We’ve all heard of climate change, either in the news or the classroom or everyday conversation. Still, nearly half the U.S. population isn’t sure if it’s real or if we as humans are causing it. For the scientific community, though, there is no debate: humans are changing the climate, and it will only get worse as we emit more and more greenhouse gases by burning fossil fuels. But not all of us are scientists. Not all of us know the words fossil fuels or greenhouse gases and how they relate to turning on the lights or driving to the grocery store. Not all of us understand what carbon dioxide emissions are and what that has to do with temperature. Without the background knowledge needed to understand climate change, of course many of us are left puzzled, especially when the media broadcasts so many mixed messages. I will clear up that confusion by starting with the basics: the fundamental relationship between carbon and the global climate.Carbon interacts with the world around us in a variety of ways to form the carbon cycle. As a complex web of give and take between the atmosphere, ocean, land, and living things, it is an essential process that allows our habitable Earth to exist. Disturbing the carbon balance could alter the very nature of the planet we know today.
Let’s start by getting to know the notorious carbon atom. Of the 94 naturally occurring chemical elements found on Earth, carbon is the sixth most abundant. Named after the Latin word for charcoal, carbon exists in several different structural forms called allotropes, each exhibiting very different physical properties and chemical behaviors. The three naturally occurring allotropes include graphite, diamond, and amorphous carbon, or what you might know as soot. Carbon also joins together with other elements to form millions of compounds (two or more elements bonded together) essential for life on Earth. These various forms recycle through organisms, the soil, our oceans, and the air we breathe, allowing our fixed supply of carbon to be used continuously by plants, animals, and us. In the nonliving environment, carbon exists as carbon dioxide gas scattered about in the atmosphere or dissolved in water bodies. It can also be found as limestone (calcium carbonate), decaying organic matter in soil (also called humus), or underground deposits of the three fossil fuels: liquid petroleum, natural gas (chemically called methane), and coal. Living organisms require carbon as an integral component of their physical makeup, too. Carbohydrates, lipids, proteins, and nucleic acids, for example, are all composed of carbon. In fact, carbon is the second most common element found in the human body, accounting for 18 percent of our biomass.
Photosynthesis is the primary means of transmitting carbon from the nonliving environment to the living, thereby naming the plants and algae that carry out this process primary producers. By using sunlight to transform atmospheric carbon dioxide into storable carbohydrates and oxygen, plants not only provide us with air to breathe, they also convert inorganic carbon into a form animals can use and exchange all across the food web. Every time you take a bite of your spinach salad or turkey sandwich you participate in the carbon cycle. Whether eating plants or an animal that ate plants you are consuming the carbon your body needs to function. In this way, we and all other living things temporarily store carbon.
On the other hand, we are also responsible for returning that carbon to the environment. We do this in two ways, the first of which is respiration, the scientific name for breathing. Just as plants use photosynthesis to convert carbon dioxide into oxygen, animals, including us (microbes and plants, too!), use respiration to reverse the process. Oxygen constitutes twenty-one percent of the air we breathe, but what we exhale is carbon dioxide. As you can see, a mutually beneficial relationship happens between the animal kingdom and the plant world. They provide us with oxygen so that we can convert it back to carbon dioxide. Everybody wins! As a necessary function of life, we continue exhaling carbon dioxide until that life inevitably comes to an end, but our carbon contribution doesn’t end there. The second way we give back carbon is decomposition, which takes place after we die. Organisms such as bacteria and fungi living in the water or soil break down the carbon stored in dead plant and animal tissues and respire it back into the atmosphere. In some cases, however, certain forms of carbon are so difficult for decomposers to break down they persist for many years in the soil. In fact, soils store as much carbon as land plants and the atmosphere combined.
The sediment at the seafloor has a similarly huge potential for carbon storage. In the oceans, the decaying plant and animal matter called detritus slowly sink thousands of feet until reaching the bottom. Typically, decomposers come in and contribute their part in breaking down and recycling the dead material, however, in conditions devoid of oxygen, the decomposers cannot survive. Instead, the detritus settles to the bottom getting buried by layers and layers of mud, rock, and sand. The weight of these sediment layers compacts the organic material so that after millions of years, the combined forces of pressure, heat and bacterial processes “cooks” it into the highly carbon concentrated materials we know as crude oil or natural gas. Coal forms in a similar way, though usually in a non-marine setting, such as swamps. We call these vast carbon reserves fossil fuels because they are exactly that -- fossils! Most of them formed during the Carboniferous Period of the Paleozoic Era 360 to 286 million years ago – that’s before the dinosaurs! This enormous quantity of decayed material squeezed into a highly concentrated area for hundreds of millions of years made possible the huge source of energy we rely on today. The Carboniferous Period, with swamps covering the earth, experienced much warmer global temperatures than we know today, and like the majority of Earth’s extensive history, substantially higher carbon dioxide levels. Atmospheric carbon dioxide concentrations declined from about 1500 ppm (parts per million) in the early part of the Carboniferous period to just 350 ppm less than 100 million years later. To put this in perspective, average carbon dioxide concentrations today are around 380 ppm. Burning reserves of coal, oil, and natural gas to power our cars or heat our houses, releases back into the atmosphere this massive amount of carbon that took almost 100 million years to capture, and we are doing it in just a matter of decades.
Adding all of this carbon to the atmosphere is problematic because carbon dioxide is a greenhouse gas. This means that, like the name sounds, these gases cause our atmosphere to act like a greenhouse, trapping heat from the sun instead of releasing it back into the solar system. This greenhouse effect makes our planet warm enough for us to live on so we need it to survive, but altering the concentration of those gases is like altering hormone levels in your body - a tiny amount goes a really long way. The climate we know today has been relatively stable for the past tens of thousands of years, providing the conditions in which humans and the plants and animals we know have evolved. Changing those conditions even slightly, like increasing the average global temperature by just one degree Celsius, will have dramatic consequences difficult to predict. Many species are sensitive to temperature and can only live within the narrow range they have evolved to tolerate. A slight change in global average temperature can mean much more noticeable changes in those species’ habitats, limiting their ability to survive. Warmer temperatures also impact the hydrologic cycle, which recycles water between the atmosphere, oceans, and land. Warm air not only melts snowpack and glacial ice, it holds more water than cold air so that precipitation occurs much heavier, leading to less frequent but more intense storms. This can have serious consequences such as an unequal distribution of water as well as flooding and erosion.
But carbon dioxide is not the only greenhouse gas within the carbon cycle. Methane, though a less frequent offender, is 21 times more effective at trapping heat than carbon dioxide. The same way plants, animals, and microbes produce carbon dioxide by breathing, some animals, called ruminants, additionally produce methane simply through digestion. These animals, including but not limited to many livestock such as cows, sheep, and goats, have a rumen, which is just a fancy name for a special second stomach designed to digest tough plant materials using the help of resident fermenting microbes. As an anaerobic process, meaning without oxygen, the byproduct of fermentation later belched out by the animal is methane. The United States Environmental Protection Agency (EPA) reports that ruminant livestock produce about 80 million metric tons of the gas annually, designating them one of the largest methane sources in the world. Fermentation also takes place in several other sectors of the carbon cycle that contribute significant methane emissions including anaerobic soils, particularly in wetlands, and human made landfills. Some soils containing methanoptrophic bacteria, so named for their “love of methane”, act as a sink to absorb the injurious gas, utilizing methane as their only source of carbon and energy. Unfortunately, the carbon uptake from these microbes is relatively minimal.
So since we are building up more carbon in the atmosphere, we need to semi-permanently store the extra supply. Forests, due to their high density of trees and other plant life, act as a major storage facility since carbon constitutes nearly half the mass of a tree. A typical 25-inch diameter redwood, for example, can store about a ton of carbon. Destroying forests, on the other hand, creates a substantial carbon source. Burning forests, either through natural fires or human induced measures, liberates the hundreds of tons of carbon locked up in the woody biomass back into the sky. Furthermore, the deforestation that ensued over the past century left fewer trees to perform the photosynthesis needed to take up the excess carbon. With fewer trees available for carbon exchange through photosynthesis, increasing levels of carbon dioxide remain trapped in the atmosphere.
Fortunately, land plants are not the only photosynthetic organisms out there. Phytoplankton, the various types of small or microscopic algae found in natural waters, account for roughly half of the photosynthetic activity on our planet. Aquatic systems also store carbon by dissolving atmospheric carbon dioxide in the water. This process occurs to ensure equilibrium between the atmosphere and the ocean. Having taken up as much as one third of the emitted carbon dioxide, without the ocean’s contribution as a carbon sink, atmospheric carbon dioxide concentrations would have skyrocketed up to 500 or 600 ppm.. Unfortunately, absorbing all this carbon develops problems for many marine inhabitants. Due to its massive size, it takes an enormous amount of added carbon to alter the ocean’s chemical makeup but within the past century it seems we have managed to increase the ocean’s acidity by thirty percent! Dissolving carbon dioxide in water produces carbonic acid, which then dissociates into bicarbonate ion or further into carbonate ion. Protons released along the way make the water acidic. The tendency for carbon to exist in its different dissociated forms changes as carbonate ions neutralize the excess protons to form bicarbonate. Numerous organisms such as corals, mollusks, and several types of phytoplankton need that carbonate, though, to form their calcium carbonate shells or skeletons. Effects on these communities can already be seen as the acidified ocean limits the availability of carbonate and do inhibits their ability to formulate these fundamental physical structures. Because most of that carbon was locked up in ocean sediments for so long, marine ecosystems have not seen such dramatic changes in millions of years. Paleontological studies show that such shifts have historically resulted in a widespread loss of sea life, including the phytoplankton that contribute so vastly to our oxygen supply
To sum up, our planet contains a fixed supply of carbon, a large portion of which was trapped underground as fossil fuels. Burning those fuels and increasing what gets used in the carbon cycle budget has and will continue to have noticeable impacts on terrestrial and aquatic ecosystems. As we continue to fill up our gas tanks with oil and burn more coal for electricity and the other countless ways we rely on fossil fuels, the levels of carbon dioxide in the atmosphere trapping in heat will increase. Oceans will continue to absorb it to remain in equilibrium with the atmosphere so that surface temperatures get warmer while aquatic pH levels get lower. All of these changes produce negative consequences that only time will truly reveal, however our best predictions are quite grim. In the past, significant climate changes have occurred after volcanic eruptions or through other natural forces emitting enormous amounts of carbon. This time we are the culprits. We are burning fossil fuels and releasing the extra carbon and only we can make it stop. While we can’t do anything about the carbon we have already emitted, it is imperative that we stop as soon as possible before our planet becomes an unrecognizably hostile place.
Let’s start by getting to know the notorious carbon atom. Of the 94 naturally occurring chemical elements found on Earth, carbon is the sixth most abundant. Named after the Latin word for charcoal, carbon exists in several different structural forms called allotropes, each exhibiting very different physical properties and chemical behaviors. The three naturally occurring allotropes include graphite, diamond, and amorphous carbon, or what you might know as soot. Carbon also joins together with other elements to form millions of compounds (two or more elements bonded together) essential for life on Earth. These various forms recycle through organisms, the soil, our oceans, and the air we breathe, allowing our fixed supply of carbon to be used continuously by plants, animals, and us. In the nonliving environment, carbon exists as carbon dioxide gas scattered about in the atmosphere or dissolved in water bodies. It can also be found as limestone (calcium carbonate), decaying organic matter in soil (also called humus), or underground deposits of the three fossil fuels: liquid petroleum, natural gas (chemically called methane), and coal. Living organisms require carbon as an integral component of their physical makeup, too. Carbohydrates, lipids, proteins, and nucleic acids, for example, are all composed of carbon. In fact, carbon is the second most common element found in the human body, accounting for 18 percent of our biomass.
Photosynthesis is the primary means of transmitting carbon from the nonliving environment to the living, thereby naming the plants and algae that carry out this process primary producers. By using sunlight to transform atmospheric carbon dioxide into storable carbohydrates and oxygen, plants not only provide us with air to breathe, they also convert inorganic carbon into a form animals can use and exchange all across the food web. Every time you take a bite of your spinach salad or turkey sandwich you participate in the carbon cycle. Whether eating plants or an animal that ate plants you are consuming the carbon your body needs to function. In this way, we and all other living things temporarily store carbon.
On the other hand, we are also responsible for returning that carbon to the environment. We do this in two ways, the first of which is respiration, the scientific name for breathing. Just as plants use photosynthesis to convert carbon dioxide into oxygen, animals, including us (microbes and plants, too!), use respiration to reverse the process. Oxygen constitutes twenty-one percent of the air we breathe, but what we exhale is carbon dioxide. As you can see, a mutually beneficial relationship happens between the animal kingdom and the plant world. They provide us with oxygen so that we can convert it back to carbon dioxide. Everybody wins! As a necessary function of life, we continue exhaling carbon dioxide until that life inevitably comes to an end, but our carbon contribution doesn’t end there. The second way we give back carbon is decomposition, which takes place after we die. Organisms such as bacteria and fungi living in the water or soil break down the carbon stored in dead plant and animal tissues and respire it back into the atmosphere. In some cases, however, certain forms of carbon are so difficult for decomposers to break down they persist for many years in the soil. In fact, soils store as much carbon as land plants and the atmosphere combined.
The sediment at the seafloor has a similarly huge potential for carbon storage. In the oceans, the decaying plant and animal matter called detritus slowly sink thousands of feet until reaching the bottom. Typically, decomposers come in and contribute their part in breaking down and recycling the dead material, however, in conditions devoid of oxygen, the decomposers cannot survive. Instead, the detritus settles to the bottom getting buried by layers and layers of mud, rock, and sand. The weight of these sediment layers compacts the organic material so that after millions of years, the combined forces of pressure, heat and bacterial processes “cooks” it into the highly carbon concentrated materials we know as crude oil or natural gas. Coal forms in a similar way, though usually in a non-marine setting, such as swamps. We call these vast carbon reserves fossil fuels because they are exactly that -- fossils! Most of them formed during the Carboniferous Period of the Paleozoic Era 360 to 286 million years ago – that’s before the dinosaurs! This enormous quantity of decayed material squeezed into a highly concentrated area for hundreds of millions of years made possible the huge source of energy we rely on today. The Carboniferous Period, with swamps covering the earth, experienced much warmer global temperatures than we know today, and like the majority of Earth’s extensive history, substantially higher carbon dioxide levels. Atmospheric carbon dioxide concentrations declined from about 1500 ppm (parts per million) in the early part of the Carboniferous period to just 350 ppm less than 100 million years later. To put this in perspective, average carbon dioxide concentrations today are around 380 ppm. Burning reserves of coal, oil, and natural gas to power our cars or heat our houses, releases back into the atmosphere this massive amount of carbon that took almost 100 million years to capture, and we are doing it in just a matter of decades.
Adding all of this carbon to the atmosphere is problematic because carbon dioxide is a greenhouse gas. This means that, like the name sounds, these gases cause our atmosphere to act like a greenhouse, trapping heat from the sun instead of releasing it back into the solar system. This greenhouse effect makes our planet warm enough for us to live on so we need it to survive, but altering the concentration of those gases is like altering hormone levels in your body - a tiny amount goes a really long way. The climate we know today has been relatively stable for the past tens of thousands of years, providing the conditions in which humans and the plants and animals we know have evolved. Changing those conditions even slightly, like increasing the average global temperature by just one degree Celsius, will have dramatic consequences difficult to predict. Many species are sensitive to temperature and can only live within the narrow range they have evolved to tolerate. A slight change in global average temperature can mean much more noticeable changes in those species’ habitats, limiting their ability to survive. Warmer temperatures also impact the hydrologic cycle, which recycles water between the atmosphere, oceans, and land. Warm air not only melts snowpack and glacial ice, it holds more water than cold air so that precipitation occurs much heavier, leading to less frequent but more intense storms. This can have serious consequences such as an unequal distribution of water as well as flooding and erosion.
But carbon dioxide is not the only greenhouse gas within the carbon cycle. Methane, though a less frequent offender, is 21 times more effective at trapping heat than carbon dioxide. The same way plants, animals, and microbes produce carbon dioxide by breathing, some animals, called ruminants, additionally produce methane simply through digestion. These animals, including but not limited to many livestock such as cows, sheep, and goats, have a rumen, which is just a fancy name for a special second stomach designed to digest tough plant materials using the help of resident fermenting microbes. As an anaerobic process, meaning without oxygen, the byproduct of fermentation later belched out by the animal is methane. The United States Environmental Protection Agency (EPA) reports that ruminant livestock produce about 80 million metric tons of the gas annually, designating them one of the largest methane sources in the world. Fermentation also takes place in several other sectors of the carbon cycle that contribute significant methane emissions including anaerobic soils, particularly in wetlands, and human made landfills. Some soils containing methanoptrophic bacteria, so named for their “love of methane”, act as a sink to absorb the injurious gas, utilizing methane as their only source of carbon and energy. Unfortunately, the carbon uptake from these microbes is relatively minimal.
So since we are building up more carbon in the atmosphere, we need to semi-permanently store the extra supply. Forests, due to their high density of trees and other plant life, act as a major storage facility since carbon constitutes nearly half the mass of a tree. A typical 25-inch diameter redwood, for example, can store about a ton of carbon. Destroying forests, on the other hand, creates a substantial carbon source. Burning forests, either through natural fires or human induced measures, liberates the hundreds of tons of carbon locked up in the woody biomass back into the sky. Furthermore, the deforestation that ensued over the past century left fewer trees to perform the photosynthesis needed to take up the excess carbon. With fewer trees available for carbon exchange through photosynthesis, increasing levels of carbon dioxide remain trapped in the atmosphere.
Fortunately, land plants are not the only photosynthetic organisms out there. Phytoplankton, the various types of small or microscopic algae found in natural waters, account for roughly half of the photosynthetic activity on our planet. Aquatic systems also store carbon by dissolving atmospheric carbon dioxide in the water. This process occurs to ensure equilibrium between the atmosphere and the ocean. Having taken up as much as one third of the emitted carbon dioxide, without the ocean’s contribution as a carbon sink, atmospheric carbon dioxide concentrations would have skyrocketed up to 500 or 600 ppm.. Unfortunately, absorbing all this carbon develops problems for many marine inhabitants. Due to its massive size, it takes an enormous amount of added carbon to alter the ocean’s chemical makeup but within the past century it seems we have managed to increase the ocean’s acidity by thirty percent! Dissolving carbon dioxide in water produces carbonic acid, which then dissociates into bicarbonate ion or further into carbonate ion. Protons released along the way make the water acidic. The tendency for carbon to exist in its different dissociated forms changes as carbonate ions neutralize the excess protons to form bicarbonate. Numerous organisms such as corals, mollusks, and several types of phytoplankton need that carbonate, though, to form their calcium carbonate shells or skeletons. Effects on these communities can already be seen as the acidified ocean limits the availability of carbonate and do inhibits their ability to formulate these fundamental physical structures. Because most of that carbon was locked up in ocean sediments for so long, marine ecosystems have not seen such dramatic changes in millions of years. Paleontological studies show that such shifts have historically resulted in a widespread loss of sea life, including the phytoplankton that contribute so vastly to our oxygen supply
To sum up, our planet contains a fixed supply of carbon, a large portion of which was trapped underground as fossil fuels. Burning those fuels and increasing what gets used in the carbon cycle budget has and will continue to have noticeable impacts on terrestrial and aquatic ecosystems. As we continue to fill up our gas tanks with oil and burn more coal for electricity and the other countless ways we rely on fossil fuels, the levels of carbon dioxide in the atmosphere trapping in heat will increase. Oceans will continue to absorb it to remain in equilibrium with the atmosphere so that surface temperatures get warmer while aquatic pH levels get lower. All of these changes produce negative consequences that only time will truly reveal, however our best predictions are quite grim. In the past, significant climate changes have occurred after volcanic eruptions or through other natural forces emitting enormous amounts of carbon. This time we are the culprits. We are burning fossil fuels and releasing the extra carbon and only we can make it stop. While we can’t do anything about the carbon we have already emitted, it is imperative that we stop as soon as possible before our planet becomes an unrecognizably hostile place.
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