Climate can be defined as the average weather conditions of an area. Typically, it is measured in terms of mean annual temperature, precipitation, and solar radiation. Factors such as elevation, topography, latitude, distance from sea, and vegetation can all contribute to the climate of an area. In recent decades, a great deal of attention has been paid to a type of climate change referred to as global warming. The global increase in atmospheric temperatures has been largely attributed to an increase in atmospheric carbon dioxide, primarily as a result of burning of fossil fuels. Carbon dioxide, like other important compounds, acts as a green gas by trapping heat inside the earth’s atmosphere. Among the many ways that climate change may impact plants and animals, the most studied have been related to how warming temperatures may change the timing of annual biological events (phenology) (IPCC 2007, Parmesan 2006) and how warming may change elevational and latitudinal ranges (Chen et al. 2009, Parmesan 2006, Walther et al. 2004).
Phenology refers to the timing of annual biological events in plants and animals. For plants, phenology may refer to the first flush of leaves in spring, the first flowering or fruiting dates, or when leaves turn color in the fall. For animals, phenological events could refer to the breaking of hibernation or diapause, egg-laying dates, the timing of migration or when different developmental stages are reached.
Climate change effects phenology
Phenology is important to climate change studies because the timing of biological events, in both natural and agricultural systems, is often dependent on seasonal temperatures, snowmelt, rain fall and freeze dates. For example, as temperatures have continued to increase, many phenological events have been found to be occurring earlier in the season than previously recorded. Observed trends such as earlier dates of frog breeding, arrival of migrant birds to spring habitat, and earlier flowering dates have been attributed to a warming climate (Parmesan & Yohe 2003).
In predator-prey, parasite-host, pollinator-plant and herbivore-plant interactions, it is often the case that a given species may be strongly dependent on the presence of another. However if species respond differently to climatic change, these close interactions may become unsynchronized. For example, if early season plants use snowmelt to determine flowering times and their pollinators use temperature to break diapause, the interactions between the two species can become temporally disrupted if snowfall levels are disrupted more than changes in temperature (Hegland et al. 2009, Memmott et al. 2007). In another case, spring migration dates in the Great Tit, Parus major, have been shown to not have changed, although the earlier warming at sites they migrate to have led to caterpillars developing earlier than previously recorded. This has led to a decline in caterpillars that are available as food items to feed developing fledglings (Visser et al. 2006).
Elevational and latitudinal ranges
Species ranges are not only defined by their ecological roles and the distribution of important resources, they are also determined by species tolerances to different climatic factors. Along an elevational gradient, for example, different plant and animal communities form distinct life zones that are predictable given a range of climatic variables, such a precipitation and temperature. Because increases in latitude, from the equator to the poles, lead to a similar decline in annual temperatures and season length as that found moving up an elevational gradient, it is no surprise that similar plant and animal communities associated with higher elevations in Colorado (such as the subalpine or alpine) become dominate communities at higher latitudes.
Climate change effects species ranges
As global climates continue to increase in temperature, species have been found to shift their ranges to reflect the changing climatic conditions. On a variety of elevational and latitudinal gradients, numerous studies have found that plant and animal species normally found at lower evaluations are becoming more common at higher elevations, that some cool adapted species are disappearing from their lower ranges and that the relative abundance of different species with communities are changing (Parmesan et al. 1999, Walther et al. 2005, Chen et al. 2009).
As species are adapted to live within different climatic ranges, changes in precipitation and temperature can affect whether a species can continue to inhabit certain areas. For species that are negatively impacted by warming temperatures, there is a concern that climate change can also cause populations to become locally extinct and that these disappearances can eventually lead to the loss of species. Pika populations, for example, have been found to disappear from lower elevations and climate data has shown that the loss of populations at lower elevations is consistent with warming patterns (Grayson 2005). Climatic changes may not only impact species ranges directly, they can also effect these ranges indirectly though the loss of important habitats. The polar bear, for example, has become threatened due to the shrinking levels of summer sea ice in the arctic.