Greenhouse Gases

When you lay on the beach and soak up the sun, you don’t see the invisible infrared waves that your body is absorbing, but you can feel them as warmth. Certain gases have the ability to absorb this infrared radiation in the same way: as heat energy. Gases that trap heat in the atmosphere are known as greenhouse gases, perhaps for the way that Earth’s atmosphere functions similarly to a greenhouse.

Water vapor is the most abundant greenhouse gas. Since air temperature determines evaporation rates (much like the heat setting on a stove determines how much water boils and evaporates out of a pot), it remains unchanged from human behavior. As of 2021, carbon dioxide (CO2) was the most significant greenhouse gas, making up 76% of the global greenhouse gas emissions from human activity. Methane and nitrous oxide accounted for another 22%, and fluorinated gases were responsible for 2%.

In the natural world, Earth’s carbon dioxide budget is balanced by sources and sinks. Sources of carbon dioxide include volcano emissions, decay of organic matter, and respiration by organisms that are aerobic (meaning they use oxygen). Humans are aerobic organisms- we inhale oxygen and breathe out carbon dioxide. Carbon sinks include land plants, which take up CO2 during photosynthesis, as well as oceanic processes. The “solubility pump” takes place when atmospheric carbon is dissolved into surface waters of the ocean and sinks. The “biological pump” refers to phytoplankton removing CO2 from the atmosphere to make organic matter and form their shell. The “microbial carbon pump” involves bacteria, which absorb carbon and transport it to the deep ocean. So if Earth has the carbon dioxide budget balanced with sources and sinks, why is the planet warming?

Anthropogenic activity (the influence of humans in nature) has become a new carbon source for Earth, and a large one at that. Fossil fuels (oil, coal, and natural gas) are burned for transportation, heating, and electricity production. This process accounts for 87% of total global CO2 emissions. China, the United States, and the European Union are the three largest CO2 emitters in the world on an absolute basis. Since the industrial revolution, carbon dioxide levels have risen so rapidly that the natural sinks cannot keep up.

Source: Boden et al., U.S. Department of Energy

On the pH scale, values range from 0-14, with 0 being the most acidic, 7 being neutral, and 14 being the most basic. As the ocean absorbs CO2, it leads to ocean acidification (click here to read more). As of 2023, the pH of the ocean has dropped by 0.1 units- and I know that doesn’t seem like much, but this represents a 30% increase in acidity. The “positive feedback loop” explains the process of how CO2 enters the ocean and ultimately allows more CO2 to become absorbed.

First, CO2 in the atmosphere enters the sea. It mixes with water and ultimately becomes bicarbonate plus a hydrogen ion. The addition of hydrogen ions lowers the pH of the water and causes ocean acidification. Under a more acidic ocean, the chemical which makes up shells and coral skeletons (CaCO3) dissolves. It acts like Tums- when you have acid reflux or heartburn, you take an antacid to raise your stomach pH and neutralize the acid. The dissolving of shells and coral neutralizes ocean acidification, but it also allows the ocean to absorb more CO2. This is due to air-sea gas exchange (which means gas molecules are transferred from water to the air and vice versa) that occurs at the surface of the ocean. If the ocean has a low concentration of CO2, then it will absorb more from the air above it. As the oceans become more acidic, coral and shelled animals will become more scarce.

In the 2015 Paris Agreement, the target to keep global warming less than 1.5°C greater than pre-industrial levels was adopted; by November of 2022, the world had already warmed to an average of 1.3°C. NASA commented on the changes we may see between a 1.5 and 2°C increase, and though it seems like such a small number, the effects may be massive. An estimated 61 million more people would see severe droughts at 2°C than at 1.5°C and approximately 200 million more people would experience water scarcity. Fires, extreme weather, sea level rises, ice caps melting, biome shifts, and invasive species would all be more prevalent as well.

As carbon becomes more present in our atmosphere, some of Earth’s natural sinks may also become less effective, allowing atmospheric CO2 to build at an exponential rate. Scientists who measure geological history with ice cores have found that our current CO2 levels are the highest the planet has seen at least 800,000 years. Carbon remains in the atmosphere for 300-1000 years, meaning even if we were to cut carbon dioxide emissions in half, the amount of CO2 in the atmosphere would continue to increase. It can be thought of as a bathtub with a stopper in it. Anthropogenic activity has nearly filled the bathtub, and even if we turn the water pressure down, the level would continue to rise. So where does that leave us?

Let’s turn to cutting down CO2 emissions: we know that fossil fuel combustion is the leading contributor to greenhouse gases, and therefore climate change. Better building insulation, fuel-effective transportation (we’re looking at you, private jets), reducing electricity usage, and using renewable energy such as solar panels are all great places to start. A quote by John Green in The Anthropocene Reviewed states that “there is another peculiarity of modern air-conditioning: cooling the indoors warms the outdoors. Most of the energy that powers air-conditioning systems comes from fossil fuels, the use of which warms the planet, which over time will necessitate more and more conditioning of air”. But this is not an attempt to place the blame on the individual; most people cannot reasonably walk into an appliance store and find a carbon-neutral setup within their budget. Our options are limited, and the ones given to us are poor. Changes need to be implemented at the corporation level, in skyscrapers and cruise ships, and factories that spew greenhouse gases.

One tactic to reduce atmospheric CO2 takes a different approach: carbon capture and sequestration. This is a relatively new technology (with many new experiments ongoing) that seeks to remove carbon from the source. Some techniques involve capturing the carbon emitted from factories and turning it into a liquid form where it can be stored in the deep sea, subsurface geological formations, or old oil fields. A Swiss company, Climeworks, draws air through a fan, where it passes through a filter, traps CO2 particles, and emits pure air. The CO2 is then heated and turned into a liquid, where it is stored deep underground alongside basalt rocks. The basalt reacts with the CO2 through a natural process called carbon remineralization, and the liquid CO2 turns to stone, allowing it to remain stored for over 10,000 years. This remineralization process is one of the safest, most effective, and long-lasting solutions for carbon storage to date.

Greenhouse gases, primarily carbon dioxide, are leading to the warming of the planet at rates never seen before. If we wish to protect Earth from further negative changes, action needs to be taken to reduce fossil fuel usage. A healthy environment for everyone will take systematic changes, potentially following suit of the Montreal Protocol. As science and technology progress, we may see a light at the end of the global warming tunnel; a hope for a world in which refrigerating food and driving to work doesn't harm us in the long run.

References

Buis, A. (2020). A degree of concern: Why global temperatures matter – climate change: Vital signs of the planet. NASA. https://climate.nasa.gov/news/2865/a-degree-of-concern-why-global-temperatures-matter/

Boden, T.A., Marland, G., and Andres, R.J. (2017). Global, Regional, and National Fossil-Fuel CO2Emissions. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tenn., U.S.A. doi 10.3334/CDIAC/00001_V2017

Climeworks. (2023). Direct air capture: A technology to fight climate change. https://climeworks.com/direct-air-capture

Green, J. (2021). Air-Conditioning. In The anthropocene reviewed: Essays on a human-centered planet (pp. 73–78). essay, DUTTON.

Libes, S. M. (2009). Introduction to marine biogeochemistry. Academic.

Lindsey, R. (2023). Climate change: Atmospheric carbon dioxide. NOAA Climate.gov. https://www.climate.gov/news-features/understanding-climate/climate-change-atmospheric-carbon-dioxide#:~:text=Carbon%20dioxide%20is%20Earth’s%20most,including%20back%20toward%20Earth’s%20surface

Mann, M. E. (2023, May 22). Greenhouse gas. Encyclopedia Britannica. https://www.britannica.com/science/greenhouse-gas

United States Environmental Protection Agency. (2023). Overview of Greenhouse Gases. EPA. https://www.epa.gov/ghgemissions/overview-greenhouse-gases