What Causes Carbon Emissions

By now, most of us have become keenly aware that carbon emissions (CO₂ emissions) are accumulating in the Earth’s atmosphere. These increased carbon emissions are causing global temperatures to increase and are changing the climate of our planet. In order to really understand the impacts of carbon emissions, we must first understand where they originate, from both natural and human sources.

Natural sources of carbon emissions

While most of the carbon emissions that are changing our climate are produced through human activity, there are also natural sources of carbon emissions.

Carbon emissions are naturally produced through animal and plant respiration, from the soil, through the decomposition of deceased organisms and other organic matter, carbon dioxide releases from the ocean, a small amount from volcanic eruptions, and wildfires.

In nature, carbon dioxide is used by trees and other green plants during photosynthesis and it is absorbed by animals when they consume plants. Carbon dioxide is naturally stored in the bodies of plants and animals, in the soil, and in the ocean, where kelp, marine algae, and other photosynthetic organisms utilize it during photosynthesis.

Carbon dioxide is required for photosynthesis by plants and other photosynthetic organisms, and under natural conditions, the carbon “sinks” of the Earth’s oceans, plants, and the soil are more than sufficient to store and use all of the carbon produced. However, since the Industrial Revolution, mankind has been burning the stored carbon within fossil fuels at a very fast rate, changing the landscape, and we have exceeded the capacity of these natural systems to compensate for our increased levels of carbon emissions.

Human sources of carbon emissions

Burning the stored energy of fossil fuels over the last 150 years has allowed humanity to develop many of the amazing things that we have in our modern world today. However, much of this development and fossil fuel use has been at a rate far beyond the Earth’s ability to compensate for all of the carbon emissions that we have been producing. In fact, human activities produce about 135 times the carbon dioxide that volcanoes do every year, with volcanic CO₂ emissions producing about 0.13-0.44 billion metric tons/yr, and human activity producing more than 35 billion metric tons/year [1].

It has been estimated that CO₂ levels in the atmosphere have increased by 36% since the Industrial Revolution, and that more than 50% of that increase happened after 1973. CO₂ levels increased from 280 ppm prior to the mid-1700s to the current levels of more than 407 ppm [2].

By far, the largest human sources of carbon emissions are coal, oil, and gas, and cement, equaling approximately 70% of human carbon emissions, but land use changes, such as agriculture and deforestation have also become significant sources of human-sourced carbon emissions of approximately 30% [3].

Fossil fuels are burned when vehicles are driven and also in power plants and industrial plants. Fossil fuels are burned to produce electricity that is used throughout much of our industrialized world today.

Agriculture contributes to carbon dioxide emissions by actions such as deforestation to clear land for agriculture, heavy soil tillage and soil erosion, and machine intensive farming equipment that use fossil fuels. When soils are tilled heavily, the opportunity for long-term storage of carbon in the soil is lost, and cultivation of previously undisturbed soils leads to the the release of stored carbon into the atmosphere [4].

Deforestation decreases the total size of the forested carbon sinks that are available on earth, thereby increasing the levels of CO₂ emissions in the atmosphere. When the trees in forests are cut down, stored carbon dioxide from the soil is released into the atmosphere due to a lack of carbon-storing trees [3]. There are especially negative impacts when trees are burned and their stored carbon is released into the atmosphere [2].

To see where most of the global carbon emissions are generated and how they have increased from 1961-2017, check out the Global Carbon Atlas.