Climate Change
Climate Change Indicators in the United States
Weather is the state of the atmosphere at any given time and place. Most weather takes place in the lower layer of the atmosphere, the troposphere. Familiar aspects of weather include temperature, precipitation, clouds, and wind. Severe weather conditions include hurricanes, tornadoes, and blizzards.
Shifting storm patterns will likely cause some areas to experience more droughts. Extreme weather events such as storms, floods, and hurricanes will likely also become more intense.Climate is the average weather in a given place, usually over a period of more than 30 years. While the weather can change in just a few hours, climate changes occur over longer timeframes. Climate is defined not only by average temperature and precipitation, but also by the type, frequency, and intensity of weather events such as heat waves, cold waves, storms, floods, and droughts. Climate has natural year-to-year variations, and extremes in temperatures and weather events have occurred throughout history.
The Earth's climate depends on the balance between the amount of energy received from the sun and the amount of energy that is absorbed or radiated back into space. Natural influences can alter how much heat is reflected or absorbed by the Earth's surface, including changes in the sun's intensity, volcanic eruptions, and multi-year climate cycles such as El Niño. Human activities such as deforestation and the production of greenhouse gases also affect this balance. These alterations, in turn, affect climate on local, regional, and global scales.
Generally, increases in the Earth's surface temperature will increase evaporation from the oceans and land, leading to more overall precipitation. However, this additional precipitation will not be distributed evenly, and shifting storm patterns will likely cause some areas to experience more severe droughts. Scientists have suggested that extreme weather events such as storms, floods, and hurricanes will likely also become more intense. There is natural variability in the intensity and frequency of such events, however, so care must be taken to determine whether observed trends reflect long-term changes in the Earth's climate system.
Climate variations can directly or indirectly affect many aspects of human society—in both positive and disruptive ways. For example, warmer temperatures might reduce heating costs and improve conditions for growing some crops, yet extreme heat can cause illness or death among vulnerable populations. Precipitation can replenish water supplies and nourish crops, but intense storms can damage property, cause loss of life and population displacement, and temporarily disrupt essential services such as transportation, telecommunications, and energy and water supplies.