The real reason why global warming doesn’t matter

March 14, 2007

Because energy disaster looms anyway. Pretty soon, one of three things will happen : one, we achieve a sustainable low energy culture; two, we solve all the worries of nuclear power and have a high energy lifestyle; or three, civilisation collapses and we revert to a mediaeval economy.

I watched the Channel 4 documentary “The Great Global Warming Swindle” and have been trawling the blogosphere for comment since. Reactions divide pretty evenly in two. One half is along the lines of “Completely convincing ! I always suspected global warming was a hoax and now its been proved !” and the other half, who say “Sigh. Where do I start explaining the mistakes ? And these guys are all marxists with a weird agenda anyway.” As a piece of agit-prop, it was superb. Beautifully made, clearly argued, with just enough emotion to engage you, but not so much you get suspicious. Although there were one or two semi-cranks interviewed, there was also an impressive list of real scientists. However, at least one of those has now complained that his views were misrepresented…

As an astronomer, the argument that the dominant factor in climate change is cloud cover variation caused by changes in solar cosmic ray flux is of course appealing. (There is a useful explanation here, and some informed criticism here) There is a small chance that this completely explains climate change, but mostly it just adds a systematic uncertainty, making it harder to estimate the correct magnitude of anthropogenic climate change. The C4 show mocked the “precautionary principle” but its correct; given how long the world economy supertanker takes to turn around, can we take the risk that its all an illusion ?

So now the scary bit. As the oil runs out, we may end up with catastrophically less energy consumption, and correspondingly less carbon production, and so avoid global warming and just have darkness, poverty, and misery instead.

So… when the question of when the hydrocarbon reserves will run out is another famously contentious issue of course. I am not a technical expert, but I did read an excellent popular book – “The End of Oil” by Paul Roberts. Coal may last somewhat longer, but it has to go eventually, and meanwhile we keep getting greedier …Roberts does a nice analysis of growing energy needs. With our current rate of energy consumption growth and population growth, and assuming that developing nations catch up with the West, but also allowing for continuing improvements in energy efficiency, Roberts estimates that by the year 2100 the world energy consumption will be 50 TW. (50 TeraWatts, or 50 times a million million Watts).

Decades before this the oil and coal will be running out or becoming unproductive to extract; and many years before this the increasingly difficulty of extraction will be leading to horrible international tensions.. this is starting now of course. So new energy sources must come to our rescue !! Biofuels, hydrogen, wave power, solar energy, wind farms .. the more the better !

But what Roberts, and most others, don’t point out is that there is a renewable bottom line : the solar constant. All renewables are driven by solar energy – plants are recycled sunlight, the wind is driven by solar heating, and so on. Hydrogen cells are just a storage mechanism. Something has to make the energy first. Hydrocarbons of course represent millions of years of accumulated sunlight stored up underground. Once they are used up, we can’t use more energy than is falling on the surface of the Earth. There are only two exceptions. The first is nuclear power. The second is geothermal energy. However the heat emerging from the entire land surface of the Earth is somewhat less than the current world energy consumption, so this will never be a big factor.

So how much sunlight is there ?

The total amount of solar radiation falling on the surface of the earth is roughly 1.7 x 10**17 Watts. Thats everything – all wavelengths, falling on the oceans, Antarctica, or whatever. How much can we use ? Half of this is reflected. We could maybe at most cover 1% of the Earth with photo-cells with 10% efficiency, or perhaps 10% with biofuel crops at 1% efficiency. All in all, in round terms we might get half of one thousandth of the above if we are lucky. Thats 85 TW max.

The astute reader will now notice that this (85 TW) is close to the predicted world energy consumption in 2100 (50 TW). A somewhat bigger growth, or a somewhat less optimistic return on solar energy, and we simply won’t make it. We are perilously close to a magical dividing line in human history. There are three paths from here :

(1) We solve the problems of nuclear power and get as much as we want.

(2) We build a global lifestyle that stabilises at 5kW each.

(3) We do nothing until war and chaos destroy the global infrastructure and we revert to a mediaeval economy.

Even scarier, uranium supplies are finite so nuclear fission may be no good either. (Understandably, this is vigorously denied by the Uranium Information Centre of Australia ..) So how about fusion ? Well its promising but we have been trying for decades and still can’t get out more energy than we put in, let alone produce energy on an industrial scale.

Maybe I should teach my kids how to use a bow and arrow, and move to the Hebrides.