This essay offers a defense to the position that humans are responsible for global warming. What is carbon dioxide? Before attempting to answer any observation-based questions about carbon dioxide, take a moment identifying carbon dioxide helps ensure a clear understanding of the element. According to Princeton University (n.d.), “Carbon dioxide, carbon dioxide, is a heavy, odorless, colorless gas formed during respiration and the decomposition of organic substances.” This natural element exists in the Earth's atmosphere where it circulates among water, plants, soil and animals. Current levels of carbon dioxide Knowing the levels of carbon dioxide in the atmosphere helps scientists understand how the gas affects the Earth, its atmosphere and any potential global warming. Carbon dioxide levels, measured in parts per million (ppm), define a unit of measurement “as a measurement of small levels of pollutants in air, water, body fluids, etc. Parts per million are the mass ratio of the polluting component to that solution” (TET, n.d.). Increasing every year since 1958, the current level of atmospheric carbon dioxide is 396.81 ppm according to co2now.org (2014). Scientists believe they have only a short window of time to get this and other greenhouse gases under control before the planet crosses the point of no return. With a level of 396.81 ppm of carbon dioxide in the atmosphere, you might wonder if this level is the highest level Earth has seen in the last 450,000 years. According to the graph found on the Planet Seed website (2014), this is the highest level of carbon dioxide recorded in that period. Indeed, the graph clearly shows a peak in carbon dioxide levels in the last portion of the g...... middle of paper ......3). Overview of greenhouse gases. Retrieved from http://www.epa.gov/climatechange/ghgemissions/gases/co2.htmlHilderman, R. (2011). Fossil fuels and atmospheric levels of carbon dioxide. Retrieved from http://www.motherearthnews.com/nature-and-environment/fossil-fuel-and-atmospheric-levels-of-carbon-dioxide.aspxMarshall, C. (2013). A small-scale US laboratory experiment removes CO2 from the atmosphere at a relatively low cost. http://www.eenews.net/stories/1059981902Planet Seed. (2014). Global climate change and energy CO2 and temperature changes. Retrieved from http://www.planetseed.com/parentarticle/co2-and-temperature-changePrinceton University. (n.d.). WordNet Search - 3.1. Retrieved from http://wordnetweb.princeton.edu/perl/webwn?s=co2The Engineering Toolbox (TET). (n.d.). PPM: parts per million. Retrieved from http://www.engineeringtoolbox.com/ppm-d_1039.html