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Introduction to Climate Change

Our climate is changing

Our climate is changing (filo, iStockphoto)

Our climate is changing

Our climate is changing (filo, iStockphoto)

Let's Talk Science

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Learn more about the causes and impacts of global climate change.

What is climate change?

Climate change is a change in the usual weather patterns in a region. In the last couple of decades, temperatures have risen in the Earth’s climate. This change is impacting local climates all around the world.

Changes in weather happen all time. But weather and climate are not the same thing. Weather is the day to day change in temperature and precipitation in a place. You can describe the weather in your community by looking outside. If it’s snowy right now, that’s today’s weather. Climate, on the other hand, is the usual weather in a place over a long period of time. It is possible for weather to change quickly. For example, it might be sunny in the morning and rainy in the afternoon. Climate changes much more slowly. Earth’s climate has been about the same for 9000 years.

Analogy of weather and climate using clothes and clothing in a closet
Weather versus climate as shown by your clothes (Let’s Talk Science using images by Kubkoo, nataka and vectorikart via iStockphoto based on an image by the NOAA).

How do we know the world’s climate is changing?

The world’s average temperature has changed throughout history. Sometimes the world’s temperature has been warmer and sometimes it has been colder. Glacial periods happen when the Earth experiences colder temperatures. Factors like ocean currents and volcanic eruptions caused these shifts. These changes are part of a natural cycle of heating and cooling. This usually happens over tens of thousands of years.

Graph of global temperatures from 1880 to 20202
Global temperatures from 1880 to 2020 (Source: Global Climate Change, NASA).

But now Earth’s climate is changing faster than it ever has during human history. Earth’s average temperature has increased by 1 °C over the past 100 years. In fact, 2015 to 2020 were the hottest on recordGlobal warming refers to this trend of rising global temperatures. Global warming is one of the ways that Earth’s climate is changing. Global warming is one aspect of climate change. Climate change also involves changing global weather patterns, ocean currents, and other systems.

We are already experiencing these impacts. Scientists have observed many changes. These include rising sea levels, melting ice and increasing extreme weather events. These changes affect each region differently. For example, snow and ice are melting so quickly that the Arctic could have no summer sea ice by 2035. Coastal areas are experiencing more flooding. These are all evidence of climate change.

Map of arctic sea ice 2019
Image from the National Oceanic and Atmospheric Administration (NOAA) comparing the area of sea ice in summer 2019 to the median area from 1981-2010 (Source: NOAA).

Why is the climate changing?

These changes to Earth’s climate are not natural shifts. Scientists are confident that human activities are leading to climate change. Human activities release gases that change the makeup of Earth’s atmosphere. These gases are making our atmosphere better at trapping the Sun's heat. We call this the greenhouse effect.. The greenhouse effect is the main cause of rising temperatures.

So what is the greenhouse effect? Plants can grow better in a greenhouse because it stays warmer than the outside air. This is because heat from the Sun is able to enter the clear glass or plastic. The heat warms the air inside. The heat from the trapped air keeps the greenhouse warm.

Image showing how a greenhouse traps heat
A greenhouse traps heat (Source: NASA/JPL-Caltech)

Earth’s atmosphere also acts like a greenhouse. Sunlight reaches our planet and warms it. Some of the heat is reflected back into space. Some of the heat is trapped by gases in Earth’s atmosphere. These greenhouse gases include carbon dioxide (CO2), water vapour, methane, and nitrous oxide.

Greenhouse effect animation
A simplified animation of the greenhouse effect (Source: NASA-JPL/Caltech).

The greenhouse gases in our atmosphere help keep our planet warm enough for us to survive. Too little greenhouse gas would make the Earth too cold for humans. But, too much greenhouse gas in the atmosphere makes the Earth too warm. Over the past century, humans have added a lot of greenhouse gases to our atmosphere.

Did you know?

The average temperature on Earth would be -18°C without the greenhouse effect. 

Carbon dioxide is the most common greenhouse gas in our atmosphere. Carbon moves between the Earth, living things, and the atmosphere in the carbon cycle. Like all animals, humans add carbon dioxide to the atmosphere when we breathe. We also emit a lot more carbon dioxide when we burn fossil fuels. These are fuels we dig up like oil, gas and coal which are made of plant and animal remains from millions of years ago. We burn fossil fuels when we drive cars, heat our homes, and generate electricity. Humans have burned large amounts of fossil fuels over the last century.

The amount of carbon dioxide in the air is now nearly 50% more than at the start of the industrial age. A quarter of that change has happened in the last 20 years. Carbon dioxide concentrations haven’t been so high for over three million years.

Graph of carbon dioxide levels over time
Carbon dioxide levels over time (Source: NASA).

Methane (CH4) is the next most common greenhouse gas. Methane traps roughly 30 times more heat than carbon dioxide. This makes methane an important gas to keep an eye on. The main sources of methane in Canada are from fossil fuels use, farming, and waste.

Climate change: Earth's giant game of Tetris (2014) by TED-Ed (2:48 min.).

What are the impacts of climate change?

Increasing the global temperature by a few degrees may not seem that bad. This is especially true if you live in a relatively cold country like Canada. But, think about how you feel when you have a fever. Raising your body temperature by just a couple degrees can make you feel terrible. Like our bodies, Earth is a series of intertwined systems. Rising global temperatures have complex and sometimes unexpected impacts that affect us all. Even one more degree of increase could be disastrous for Canada and the world.

The impacts of climate change are complex and different for every region. In some places, higher temperatures could lead to more droughts and heat waves. Rising temperatures could also increase the amount of water that evaporates. This could lead to more frequent and intense storms in some areas. Climate change could continue to lead to melting ice and glacierswarming oceans, and rising sea levels. These changes impact people, plants, and animals.

Dry lake bed
Dry lake bed (Source: piyaset via iStockphoto).


Additionally, climate change will continue to affect our planet for many years. Carbon dioxide stays in the atmosphere for hundreds of years. It can take some time for Earth's complex systems to respond to changes.

How can we tackle this problem?

Our response will determine how much our climate will change. There are two main ways to deal with climate change. These are adaptation and mitigationAdaptation is about finding ways to cope with our changing climate. For example, cities could adapt to rising sea levels by building walls or pumps.

Flooded neighbourhood surrounded by sandbags
Flood protection sandbags with flooded homes in the background (Source: Marc Bruxelle via iStockphoto).

Mitigation is about finding ways to reduce greenhouse gas emissions. For example, we could burn less fossil fuel by making our homes not as warm inside in winter. We can also change the way that we do things to reduce our need for fossil fuels. For example, we could use solar or wind power to generate electricity.

Solar panels in the foreground and wind turbines in the background
Solar panels and wind turbines (Source: zhongguo via iStockphoto).

Another mitigation option is what’s called geoengineering. This involves removing carbon dioxide from the atmosphere. So far these methods are very expensive. They may also be harder to do than burning less fossil fuels. But, they may turn out to be important in the future if we discover cheaper and safer ways to do it.

Climate change is a difficult issue to solve because of its global scale and complexity. Luckily, increasing numbers of people are concerned about climate change. Young people in particular are encouraging governments and businesses to take action. Many organizations are trying to reduce greenhouse gas emissions. Government plansinternational agreements, and emerging technologies will all need to play a role. There is a lot of work and research that still needs to be done for us to address climate change. But we humans are up for it!


What is the Greenhouse Effect?

Learn more about the greenhouse effect with this hands-on activity from Let’s Talk Science. 

Google Earth Timelapse Imagery

See how the Earth has changed over the past thirty years through Google Earth images. 

What is Climate Change?

Learn more about climate change from NASA Kids. 

NASA Earth Minute: Usual Suspects

Learn about the causes of climate change in this video from NASA. 

Climate 101 with Bill Nye

Learn about the basics of climate change in this video with Bill Nye.