Wind Power and Climate Change .
). Version of
This note describes my
interpretation of the significance of recent scientific work on the effect of
wind power on local and global climate. This is a non-technical overview
written to provide basic answers to some of the many questions I have received
about our paper in Proceedings of the
Results from climate modeling studies by myself and others
suggest that large-scale use of wind power can alter local and global climate.
Wind turbines can change wind patterns which can in turn change the climate by
(slightly) altering amount of heat and moisture transported by the winds. The fact that an enormous number of wind turbines can
change the climate is not important; many human activities can change the
climate if they occur at a sufficiently large scale.
I think the work on the
climatic effects of wind power raises three interesting questions. First, will
climate change due to wind turbines be noticeable in the face of other climate
changes caused by humans? Second, how does the unintended climate change due to
wind turbines compare to their intended effect in reducing global warming?
Third, what will be the impact of climate change caused by wind-power?
Will climate change due to wind turbines be noticeable
in the face of other climate changes caused by humans?
Our results suggest that on a
global scale the answer to this question is no. Unless the use of wind power
grows so large that it supplies roughly as much power as the entire current
global electric power system, the large-scale climatic effects of wind power
will likely be negligible. It is plausible, however,
that significant local climate change
could occur in areas where wind farms are concentrated even if wind supplies a
small fraction of global electricity demand.
How does the unintended climate change due to wind turbines
compare to their intended effect in reducing global warming?
The primary reason for
building large amounts of wind-power is to reduce the carbon dioxide emissions
that cause climate changes such as global warming by replacing coal-fired power
plants (and other carbon dioxide emitting power sources) with wind power.
Suppose one builds a single wind-turbine and uses its power to replace
electricity from a conventional coal-fired power plant. By reducing carbon
dioxide emissions, the wind turbine will have a tiny (unmeasurable) effect in
reducing global climate change. The wind-turbine will also cause a tiny and
likewise unmeasurable amount of climate change by altering wind patterns. The
question is what is the ratio of these two climatic changes? What is the ratio
of climatic cost to benefit? This question matters for any amount of wind-power
if it is build with the intention of reducing climate change.
We cannot answer this second
question definitively. Our results show that while the climatic benefits of
wind-power exceed the unintended effects, the unintended effects seem to be
large enough that more research is needed before we can decide whether or not
they can be ignored.
We can put this somewhat
evasive answer in context by imagining another possible outcome of our study.
Suppose for example, we had found that the unintended effects were a thousand
times smaller than the benefits. We could then have published a paper stating
conclusively that these climatic effects could be ignored. There would have
been no need to do further work aimed at reducing the uncertainties in our
estimate because it would make no difference whether the unintended effects
were a hundred or a thousand times smaller than the intended climatic benefits.
But that is not what happened. We found that the unintended effects may be
(very roughly) as large as a fifth of the intended climatic benefits. Because
there are substantial uncertainties in this estimate we still cannot say
whether it will make sense to consider these unintended climatic effects in
future decisions about the development of wind-power. We must fall back on the
classic academic conclusion that more work is needed.
One of the largest
uncertainties in our results is a quantity we call the atmospheric efficiency,
the ratio of electric power extracted from a wind farm to the amount the wind
farm alters local winds. Results from a high resolution model of local weather
published by Somnath Somnath Baiyda Roy and
collaborators in the Journal of Geophysical Research, suggest that the
turbulence created by wind farms can have significant impacts on the climate
near a wind farm. These results suggest, but do not prove, that the atmospheric
efficiency may be significantly lower than the value we used in the our paper, which in turn suggests that we may be
underestimating effects of wind turbines on climate. Additional research is
needed to resolve these questions.
Finally, is worth noting that
questions about the comparison between the intended and unintended climatic
effects of wind-power cannot be resolved by climate science alone. The
unintended climatic impacts of wind power occur immediately whereas the
intended climatic benefit are initially zero and grow slowly with time as
electricity from wind reduces carbon dioxide emissions and slows the growth of
carbon dioxide concentrations in the atmosphere. A comparison of the effects—a
climatic cost/benefit calculation—depends, among other factors, on (i) how impacts at different times and locations are
aggregated, (ii) the effectiveness of electricity from wind in reducing carbon
dioxide emissions, and, (iii) the assumed future course of carbon dioxide
emission during the next century or two, the “baseline scenario”.
What will be the impact of climate changes caused by
use of wind-power?
Wind-power may alter local or
global climate, but the resulting climate change will not be like global
warming caused by carbon dioxide emissions. The climate changes caused by wind
power may not be harmful. Indeed, our initial results suggest that the (very
small) climate changes due to wind-power may slightly reduce the much larger
impacts of climate changes due to global warming. It is possible that
wind-power provides a double benefit both by reducing global warming and by
creating additional climate changes that slightly reduce the impacts of that
warming. Additional research is needed to understand the impact of the climate
changes that might arise from wind-power.
Implications for climate policy
We should not be too
surprised that extracting wind-power might affect the climate. Our appetite for
energy is now so large that we should expect some environmental consequences if
we draw a significant fraction of our energy needs from natural systems. We
should not abandon renewable sources of energy, but we should not ignore to the
environmental impacts of large-scale renewable energy systems.
While it is important to
consider the environmental impacts of wind-power and other large-scale energy
technologies, we must keep our eye on the ball. Our existing energy system
based on such as coal, oil and gas has enormous environmental impacts. Carbon
dioxide emissions from use of these fuels will cause large-scale climatic
change within a single human lifetime. We should act now to reduce our
emissions of carbon dioxide; and we should to protect the people and ecosystems
most vulnerable to the inevitable climatic change to which our historical
emissions of greenhouse gases have already committed us.