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Carbon Brief Staff

11.09.2012 | 1:00pm
ScienceNew models suggest wind power won’t cause global warming
SCIENCE | September 11. 2012. 13:00
New models suggest wind power won’t cause global warming

Two new studies have suggested that wind turbines have less of a warming impact on the temperature of the atmosphere than previous studies have suggested, unless deployed at a level that far exceeds current global power demand.

Wind turbines have the potential to affect temperatures because they reduce wind speed, a process that has a slight warming effect on the atmosphere. In addition, the kinetic energy produced by turbines returns to the air as heat, after the electricity they produce is used. Previous studies, such as one released last year by the Max Planck Institute for Biogeochemistry, had suggested that this warming effect could be so severe that it could negate some of the climate benefits of switching to wind energy from fossil fuels.

Measuring wind’s climate effects

The first piece of research, released in the journal Nature Climate Change on Sunday, finds that wind power on the scale needed to meet global power demand would only have a tiny effect on the climate.

According to a team led by Ken Caldeira from the Carnegie Institution for Science, harvesting wind power could have substantial climate effects  – but only if it’s deployed on a truly massive scale that far exceeds current global energy demand.

But even at the (relatively large) level of meeting current global energy demand, the paper says these effects would be small, as long as turbines are spread out evenly. Meeting global demand with wind power might affect surface temperatures by around 0.1 degree Celsius, the research estimates, and affect precipitation by around one per cent, although it’s not clear to us whether this means up or down.

The paper as a whole looked at the potential for wind to produce large volumes of power. It concludes that winds at high altitudes could provide more than 1,800 terawatts of power, while surface winds have the potential to produce more than 400 terawatts. If this seems like a lot – the world currently uses about 18 terawatts of power – it’s important to be clear that this is an examination of the geophysical limitations to wind power extraction, and doesn’t consider technical or economic factors.

As Caldeira points out:

“Looking at the big picture, it is more likely that economic, technological or political factors will determine the growth of wind power around the world, rather than geophysical limitations.”

Aiming high

In the second paper, released online before print in the journal Proceedings of the National Academy of Sciences yesterday, scientists used a new model to test research which suggested that the way wind turbines move air around could create a warming effect.

The researchers say they were puzzled by the Max Planck Institute’s conclusion that that turbines could possibly have the same warming effect on the planet as a doubling in carbon dioxide levels. Researchers Cristina Archer from Delaware and Mark Jacobson from Stanford argue previous assessments have failed to correctly model atmospheric changes caused by wind turbines because they model change at the surface of the planet, and we should be measuring atmospheric changes at the height of the turbine hubs – the area where turbines reduce wind speed the most.

Modelling temperatures around the turbine blades suggests that wind power doesn’t affect the climate at any practical level of extraction – the paper discusses a scenario of 7.5 terawatts of wind worldwide, nearly half of the world’s current energy demand.

The researchers find that wind power could decrease wind speed at the height where the hubs are located and also, to a lesser extent, on the ground – but again, only if it were deployed on a really massive scale.

Compared to fossil fuels

Previous research also fails to compare turbines’ warming effect with that of other sources of energy, according to Archer and Jacobson. They point out that any changes wind farms cause to temperatures are small compared to the effects of nuclear, coal or natural gas – not least because wind doesn’t emit greenhouse gases. As the paper explains:

“If wind turbines generate 5.75 terawatts, such power ultimately returns to the air as heat following electricity use. This heat does not depend on the electricity source, thus it is also released when coal, nuclear and natural gas produce electricity. Such generators, though, produce additional heat due to combustion or nuclear reaction and [fossil fuels] emit global warming pollutants. As such, wind turbines reduce direct heat and pollutant emissions compared with conventional generators”.

Obvious perhaps, but useful context the next time ‘Wind turbines cause global warming!’ pops up.

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