What is climate change?

Climate change is simply a change in the expected weather. It can be measured in specific regions or for the whole earth. Climate change can either refer to a change in average temperature or a change in the timing, location, or severity of weather events compared to historical averages. For example, more or fewer heavy snowstorms, increases or decreases in total rainfall, or a change in the length of the growing season, are all examples of climate changes.

Factors that influence climate are called climate forcings. These include variations in solar radiation, oscillations in the Earth's orbit and orientation, mountain formation and erosion, changes in vegetation on the land surface, and changes in greenhouse gas* concentrations. There are a variety of climate change feedbacks that can amplify or diminish initial climate forcings. Some parts of the climate system, such as the oceans and ice caps, respond slowly in reaction to climate forcing because of their large mass. Therefore, the climate system can take centuries or longer to fully respond to new forcings.

The release of greenhouse gases from human use of fossil fuels and deforestation is an important current climate forcing causing climate change. *Greenhouse gases are molecules such as carbon dioxide and methane, that absorb and re-radiate heat in the atmosphere. Even though greenhouse gases are relatively minor components of the atmosphere, small increases in their concentrations have large effects on atmospheric temperature.

Is the climate warming?

According to NOAA and NASA data, the Earth's average surface temperature has increased by about 1.2 to 1.4F in the last 100 years. The eight warmest years on record (since 1850) have all occurred since 1998, with the warmest year being 2005. Most of the warming in recent decades is very likely the result of human activities. Other aspects of the climate are also changing such as rainfall patterns, snow and ice cover, and sea level. If greenhouse gases continue to increase, climate models predict that the average temperature at the Earth's surface could increase 3.2 to 7.2F by the end of this century. Scientists are certain that human activities are changing the composition of the atmosphere, and that increasing the concentration of greenhouse gases will change the planet's climate. But they are not sure by how much it will change, at what rate it will change, or what the exact effects will be.

Visit the US EPAs climate change site for more details.

Visit RealClimate.org for more depth and to clarify myths and misunderstandings about climate change science.

What does climate change mean for high-elevation species and ecosystems?

High-elevation species and ecosystems are at particular risk from climate change. Most high-elevation species are adapted to tolerate and thrive under cold snowy conditions, with short growing seasons. As climate warms, subalpine and alpine species may find the new climate unsuitable and attempt to become established at even higher elevations. But alpine species are already at the top of many mountain ranges and may be unable to migrate upward. Snow pack, nutrient availability, and water availability will also change in response to a warmer climate, affecting the way ecosystems acquire and use carbon. These changes will affect snow and water-based recreation, nature tourism, and wildlife viewing and hunting, all of which contribute to the economies of western mountain states.

Warming temperature also allows animals that previously were restricted from high-elevations by cold temperatures to establish populations there. One example of this is the ongoing and unprecedented mountain pine beetle (MPB) epidemic that is devastating forests of western North America. The MPB outbreak is correlated with climate warming and the MPB is currently exploiting pine tree populations that were previously in environments that were too cold to sustain beetle populations. The ecological and economic consequences of this epidemic are sufficiently large to cause catastrophic losses to local western economies. In addition, vast expanses of dead trees are decaying and releasing carbon dioxide previously held in their wood. An area of trees larger than the state of Pennsylvania has been killed by MPB in British Columbia, Canada and the carbon emission from these trees has been estimated to negate all carbon emission reduction strategies currently underway and planned by the country. In addition, the dead needles and branches increase the risk of wildfire for several years following tree death.

What can you do to help?

Greenhouse gases are emitted when we burn fossil fuels for energy to drive our cars and generate electricity. Growing food with a lot of fertilizer and raising livestock also contributes. Greenhouse gas emissions can be reduced through simple measures like using high efficiency light bulbs in your home and properly inflating your tires to improve your car's fuel economy. More substantial reductions can be achieved by insulating your home well and using public transportation. The What You Can Do section of the EPAs climate change site identifies over 25 action steps that individuals can take to decrease greenhouse gas emissions, increase the nation's energy independence and also save money.

You can assess your contribution to climate change, by using EPA's personal greenhouse gas emissions calculator to estimate your household's annual emissions. Once you know about how much you emit, you can use the tool to see how simple steps you take at home, at the office, on the road, and at school can reduce your emissions.