It is now a widely-accepted conclusion that the earth has become warmer over the last century. The Intergovernmental Panel on Climate Change (IPCC), established by World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) to monitor climate, estimated that the average surface temperature of the earth has increased during the last hundred years by about 0.6° ± 0.2°C. It is also generally accepted that at least part of this warming is due to the increase in greenhouse gas emissions, primarily CO2. The scientific disagreements that do still exist primarily concern detailed aspects of the processes that make up these general themes. The impacts of these warming trends are currently not being taken into account when examining wind power potential for a region.
The evidence for changing wind patterns because of global warming is consistent with theory. The standard scenario for global warming suggests that the greatest impact will be the warming of the polar regions. A primary forcing mechanism for generating winds in the midlatitudes is the difference in temperature between polar and tropical air masses. In theory, the reduction of the thermal difference between polar regions and the tropics should reduce the mean midlatitude wind speeds. There have been anecdotal wind trend studies done at a few locations that indicate that this may indeed be happening.
Even though these anecdotal studies tend to support the idea that wind speeds are decreasing in accordance with the theory of global warming, the impact of urbanization of an area could mimic this same trend. Wind speed is greatly reduced in urban areas versus open areas. The reduction in speed is typically on the order of 60% from a fully rural to fully urban land use. Also, the amount of reduction depends on the season. For example, trees in summer would tend to have more of a reduction effect than in the winter. It is possible that apparent changes in wind patterns are not actually due to global climate change but rather due to regional changes in land use as areas that were previously forests or cropland become more urbanized.
AWS Truewind has performed research to analyze the NCAR-NCEP Global Reanalysis 50+ year data set to look for global and regional trends in wind climatologies. High resolution simulations using a mesoscale model (MASS) have been conducted over the past 50 year period for regions that show substantial changes in wind patterns. To ensure that the climatologies produced by the model are a reasonable representation of the actual climatology changes, point observation wind climatologies have been compared with the mesocale model-generated and Reanalysis-generated climatologies for the same point.
The results have been analyzed for the significance and implications to the wind power industry from both a global and regional perspective. It is important to understand the cause of the wind trends because wind farm siting decisions and national and local wind energy policies would likely be affected. If the wind trends are the result of global warming, this will change the general wind patterns for entire regions of the globe. However, if the cause of the wind trends is primarily due to land use changes or other local effects, there might be ways to compensate for this within a given region. It is therefore important to determine the true causes and magnitude of such trends, in order to encourage the siting of wind farms in the best long-term locations and to develop an energy policy that makes the best use of available resources for renewable energy.