't we be more concerned about the feedback effects than the CO2?

Couldn't the feedback effects be triggered by a 0.3% rise in temperature, which would be caused by a 1.2% increase in radiation from the sun, which would occur if the sun started burning more brightly, or if we moved 0.6% closer to the sun?

Well the difference between the perihelion and the aphelion of the earth's orbit around the sun is about 3%, implying a variation of 9% in the energy reaching the earth, or a 2.25%, 6.5 degree temperature increase, so where are those feedback effects?

Economics is easy, and its just like physics really. Think of economic value as energy, markets as heat flow.

Well almost: