Climates of Earth Chapter Notes | Science for Grade 6 PDF Download

Introduction

Climate is the average weather of a place over a long time. It tells us what kind of weather, like temperature, rain, or wind, a place usually has. This chapter explains why different places on Earth have different climates. We will learn about the Sun’s energy, mountains, oceans, and other factors that make climates vary. From hot rain forests to cold polar regions, we will explore how these factors create unique climates around the world.

What is climate?

• Climate is the average weather in a place over many years.
• Weather tells us about the conditions at a specific time, like if it’s rainy or sunny today.
• Climate describes patterns, like mild winters or hot summers, in a region.
• Factors like temperature, rainfall, and wind speed help define a place’s climate.
• Different places on Earth have different climates because of various factors.

What is the most important influence on climate?

• The Sun is the biggest factor affecting Earth’s climate.
• Earth is round, so different areas get different amounts of sunlight.
• Places near the equator get more sunlight and are warmer.
• Polar regions get less sunlight, making them colder.
• Snow and ice in polar regions reflect sunlight (high albedo), keeping these areas cold.
• Middle latitudes (between 30° and 60°) have hot summers and cold winters.
• Latitude, or how far a place is from the equator, greatly affects its climate.
• Land heats up faster than oceans, so continents have more extreme temperatures.
• Oceans have a smaller temperature range because water heats and cools slowly.

Life at the Top of the World

• Earth’s temperatures are going up, and sea ice is melting.
• This change affects entire ecosystems and may harm polar bear survival.
• The Arctic is a huge, icy area that is very cold.
• It is home to many species that thrive in its icy climate.
• Many ecosystems depend on the Arctic’s ice to survive.
• As temperatures rise, ice in the Arctic melts more.
• Sea ice follows a natural cycle in the Arctic, spreading in winter and shrinking in summer.
• With rising temperatures, sea ice forms later and melts earlier each year.
• Over the last few decades, the amount of ice in the Arctic has decreased a lot.
• The melting ice threatens the Arctic’s top predator, the polar bear.
• Polar bears travel across sea ice to hunt for seals.
• As sea ice breaks up and melts, polar bears must swim longer distances to find food.
• Late freezes and early thaws of sea ice mean shorter hunting seasons for polar bears.
• Shorter hunting seasons reduce the number of seals polar bears can catch.
• If warming continues, polar bear numbers could decrease, and they might become extinct.
• The future of Arctic life is uncertain due to these changes.
• Scientists use satellite images to monitor Arctic sea ice.
• Images from 1979 and 2016 show the Arctic sea ice area has shrunk by half since over 35 years ago.

• Scientists study the impact of increasing average temperatures on Arctic ecosystems.
• As Earth’s climate keeps warming, life in the Arctic must adjust to new conditions.

How do mountains affect climate?

• Mountains affect climate by acting as barriers to prevailing winds.
• This creates unique rainfall patterns known as rain shadows.
• A rain shadow is an area with low rainfall found on the downwind (leeward) side of a mountain.
• As air rises over the mountain, it expands and cools, causing water vapor to condense and form rain.
• The windward side of the mountain (the side facing the wind) usually has a wet and cool climate.
• On the leeward side (the side sheltered from the wind), the air becomes drier and warmer as it descends.
• Because of these dry conditions, deserts often form on the leeward sides of mountains.

Did You Know?

Mountains have a big impact on climate. As you go higher in altitude, there are fewer air molecules, which causes air pressure to decrease. With the same amount of thermal energy, lower air pressure results in cooler temperatures—this is why mountain climates are generally cooler than those at sea level. Also, rainfall patterns vary on each side of a mountain. The side facing the rain gets plenty of moisture, allowing lush vegetation to grow, while the leeward side stays dry, supporting only sparse plant life.

How do oceans affect temperatures and precipitation on land?

• Oceans and large lakes affect the climate of nearby land.
• Coastal areas have more stable weather than inland areas.
• Water has a high specific heat, meaning it takes more energy to heat or cool it.
• In summer, water stays cooler, making coastal areas milder.
• In winter, water releases heat slowly, keeping coastal areas warmer than inland.
• Inland areas have hotter summers and colder winters.
• Ocean currents, like the California Current (cold) or Gulf Stream (warm), affect climate.
• Warm ocean currents make nearby areas warmer and wetter.
• Cold ocean currents make areas cooler and drier.
• When ocean water evaporates, it adds moisture to the air, leading to rain or storms.

Pacific Wind and Current Changes Bring Warm, Wild Weather

• El Niño is a weather event where the Pacific Ocean becomes warmer than usual.
• It changes weather patterns around the world.
• During El Niño, trade winds (blowing from the Americas to Asia) weaken or reverse.
• This moves warm water from the western Pacific to the Americas.
• It reduces cooler water rising from the deep ocean, changing currents.
• El Niño causes heavy rain in dry areas like Peru, Chile, and the southwestern U.S.
• It can cause droughts in wetter areas like the Brazilian Amazon or northeastern U.S.
• El Niño happens every 2 to 7 years, alternating with La Niña (cooler Pacific waters).
• Scientists don’t fully know what starts El Niño, but it affects weather globally.

Why do some regions have rain forests and others deserts?

• Rain forests have high rainfall, warm temperatures, and lots of plants and animals.
• They cover only 2% of Earth’s land but have nearly half of all land-based life.
• Deserts are dry areas with little rain and sparse plants (less than 15% ground cover).
• High-pressure systems have sinking, dry air, leading to drier climates.
• Low-pressure systems have rising, moist air, leading to wetter climates.
• Deserts are often found in high-pressure zones, while rain forests are in low-pressure zones.
• Plants affect climate by absorbing sunlight, keeping land cooler.
• Plants release water vapor through transpiration, helping form clouds.

How are climates classified?

• In 1918, Wladimir Köppen created a system to classify Earth’s climates.
• He used average monthly temperatures, precipitation, and native plants to classify climates.
• Köppen’s system has five main climate types: polar, continental, dry, tropical, and mild.
• Polar climates include tundra and ice cap.
• Continental climates have warm summer, cool summer, or subarctic types.
• Dry climates include semiarid and arid types.
• Tropical climates include tropical wet and tropical wet and dry types.
• Mild climates include Mediterranean, humid subtropical, and marine west coast types.
• Highland climates are found in mountainous areas.