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8.15: The Greenhouse Effect and Global Warming

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    What is the Greenhouse Effect?

    The greenhouse effect is the trapping of the sun's warmth in a Earth’s lower atmosphere. This happens because lower atmosphere due to the greater transparency of the atmosphere to visible radiation from the Sun than to thermal infrared radiation emitted from the surface (Figure 8.44). A glass green house will let sunlight in, but captures some of the thermal energy within the enclosed interior. A greenhouse gas is any gas that absorbs and emits energy in the Thermal infrared range. Primary greenhouse gases in earth's atmosphere include: water vapor (H2O), carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and ozone (O3).

    The greenhouse effect.
    Figure 8.44. The greenhouse effect is enhanced by the presence of greenhouse gazes in the atmosphere.

    Global Warming and Earth's Greenhouse

    Earth is currently growing warmer at an alarming rate! The weather records compiled from around the world indicated that there has been a significant rise in global temperatures over the past century. This rise in temperature is linked to the increasing amount of carbon dioxide and other greenhouse gases accumulating in the atmosphere (Figure 8.45). The rise in carbon dioxide and other greenhouse gases is a result of consumption of fossil fuels, deforestation, and other human impacts since the start of the Industrial Revolution in the 19th century.

    Figure 8.46 compares the rise in atmospheric CO2 to the decrease in the ratio of stable carbon isotopes 13C/12C.
    The cyclic patterns in the graph is a result of the annual growth of plants in the northern hemisphere. During the summer months plant growth consumes CO2, reducing CO2 concentrations in the air. In the winter months the decay of organic matter increases CO2 concentrations. The overall trend shows that atmospheric concentrations of CO2 is increasing. The cyclic pattern in the 13C/12C also reflects the plant-growth cycles, but also shows the dilution of 13C concentrations by the influx of carbon from fossil fuels. Carbon in fossil fuels (coal and oil) are enriched in12C.

    There are many knowns and unknowns about the future of global warming. Highlights include sea-level rise, climate changes, changes in storm intensity and regional precipitation, changes in air and ocean chemistry (acidification), and other impacts on humanity and natural ecosystems.

    Camparison of carbon dioxide concentrations to global temperature changes Greenhouse trends of carbon dioxide and carbon-13
    Figure 8.45. Changes in global temperature with the rise in atmospheric CO2. Figure 8.46. Changes in atmospheric 13C/12C concentrations.

    Select resources about Carbon's role in the global environment:
    Atmospheric Carbon Tracker Animation (NOAA)
    The Carbon Cycle (NASA)
    Environmental consequences of ocean acidification (United Nations)
    Ocean acification: Issue briefs (United Nations)

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