Everyone talks about carbon dioxide, or CO2, driving temperature and climate change. The greater the concentration of CO2 is in the atmosphere, the warmer the Earth is, and vice versa. "How do scientists know that?" Ask a geologist, geochemist, oceanographer, climatologist, earth scientist, astronomer, paleontologist or anyone who studies Earth science and they will be able to tell you that CO2 in Earth's atmosphere acts as the planet's thermostat.
Most people understand how a thermostat works. In the context of regulating temperature, it's set to a "value," and when the temperature drops below that value, the heat comes on. Alternatively, when the temperature goes above that value, the cooling may kick in. A thermostat keeps your house from overheating or freezing; in other words, a thermostat keeps your house livable. So, how did scientists come to the realization that CO2 acts as the Earth's thermostat? They were faced with a puzzle called the Faint Young Sun Paradox.
When the Earth was first formed, 4.6 billion years ago, the sun was about 25 percent to 30 percent weaker than today. Since that time the strength of the sun has gradually increased. With a weaker sun, the Earth should have been frozen for the first 2.5 billion to 3 billion years because the solar output would have been insufficient for the planet to maintain liquid water. But the Earth wasn't frozen; sedimentary deposits suggest that the Earth did have liquid water and during this time life evolved on Earth. Therefore, even with the faintness of the young sun, the Earth was still habitable. Hence the paradox. The Earth has always been habitable, since its formation the atmospheric conditions have fluctuated within a pretty narrow window of composition. Therefore, scientists proposed that the Earth must have a natural thermostat that regulates the temperature. Greenhouse gases, that keep the atmosphere warm and habitable, are implicated as part of this thermostat.
Naturally, CO2 is emitted into the atmosphere primarily through the respiration of living organisms and volcanic eruptions. A large amount of CO2 is released from natural sources — in fact, this value is greater than the amount of CO2 released by humans. However, this CO2 is also naturally removed from the atmosphere through photosynthesis, adsorption in the oceans and the chemical weathering of rocks. This is the thermostat at work.
A straightforward scenario often used in teaching climate science is the following feedback: volcanoes erupt rapidly along the seafloor releasing CO2 into the atmosphere, CO2 causes the temperatures to increase (because CO2 is a greenhouse gas), rising temperatures cause increased precipitation and vegetation growth, which enhances chemical weathering of rocks. As the rocks weather, through the process of chemical hydrolysis, CO2 is removed from the atmosphere. When CO2 is removed from the atmosphere the Earth cools, suppressing the initial warming. This process, and similar others, has likely helped to keep Earth's climate balanced over billions of years. If the rates of production and removal of CO2 were out of balance, we would observe drastic changes in CO2 and climate in the geological record.
There is no question CO2 acts as a thermostat that helps drive climate change. There is no question given the abundance of existing data that CO2 and temperature are related; over the last 500,000 years CO2 has fluctuated between about 180 ppm and 300 ppm with temperature showing a positive correlation. In the context of today and the influence of humans on the climate system, there can be little question that we are influencing the CO2 concentrations of the atmosphere. Only about 40 percent of the man-made CO2 is absorbed into the oceans, the rest resides in the atmosphere, warming the planet. In fact, evidence illustrates that humans started to impact the climate system with the advent of farming. About 7,000 years ago, the concentrations of methane, another greenhouse gas, rose rapidly in the atmosphere, coinciding with the increase in irrigated rice fields in southern Asia.
It's time we stop talking about "alleged climate change." Environmental Protection Agency Administrator Scott Pruitt, a climate change denier, has recently called into question CO2 as a climate change driver. In fact, Pruitt believes that Congress should weigh in on whether or not CO2 should be regulated as a harmful pollutant; they are being asked to continue to debate, review and analyze the data.
Congress should not deny or ignore the vast amount of information that has been collected over the last century supporting climate change. The time for debating whether or not CO2, and other greenhouse gases, help drive climate change is past. CO2 should be regulated as a harmful pollutant and efforts should be focused on effectively turning over to renewable resources for our energy supply.