Climate

The average course or condition of the weather at a place usually over a period of years.

Suppose you were going on a vacation to a tropical island. What would you pack? A swim suit and flip flops? What about a trip to Alaska? Maybe a warm coat and boots? You would know what to pack because of the climate of those places.

Climate is a part of everyone's lives, no matter where we live on planet Earth. People all over the world have adapted in various ways to the climates in which they live. Climate influences not only the clothes we wear, but the kinds of plants we can grow, the kinds of animals we see, the kinds of houses we live in, and the ways that people work and play. Let's learn more about climate.

Climate is not the same thing as weather. Weather is the day-to-day conditions in a certain location, including rainfall, snow, heat, wind, clouds,  humidity, and storms. Weather is what you see outside your window. Weather can change from day to day, and even from hour to hour. It might be sunny and warm one day, but cool and wet the next. Maybe in the nighttime, there will be a thunderstorm or a strong wind. The next morning, there might be no wind at all. Weather is temporary, which is why people often check the weather forecast to see what kind of weather is predicted for tomorrow.

Climate, on the other hand, is the average weather in a large area over a long period of time - 30 years or more. Weather patterns, observed over many years, help describe a region's climate. Usually, the climate of an area remains the same, changing only slowly over hundreds or thousands of years. A desert area may have an occasional rainstorm (weather) - but the climate doesn't change; it's still a hot, dry climate. There is a saying that describes the difference: "Climate is what you expect, weather is what you get."

Meteorologists study and predict short-term weather, while climate scientists, or climatologists, study climate. Climatologists measure and analyze long-term weather patterns over time. They study climates of the past, factors that influence weather, and the effects of weather patterns on the environment. They predict future trends for the years to come.

Climate scientists measure an area's temperature and precipitation over time to describe its climate. But what makes the climate of an area the way it is? Why is the climate of Brazil different from the climate of Canada?

The basis of all climate on the earth is the way the sun's energy moves in and out of the atmosphere and moves around the planet. Many factors influence the way that the sun's energy is spread around and determine an area's climate.

One of those factors is latitude. If you look at a globe of the earth, you can imagine a line circling around the middle of the earth. That imaginary line is the equator and is considered to be zero degrees latitude. Other circular lines north and south of the equator are latitude lines. The climate varies with latitude or distance from the equator. Because the sun's rays shine most directly at the equator, the climate in those areas is very warm. Places far from the equator receive less intense sunlight. At latitudes closer to the north and south poles, the climate is colder.

Another factor is altitude or elevation. High-altitude areas such as mountains have cooler temperatures than lower areas. At higher altitudes, the air is thinner and less able to absorb and store heat.

Nearness to large bodies of water influences climate. Areas near oceans are usually milder and wetter than inland areas and have less temperature variation. The ocean absorbs and stores large amounts of heat, which it exchanges with the atmosphere to impact climate. Areas further inland from the ocean will have more extreme temperature ranges. One interesting fact is that the southern hemisphere of the earth has more ocean area than the northern hemisphere, so climate conditions over land in the south are more moderate than at similar latitudes in the north.

The surface temperature of ocean water varies with latitude, as shown below. Red colors indicate warmer ocean water and blue indicates cooler ocean water.

Ocean currents, both warm and cool, help to regulate climate as they transport water around the globe. Prevailing wind patterns also influence climate as air masses move across the land. The interactions between the sun's energy and how the atmosphere and oceans move heat around the earth produce different climates in different parts of the world.

Two locations at similar latitudes on the globe may have quite different climates due to the influence of winds and ocean currents. For example, the warm Gulf Stream current makes the climate of England milder than that of Canada, even though latitude is the same.

The surface features of land also impact climate. Places with a lot of ice and snow (light colors) tend to reflect more sunlight back into the atmosphere, providing a cooling influence on climate. Dark-colored oceans tend to absorb more heat. The amount and type of vegetation influence evaporation and temperature. Mountain ranges are barriers to air movement and often act as boundaries between climate zones.

The Koppen system, developed by climate scientist Wladimir Koppen, is the most common system for classifying types of climate. In this system, based on temperature, precipitation, and seasonal variation, the climates of the earth are divided into five main categories: tropical (A), dry (B), temperate (C), continental (D), and polar (E). The picture below shows roughly where those climate zones appear on the earth.

The image below shows most of the United States classified into climate zones. The "H" zone refers to highlands or mountains, where the climate is due to altitude and differs from the surrounding area.

Each of these five climate types can be broken down into sub-categories.

Tropical climates are found near the equator in parts of South America, Africa, India, and Indonesia. Tropical wet climates are hot and humid, with high rainfall and warm temperatures all year round. A tropical wet and dry climate is also warm but with distinct rainy and dry seasons.

Dry climates have hot days and little rainfall. Arid climates, with less than ten inches of rain a year, are found in the southwest United States, north Africa, and much of Australia. Semi-arid climates, are found in central Asia and U.S. Great Basin states such as southern Idaho, have slightly more rain and may be higher in elevation.

Temperate or Moderate climates are "medium" climates with warm summers and mild winters. Much of the eastern United States has a sub-climate known as humid subtropical. The Pacific Northwest coast has a marine climate that is mild and rainy all year, while the California coast has a Mediterranean climate with hot, dry summers and mild winters. All of these are mid-latitude temperate climates.

Continental climates have cold, snowy winters. The humid continental climate has a lot of seasonal temperature variation and is found in much of Europe and the northern United States, including north Idaho. The subarctic climate, with its short, cool summers and long, cold winters, is found in large portions of Alaska, Canada, and Russia.

Polar climates are cold and dry, with long winters and very short summers. The Arctic region has a polar climate. A climate known as icecap, where temperatures are always below freezing, is found in places such as Greenland and inland Antarctica. Highland climate may be polar at the tops of mountains but temperate on the lower slopes. Learn more about climate zones.

A biome is not quite the same as a climate. A biome is made up of the plants and animals that live in a certain type of climate. Since the climate of an area determines what type of biome can exist in that region, the enormous variety of life on Earth is largely due to the variety of climates that exist. Biomes are usually labeled by the major type of vegetation. So, a tropical climate may be associated with a rainforest biome, a dry climate with a desert biome, a polar climate with tundra biome, and a temperate climate with a deciduous forest. The living things of a biome in one part of the earth share certain characteristics with living things of a similar biome elsewhere in the world because their environment has many of the same advantages and challenges. For example, different species of cactus live on different continents, but they have adapted to the dry desert in similar ways. Learn more about biomes around the world.

In addition to the regional climates described above, scientists also study the global climate. Global climate is a description of the climate of a planet as a whole. Global climate depends on the amount of energy received from the Sun and the amount of energy trapped in the atmosphere. Global climate scientists study the factors that affect the climate of our whole planet.

Although climate does not change from day to day like weather, it can change slowly over hundreds or thousands of years. The Earth's climate has warmed and cooled many times in the past. Scientists know that the earth was warmer and wetter when dinosaurs roamed the earth. You may have heard of the Ice Age; at different times in the past, glaciers have covered large portions of Earth with ice. Evidence shows that the Sahara Desert was once covered by ocean during a warm "wet age." More recently, the "Little Ice Age" from the 14th through the 19th centuries was a time of colder climates all around the world.

Climates of the past are called paleoclimates. Scientists study paleoclimates to learn more about Earth long ago. They look for clues to figure out what climates used to be like. One way they do this is by studying tree rings. Each year that a tree is alive, it grows another ring, making its trunk wider. The thickness of a ring depends on what the climate was like at that time.

Another way scientists learn is by studying ice cores, drilled from deep below the surface of the ice in polar regions. Scientists analyze the frozen layers in an ice core to learn about temperatures and carbon dioxide levels long ago. They also study fossils and layers of mud and sand in lakes to learn about paleoclimates.

The graph below shows what scientists have learned about carbon dioxide (CO2) in Earth's atmosphere over the last 600,000 years.

Why do climates change? Climate change can happen for many reasons. The earth goes through natural cycles of warming and cooling, as can be seen from the study of the past. Some factors, such as volcanoes, produce short-term climate change. In a large volcanic eruption, ash particles from the explosion can block out the sun's rays, causing a change in Earth's climate that can last for years. A condition known as El Niño sometimes happens in the Pacific Ocean, where the usual strong trade winds blow in the opposite direction from normal. The resulting changes in sea temperature can cause a change in climate. Climate can also be affected when there is a change in the amount of the sun's energy that reaches Earth.

In recent years, human activity has had an impact on climate as well. Temperatures in areas with large cities, built with lots of asphalt, steel, and cement, are higher than in rural areas. Cutting down forests removes the cooling influence of trees and affects the local climate.

Our earth is currently in a period of warming. Scientists are concerned because the Earth is warming faster than it has in the past. They believe that human activity is contributing to the climate change known as global warming, the rise of the earth's average surface temperature.

Have you ever visited a greenhouse where plants are grown? Panels of glass trap heat from the sun and moisture from the air to keep the greenhouse warmer than the outside air. Earth is something like a giant greenhouse. When sunlight enters the earth's atmosphere, some of the sun's heat is trapped by a layer of gases and prevented from escaping back into space.

Carbon dioxide, methane,  nitrous oxide, and water vapor are known as "greenhouse gases" because they trap warmth from the sun and keep the earth warm enough to live on. This is good because, without any greenhouse gases, Earth would be an icy wasteland.

But too much greenhouse gas means an increase in Earth's temperature as more heat is trapped. Since 1900, the level of carbon dioxide in the atmosphere has increased by 30%. One reason for this increase is the burning of fossil fuels such as oil, gas, and coal in cars, planes, power plants, and factories. When these fuels are burned, carbon is released into the air as carbon dioxide. Cutting down forests also contributes to greenhouse gases, since trees that naturally remove carbon dioxide are gone.

As a result, Earth is getting warmer. Its average surface temperature has increased by almost 2º Fahrenheit over the past hundred years. That may not sound like very much, but it is changing our global climate. The past five years have been some of the hottest ever recorded.

What are the effects of global warming?

• Polar areas are warming faster than other parts of the world. As the light-colored ice and snow melts, less of the sun's energy is reflected back out into space and more heat is absorbed on Earth. Temperatures continue to rise.
• Permafrost, the Arctic ground just below the surface that stays permanently frozen, is thawing. When this happens, microbes begin decomposing organic material, releasing carbon dioxide and methane. Northern towns, buildings and roads built on permafrost become unstable.

Arctic sea ice is melting. Animals that depend on sea ice, such as polar bears, are becoming threatened or endangered. Glaciers are melting. All over the world, glaciers have shrunk. The sea level is rising due to melting glaciers and the expansion of warmer seawater. Sea levels have risen 7 inches in the last 100 years. Rising sea levels put many coastal communities in danger. Oceans are warming and becoming more acidic. Warmer waters endanger the health of coral reefs and other kinds of ocean life. Higher temperatures have caused more extreme weather events. In some places, there has been more rainfall and increased flooding. In others, warmer temperatures have increased evaporation rates and caused droughts. Hurricanes and heat waves have become more intense and more frequent. Warming temperatures affect growing seasons, bird migration, pollinator life cycles, and wildlife habitat. Some living things rely on temperature to figure out when to migrate or reproduce. Other animals must adapt to new conditions or move to other areas when habitats change. Some species may become extinct. On the other hand, warmer conditions may cause unwanted or disease-carrying insect pests to increase.

Learn more about the effects of climate change.

Earth-observing satellites collect a lot of information about current climate conditions. Climate scientists analyze this information and use climate models to predict how the atmosphere, oceans, land surfaces, and ice will interact. They expect Earth's average temperature to continue to rise and our planet's climate to continue to change.

There are things you can do to help! You can take steps in your everyday life to slow down global warming. Talk to your parents about the issue of climate change. As a family, make some choices that will reduce your "carbon footprint" - your contribution to global warming.

• Whenever possible, walk or ride your bike instead of using the car. Burning one gallon of gasoline puts 19 pounds of carbon dioxide into the atmosphere. Biking or walking just one mile a day for a year could prevent 330 pounds of carbon dioxide!
  
• When you must travel by car, encourage your family to carpool and combine errands into one trip.
• Reduce and reuse as much as possible. Factories emit carbon dioxide when making new things, so fix up what you have instead.
• Since the production of energy often emits greenhouse gases, cut down on the amount the energy you use. Turn off appliances when you are not using them. Reduce the use of air conditioning by opening windows or using a fan. Wear a warm sweater instead of turning up the heat.
• Try to eat mostly in-season and locally grown fruits and vegetables. This cuts down on the energy used to grow and transport food, which reduces the release of heat-trapping gases.
• Plant trees. Trees help fight climate change naturally by pulling carbon dioxide out of the air through photosynthesis.
• Send a letter to your mayor, senator, or other elected official, asking them to do something about climate change. Write a letter to the editor of your local or school newspaper. Encourage your parents to vote for people who care about climate change.
• Learn as much as you can about climate change and share what you know with others. The more people understand the problem, the more we can work together to find solutions.