These photos were taken in the same place, 63 years apart. What a difference a few decades can make! The earlier photo shows the massive Riggs Glacier in Alaska. The later photo shows what has happened to it. Why did so much of the glacier melt? The answer is climate change.
What is climate? Why does it change? The answer to the first question is easy. The answer to the second question is harder. You’ll learn answers to both questions when you read this chapter.
One winter day in Chicago, the temperature hit 20° C (68° F). This would be normal for Miami in the winter, but in Chicago, it felt like a heat wave. The scene in Figure below is more typical for Chicago in the winter. The “heat wave” on that winter day is an example of weather. The typical temperature for that day is part of Chicago’s climate.
Cold and snow are typical for Chicago in the winter.
Climate is the average weather of a place over many years. It includes average temperatures. It also includes average precipitation. The timing of precipitation is part of climate as well. What determines the climate of a place? Latitude is the main factor. A nearby ocean or mountain range can also play a role.
Latitude is the distance north or south of the equator. It’s measured in degrees, from 0° to 90°. Several climate factors vary with latitude.
Temperature changes with latitude. You can see how in Figure below
Find the cool spot in Asia at 30
Global air currents affect precipitation. How they affect it varies with latitude. You can see why in Figure below.
Global air currents are shown on the left. You can see how they affect climate on the right.
Global air currents cause global winds. Figure below shows the direction that these winds blow. Global winds are the prevailing, or usual, winds at a given latitude. The winds move air masses, which causes weather.
The direction of prevailing winds determines which type of air mass usually moves over an area. For example, a west wind might bring warm moist air from over an ocean. An east wind might bring cold dry air from over a mountain range. Which wind prevails has a big effect on the climate. What if the prevailing winds are westerlies? What would the climate be like?
The usual direction of the wind where you live depends on your latitude. This determines where you are in the global wind belts.
When a place is near an ocean, the water can have a big effect on the climate.
Even places at the same latitude may have different climates if one is on a coast and one is inland.
Ocean currents carry warm or cold water throughout the world’s oceans. They help to even out the temperatures in the oceans. This also affects the temperature of the atmosphere and the climate around the world. Currents that are near shore have a direct impact on climate. They may make the climate much colder or warmer. You can see examples of this in Figure below.
The Gulf Stream moves warm equatorial water up the western Pacific and into northern Europe, where it raises temperatures in the British Isles.
Did you ever hike or drive up a mountain? Did you notice that it was cooler near the top? Climate is not just different on a mountain. Just having a mountain range nearby can affect the climate.
Air temperature falls at higher altitudes. You can see this in Figure below. Why does this happen? Since air is less dense at higher altitudes, its molecules are spread farther apart than they are at sea level. These molecules have fewer collisions, so they produce less heat.
Air temperature drops as you go higher.
Look at the mountain in Figure below. The peak of Mount Kilimanjaro, Tanzania (Africa, 3° south latitude) is 6 kilometers (4 miles) above sea level. At 3°S it’s very close to the equator. At the bottom of the mountain, the temperature is high year round. How can you tell that it’s much cooler at the top?
. Mount Kilimanjaro has very different climates at the top and bottom.
Mountains can also affect precipitation. Mountains and mountain ranges can cast a rain shadow. As winds rise up a mountain range the air cools and precipitation falls. On the other side of the range the air is dry and it sinks. So there is very little precipitation on the far (leeward) side of a mountain range. Figure below shows how this happens.
What role do prevailing winds play in a rain shadow?
1. What is climate?
2. Describe how temperature changes with latitude.
3. Why are many deserts found near 30° latitude?
4. How does altitude influence temperature?
5. What is a rain shadow?
6. An ocean current flows from north to south off the western coast of a continent. The current flows close to land at 50° N latitude. Predict how the current affects the climate of the coast at that latitude. Explain your prediction.
7. Explain how prevailing winds influence climate.
8. Compare and contrast coastal and inland climates.
In this lesson, you read how latitude, oceans, and mountains affect climate.
The same latitudes should have the same types of climate all around the globe, but many other factors play a role in climate. Oceans and mountain ranges also influence climate in the same ways worldwide. You can see this in Figure below. The major climate types are determined by a lot of factors, including latitude. You can see where the climate types are on the map and then read about them below.
Find where you live on the map. What type of climate do you have?
Major climate types are based on temperature and precipitation. These two factors determine what types of plants can grow in an area. Animals and other living things depend on plants. So each climate is associated with certain types of living things. A major type of climate and its living things make up a biome. As you read about the major climate types below, find them on the map in Figure above.
Tropical climates are found around the equator. As you'd expect, these climates have warm temperatures year round. Tropical climates may be very wet or wet and dry.
Africa is famous for its grasslands and their wildlife.
Dry climates receive very little rainfall. They also have high rates of evaporation. This makes them even drier.
Dry climates may be deserts or steppes. Sonoran Desert in Arizona (22
Temperate climates have moderate temperatures. These climates vary in how much rain they get and when the rain falls. You can see different types of temperate climates in Figure below.
How do these climates differ from each other?
Continental climates are found in inland areas. They are too far from oceans to experience the effects of ocean water. Continental climates are common between 40° and 70° north latitude. There are no continental climates in the Southern Hemisphere. Can you guess why? The southern continents at this latitude are too narrow. All of their inland areas are close enough to a coast to be affected by the ocean!
Conifer forests are typical of the subarctic in Alaska.
Polar climates are found near the North and South Poles. They also occur on high mountains at lower latitudes. The summers are very cool, and the winters are frigid. Precipitation is very low because it’s so cold. You can see examples of polar climates in Figure below.
Polar climates include polar and alpine tundra. Polar Tundra in Northern Alaska (70
A place might have a different climate than the major climate type around it. This is called a microclimate. Look at Figure below. The south-facing side of the hill gets more direct sunlight than the north side of a hill. This gives the south side a warmer microclimate. A microclimate can be due to a place being deeper. Since cold air sinks, a depression in the land can be a lot colder than the land around it.
Hills and other features can create microclimates.
1. Define biome.
2. Identify two types of tropical climates.
3. How do steppes differ from deserts?
4. Where are Mediterranean climates found?
5. Describe a marine west coast climate.
6. What is permafrost?
7. What is a microclimate? Give an example.
8. Identify the type of climate in the green-shaded areas on the map below (Figure below). Describe this type of climate.
9. Some tropical climates have rainforests. Others have grasslands. What explains the difference?
10. Compare and contrast two types of continental climates.
Earth’s overall climate is getting warmer.
The weather changes all the time. It can change in a matter of minutes. Changes in climate occur more slowly, and the changes tend to be small. But even small changes in climate can make a big difference for Earth and its living things.
Earth’s climate has changed many times through Earth's history. It’s been both hotter and colder than it is today.
Over much of Earth’s past, the climate was warmer than it is today. Picture in your mind dinosaurs roaming the land. They're probably doing it in a pretty warm climate! But ice ages also occurred many times in the past. An ice age is a period when temperatures are cooler than normal. This causes glaciers to spread to lower latitudes. Scientists think that ice ages occurred at least six times over the last billion years alone. How do scientists learn about Earth’s past climates?
The last major ice age took place in the Pleistocene. This epoch lasted from 2 million to 14,000 years ago. Earth’s temperature was only 5° C (9° F) cooler than it is today. But glaciers covered much of the Northern Hemisphere. In Figure below, you can see how far south they went. Clearly, a small change in temperature can have a big impact on the planet. Humans lived during this ice age.
Pleistocene glaciers covered an enormous land area. Chicago is just one city that couldn't have existed during the Pleistocene.
Since the Pleistocene, Earth’s temperature has risen. Figure below shows how it changed over just the last 2000 years. There were minor ups and downs. But each time, the anomaly (the difference from average temperature) was less than 1° C (1.8° F).
Since the mid 1800s, Earth has warmed up quickly. Look at Figure below. The 14 hottest years on record have all occurred since 1900. Eight of them have occurred since 1998! This is what is usually meant by global warming.
Natural processes caused earlier climate changes. Human beings are the main cause of recent global warming.
Several natural processes may affect Earth’s temperature. They range from sunspots to Earth’s wobble.
Recent global warming is due mainly to human actions. Burning fossil fuels adds carbon dioxide to the atmosphere. Carbon dioxide is a greenhouse gas. It’s one of several that human activities add to the atmosphere. An increase in greenhouse gases leads to greater greenhouse effect. The result is increased global warming. Figure below shows the increase in carbon dioxide since 1960.
How much more carbon dioxide was in the air in 2005 than in 1960?
As Earth has gotten warmer, sea ice has melted. This has raised the level of water in the oceans. Figure below shows how much sea level has risen since 1880.
How much did sea level rise between 1880 and 2000?
Other effects of global warming include more extreme weather. Earth now has more severe storms, floods, heat waves, and droughts than it did just a few decades ago. Many living things cannot adjust to the changing climate. For example, coral reefs are dying out in all the world’s oceans.
Earth’s temperature will keep rising unless greenhouse gases are curbed. Look at the projections in Figure below. The temperature in 2100 may be as much as 5° C (9° F) higher than it was in 2000. Since the glacial periods of the Pleistocene, average temperature has risen about 4° C. That's just 4° C from abundant ice to the moderate climate we have today. How might a 5° C increase in temperature affect Earth in the future?
Projections of several different models are shown here. They all predict a warmer future.
Warming will affect the entire globe by the end of this century. The map in Figure below shows the average temperature in 2070 to 2100. This is compared with the average temperature in 1960 to 1990. In what two places is the temperature increase the greatest? Where in the United States is the temperature increase the highest?
The Arctic and the Amazon basin will experience the greatest temperature changes.
As temperature rises, more sea ice will melt. Figure below shows how much less sea ice there may be in 2050 if temperatures keep going up. This would cause sea level to rise even higher. Some coastal cities could be under water. Millions of people would have to move inland. How might other living things be affected?
In the 2050s, there may be only half as much sea ice as there was in the 1950s.
You’ve probably heard of El Niño and La Niña. These terms refer to certain short-term changes in climate. The changes are natural and occur in cycles. To understand the changes, you first need to know what happens in normal years. This is shown in Figure below.
This diagram represents the Pacific Ocean in a normal year. North and South America are the brown shapes on the right.
During an El Niño, the western Pacific Ocean is warmer than usual. This causes the trade winds to change direction. The winds blow from west to east instead of east to west. This is shown in Figure below. The warm water travels east across the equator, too. Warm water piles up along the western coast of South America. This prevents upwelling. Why do you think this is true?
These changes in water temperature, winds, and currents affect climates worldwide. The changes usually last a year or two. Some places get more rain than normal. Other places get less. In many locations, the weather is more severe.
How do you think El Ni
La Niña generally follows El Niño. It occurs when the Pacific Ocean is cooler than normal. Figure below shows what happens. The trade winds are like they are in a normal year. They blow from east to west. But in a La Niña the winds are stronger than usual. More cool water builds up in the western Pacific. These changes can also affect climates worldwide.
How do you think La Ni
Some scientists think that global warming is affecting the cycle of El Niño and La Niña. These short-term changes seem to be cycling faster now than in the past. They are also more extreme.
1. What is an ice age?
2. Describe the Pleistocene ice age.
3. Outline recent changes in Earth’s temperature.
4. What does global warming usually refer to?
5. Identify three natural causes of climate change.
6. List two effects of global warming.
7. Create a public service announcement about global warming. Explain how global warming is related to human actions and what people can do to reduce it. (Hint: How can people produce less carbon dioxide?)
8. Compare and contrast El Niño and La Niña.
9. Nearly all scientists are united in saying that human activities are causing much of the warming we see. Why do you think politicians are reluctant to believe them? Why is the public reluctant to believe them?
A place’s climate determines what kinds of plants and animals can live there.
Opening image, 1941 photo copyright William Osgood Field, National Snow and Ice Data Center/World Data Center for Glaciology; 2004 photo copyright Bruce F. Molnia, USGS. Image compiled by Robert A. Rohde / Global Warming Art. CC-BY-SA, http://www.globalwarmingart.com/wiki/File:Muir_Glacier_jpg