Climate is the long-term average weather conditions that occur in a particular region. Climate A region’s climate depends on average temperature and precipitation, as well as how these variables change throughout the year. What is climate?

The latitude of a location affects climate. What affects climate?

The amount of solar energy per unit of Earth’s surface area depends on latitude. Earth’s curved surface causes latitudes closer to the equator to receive more direct sunlight than latitudes farther north or south. What affects climate? (cont.)

Latitudes near the poles receive less solar energy and have lower average temperatures. What affects climate? (cont.)

Latitudes near the equator tend to have warmer climates than higher latitudes. What affects climate? (cont.)

Climate is influenced by altitude. Temperature decreases as altitude increases in the troposphere.

Mountains influence climate because they are barriers to prevailing winds. What affects climate? (cont.)

An area of low rainfall on the downwind slope of a mountain is called a rain shadow.rain shadow What affects climate? (cont.)

The high specific heat of water causes the climates along coastlines to remain somewhat constant. Prevailing winds extend the moderate temperatures farther inland. What affects climate? (cont.)

Ocean currents modify climate. The Gulf Stream is a warm, northward current along the east coast of North America. The Gulf Stream brings warmer temperatures to portions of the United States and Europe. What affects climate? (cont.)

Climates are classified into five types based on their temperature, precipitation, and native vegetation. Classifying Climates

A city’s roads and buildings absorb solar radiation. Cities are often warmer than the surrounding area. This urban heat island is one form of microclimate. Classifying Climates (cont.)

A microclimate is a localized climate that is different from the climate of the larger area surrounding it.microclimate Classifying Climates (cont.)

Climate influences how humans determine the crops they grow. Climate influences how humans design buildings. How Climate Affects Living Organisms

Animals and plants have adapted to the climates in which they live. CORBIS Ingram Publishing/SuperStock

Much of our knowledge about past climates comes from natural records of climate. Long-Term Cycles ice cores from glaciers and ice sheets fossilized pollen ocean sediments growth rings of trees

Long-Term Cycles (cont.) Ice ages are cold periods lasting from hundreds to millions of years when glaciers cover much of Earth. Ice ages Glaciers and ice sheets advance during cold periods and retreat during interglacials—the warm periods that occur during ice ages. interglacials

The most recent ice age began about 2 million years ago. At that time, about half the northern hemisphere was covered by ice. About 10,000 years ago, Earth entered its current interglacial period, called the Holocene Epoch. Long-Term Cycles (cont.)

Earth’s orbit varies between elliptical and circular about every 100,000 years. As Earth’s orbit changes shape, Earth’s climates change. Long-Term Cycles (cont.)

When Earth’s orbit is more circular, Earth averages a greater distance from the Sun, resulting in below-average temperatures on Earth.

Changes in the angle of Earth’s tilt affect the range of temperatures throughout the year. The tilt of Earth’s axis changes in 41,000-year cycles. Long-Term Cycles (cont.)

Movement of Earth’s continents and changes in ocean circulation influence long-term climate cycles. Long-Term Cycles (cont.)

In addition to long-term climate cycles, climate also changes in short-term cycles. Short-Term Cycles

The changing seasons is an example of short-term climate change. Short-Term Cycles (cont.)

Changes in the amount of solar energy received at different latitudes during different times of the year give rise the seasons.

When the northern hemisphere is tilted toward the Sun, there are more daylight hours than dark hours, the temperatures are warmer, and it is summer.

When the northern hemisphere is tilted away from the Sun, daylight hours are fewer than nighttime hours, temperatures are colder, and it is winter.

The seasons change as Earth makes a revolution around the Sun. revolution Short-Term Cycles (cont.)

In the northern hemisphere, summer begins when the northern hemisphere is tilted toward the Sun.

In the northern hemisphere, fall begins when the neither hemisphere is tilted toward the Sun.

In the northern hemisphere, winter begins when the northern hemisphere is tilted away from the Sun.

In the northern hemisphere, spring begins when, once again, neither hemisphere is tilted toward the Sun.

The El Niño/Southern Oscillation (ENSO) causes another type of short-term climate change.El Niño/Southern Oscillation

During ENSO, the trade winds weaken and warm water surges back toward South America.

A complete ENSO cycle occurs every three to eight years, with the following effects: lots of precipitation along the western coast of South America droughts in normally wet regions increased number of violent storms in California and southern U.S. Short-Term Cycles (cont.)

The North Atlantic Oscillation (NAO) is another cycle that can change the climate for decades at a time. The NAO affects the strengths of storms throughout North America and Europe by changing the position of the jet stream. Short-Term Cycles (cont.)

A third short-term climate change is a monsoon. A monsoon is a seasonal change in wind direction caused by changing temperatures over the ocean and land.monsoon Short-Term Cycles (cont.)

A drought is a period with below-average precipitation that can lead to crop damage and water shortages.drought Droughts are often accompanied by heat waves—periods of unusually high temperatures. Other Short-term Climate Changes

Droughts and heat waves occur when large hot- air masses remain in one place for weeks or months. A cold wave occurs when a large polar air mass stays over a region for days or weeks. Other Short-term Climate Changes (cont.)

Average temperatures on Earth have been increasing for the past 100 years. Regional and Global Climate Change

Temperature change has not been steady throughout the past 100 years. Regional and Global Climate Change (cont.)

The rise in Earth’s average temperature during the past 100 years is often referred to as global warming.global warming In 2007, the Intergovernmental Panel on Climate Change (IPCC) concluded that most of this temperature increase, or global warming, is due to human activities. Human Impact on Climate Change

These activities include burning fossil fuels and the large-scale cutting and burning of forests, which release greenhouse gases into the atmosphere. Gases in the atmosphere that absorb Earth’s outgoing infrared radiation are greenhouse gases.greenhouse gases Human Impact on Climate Change (cont.)

Greenhouse gases help keep temperatures on Earth warm enough for living things to survive— a phenomenon called the greenhouse effect. Human Impact on Climate Change (cont.)

Recently, global temperatures and carbon dioxide, CO 2, concentration in the atmosphere have both increased. Human Impact on Climate Change (cont.)

Higher levels of greenhouse gases, like CO 2, create a greater greenhouse effect. Most scientists suggest that global warming is due to the greater greenhouse effect. Humans use deforestation to obtain fuel or clear farm land. Human Impact on Climate Change (cont.)

DeforestationDeforestation is the large-scale cutting and/or burning of forests. Human Impact on Climate Change (cont.)

Deforestation affects global climate because there are fewer living trees to help remove CO 2 from the air. The burning of cut trees also adds more CO 2 to the atmosphere. Natural sources of CO 2 include volcanic eruptions and forest fires. Cellular respiration in organisms contributes additional CO 2. Human Impact on Climate Change (cont.)

The burning of fossil fuels also releases tiny liquid or solid particles into the atmosphere called aerosols. Most aerosols reflect sunlight back into space, preventing some of the Sun’s energy from reaching Earth and potentially cooling the climate over time. Human Impact on Climate Change (cont.)

When clouds form in areas with large amounts of aerosols, the cloud droplets are smaller and reflect more sunlight than clouds with larger droplets. Human Impact on Climate Change (cont.)

Increasing temperatures can impact the environment in many ways. Melting glaciers and polar ice sheets can cause sea levels to rise and coastal ecosystems to be disrupted. Climate and Society

Extreme weather events can become more common. Permanently higher temperatures and other ecosystem changes can affect migration patterns of insects, birds, fish, and mammals. Climate and Society (cont.)

Climate forecasts help governments decide how to respond to future climate changes. A global climate model (GCM) is a set of complex equations used to predict future climates.global climate model GCMs use math and science to predict future climate changes. Predicting Climate Change

Summer arctic sea ice is expected to disappear by the end of this century. Sea levels are expected to keep rising for several centuries. Predicting Climate Change (cont.)

Increasing populations can affect climate change. Predicting Climate Change (cont.)

It is predicted that by the year 2030, two of every three people on Earth will live in urban areas. Large areas of forests are being cleared for expanding cities. Significant amounts of greenhouse gases and other pollutants will be added to the atmosphere. Predicting Climate Change (cont.)

There are ways to reduce pollution and greenhouse gases. Predicting Climate Change (cont.) developing alternative energy sources, such as solar and wind energy building energy-efficient buildings controlling greenhouse gases and pollution by conserving fuel and recycling