Climate is the long-term pattern of weather in a particular area. Weather can change from hour to hour, day to day, month to month or even from year to year. Climate refers general weather patterns over 30 years or more. These patterns define a climate. A desert might experience a rainy week, but over the long term, it receives very little rainfall. It has a dry climate.

Climates do change. Natural changes happen very slowly, over hundreds or even thousands of years. As the climate of an area changes, the organisms that live in that area must adjust, relocate or risk dying out.

Earth's Changing Climate

Earth is over 4.5 billion years old. Its climates have changed many times.

Earth has experienced several major ice ages. There have been at least four in the past 500,000 years. During these periods, Earth's temperature decreased, causing ice sheets and glaciers to expand. We are still in an ice age, which began about two million to three million years ago. Around 20,000 years ago, the ice caps began melting.

Warmer temperatures have caused the glaciers to shrink. The glaciers have not disappeared completely, however. They still exist in Antarctica and Greenland. Scientists think we live in an "interglacial period," or a time between glaciers. They have gone away somewhat for now, but hundreds of years from now, the glaciers may grow again.

Scientists who study climate look for proof of past climate change in many different places. Like clumsy criminals, glaciers leave behind many clues. They scratch and rub rocks as they move. They leave little bits of material behind known as "glacial till." This sometimes forms mounds or ridges. Glacier movements also form long, oval-shaped hills. If you see a piece of land with any of these signs, it suggests that a glacier was once there.

Some types of rocks only form from materials left behind from glaciers. When scientists find these rocks, it also tells them that glaciers were once there.

Scientists also have proof of glaciers from fossils. Fossils show what kinds of animals and plants lived in certain areas. Looking for fossils of animals that lived in the cold can show scientists how far across the planet the glaciers reached.

Fossils from the Cretaceous period (145 million to 66 million years ago) show that Earth was once much warmer than it is today. Breadfruit (Artocarpus altilis)—also called "jackfruit"—trees are now found on tropical islands. However, millions of years ago, they even grew on Greenland.

Climate changes happen over shorter periods, as well. For example, there was a "Little Ice Age" that lasted only a few hundred years. It lasted from the 14th century to the 19th century. During this time, average temperatures around the world were 2 degrees Celsius (3.6 degrees Fahrenheit) cooler than they are today.

A change of two degrees might not seem like much, but it was enough to cause major changes. Glaciers grew larger and sometimes engulfed whole mountain villages. In some places, like Europe, winters were longer than usual, limiting the growing seasons of crops. This led to crop failure and starvation. In Africa and South and Central Asia, people faced extreme droughts. However, the climate remained stable in China.

Natural Causes of Climate Change

Climates change for many reasons. Some of these reasons have to do with Earth's atmosphere. Forces outside Earth's atmosphere can also affect climate. Earth's relationship to the sun also affects climate. This includes how Earth is tilted and how it orbits around the sun. These change slowly over time and affect how much of the sun's light reaches different parts of the world at different times. The 100,000-year cycles of ice ages are most likely caused by changes in these things.

Large meteorites hitting Earth can also cause climate change. If a meteorite hits Earth, it can send millions of tons of dirt and dust into the atmosphere. This would block some of the sun's rays, making it cold and dark. Many plants and animals would die.

Nonavian dinosaurs went extinct partially due to a huge meteorite about 10 kilometers (6.2 miles) wide hitting Earth. When the meteorite hit the ground, it sent enough dirt and dust into the atmosphere to block some of the sun’s rays. The climate became too cool and dark for dinosaurs to survive. Their bodies could not adjust to the cold, and the dark killed many plants that they ate. Without the plants, the plant-eating dinosaurs died. And without those plant-eating dinosaurs, the dinosaurs that ate them died too.

Another cause of climate change is called the greenhouse effect. The greenhouse effect happens when gases like carbon dioxide trap the sun's heat in the atmosphere. Gases that do this are called greenhouse gases. They keep Earth warm. Without any greenhouse gases in the atmosphere, most life on Earth would freeze to death.Plate tectonics also play a role in climate changes. Earth is made of many layers. The top part is the crust, and just beneath that is the mantle. Together, these make up the "plates" in plate tectonics. There are 15 major plates that cover the planet's surface. They move about as fast as our fingernails grow.

Earth's continental plates have moved a great deal over time. More than 300 million years ago, the continents were merged together as one giant landmass called Pangaea. As the continents broke apart and moved, their positions on Earth changed. The movements of ocean currents also changed. Both of these changes affected the climate.

Volcanoes are formed by tectonic plate movements. Volcanoes, on land and under the ocean, release greenhouse gases. If a volcanic eruption only reaches the lowest level of the atmosphere, known as the troposphere, the additional gases contribute to warming through the greenhouse effect. But, if the eruption is powerful enough to reach the next level of the atmosphere, the stratosphere, particles reflect sunlight back into space causing regional cooling periods.

Human Causes of Climate Change

Some human activities release greenhouse gases, which fuel climate change. For example, humans burn fossil fuels, such as coal, oil and natural gas. People often use them for transportation and electricity. Burning fossil fuels releases greenhouse gases, like carbon dioxide. Trees soak up carbon dioxide, so cutting down forests also adds to the greenhouse effect. Factories send greenhouse gases into the atmosphere too.

Industries that produce and burn fossil fuels have put large amounts of greenhouse gases into the atmosphere. Some large companies have said they are reducing their emissions. However, some environmentalists don’t think they are doing a good enough job.

Some industries, like the fossil fuel industry, have worked to convince the public that they are not causing climate change. This has slowed progress on fighting human-caused climate change. The people leading these industries did this, even though they knew the risks and consequences.

Not all countries and people emit equal amounts of greenhouse gases. Lower-income countries often release fewer greenhouse gases than wealthier, industrialized nations. Throughout the early 2020s, the top greenhouse producing countries were the United States, the European Union countries, China and India. Wealthier individuals also contribute more to climate change.

Activities that release greenhouse gases are causing dangerous changes in Earth's climate. Average temperatures around the world have risen 1.2 degrees Celsius (2.16 degrees Fahrenheit) since about 1880. The hottest years in recorded history occurred from 2015–2024 This warming trend shows that the greenhouse effect is increasing because of human activity. This is often referred to as “global warming.”

The amount of carbon dioxide in the atmosphere has increased by about 50% since the 1700s. Other greenhouse gases are increasing, as well. Methane is one example. Methane is a greenhouse gas produced by rotting plants and animals. Large landfills, filled with rotting waste, release tons of methane into the atmosphere. Methane is also generated when cows that are raised for food make this gas during digestion. Methane also leaks from oil and gas facilities.

Some chemicals that are used in refrigeration, air conditioning and aerosol sprays are also greenhouse gases. Many countries are working to get rid of them. Some have laws to prevent companies from manufacturing them.

Global Warming Today

As the amount of greenhouse gases in the atmosphere rises, so does the temperature of Earth. The impacts of climate change are already happening.

Ice caps are melting. This is causing the sea level to rise. Coastal areas, including islands, have experienced flooding and erosion, forcing local people to move elsewhere. Severe climate change is also bringing more severe weather patterns, such as extreme hurricanes and typhoons. More precipitation is falling in some places, while already dry regions are getting far less rain. Hot, dry conditions in areas easily burned by fire are making wildfires more common. This has even worse effects, including low air quality and the destruction of habitats. Scientists also predict that climate change will threaten crop health. As climates change, so do the homes of many living things. Animals may not be able to survive in their current homes. Climate change threatens the diversity of life on this planet. Human societies depend on specific crops for food, clothing and trade. If the climate of an area changes, the same crops may not grow. As the planet warms, tropical diseases may spread to new places.

Climate change has a negative impact on people’s mental health too. National Geographic Explorer Kate Burrows is exploring how climate change and natural disasters force people to leave their homes and how this affects their mental health. She found that landslides in Indonesia hurt family relationships and the larger community. Her work shows that care delivered after disasters must help community needs and mental health.

The problems with climate change aren’t equal among all people or areas of the world. Wealthier countries can more easily lessen the impacts of climate change. They can more easily rebuild after disasters, such as hurricanes. Some countries contribute very little to climate change. But these countries often have less money and resources and face greater obstacles in rebuilding and adjusting to climate change. Wealthier people also have greater ability to protect themselves from climate change. This creates inequalities even within wealthy countries.

In many societies, people of certain races, income levels, genders and other factors may be hurt more by climate change. This is part of an idea called environmental justice. It describes how environmental issues are experienced unequally across society. This is because many countries have had laws that discriminate against certain groups of people. For example, the United States had harmful policies that discriminated against Black people, forcing them to live in less desirable areas. Today, those neighborhoods and communities are more vulnerable to environmental issues.

However, people around the world are committed to acting on climate change and fighting injustice.

What Can Be Done About Climate Change?

The temperature will continue to rise unless action is taken. The last decade’s average warming was 1.2 degrees Celsius (2.16 degrees Fahrenheit) above what it was in 1880. This is already affecting the climate. The world must reduce the amount of greenhouse gases released into the atmosphere.

Countries around the world are working together on climate change. One of the most notable efforts is the 2015 Paris Agreement. It aims to keep warming at less than 1.5 degrees Celsius (2.7 degrees Fahrenheit) above what it was before humans began emitting so many greenhouse gases. Countries that join the agreement must create a plan to reduce greenhouse gas emissions and report on their progress. The Paris Agreement includes financial resources for low-income countries to help them fight climate change. While this agreement has not made enough progress to stop warming at 1.5 degrees Celsius, it has still reduced emissions.

There are also regional and local efforts to fight climate change. Small island nations are especially at risk from climate change. They face sea level rise, extreme weather and marine heatwaves. Even though these nations do not have as many financial resources as wealthier countries, they are taking a stand against climate change. They are using nature-based solutions to fight climate change. For example, environmental groups in the Bahamas are working to restore mangroves. These shrubs and trees grow along shorelines, and they absorb carbon dioxide and provide protection against storms. Many of these efforts included students, government officials and local fishing guides.

In the 1980s, in Niger, farmers started improving their lands by regrowing old trees and shrubs that still had root systems or seeds. This practice is called farmer managed natural regeneration. Niger faces drought and many of its people have a hard time getting enough food. This is made worse by climate change, but farmer managed natural regeneration helps lands that had trouble growing crops in the past. In Niger alone, this has restored over 200 million trees and improved the soil. The trees planted also help remove carbon dioxide out of the atmosphere. Dozens of countries now use this plan.

Individuals can also take action on climate change. There are many ways to do this, including:

Driving less” Use public transportation, carpool, walk or ride a bike.

Flying less: Airplanes produce huge amounts of greenhouse gas emissions.

Eating less meat: Cows are one of the biggest methane producers.

Supporting alternative energy sources that don’t burn fossil fuels, such as solar power and wind energy.