Climate, the long-term description of weather, is the variation of temperature, wind, cloudiness, precipitation, and humidity. Plants and animals are adapted to local climates and drivers of ecosystem change such as fire and insect outbreaks. Ecological changes in the dynamics of plants, animals, and ecosystems associated with a change in climate have been observed: advance of spring events such as hibernation, green-up of vegetation, migration, and breeding, ; species distribution changes across their historical ranges; and community composition changes. Determining if climate is the causal factor in any change in plant, animal, or ecosystem dynamics requires careful study. Evidence for climate as a causal factor in observed changes in plant, animal, or ecosystem dynamics is strongest when (1) the climate signal associated with the observed ecological change is identified and is consistent with projections of climate change; (2) the study period is long, and area of the species range is large; and (3) potential confounding factors--other disturbances, land use change, stand condition – have been included in the analysis. Most of such studies in the Western United States tend to be of a shorter time frame and smaller geographic scale. These studies do reflect the types of 20th- century observed changes in plant, animal, and ecosystem dynamics seen in other parts of the world. As climate changes can be gradual or abrupt, ecosystem, plant, and animal responses to climate change will also be gradual or abrupt. Dynamic changes will be influenced by alterations in disturbances (fire, insects) and surprises (invasive species, climatic extremes).