Checking the facts

The IPCC's projections for the future effects of climate change are generated, as is well known, by an array of computer models which attempt to reproduce the highly complex inter-connected aspects of the Earth's atmosphere and climate. This approach has often been criticised because it places undue reliance on a set of assumptions and treats the output as though it represented reality. But, setting aside these concerns, what if some of the basic data used as inputs for the models was wrong? As the saying goes, "garbage in, garbage out".

Serious questions have previously been asked about the economic growth scenarios used. Broadly, these assume growth rates for developing countries which many economists regard as unrealistically high, leading to a modelled global economy which, by the end of the present century, would have a much greater energy demand than would be likely for more reasonable rates of growth. David Henderson and Ian Castles also pointed out in 2002 that economic growth was modelled on the basis of market exchange rates rather than the more meaningful purchasing power parity, again artificially inflating the size of many economies. Even the lowest growth scenario postulated a 70-fold increase in GDP/capita for developing countries in Asia from 1990 to 2100. Nothing close to this has ever been achieved before.

But there are other areas of concern. The IPCC "business as usual" baseline assumes limitless supplies of fossil fuels over the next century or more, such that the vast increase in energy needed to enable the enormous projected growth in the global economy would essentially all be supplied by oil, gas and coal. The underlying trend of reducing carbon intensity in growing economies does not seem to have been taken into account, but there is an even more basic issue regarding exploitable reserves of fossil fuels.

According to the 2009 BP Statistical Review of World Energy, proven reserves of oil stand at 1,258bn barrels (42 years at current consumption rate), of gas 185 trillion cubic metres (60.4 years) and coal 826bn tonnes (122 years). Total world energy consumption in 2008 was 11.3bn tonnes of oil equivalent (btoe), including nuclear, hydro and other forms of power.

Reserves are a flexible concept, since they increase not only as more discoveries are made but also as prices increase so as to make the more difficult-to-reach reserves economic to exploit. Thus, in the case of oil, the reserves-to-production ratio has risen with time (even as consumption has increased) and remained above 40 years for the last decade. Some economists therefore see fossil fuel resources as effectively infinite: as the price rises, so do exploitable reserves. Of course, once the price rises too far and remains there, the incentive to use other forms of energy increases greatly. So consumption of oil, gas or coal would be expected to fall steadily as it becomes more difficult to extract it at the same rate.

But there is another school of thought, which believes in the concept of Peak Oil. As a global concept, it is an extension of the (correct) prediction made by geophysicist King Hubbert in 1956 that US oil production would peak around 1970, even with the most optimistic view of likely reserves. Others have previously questioned the likelihood of IPCC assumptions on fossil fuel use being right, but Prof David Rutledge of Caltech has analysed the situation in some detail. (Readers can access Prof Rutledge's lecture and slides at http://rutledge.caltech.edu/ and form their own opinion.)

Not only does he conclude that exploitable global oil reserves are finite, but he questions the prevailing view that there are sufficient coal reserves for well over a century (indeed, unlike oil, proven coal reserves have fallen over recent decades). He estimates total exploitable reserves of oil, gas and coal at 938 Gtoe (gigatonnes oil equivalent). On that basis, we have already used about 40% of the total, and 90% of total resources would be exhausted by 2068.

Compare this with the IPPC view from their Fourth Assessment Report (AR4). The scenario which gives the lowest economic growth and energy usage figures still projects cumulative fossil fuel use by 2100 of more than the total reserves estimated by Prof Rutledge. Other scenarios project at least twice this figure, with usage still accelerating at the beginning of next century. But using the figure of 938 Gtoe, the projected peak for atmospheric carbon dioxide concentration is 450ppm, and calculated average temperatures would rise by 2°C, assuming the IPCC figure of 3° rise for a doubling of CO2 level.

If this view is right, all the effort currently aimed at drastically reducing carbon dioxide emissions is unnecessary, as peak atmospheric concentrations of the gas and the likely average temperature rise fall below what is considered to constitute "dangerous" climate change. If the conclusions are only part correct, and total reserves are underestimated, this work still calls into question the more extreme of the IPCC scenarios, under which fossil fuel use would still be growing strongly by the turn of the century.

Either way you look at it, this suggests that much of the output of the IPCC's models bears little relationship to the real world. With so much at stake, the least we can expect is for scientists and policymakers to make sure that they are using the right data. Garbage in, garbage out.


Ocean "acidification"

In what is increasingly looking like a fallback position for the carbon-control lobby, the issue of ocean acidification is getting a higher profile. The argument goes that, whatever happens to the air temperature, a higher level of carbon dioxide in the atmosphere will lead to greater concentrations in the oceans (which is unarguably true). However, CO2 affects pH by forming a weak acid (carbonic acid) when it dissolves. Everything being equal, more carbon dioxide will move the pH in the acid direction and this, argue some, will ultimately be dangerous for sea life, since many creatures will find it increasingly difficult to use the calcium in seawater to produce their shells.

In practice, the situation is more complex than that. First, the oceans are actually slightly alkaline, with an average pH of 8.2 (although alkalinity varies by about 0.3 unit from area to area). To become acid, the pH must fall below 7 (neutrality). So far, in moving from the generally-accepted pre-industrial figure for atmospheric carbon dioxide concentration of 280ppm to the present roughly 380ppm, ocean pH has dropped on average by about 0.1 unit.

It has been projected that, by 2050 a doubling of carbon dioxide in the air to 560ppm would reduce ocean pH by over 0.2 unit, bringing it just below 8, and that this could go as low as 7.8 by 2100. The problem is that we are looking at the output of models once again, and no-one really knows how long it would take excess CO2 to be taken up by the deeper ocean, or whether the buffering capacity of the complex mix of ions in seawater – and the seabed and shorelines they are in contact with – has been properly taken into account.

But, even more importantly, if fossil fuel reserves really are as constrained as Prof Rutledge suggests, atmospheric carbon dioxide levels would peak at 460ppm. The scope for ocean "acidification" could therefore be much less than assumed. The same garbage in, different garbage out.



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