October 5, 2018

expert reaction to research on climatic impact of wind power

Research published in Joule shows that wind power reduces emissions while causing climatic impacts such as warmer temperatures.

 Dr Alona Armstrong, NERC Industrial Innovation Fellow and Senior Lecturer in Energy & Environmental Science at the Lancaster Environment Centre, said:

“What this study, and others, suggests is that wind farms can cause localised and regional warming – not global warming. Studies have also shown wind farms can cause cooling further away.

“If you turn the wind turbines off the warming effect will disappear. In contrast, if we turn off fossil fuel plants, the planet will stay warm.

“In the energy debate warming is commonly the headline as it is driving the energy transition. However, as we transition to low carbon sources it will be increasingly important to consider a fuller suite of environmental impacts, for example land take and resource use.”

Prof Kevin Anderson, Professor of Energy and Climate Change at the University of Manchester and Deputy Director of the Tyndall Centre for Climate Change Research, said:

 “David Keith always adds curious nuances to a debate.  Here his work on wind power needs to be considered alongside other similarly interesting but ultimately minor factors.

“A significant proportion of the energy used to propel the globe’s 1.5 billion passenger and commercial vehicles and to keep the 100 thousand flights per day in the sky goes into pushing huge quantities of air out of the way.  Add to this how cities and towns not only create heat islands but also move, channel and absorb energy from the wind. All of these will have some small impact on the climate at some particular scale. But let’s not get lost in the noise. Whilst scientists and academics rightly spend hours poring over every detail, the headline message remains unchanged. The climate change we are witnessing and looks set to continue arises primarily from burning fossil fuels – with deforestation and eating meat also important factors. So great to see David’s paper – but let’s keep it in perspective and not use it as yet another excuse for kicking real mitigation still further into the long grass.”

Prof Stephen Mobbs, Director of the National Centre for Atmospheric Science, said:

“This is an interesting study, which is balanced and consistent with other studies on the topic of the atmospheric effects of wind farms.

“The study uses the Weather Research and Forecasting (WRF) atmospheric model, with the addition of a representation of the local effects of wind turbines. The model has been run to simulate a year of operating wind farms to provide 14% of current US energy consumption (an increase of 18 times over current US onshore wind energy generation capacity).

“It is already well known (and indeed quite obvious) that wind turbines create increased mixing of the lower part of the atmosphere and also generate some additional atmospheric turbulence. These processes have the largest effect at night, because during the daytime the atmosphere is already usually quite well mixed.  The effect at night is to mix warmer air downwards towards the normally cold surface, increasing surface temperatures. There are also other consequences, such as potentially increasing surface evaporation rates slightly.

“It is crucial to understand that wind turbines *do not* significantly warm the atmosphere. They simply redistribute heat in the atmosphere, which is already naturally present, so that more heat is present near the surface. This contrasts with the effects of greenhouse gases such as carbon dioxide; increasing carbon dioxide causes a real increase in the energy (and hence temperature) content of the atmosphere.

“This study confirms the results of previous local modelling and measurement studies of wind farms (including our own in the National Centre for Atmospheric Science). It integrates this up for the whole of the US, predicting increases in average surface temperature over the regions of the extensive wind farms of 0.5-1.0 degrees.

“The study then attempts to compare the surface temperature increase due to wind farms with the consequently avoided temperature increase due to not burning fossil fuels (estimated globally, not just over the US). The study explains and caveats the results rather well. It is crucially important to understand the caveats, because the potential for misunderstanding is considerable. If all US power generation by fossil fuel burning were suddenly replaced by wind farms, then the surface temperature effect from the wind farms would be felt immediately.

“However, the avoided global atmospheric warming due to not adding greenhouse gases to the atmosphere would grow cumulatively over time.

“The study estimates that it could take up to a century before the surface effect of avoided greenhouse gas induced warming exceeded the effect of the turbines, but the study points out two crucial factors:

1) The effect of greenhouse gases is cumulative and will last for many thousands of years (essentially indefinitely in policy terms) whereas the effects of wind farms would stop immediately if they were turned off.  If we are to limit the total emission of greenhouse gases, the sooner action is taken the greater the limitation.

2) Wind farms do not add any significant heat to the atmosphere; they only redistribute it.

“The study provides a good discussion of other limitations and caveats.

“Overall, this appears to be a useful and balanced contribution to the development of energy policy. It most certainly does not suggest that the environmental effects of wind farms (which are local and immediately reversible) are in any way comparable to those of burning fossil fuels (which are global and irreversible on human time scales).”

Prof John Shepherd FRS, Emeritus Professor in Earth System Science at the University of Southampton, said:

 “The model results support observations that wind turbines cause some near-surface warming, because they increase mixing of the lower atmosphere, as do trees and tall buildings. The effect is quite small, and occurs mainly at night (when temperatures are often higher well above the ground). Unlike burning of fossil fuels, the warming is due to the redistribution rather than addition of heat. It occurs immediately, and is mostly confined to the continental area where the power is being generated. The warming only happens once (for a given level of power being generated), so unlike burning fossil fuels it does not build up cumulatively over many centuries and all over the world. The headline figure of 0.24 C of warming sounds a lot, but this relates to a very large deployment of wind turbines (enough to generate all current US electricity) and applies only to the continental USA: it therefore equates to about 65 times less of global warming. Comparing the effects with those of fossil fuels is quite complicated, but overall (as the authors say) wind power “still beats fossil fuels under any reasonable measure of long-term environmental impacts”.

 Dr Judith Wolf, renewable energy physicist at the National Oceanography Centre, said:

“The headline of the press release is controversial and needs careful understanding to put it in the correct context. The new paper by Keith and Miller is not saying that we should not use wind energy as a relatively ‘green’ energy resource, but it does warn that there are climate impacts of using wind power, because extracting kinetic energy from the wind has effects on the atmospheric boundary layer, causing a redistribution of heat, leading to a non-negligible warming of the surface land temperature at night.

“The authors review recent studies which have mostly found a night-time warming effect of wind farms, and scale up the effects to estimate the effects of producing a substantial amount of the US electricity demand by onshore wind power. Their methodology is not controversial, using a well-validated regional atmospheric model although there are some necessary assumptions in order to perform the calculations, which are discussed within the study in Box 1. They provide plausible results which are a useful contribution to the debate about decarbonising our energy production.”

Prof Bob Lowe, Chair of Energy and Building Science at the UCL Energy Institute, said:

“While the mechanisms at work have been understood for some years, this paper shows that wind turbines may impact temperatures at the regional scale. However, the paper does not provide evidence as to the possible impact of large-scale deployment of wind turbines on the climate of the world as a whole. To begin to address this crucial problem, one would need to model climate at the global rather than regional scale.  In particular, the Arctic is omitted from Keith & Miller’s analysis. They can therefore say nothing about impacts of positive feedback mechanisms associated with the Arctic, or the possibility that large-scale deployment of wind power will move us closer to, or away from potential climate tipping points.

“We are, however, certain that the combustion of fossil fuels changes global climate. While we acknowledge the importance of ongoing research on potential climate impacts of large-scale deployment of renewables, and of technologies such as BECCS, it would, in our view, be a mistake to slow the deployment of wind power in the light of this paper.”

Prof Roger Kemp FREng, Professorial Fellow at Lancaster University, said:

“This paper is about the local effects of wind turbines. A wind farm that extracts energy from the wind will generally reduce the windspeed downwind of the turbines. This will have small and localised effects on the weather – with less wind, the land might become slightly warmer and, depending on the land characteristics, less wind could also result in less evaporation leading to slightly lower humidity.

“The USA uses about 4,100 TWh of electricity per year [source: Wikipedia].  Averaged over the year, that is 470 GW. The load factor of wind turbines in the US is 34%.  (Load factor, or capacity factor, is the actual yearly output compared with what it could be if the wind were blowing strongly 24/7 all year.)  Keith and Miller’s paper assumes all US electricity is provided by wind power. Assuming the same load factor and making some allowances for peak wind not aligning with peak load, that represents more than 1000 large turbines which, their calculations suggest, would result in an increase of 0.24 degrees C over the US landmass.

“What the summary of the paper does not do is to consider how turbines affect global temperature rise. Global warming is determined mainly by the balance between heat input from the sun and heat radiated by the earth into outer space. The number of wind turbines on earth does not affect the heat input from the sun, neither does it affect the layer of “greenhouse gases”, principally carbon dioxide, which prevent the radiated heat escaping to outer space. If the land temperature over a certain area is slightly higher, it will result in increased radiation from that area which would tend to lower the net heat input to the earth. Thus, one might expect a slightly lower global average temperature. However, marginally reduced wind in one area could cause other local changes in the complex climate system so no-one could guarantee exactly what would happen.”

‘Climatic Impacts of Wind Power’ by Lee M. Miller and David W. Keith was published in Joule at 4pm UK time Thursday 4 October 2018.

Declared interests

Dr Armstrong: “I receive funding for energy-environment research, much of which is in collaboration with solar industry stakeholders. I have also previously contributed to the development of ‘Guidance on the assessment of peat volumes, reuse of excavated peat and the minimisation of waste’ produced by wind farm developers.”

Prof Shepherd: No interests to declare.

No others received.