Carbon is the 6th element (atom) on the periodic table. Its unique property is it’s ability to bond to many other atoms including other Carbon atoms to make large, complex molecules. Carbon is the atom of life.
Most of the 65 billion metric tons of Carbon on Earth is locked up in rock. The rest is in the air, ocean, soil and fossil fuels. The figure above shows the Carbon cycle. Carbon naturally moves from one location to another. In one form, carbon bonds with two oxygen atoms to form Carbon Dioxide or CO2.
Plants (including algae in the oceans) consume CO2 to make sugars (food source) and release oxygen (O2) back into the atmosphere through the process of photosynthesis. The CO2 becomes locked up in the plants. When the plants die, the carbon moves to the soil. Under certain processes the carbon is converted to rock (limestone) coal, oil and natural gas over long periods of time.
The chart above shows the elements that make up air. At 0.038%, CO2 is a small but critically important component. While CO2 is not harmful (not toxic or flammable) in itself, it is a greenhouse gas. The figure below shows how greenhouse gases work. Short wave (e.g. visible and ultra violet light) enter the Earth’s atmosphere. At short wavelengths, the radiation mostly passes through the air until it contacts the Earth. The ground and oceans absorb the short wave radiation and re-radiate it back into the atmosphere but at a longer wavelength (infrared). Greenhouse gases absorb the long wavelength (infrared) radiation trapping the heat in the atmosphere.
Some greenhouse effect is a good thing. Without any greenhouse gases, the average Earth temperature would drop from 59 °F (15 °C) to around 0 °F (-18 °C). There are many greenhouses gases including Methane (livestock) and most refrigerants but CO2 represents about two thirds and human activity is main source of the emissions.
CO2 is released to the atmosphere from the burning of fossil fuels such as coal, oil, natural gas. By taking core samples from the ice sheets in Greenland and Antarctica and testing the trapped air, CO2 levels can be traced back hundreds of thousands of years (far before the influence of mankind).
The figure above shows the atmospheric CO2 levels over millennia. The recent change in level starts with the industrial revolution where fossil fuels start to be consumed in large quantities. It is important to note that CO2 levels are a measurement, not a theory – it is really happening.
Global temperature changes naturally. 20,000 years ago there was a mile of ice on top of Canada, Northern Europe and parts of the United States. To form that ice, the ocean levels dropped 400 ft (125m) from today’s levels.
CO2 levels change naturally too. The chart above shows long term global temperature and CO2 levels. There is a very strong correlation between CO2 levels and global temperature.
The figure above shows the global temperature and the CO2 levels since the start of the industrial revolution. This continues to show the relationship between CO2 and global temperature. The timing of the rapid change starts with mankind’s increased use of fossil fuels starting with the industrial revolution. The strong correlation has lead the Intergovernmental Panel on Climate Change (IPCC) to declare with 95% certainly that the recent changes in CO2 and the subsequent global temperature rise are caused by human activity.
Evaluating data and recognizing trends has provided a clear understanding that mankind is influencing the climate and the weather. Predicting the speed and severity of the changes requires powerful computer models of very complex interactions. For example, increasing global temperatures will increase cloud cover but more clouds will reflect solar radiation before it can be trapped by greenhouse gases. The role the oceans play both in storing CO2 and other greenhouse gases and the ocean currents that redistribute the heat are complex. The result is there is a range pf predictions on how mankind’s impact on climate change will be felt. The key take away is none of the predictions are indicating that the impact of climate change will be inconsequential on the quality of life for humanity and the other creatures who share the Earth.
To address the issue of climate change the United Nations has set up the United Nations Framework Convention on Climate Change (UNFCCC). Through the Kyoto Protocol and more recently the Paris agreement 185 of 197 countries have ratified the goal to limit global temperature rise 2 °C (3.6 °F) by the end of the century from pre-industrial levels.