On a per-person basis, Wyoming emits more carbon dioxide than any other state or any other country: of it per capita a year, because of burning coal, which provides nearly all of the state's electrical power.
Over the last century, the average temperature in Laramie, Wyoming, has increased 1.5 °F (0.8 °C),.
Over the course of the 21st century, climate in Wyoming may change even more. For example, based on projections made by the Intergovernmental Panel on Climate Change and results from the United Kingdom Hadley Centre’s climate model (HadCM2), a model that accounts for both greenhouse gases and aerosols, by 2100 temperatures in Wyoming could increase by 4 °F (2 °C) in spring and fall (with a range of 2-7 °F), 5 °F (2.5 °C) in summer (with a range of 2-8 °F), and 6 °F (3 °C) in winter (with a range of 3-11 °F) . Precipitation is estimated to decrease slightly in summer (with a range of 0-10%), increase by 10% in spring and fall (with a range of 5-20%), and increase by 30% in winter (with a range of 10-50%). Other climate models may show different results, especially regarding estimated changes in precipitation. The amount of precipitation on extreme wet or snowy days in winter is likely to increase. The frequency of extreme hot days in summer would increase because of the general warming trend. It is not clear how the severity of storms might be affected, although an increase in the frequency and intensity of winter storms is possible.
Impacts
Human health
Warmer temperatures could increase the incidence of Lyme disease and other tick-borne diseases in Wyoming, because populations of ticks, and their rodent hosts, could increase under warmer temperatures and increased vegetation. Increased runoff from heavy rainfall could increase water-borne diseases such as giardia, cryptosporidia, and viral and bacterial gastroenteritis.
Water resources
The headwaters of several rivers originate in Wyoming and flow in all directions into the Missouri, Snake, and Colorado River basins. Within the state, water is plentiful in some parts and scarce in others.
Winter snow accumulation and spring snowmelt strongly affect many of Wyoming’s rivers. A warmer climate could result in less winter snowfall, more winter rain, and faster, earlier spring snowmelt. In the summer, without increases in rainfall of at least 15-20%, higher temperatures and increased evaporation could lower streamflows and lake levels. Less water would be available to support irrigation, hydropower generation, public water supplies, fish and wildlife habitat, recreation, and mining.
Competition for water could increase on the plains, where agricultural and industrial users compete for available water. Similarly, in northeastern Wyoming, which has large deposits of minerals, coal, and petroleum, competition between mining, energy, and other users could intensify for the meager summer streamflows.
Groundwater levels in several areas of the state are declining because of increased pumpage for irrigation and urban development. Less spring and summer recharge could lower groundwater levels.
Tourism and recreation, important components of Wyoming’s economy, also depend on adequate supplies of clean water.
Higher temperatures and lower flows could impair water quality by concentrating pollutants and reducing assimilative capacity.
Agriculture
Warmer climates and less soil moisture due to increased evaporation may increase the need for irrigation. However, these same conditions could decrease water supplies, which also may be needed by natural ecosystems, urban populations, industry, and other users.
Under these conditions, livestock tend to gain less weight and pasture yields decline, limiting forage.
Forests
With changes in climate, the extent of forested areas in Wyoming could change little or decline by as much as 15-30%.
Hotter, drier weather could increase the frequency and intensity of wildfires, threatening both property and forests. Drier conditions would reduce the range and health of ponderosa and lodgepole forests, and increase their susceptibility to fire. Grasslands and rangeland could expand into previously forested areas in the western part of the state. Milder winters could increase the likelihood of insect outbreaks and of subsequent wildfires in the dead fuel left after such an outbreak.