Basics of Climate Change

In this writing, we hope to give you a basic foundation of climate change and relevant concepts by exploring the following key questions:

- What is climate change?

- What controls the Earth's temperature?

- What are major greenhouse gases?

- What's causing global warming?

1. What is climate change?

By definition, climate change describes a change in temperatures and weather patterns in a region over a long time period. Often climate change refers specifically to the rise in global temperatures from the mid-20th century to present.

Besides the global temperature shift, multiple lines of evidence show changes in oceans and weather including increases in ocean temperatures, sea level and acidity; melting of glaciers and sea ice; and changes in the frequency, intensity and duration of extreme weather events.

2. What controls the Earth's temperature?

The earth's temperature depends on the balance between energy entering and leaving the planet’s system. When sunlight reaches the earth’s surface, it can either be reflected back into space (albedo) or absorbed by the earth. Incoming energy that is absorbed by the earth warms the planet. Once absorbed, the planet releases some of the energy back into the atmosphere as heat (also called infrared radiation). Solar energy that is reflected back to space does not warm the earth.

Certain gases in the atmosphere absorb energy, slowing or preventing the loss of heat to space. Those gases are known as “greenhouse gases.” They act like a blanket, making the earth warmer than it would otherwise be. This process, commonly known as the “greenhouse effect,” is natural and necessary to support life. However, the recent buildup of greenhouse gases in the atmosphere from human activities has changed the earth's climate.

Please see the video below to understand how greenhouse gases actually work.

3. What are major greenhouse gases?

Greenhouse gases come from a variety of human activities including burning fossil fuels for heat and energy, clearing forests, fertilizing crops, storing waste in landfills, raising livestock, and producing industrial products.

Key greenhouse gases include Carbon dioxide (CO2) which enters the atmosphere through burning fossil fuels, solid waste, trees, and other biological materials, and as a result of certain chemical reactions, such as cement manufacturing; Methane (CH4) which is produced through both natural and human activities such as natural wetlands, agriculture activities, fossil fuel extraction and transport; Nitrous oxide (N2O) which comes mainly from agricultural activities and natural biological processes; and F-gases which are man-made gases used in coolants, foaming agents, fire extinguishers, solvents, pesticides, and aerosol propellants.

Source: NASA's Climate Kids

Different GHGs have different lifetimes in the atmosphere. They also differ from each other in their relative heat-trapping capacity (or radiative efficiency). When putting together, these two factors form a "Global Warming Potential", or GWP, for each gas. As carbon dioxide is the primary greenhouse gas contributing to recent climate change, GWPs are expressed in terms of the equivalent mass of CO2 that would cause the same amount of warming.

The table below shows key greenhouse gases and their GWPs in multiple time horizons (20 years (GWP-20), 100 years (GWP-100) and 500 years (GWP-500). It uses CO2 as the reference gas—note how its value is 1 across the top row.

Source: IPCC AR6, Working Group I, Chapter 7, page 1017

Once added to the atmosphere, carbon dioxide hangs around for a long time: between 300 to 1000 years. From the table above, we can see that methane (CH4), on the other hand, only stays in the atmosphere for an average of 12 years. It is chemically removed fairly quickly. However, while it is in the atmosphere, methane traps, on average, 83 times the heat (or infrared radiation) that an equivalent mass of CO2 would.

4. What's causing global warming?

Are we human beings the culprits of global warming? Let's watch some videos and come to a conclusion yourself. You can start a discussion on this topic in our Community.

What do you feel after reading all of this? Which topic do you want to further explore?

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