Climate Change: An Inter-disciplinary Approach to Problem Solving��Changes in Radiative Forcing

Richard B. Rood

rbrood@umich.edu

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Winter 2021

Radiative forcing: �Changes to absorption and reflection

• Earth's most important greenhouse gases
• water vapor (H₂O)
• carbon dioxide (CO₂)
• methane (CH₄)
• nitrous oxide (N₂O), commonly known as "laughing gas"
• ozone (O₃)
• chlorofluorocarbons (CFCs)
• Some are long-lived
• Some are chemically controlled
• Some cycle through oceanic and terrestrial reservoirs
• Water
• Carbon Dioxide

Radiative forcing: �Changes to absorption and reflection

• Aerosols
• Absorb
• Reflect
• Human and natural
• Regional
• Short lived

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We “force” changes to the climate

• Carbon dioxide
• Methane
• CFCs
• N₂O
• Aerosols
• Changes to the land surface

There are consequences to that ”forcing”

• Feedbacks
• That amplify the forcing
• That damp the forcing

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• Forcing and feedbacks are entangled, especially through water, clouds, and aerosols.

Radiative Forcing Changes

Climate Sensitivity

How much will the global average surface temperature increase with a doubling of carbon dioxide (CO₂)?

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A conceptual model used for analysis:

(T)emperature change is proportional to CO₂ increase

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𝛁T ∝ 𝛁CO₂ 🡪 𝛁T = n×(2×CO₂)

Climate Sensitivity

A conceptual model used for analysis:

(T)emperature change is proportional to CO₂ increase

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𝛁T ∝ 𝛁CO₂ 🡪 𝛁T = n×(2×CO₂)

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𝛁T ∝ change in radiative forcing associated with 𝛁CO₂

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Which in the actual Earth includes all of the other sources of change of radiative forcing and all of the feedbacks.

Summary

• Definitive calculation of radiative warming due to greenhouse gases since 1750 (pre-industrial)
• There is some cooling related to aerosols and changes in ozone (O₃).
• Often related to air pollution and air quality and if we “clean up” the pollution we often increase warming.
• The feedbacks are generally positive, and hence, they enhance warming.
• Little evidence of negative feedbacks that would keep us at the lower ranges of warming.