Willow ptarmigan complicated changes in plumage several times a year and the differing colour and pattern of the summer plumage: The willow ptarmigan often hybridises with the black grouse ("Tetrao tetrix") and the hazel grouse ("Tetrastes bonasia") and occasionally with the western capercaillie ("Tetrao urogallus"), the spruce grouse ("Falcipennis canadensis") and the rock ptarmigan ("Lagopus muta"). During the Pleistocene, the willow ptarmigan widely occurred in continental Europe. Authors who recognize paleosubspecies have named the Pleistocene willow ptarmigan "L. l. noaillensis" (though the older name "medius" might be the correct one). These marginally different birds are said to have gradually changed from the
Arctic haze the opposite effect of trapped warmth beneath the cloud cover. During the Arctic winter, however, there is no sunlight to reflect. In the absence of this cooling effect, the dominant effect of changes to Arctic clouds is an increased trapping of infrared radiation from the surface. Ship emissions, mercury, aluminium, vanadium, manganese, and aerosol and ozone pollutants are many examples of the pollution that is affecting this atmosphere, but the smoke from forest fires is not a significant contributor. Some of those pollutants figure among environmental effects of coal burning. Due to low deposition rates, these pollutants are not yet