Greenhouse Gases and Carbon Storage

What are greenhouse gases? 

“Greenhouse” gases occur naturally in the Earth’s atmosphere. They help regulate the planet’s temperature, like how the glass in a greenhouse retains heat or a blanket reflects your body heat to keep you warm. Adding more greenhouse gases into the atmosphere, like we do when burning fossil fuels, acts like putting a thicker blanket on the planet. The thicker the blanket of greenhouse gases, the less heat escapes into space. This causes the planet to get warmer. Common greenhouse gases include carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), fluorinated gases such as hydrofluorocarbons, perfluorocarbons, sulfur hexafluoride, and nitrogen trifluoride, and water vapor (H2O).

What is causing increased greenhouse gas concentrations?  

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Most greenhouse gases released in the United States contain carbon. Carbon naturally cycles throughout the planet and the air. There is carbon moving around “in circulation,” such as the CO2 we breath and carbon contained in plant and animal tissue. And there is carbon locked in “long-term storage”, called carbon sinks. Carbon in underground oil reserves or in trees that live hundreds of years are examples are carbon sinks. Many human activities take carbon out of carbon sinks and put it back into the atmosphere. Oil reserves that took millions of years to form are used up in decades. Forests that have stood for centuries are harvested or burned in a matter of weeks. Through these activities, we add more carbon dioxide to the atmosphere than can naturally be reabsorbed.

Efforts to slow or stop climate change revolve around righting the carbon imbalance in the atmosphere. This can be done by decreasing greenhouse gas emissions, for example by reducing fossil fuel use. Or it can involve increasing the amount of carbon being captured and stored in carbon sinks, a process called carbon sequestration.

Important sources of greenhouse gas emissions include:

• Burning fossil fuels, including oil, coal, and natural gas  
• Producing and using industrial products  
• Agriculture, including cows and some crops  
• Destroying or disrupting ecosystems that act as carbon sinks  

There are also natural sources of greenhouse gases, including volcanic eruptions, geologic seeps (such as hot springs and geothermal vents), thawing permafrost, and forest fires. Climate change and human activities can accelerate natural emissions. Warmer temperatures defrost permafrost and heat up oceans, releasing the carbon long stored in these systems. Wetlands drained for agriculture can rapidly switch from being carbon sinks to being carbon sources. And human ignitions and climate-driven dryness mean long, intense fire seasons, releasing billions of metric tons of carbon dioxide around the world each year.

Greenhouse Gas Emissions on Public Lands  

The USGS conducts research on greenhouse gas emissions and carbon sequestration in public lands. Public lands maintained by the U.S. Department of the Interior make up about one-fifth of the Nation’s land area. They include national parks, seashores, and monuments managed by the National Park Service; national wildlife refuges managed by the U.S. Fish and Wildlife Service; and working lands and offshore mineral rights managed by the Bureau of Land Management.

In 2018, the USGS estimated the amount of carbon released by and sequestered in U.S. federal lands. (USGS Scientific Investigations Report 2018-5131). We found that about one-quarter of the United States’ emissions come from combustion of coal, oil, and gas extracted from public lands.

The USGS also investigates methods of land management aimed at decreasing emissions from federal lands. We provide decision-makers, local communities, and land managers with tools to analyze tradeoffs associated with changing energy practices. We also develop natural carbon dioxide removal technologies to remove carbon from the atmosphere through carbon sequestration and to decrease natural methane emissions.

Carbon Sequestration as a Potential Climate Solution  

Carbon sequestration helps slow or possibly reverse the effects of climate change. The USGS is exploring two major approaches to carbon dioxide removal and storage.

Geologic Carbon Sequestration. Geologic carbon sequestration involves storing carbon dioxide in stable rock formations. Technology captures carbon dioxide from industrial processes, like factories and power plants, and compresses the gas into a liquid. This liquid is then injected deep underground. Another technology is called carbon mineralization, which is the process by which carbon dioxide becomes a solid mineral, such as a carbonate. It is a chemical reaction that happens when certain rocks are exposed to carbon dioxide. The USGS is an international leader in identifying rock formations with high potential for carbon storage and is exploring the mechanisms and potential consequences of this process.

Biologic Carbon Sequestration. Biologic carbon sequestration takes advantage of nature's ability to store carbon. Through photosynthesis, plants remove carbon dioxide from the atmosphere and use it as a building block to create new tissue. Some of the carbon remains preserved in soil, sediments, and wood. Ecosystems like forests and wetlands can absorb huge amounts of carbon dioxide from the atmosphere and store it for long time periods, from decades to thousands of years. The USGS helps managers and conservation agencies identify ecosystems that are particularly good at storing carbon and supports restoration and conservation of these areas. Much of this work currently focuses on carbon stored in coastal regions, known as “blue carbon.”