Friday, March 29, 2024
HomeClimateA Look at Radiative Forcing

A Look at Radiative Forcing

Radiative forcing refers to anything that changes the earth energy balance. For example, how much more energy will the earth retain if we emit 1 Gt of carbon dioxide into the atmosphere?

The graph above shows the radiative forcing caused by different greenhouse gas emissions over time. The energy is measured in Watts per square meter (W/m²).

The commonly used metric known as Global Warming Potential, or GWP, is based upon the cumulative amount of radiative forcing that a gas will cause over time. Carbon dioxide is the reference gas, so it always has a value of 1.

Try setting the values in the boxes above to 100 years, 1 Gt of CO₂, and 1 Gt of CH₄. Now hover the cursor over the lines at 100 years. Note down the ‘cumulative rf’ value for each gas.

If you divide the CH₄ value by the CO₂ value, you will have the GWP-100 for CH₄. According to the IPCC it should be between 29 and 30. That means that releasing 1 GtCH₄ is the same as releasing 30 GtCO₂ when we use a 100 year timescale.

Another way of looking at this: the GWP represents the total area under the red line (CH₄) compared to the total area under the blue line (CO₂). Since the area under the blue line is hard to see, try this instead: set the values to 100 years, 30 GtCO₂ and 1 GtCH₄ and hit submit.

Compare the cumulative radiative forcing values of each gas at 100 years. They should be almost equal. Which is exactly what we found in the other scenario–releasing 1 1 GtCH₄ causes the same cumulative radiative forcing as releasing 30 GtCO₂!

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