Solar radiation that enters Earth’s atmosphere carries energy in the form of heat. After hitting the surface of the earth, half of the heat is reflected back into space. The rest is trapped within gases in our atmosphere. Any gas that absorbs these reflected solar rays and emits them via radiant energy is a greenhouse gas.


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Water vapor is the most abundant greenhouse gas in our atmosphere. However, it is also the only one involved in a critical feedback cycle. As atmospheric temperature rises, water vapor in the atmosphere increases. The increase in water vapor leads to increased cloud coverage, shielding the earth from solar radiation and dissipating energy in the form of precipitation (rain). This feedback cycle and the greenhouse effect itself are critical to the ability of Earth to sustain life. Radiant energy from the greenhouse effect causes Earth’s average atmosphere to remain at a temperature of 59 degrees Fahrenheit. Without the greenhouse effect, life on Earth would freeze in the vacuum of space.

Major greenhouse gases

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Aside from water vapor, there are four other gases in our atmosphere contributing to the greenhouse effect:

  • Carbon dioxide (CO2)
  • Methane (CH4)
  • Nitrous Oxide (N2O)
  • Fluorinated gases

With the exception of fluorinated gases, which are synthetic, all the other greenhouse gases arise from natural environmental and organic processes. Biological activity, volcanic eruptions, and other phenomena lead to an increase in atmospheric greenhouse gas levels.

Role of human activity

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Human activity dramatically increases the emission of greenhouse gases. In 2014, the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) provided rigorous evidence demonstrating a 95% probability of significant contributions of human activity to increases in greenhouse gas levels and subsequent increases in global temperature. The IPCC is a United Nations body of 1,300 independent scientists from around the world assembled to provide an objective panel on climate change.

As measured by the EPA, the proportions of greenhouse gas emission by source of human activity are as follows:

  1. Transportation (28.9%) – primarily from burning fossil fuel for car, trucks, ships, trains, and planes.
  2. Production of Electricity (27.5%) – fossil fuel burning accounts for 62.9% of all electricity production.
  3. Industry (22.2%) – from the burning of fossil fuels, as well as chemical emissions including N2O and fluorinated gases.
  4. Commercial and Residential (11.6%) – primarily from heating and waste
  5. Agriculture (9.0%) – practices such as rice production involve CO2 emission, while livestock emit large volumes of methane.

CO2 levels

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Both water vapor and fluorinated gases absorb more heat than carbon dioxide. However, fluorinated gas levels are dwarfed by carbon dioxide emissions. Carbon dioxide also absorbs different wavelengths of radiation than water vapor while not participating in the aforementioned feedback cycle between atmospheric temperature and water vapor. These crucial differences account for the leading role of carbon emissions in global energy imbalance. The National Oceanic and Atmospheric Administration (NOAA) of the United States government reports that two-thirds of total energy imbalance contributing to climate change are a result of carbon emissions.

Due to the leading role of CO2 in anthropogenic climate change, the Scripps Institute of Oceanography began measuring earth’s atmospheric CO2 levels in 1958 from the observatory at Mauna Loa in Hawaii. Continuous recordings over the past 61 years indicate a linear (regression coefficient of 0.989) upward trend. Since 1958, the earth’s atmospheric CO2 concentration has increased by 100 ppm. This data is referred to as the Keeling Curve after Charles David Keeling, who started the monitoring program.

Long-term predictions

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It is not possible to estimate or predict the total effect of significant rises in global temperature as a result of human carbon emissions. However, it is clear that continued upward trends in average global temperature will lead to drastic shifts in the environment with distinct effects by region. As reported by NASA, continued trends will lead to heat waves and droughts, increased intensity of hurricanes, a rise in sea level, and changes in crop viability by region. The effects of climate change combined will lead to massive global instability if left unchecked.

Preventative measures

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It is not possible for any single nation to halt the progress of climate change. Twenty countries are responsible for 75% of global anthropogenic CO2 emissions, with China (28%), the United States (15%) and India (6%) as the leading sources. The 2016 Paris Agreement was signed by 196 state parties to instate a systemic global approach to reducing carbon emissions. Targets and dates are set by participating nations themselves with the requirement that future targets exceed previous targets. Viable paths to reducing carbon emission include utilizing and developing alternative fuel sources for energy, improving urban planning and public transport, and preserving natural carbon sinks among many other options.

Although a monumental task, a concerted international effort may prevent a global crisis.