Query: Dropped stations show more warming than kept stations.

Relevant passages:
Environmental impact of wind power <=SEP=> The environmental impact of wind power when compared to the environmental impacts of fossil fuels , is relatively minor . Compared with other low carbon power sources , wind turbines have some of the lowest global warming potential per unit of electrical energy generated . According to the IPCC , in assessments of the life-cycle global warming potential of energy sources , wind turbines have a median value of between 15 and 11 ( geq/kWh ) depending on whether off - or onshore turbines are being assessed .   While wind turbine installations may cover a large area , they are compatible with many land uses such as farming and grazing , as only small areas of turbine foundations and infrastructure are made unavailable for use .   Wind turbines generate some noise . At a residential distance of 300 m this may be around 45 dB , which is slightly louder than a refrigerator . At 1.5 km distance most wind turbines become inaudible .  From a fundamental biological point of view , it is known that loud noise increases stress and stress causes diseases .  Peer-reviewed research has generally supported the view that when properly sited wind turbines do not affect human health from noise . However , when improperly sited , data from the monitoring of two groups of growing geese revealed substantially lower body weights and higher concentrations of a stress hormone in the blood of the first group of geese who were situated 50 meters away compared to a second group which was at a distance of 500 meters from the turbine .   Aesthetic aspects of wind turbines and resulting changes of the visual landscape can be significant . Conflicts arise especially in scenic and heritage protected landscapes . Siting restrictions ( such as setbacks ) have often been implemented to limit any intrusive environmental impacts .   There are reports of bird and bat mortality at wind turbines as there are around other artificial structures . The scale of the ecological impact may or may not be significant , depending on specific circumstances . Prevention and mitigation of wildlife fatalities , and protection of peat bogs , affect the siting and operation of wind turbines .

Urban heat island <=SEP=> An urban heat island ( UHI ) is an urban area or metropolitan area that is significantly warmer than its surrounding rural areas due to human activities . The temperature difference usually is larger at night than during the day , and is most apparent when winds are weak . UHI is most noticeable during the summer and winter . The main cause of the urban heat island effect is from the modification of land surfaces . Waste heat generated by energy usage is a secondary contributor . As a population center grows , it tends to expand its area and increase its average temperature . The less-used term heat island refers to any area , populated or not , which is consistently hotter than the surrounding area .   Monthly rainfall is greater downwind of cities , partially due to the UHI . Increases in heat within urban centers increases the length of growing seasons , and decreases the occurrence of weak tornadoes . The UHI decreases air quality by increasing the production of pollutants such as ozone , and decreases water quality as warmer waters flow into area streams and put stress on their ecosystems .   Not all cities have a distinct urban heat island . Mitigation of the urban heat island effect can be accomplished through the use of green roofs and the use of lighter-colored surfaces in urban areas , which reflect more sunlight and absorb less heat .   There are concerns raised about possible contribution from urban heat islands to global warming . Research on China and India indicates that urban heat island effect contributes to climate warming by about 30 % . On the other hand , one 1999 comparison between urban and rural areas proposed that the urban heat island effects have little influence on global mean temperature trends . Many studies reveal increases in the severity of the effect with the progress of climate change .