What do people really mean when they talk about reducing global warming? What are greenhouse gases and why do they threaten the environment?
Technically speaking any gas that absorbs and emits radiation is a "greenhouse gas." Water vapor, methane, ozone, nitrous oxide, and carbon dioxide are all classified as greenhouse gases. However, carbon dioxide is the most prevalent of all greenhouse gases, which is one of the reasons it comes up so frequently when discussing climate change issues. According to a study conducted by the EPA in 2014, carbon dioxide made up 81% of all greenhouse gases.
Carbon dioxide exists naturally as a trace gas in the Earth’s atmosphere. Although CO2 concentrations in the air fluctuate naturally with the seasons, anthropogenic factors like fossil fuel combustion and widespread deforestation have increased the quantity of carbon dioxide present in the atmosphere, with negative climatic and environmental effects.
Since the time of the Industrial Revolution, atmospheric CO2 concentrations have increased by a worrisome 43%. On a global scale, this is a significant change. Human activities emit 29 billion tons of carbon dioxide each year, and most of this derives from the burning of fossil fuels for energy.
Carbon dioxide is a problem because it acts as a "greenhouse gas." Due to its molecular structure, CO2 absorbs and emits infrared radiation, warming the Earth’s surface and the lower levels of the atmosphere. This leads to a positive feedback cycle: as temperatures increase due to atmospheric CO2 levels, CO2 levels increase due to the warming temperatures.
Over the last 150 years, human activity has brought the amount of carbon dioxide in our atmosphere to levels that have not been seen for hundreds of thousands of years. The magnitude of this impact is immense. Humans today have so much impact on a global scale that most geologists, ecologists, and natural historians maintain that we have entered an entirely new geological epoch, known as the Anthropocene.
Ongoing scientific research has made it increasingly clear that it is in humanity's best interest, as a species, to move away from dependence on fossil fuel combustion.