Wednesday, May 02, 2012

Blow The Man Down

Something like 1% of the Solar energy Earth receives is converted into kinetic energy. Some fraction of this can plausibly be captured by wind turbines and the like, and wind power represents a rapidly growing fraction of our energy supply. A teapot sized tempest has been raised by some measurements which tend to show that wind power generation causes some local warming.

Lumo takes a look, but can't resist some of the usual nonsense, apparently intended to show that warming due to wind power could plausibly compete with that due to CO2.

The authors of the Nature Climate Change article have used satellites to look at the West central Texas as its climate evolved between 2003 and 2010. This place is where some of the world's largest wind farms are located. They found out that the warming trend converted to the usual "units of trend" used at this blog – degrees per century – is as large as 7.2 °C per century in the places with wind farms. One shouldn't automatically believe the centennial extrapolation of the trend.

Well, duh. In fact the physics make it perfectly clear that believing in a centennial trend here would be transparent idiocy. Whereas CO2 added to the atmosphere will linger for tens of thousands of years, wind turbine effects will dissipate within hours of turbine shutdown.

Consider that physics. Earth is a big heat engine, powered by the Sun, with excess heat absorbed in tropical regions being transported poleward where it is more easily radiated into space. Tapping into wind power slows that transport, so there is a first order effect which could be expected to cause some warming. Feedback type effects are another question, but the first order effect is very small even for rather large increases in wind power consumption.

The local effect has a different mechanism. Ground is a more effective radiator than the atmosphere, so the surface usually cools a lot more than the atmosphere, especially on dry, clear nights. Wind turbines stir the lower atmosphere, mixing warmer night air down at night. This can produce significant local warming, affecting irrigation needs and crop choices. It also produces a small global cooling effect, by bringing the warmer air into contact with the radiating surface.

Bottom line: if you are a farmer down wind of a wind farm, the effects may be important. Globally - not so much.