Firstly this isn’t (entirely) a post about EROEI. The EROEI of wind is generally very high so the embodied emissions of building wind turbines in unlikely to lead to more emissions than they avoid.
No, this worrying suggestion is inspired by a recent study by Chien Wang and Ronald Prinn at MIT. They used a 3-dimensional climate model populated with prodigious numbers of wind turbines and showed that this large amount of wind turbines could cause disturbance to the atmosphere and lead to surface warming. Once their model reached a new equilibrium temperature after 40 years the average warming they found was 0.15°C from the installation of 5TW of wind globally. The real nightmare scenario is if this warming turns out to be bigger than the avoided warming from displaced fossil fuelled electricity generation.
The first potential consolation is that the effects they found “appear small when they are generating less than 1 TW globally” (p. 14). Total global installed capacity in 2008 was around 10% of that. However, the figure is increasing exponentially (GWEC, 2009) so that isn’t a source of much comfort in the long run.
The second consolation is that, despite the fact that some people are using it to support statements like, “I’ve never been a fan of large-scale wind power generation, for a variety of reasons. Here’s another one: they may be more harmful to the earth’s climate than burning fossil fuel is!!”, the paper makes no mention of the avoided emissions. Maybe there’s some solace to be found there if we actually do the analysis.
As I said, the average warming found in the MIT model is 0.15°C. If the warming avoided by 5TW of wind turbines is greater than that, then wind energy is in the clear on this charge and we can all sleep soundly again.
So what would be the carbon savings from this army of turbines? 5TW of wind turbines at a capacity factor of 25% would produce 438,000 TWh over the 40 years the MIT model took to reach equilibrium.
Using the UK carbon factor of electricity of 0.591 kgCO2/kWh (from SAP 2009), the total avoided emissions will be 0.26 trillion tonnes of CO2. In fact the carbon factor of electricity is probably higher that that across much of the world so if anyone has calculated a global average figure I’d love to use it to refine this analysis.
So how much warming would be averted through this reduction in carbon emissions? A paper in Nature last year suggested that the sensitivity of climate is based on cumulative emissions and the sensitivity figure found in the paper was 1.0 – 2.1°C per trillion tonnes of CO2 emissions.
Working through from this range we see that the 0.26 trillion tonnes of avoided emissions should lead to a cooling of between 0.26 and 0.54°C over the 40 years.
Putting the warming and cooling figures together the overall effect is a cooling of between 0.11 and 0.39°C.
And because this is the oCo Carbon blog you won’t get away without a look at the effect of the EROEI of wind. The embodied energy of the turbines can be represented as a reduction in the lifespan carbon saving of the turbines. The reduction will be less than 4% if we assume an EROEI of 25 and a carbon factor of energy invested of less than that for fossil electricity. The effect of this is to change the net effect of adding 5TW of big wind to a cooling of 0.10 to 0.37°C with an average net effect of 0.23°C of cooling.
So, the avoided warming is greater than the warming caused by the atmospheric effects. Panic over. Big wind is still a good thing for the climate.
But what about the change to planetary albedo from 5TW of photovoltaic panels?
Damon Matthews, H. Et al (2009) “The proportionality of global warming to cumulative carbon emissions” Nature 459, 829-832
Wang, C. and Prinn, R.G. (2010) “Potential climatic impacts and reliability of very large-scale wind farms”, Atmos. Chem. Phys., 10, 2053-2061