How Might Global Climate Change Affect Life on Earth?
ESU501  Human Activities Are Increasing Greenhouse Gases

Another type of data that scientists can reconstruct is the amount of carbon dioxide (CO2) in the atmosphere.

Major Findings about Greenhouse Gases

  • The concentration of CO2 in the atmosphere has increased by 31% since 1750.
  • The current CO2 concentration is at the highest level in the last 420,000 years.
  • Atmospheric CO2 is increasing at a faster rate today than at any time over the past 20,000 years.
  • The current concentration of methane (CH4) is at its highest level in the last 420,000 years.

The graphs below show the changes in concentration of three different greenhouse gases over the past 1,000 years.

Adapted from IPCC, Third Assessment Report on Climate Change, 2001.

2. When did concentrations of these greenhouse gases start rapidly increasing? What might have caused these increases?

Each of these greenhouse gases affects climate differently. Some gases can trap the sun’s energy better than others. The degree to which a gas traps solar energy is called its radiative forcing value. Radiative forcing values are indicated on the right axis of the graphs. The higher the radiative forcing value, the stronger its effect on global warming.

3. Which gas affects global climate most? Which has the least effect?

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