118 The Greenhouse and Other Effects

Earth’s temperature depends on three things:

• Amount of sunlight received

  • Most is ultraviolet with short wavelength

  • About 2/3 is absorbed to warm the atmosphere

• Amount of sunlight reflected

  • Mostly reflected as infrared radiation

• Degree to which the atmosphere retains heat

  • •Water vapor, carbon dioxide, methane, nitrous oxides, and halocarbons absorb IR radiation

  • Gasses act as “blanket” to retain heat in troposphere

Three important greenhouse gases are shown symbolically in the image below: water vapor, carbon dioxide and methane.

• Greenhouse effect is a natural and necessary process.

  • Earth would be 33o colder without it.

  • All surface water would be frozen.

  • Little life would exist.

  • Natural effect is from water vapor.

• Absorption (trapping) of reflected energy by greenhouse gasses (carbon dioxide, methane, nitrous oxide, halocarbons)

  • Enhances the greenhouse effect

Carbon dioxide accounts for most of the anthropogenic greenhouse effect. It is the most studied.

Source: Vincent E Courtillot, Paul R Renne, On the ages of flood basalt events, Comptes Rendus Geoscience, Volume 335, Issue 1, 2003, Pages 113-140. https://doi.org/10.1016/S1631-0713(03)00006-3

Human Impact: considered the most influential (primarily fossil fuels, deforestation, etc.)

• Mathematical models of climate can isolate human causes from solar and volcanic forcing of climate change.

• Models found that present warming greatly exceeds natural variability.

• Models agree with climate change predicted from greenhouse gas forcing.

Source: https://en.wikipedia.org/wiki/Scientific_consensus_on_climate_change#/media/File:20200324_Global_average_temperature_-_NASA-GISS_HadCrut_NOAA_Japan_BerkeleyE.svg