Question

Question #3: Compare the short-term and long-term carbon cycling. Please define each term. Hypothesize if humans are altering each one and provide two examples. Make sure your answer is at least 500 words but no longer than 900 words.

Answer 1

carbon dioxide helps stabilize the planet’s temperature, but increasing the atmospheric concentration of carbon dioxide will increase the global temperature. Over millions of years Earth has been able to regulate the level of atmospheric carbon dioxide through the carbon cycle. The burning of fossil fuels, such as coal and oil, in our factories, power plants and cars has disrupted this balance so that higher levels of carbon dioxide accumulate in the atmosphere. To appreciate the impact our burning of fossil fuels is placing on the planet we need to understand how the Earth recycles carbon dioxide through the carbon cycle.

The carbon cycle refers to the flow of carbon between the atmosphere, rocks, oceans and biosphere (all of Earth’s life forms). Each of these is part of a reservoir which contains all the carbon on the planet. The carbon cycle is composed of two reservoirs: a long-term and a short-term. By circulating carbon through these interconnected reservoirs the planet regulates the level of atmospheric carbon dioxide.

The long-term reservoir contains about 99.9 percent of the total carbon which is found mainly in rocks and fossil fuels and takes up to millions of years to recycle carbon dioxide. In the long-term reservoir atmospheric carbon dioxide reacts with water and minerals in rocks to form calcium bicarbonate which enters rivers and ends up in the ocean where it becomes shells of various marine organisms. When these organisms die the shells accumulate on the ocean floor and are eventually transformed into rocks and petroleum. Over millions of years this transformed material is buried at depths of thousands of feet and the heat and pressure melts the rocks and converts the carbonate back to carbon dioxide. Some of these rocks become part of volcanoes and the carbonate is released as carbon dioxide via volcanic eruptions.

Carbon dioxide is also removed from the atmosphere by plants and the burial of dead plant matter. In swamps this material is transformed into coal and in river deltas the material is converted into carbonaceous shale.

Carbon is an essential element the bodies of living organisms. It is also economically important to modern humans, in the form of fossil fuels.

In the short-term reservoir, carbon is stored in the atmosphere, oceans and biosphere with the ocean containing the largest amount of carbon. It takes months to centuries to recycle carbon dioxide through the short-term reservoir. The ocean is the primary regulator of atmospheric carbon dioxide in the short-term reservoir because atmospheric and ocean carbon dioxide are in chemical equilibrium. If there is an increase in atmospheric carbon dioxide there is a corresponding increase in oceanic carbon dioxide and vice versa. There are two main ways in the short-term reservoir that carbon dioxide is removed from the atmosphere and enters the ocean.

In the first mechanism, atmospheric carbon dioxide enters the ocean by the growth and death of plants, animals and microbes. Secondly, atmospheric carbon dioxide is dissolved in the ocean which helps maintain a stable pH for life.

In the carbon cycle, carbon dioxide is removed from the atmosphere and converted to fossil fuels and rocks which are components of the long-term reservoir. Eventually the carbon dioxide in the long-term reservoir enters the ocean and atmosphere and becomes part of the short-term reservoir through volcanic eruptions and melting of rocks.

The crux of our current dilemma is that the drilling of oil and the mining of coal and their use as an energy source has disrupted the natural balance between the long-term and short-term reservoirs. When we burn fossil fuels, over half of the carbon dioxide enters the ocean and the rest stays in the atmosphere1. This disrupts the long term carbon balance because carbon dioxide can’t be transferred from the atmosphere back into the long-term reservoir fast enough. It is estimated that it will take up to hundreds of thousands of years to remove this excess carbon dioxide from the atmosphere1.

What has been the effect of disrupting this natural balance? Preindustrial revolution levels of carbon dioxide were 285 ppm. But, in 2006 the level was 385 ppm2and it is currently increasing by 2 ppm per year3! The 2006 level of atmospheric carbon dioxide is substantially higher than any time in the past 800,000 years3! Over the past 100 years, global temperature has increased 1.8o F4. In recent decades the increase in global temperature per decade is much faster than in earlier decades of the 20thCentury. In the past three decades the temperature has increased 1.4o F4! The first eight months of 2010 matched 1998 as the hottest January to August period on record5! Some people believe that the disruption of this natural carbon balance could lead to a “runaway greenhouse” in which so much carbon dioxide accumulates in the atmosphere as to create a global temperature unable to support life.

There are several natural feedback factors that will amplify a “runaway greenhouse” and increase the probability that the planet will reach a tipping point where the current gradual global temperature increase will be replaced by an abrupt and significant increase in global temperature.

• Carbon dioxidefrom the atmosphere is taken up by photosynthetic organisms and used to make organic molecules, which travel through food chains. In the end, the carbon atoms are release in respiration.

• Slow geological processes, including the formation of sedimentary rock and fossil fuels, contribute to the carbon cycle over long timescales.

• Some human activities, such as burning of fossil fuels and deforestation, increase atmospheric and affect Earth's climate and oceans.

Carbon: building block and fuel source

About 18% of your body consists of carbon atoms, by mass, and those carbon atoms are pretty key to your existence!^11start superscript, 1, end superscriptWithout carbon, you wouldn't have the plasma membranes of your cells, the sugar molecules you use for fuel, or even the{DNA} that carries instructions to build and run your body.

Carbon is part of our bodies, but it's also part of our modern-day industries. Carbon compounds from long-ago plants and algae make up the fossil fuels, such as coal and natural gas, that we use today as energy sources. When these fossil fuels are burned, carbon dioxide2CO2is released into the air, leading to higher and higher levels of atmospheric{CO}_2CO2 levels affects Earth's climate and is a major environmental concern worldwide.

Let's take a look at the carbon cycle and see how atmospheric _2CO2​ and carbon use by living organisms fit into the bigger picture of carbon cycling.

The carbon cycle

The carbon cycle is most easily studied as two interconnected subcycles:

• One dealing with rapid carbon exchange among living organisms

• One dealing with long-term cycling of carbon through geologic processes

Although we will look at them separately, it's important to realize these cycles are linked. For instance, the same pools of atmospheric and oceanic_2CO2​that are utilized by organisms are also fed and depleted by geological processes.

As a brief overview, carbon exists in the air largely as carbon dioxide {CO}_2CO2​gas, which dissolves in water and reacts with water molecules to produce bicarbonat{HCO} Photosynthesis by land plants, bacteria, and algae converts carbon dioxide or bicarbonate into organic molecules. Organic molecules made by photosynthesizers are passed through food chains, and cellular respirationconverts the organic carbon back into carbon dioxide gas.

Longterm storage of organic carbon occurs when matter from living organisms is buried deep underground or sinks to the bottom of the ocean and forms sedimentary rock. Volcanic activity and, more recently, human burning of fossil fuels bring this stored carbon back into the carbon cycle. Although the formation of fossil fuels happens on a slow, geologic timescale, human release of the carbon they contain—_CO2is on a very fast timescale.

The biological carbon cycle

Carbon enters all food webs, both terrestrial and aquatic, through autotrophs, or self-feeders. Almost all of these autotrophs are photosynthesizers, such as plants or algae.

Autotrophs capture carbon dioxide from the air or bicarbonate ions from the water and use them to make organic compounds such as glucose. Heterotrophs, or other-feeders, such as humans, consume the organic molecules, and the organic carbon is passed through food chains and webs.

How does carbon cycle back to the atmosphere or ocean? To release the energy stored in carbon-containing molecules, such as sugars, autotrophs and heterotrophs break these molecules down in a process called cellular respiration. In this process, the carbons of the molecule are released as carbon dioxide. Decomposers also release organic compounds and carbon dioxide when they break down dead organisms and waste products.

Carbon can cycle quickly through this biological pathway, especially in aquatic ecosystems. Overall, an estimated 1,000 to 100,000 million metric tons of carbon move through the biological pathway each year. For context, a metric ton is about the weight of an elephant or a small carstart.

The geological carbon cycle

The geological pathway of the carbon cycle takes much longer than the biological pathway described above. In fact, it usually takes millions of years for carbon to cycle through the geological pathway. Carbon may be stored for long periods of time in the atmosphere, bodies of liquid water—mostly oceans— ocean sediment, soil, rocks, fossil fuels, and Earth’s interior.

The level of carbon dioxide in the atmosphere is influenced by the reservoir of carbon in the oceans and vice versa. Carbon dioxide from the atmosphere dissolves in water and reacts with water molecules in the following reactions:

Then the organisms die, their remains may sink and eventually become part of the sediment on the ocean floor. Over geologic time, the sediment turns into limestone, which is the largest carbon reservoir on Earth.

On land, carbon is stored in soil as organic carbon from the decomposition of living organisms or as inorganic carbon from weathering of terrestrial rock and minerals. Deeper under the ground are fossil fuels such as oil, coal, and natural gas, which are the remains of plants decomposed under anaerobic—oxygen-free—conditions. Fossil fuels take millions of years to form. When humans burn them, carbon is released into the atmosphere as carbon dioxide.

Another way for carbon to enter the atmosphere is by the eruption of volcanoes. Carbon-containing sediments in the ocean floor are taken deep within the Earth in a process called subduction, in which one tectonic plate moves under another. This process forms carbon dioxide, which can be released into the atmosphere by volcanic eruptions or hydrothermal vents.

Human impacts on the carbon cycle

Global demand for Earth’s limited fossil fuel reserves has risen since the beginning of the Industrial Revolution. Fossil fuels are considered a nonrenewable resource because they are being used up much faster than they can be produced by geological processes.

When fossil fuels are burned, carbon dioxide is released into the air. Increasing use of fossil fuels has led to elevated levels of atmospheric Deforestation—the cutting-down of forests—is also a major contributor to increasing text levels. Trees and other parts of a forest ecosystem sequester carbon, and much of the carbon is released as text

Some of the extra produced by human activities is taken up by plants or absorbed by the ocean, but these processes don't fully counteract the increase. So, atmospheric levels have risen and contin levels naturally rise and fall in cycles over long periods of time, but they are higher now than they have been in the past 400,000 years

CO2 is a greenhouse gas. When in the atmosphere, it traps heat and keeps it from radiating into space. Based on extensive evidence, scientists think that elevated levels of and other greenhouse gases are causing pronounced changes in Earth's climate. Without decisive changes to reduce emissions, Earth's temperature is projected to increase

Also, while uptake of excess carbon dioxide by the oceans might seem good from a greenhouse gas perspective, it may not be good at all from the perspective of sea life. As we saw above, dissolved in seawater can react with water molecules to release ions. So, dissolving more in water causes the water to become more acidic. More acidic water can, in turn, reduce concentrations and make it harder for marine organisms to build and maintain their shells Both increasing temperatures and higher acidity can harm sea life and have been linked to coral bleaching.