Decenber 2013/January 2014 Teacher's Guide for Global Climate Change: a reality Check Table of Contents



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More on climate change solutions
There are two ways to look at how we can mitigate global warming/climate change. There are large-scale technological “fixes” and there are ways in which individuals can lessen the effects of climate change. But first remember that the Earth has its own methods of trying to keep the atmospheric carbon dioxide concentration in balance—the carbon cycle.

Carbon is cycled through the environment by means of chemical and physical changes. Two of those processes, already referenced, are photosynthesis and combustion/ respiration (oxidation). The former process removes CO2 from the atmosphere and the latter returns it to the atmosphere. Carbon dioxide is also soluble in water, a process that removes the gas from the atmosphere. The diagram at right illustrates these and allied processes that are part of the natural


carbon cycle.
The photosynthesis reaction, the process by which green plants remove CO­2 from the atmosphere looks like this:

6 CO2 + 6 H2O + Energy ➙ C6H12O6 + 6 O2



So we can think of plants world-wide as natural carbon sinks, which have been mentioned in passing, above. Carbon sinks are any material or process that absorbs more carbon dioxide than it produces. World-wide, plants absorb about 2 billion tons of CO2 each year, about one quarter to one third of the gas that is produced by human activity. As organic plant matter dies and decays, the carbon contained in the matter is stored in the soil, and scientists estimate that the soil stores about 2 trillion tons of carbon. Plants, then, are significant carbon sinks, and monitoring, maintaining and replenishing trees contributes to a reduction in carbon dioxide in the atmosphere and a consequent reduction in global warming.

A second major natural carbon sink is the ocean. The oceans take up a quarter of the CO2 produced by human activity. Carbon dioxide is soluble in water. As you can see from the graph at right, CO2 is much more soluble in water than oxygen. So carbon dioxide dissolves in the oceans to a great degree, removing it from the atmosphere. At some point there is an equilibrium established between the carbon dioxide dissolving and the CO2 coming out of solution. The equilibrium is determined in part by the partial pressure of CO2 in the atmosphere. So the greater the CO2 concentration in the atmosphere the more of it dissolves. As CO2 concentration increases in the atmosphere as a result of human activity more CO2 will tend to dissolve in the ocean. And current estimates indicate that once CO2 dissolves in the ocean it will remain there for as long as 500 years.
(http://www.elmhurst.edu/~chm/vchembook/174temppres.html)
However, the increasing CO2 concentration in the atmosphere is also causing a rise in temperature, and this factor tends to decrease the solubility of CO2 in the ocean since we know that gases are less soluble as temperature increases. In addition, it is the warmer water at the surface of the ocean that interacts with atmospheric CO2, limiting the solubility of the gas. Not until the warmer surface water can be very slowly mixed with the deeper cooler water can the rate of dissolving be increased. Ocean water mixing occurs slowly over years, and if the rate at which CO2 is being pumped into the atmosphere is increasing (as it is) then the net outcome is still an increase in atmospheric CO2. Nevertheless, the world’s oceans, like plants and soil are natural reservoirs of stored carbon dioxide.
So there are natural reservoirs that can store carbon dioxide. But scientists have been looking for technological ways to capture CO2 and store it. These processes are called carbon sequestration. According to the EPA:
Carbon dioxide (CO2) capture and sequestration (CCS) is a set of technologies that can greatly reduce CO2 emissions from new and existing coal- and gas-fired power plants and large industrial sources. CCS is a three-step process that includes:

  • Capture of CO2 from power plants or industrial processes

  • Transport of the captured and compressed CO2 (usually in pipelines).

  • Underground injection and geologic sequestration (also referred to as storage) of the CO2 into deep underground rock formations. These formations are often a mile or more beneath the surface and consist of porous rock that holds the CO2. Overlying these formations are impermeable, non-porous layers of rock that trap the CO2 and prevent it from migrating upward.

(http://www.epa.gov/climatechange/ccs/)


The EPA diagram below illustrates the way in which sequestration is accomplished at an electric power plant site. Electric power plants produce nearly 40% of emitted CO2.


(http://www.epa.gov/climatechange/ccs/)

A note about sequestration language—the natural methods of carbon dioxide storage, like oceans and plants, are usually referred to as biologic or terrestrial sequestration. The technological methods are called geologic sequestration.


The sidebar in the article also describes ways that individuals can reduce the effects of climate change. For example, the article says to take public transportation whenever possible. How will that reduce the effects of climate change? When private cars burn gasoline one of the resulting products of the combustion reaction is carbon dioxide:
2 C8H18 + 13 O2 ➙ 16 CO2 + 18 H2O
Therefore, reducing the use of private vehicles by riding public transportation also produces less CO2 and thus mitigates climate change. Using examples like this connects the chemistry concepts to the climate change issue.
Another example of individual action is retrofitting homes for energy efficiency. If homes are heated with oil or natural gas, one of the combustion products will be carbon dioxide. If homes are heated by electricity you can note to students that most electricity is produced in the U.S. by the combustion of coal or petroleum, and so the CO2 reduction solution still applies. By increasing building insulation we decrease the fuel consumed and as a result decrease the carbon dioxide emitted.
The U.S. Environmental Protection Agency has a detailed guide to the ways in which individuals can reduce greenhouse gas emissions: http://www.epa.gov/climatechange/wycd/index.html, and an online calculator to help you estimate your own greenhouse gas emissions: http://www.epa.gov/climatechange/wycd/ calculator/ind_calculator.html. See “More on climate change solutions” for Web sites that provide added examples.

Connections to Chemistry Concepts





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