Download Hayden,Katy_Coal Impacts on Global Climate

Katy Hayden
HCOL 185
Brian Beckage
Coal Impacts on Global Climate
Beginning around the 1800’s, coal has been a major source of energy around the world.
Since then, the methods for extracting coal from the earth and using it have developed and had
a major impact on the world in terms of energy use. However, this is not the only way the
extraction and use of coal is impacting the world; it also effects the earth’s environment and
climate in many ways. Mining itself releases a number of toxic chemicals, sulfur dioxide,
nitrogen oxides, and hydrogen cyanide. It also produces methane, which carries a heavy weight
in the long-term global climate. On top of that, the burning of coal for energy releases high
levels of carbon dioxide, a greenhouse gas which plays a crucial role in climate change. Taking
all these factors into account shows that the mining and use of coal is a major player in the
changing climate.
The first step in harnessing coal’s energy is its extraction from the earth – the mining
process. While the combustion of coal has a greater environmental impact than its mining, the
latter generates a very important greenhouse gas: methane. The mining process releases
methane in two different ways. First, it disrupts the coal within the coal seam through extensive
fracture. Second, it opens pathways through the strata, or layers of sedimentary rock, through
which the gas leaves the confines of the seam1. Undisturbed coal seams can contain up to
about 23 m3 of methane per ton of coal. Modern coal extraction methods are able to recover
some of this methane to be used as an energy resource, but only about 50% of it 2. This leaves
11.5 m3 of methane escaping into the atmosphere for every ton of coal that is mined. Although
the amount of methane emitted in the process of utilizing coal is lower than that of carbon
dioxide, it cannot be dismissed because it is about 25 times more effective at trapping heat,
which is to say that over a 100-year period, its global warming potential is 25 times higher than
that of CO23. Knowing this can shed light on how much potential coal has to raise the global
temperature, but it is important to take into account the other factors that contribute to the
temperature rise.
Once the coal has been extracted from the earth, it must be converted to energy
through one of a variety of processes, such as gasification, liquefaction, and combustion.
Combustion is the most common process used to harness the energy of coal, as it produces
electricity, which is the main use of coal4. This process creates most of the global warming
potential that coal holds, because of the levels of carbon dioxide that it releases and the impact
that carbon dioxide has on the climate. Each ton of coal that is burned produces 2.86 tons of
carbon dioxide. For the amount of heat produced, this is 11% more carbon dioxide than is
produced by oil, and 67% more than natural gas4. As the atmospheric concentration of carbon
dioxide increases as more fuel is consumed, the global temperature will increase with it. Carbon
dioxide does not absorb much short-wave radiation, i.e. sunlight radiating towards the earth,
but it does absorb long-wave radiation, which is infrared or heat radiation. This means that
sunlight reaches the earth unimpeded by carbon dioxide (though partially deflected by other
factors), but as the infrared heat radiation travels away from the earth, a portion of it is
absorbed by the carbon dioxide and re-radiated back towards the earth, causing the heat to be
trapped and remain in the atmosphere.
As previously stated, 1 ton of coal produces 2.86 tons of carbon dioxide. It also produces
roughly 22 gigajoules of energy, and as Figure
1 shows, it accounts for about 41% of the
electricity generated for world use. For every
15 gigatons of carbon dioxide that are
released into the atmosphere, there is an
increase of 1 part per million (ppm) of CO2,
Figure 1 Total World Electricity Generation by Fuel (2009)
Source: IEA 2011
and a 50 ppm increase in CO2 constitutes a
1˚C increase in global temperature5. Current estimates suggest that approximately 903 billion
tons of coal remain on earth, although with current technologies it will only be possible to
extract 435 billion6. With this information, it is possible to estimate by how much coal can
potentially increase the global temperature.
If all 435 billion tons of coal which current technology can extract from the earth is, in
fact, extracted and combusted for electricity, 1244.1 billion tons of carbon dioxide will be
produced. At 15 billion tons per 1 ppm increase, this level of carbon dioxide would cause an
82.94 ppm increase in the CO2 levels of the atmosphere. With a 1˚C increase for every 50 ppm,
82.94 ppm would cause a 1.66˚C increase in global temperature. This, however, is under the
conditions that all of the carbon dioxide emitted reached the atmosphere. This is not the case.
There are many sources that sequester carbon, or capture it and store it over long periods of
time, so that it does not remain in the atmosphere. It is difficult to determine just how much
carbon is sequestered in total, but oceans are the largest carbon sinks, absorbing over a quarter
of anthropogenic carbon emissions7. This means that at least 311 billion tons of CO2 will be
sequestered into the oceans, dropping the atmospheric increase to 62.21 ppm and the global
temperature increase to 1.24˚C. Unfortunately, it is not adequate to rely on the oceans to fix
the problem for a variety of reasons. First, they only reduce the potential climate change by
0.42˚C, still leaving the impact of carbon from coal at a significant level. Second, allowing these
levels of carbon to be sequestered into the oceans causes other problems for marine biological
ecosystems in turn, such as pH reduction, carbonate dissolution, and the smothering of various
living systems8. Finally, the oceans cannot be continually relied on to sequester the carbon
produced by humans and by coal production because new research suggests that their ability to
absorb atmospheric CO2 may be declining. As the temperature of the oceans rise with the
atmospheric temperatures, they can hold less carbon dioxide, which means more will be left in
the atmosphere causing temperatures to rise further, creating a positive feedback loop 9.
Although more research needs to be done in this area, if correct these findings could mean that
the impact of coal-produced carbon on global temperature would rise towards 1.66˚C again.
NASA scientists in 2006 determined that global warming of more than 1˚C relative to the
global temperature in 2000 will constitute a “dangerous” warming in terms of sea level effects
and species extermination, but now it has become clear that it will be extremely difficult, if not
altogether impossible to stop warming of this level, so the generally accepted goal has become
to keep warming under 2˚C10. As shown, the coal reserves currently available to the world now
have the potential to cause up to 75% of this warming solely from carbon emissions, although it
will not be immediate. Table 1 shows the levels of world coal consumption for the years 20072010. In 2007 the world consumed 7.02 billion tons of coal, and in 2010, 7.99 billion. The
average change was a 4.5% increase each year. At this rate of increase, the 435 billion tons of
Year
Coal consumption
(billion tons)
% Change
2007
7.02
---
Table 1: World Coal Consumption11
2008
2009
7.33
7.32
+4.4%
-0.1%
2010
7.99
+9.2%
remaining available coal could last until the year 2036. The world may not, therefore, see the
1.24˚ rise in temperature until that time, but this means that it may only be 24 years until the
impacts of ‘dangerous’ global warming as stated by James Hansen et al, such as sea level rise
and extinction of species, occurs. However, if the world were to hypothetically keep its coal
consumption levels at a constant rate for the next 5 years and then decline by merely 1% per
year, the current coal reserves could hold out until 2075.
There is an alternative scenario to the world reducing its coal use, one that holds a
negative result for the goal of staying below 1˚ of global warming. In the 24 years before the
current available coal reserves run out, it is possible that new technologies will be developed
that allow the extraction of more of the 468 billion tons of coal which are not currently
available. If this was to happen and coal consumption remained at its current rate of growth, it
would take only until 2049, a mere additional 13 years, to use up these resources and release
the carbon dioxide impacts on the climate. In addition, the impacts would be greater. While
utilizing the 435 billion currently available tons would cause between a 1.24 and 1.66˚ increase
in temperature, using the full 903 billion tons would have a much greater effect. Even if the
oceans continue to absorb at least a quarter of the carbon dioxide put into the atmosphere,
utilizing all of the 903 billion tons of coal would result in a 2.58˚C increase in temperature. This
is well above the 1˚ of ‘dangerous’ global warming as a result of solely the carbon dioxide
released by coal – not taking into account the other ways coal contributes to climate change,
such as methane and trace gases. While coal is one of the largest sources of worldwide
anthropogenic carbon dioxide4, it is not the only source, and there would be other contributors
raising the 2.58˚ change.
Coal has been a source of power since the Industrial Revolution, growing in demand
until today it constitutes 40% of all electricity produced around the world. Its consumption
rates are still growing, and this will inevitably have an impact on the world’s climate. It is one of
the greatest contributors to anthropogenic atmospheric carbon dioxide, which is a greenhouse
gas with one of the highest impacts on global temperature. If world consumption continues
growing at the rate is has been, the 435 billion tons of remaining available coal will last less
than a quarter of a century. By that point the coal could have already contributed up to 1.66˚ of
global warming, which is higher than the ‘safe’ levels of warming. If the world decreases its coal
consumption and finds another resource for generating electricity, the coal reserves can last
longer and the temperature change could be staved off for a while. Alternatively, technologies
could be developed to recover more of the remaining coal on earth in order to generate more
electricity – this solution would more than double the amount of temperature change. In either
scenario, the worldwide utilization of coal will have a significant impact on the global climate.
References
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Coal Mining. Energy Conversion Management, Vol. 37, pp. 801-806. 1996.
2. Storing CO2 in Unminable Coal Seams. IEA Greenhouse Gas R&D Programme. 2010.
3. Dow, K. and T. Downing. The Atlas of Climate Change: Mapping the World’s Greatest
Challenge. 3rd Edition. 2011.
4. Edgar, T.F. Coal Processing and Pollution Control. 1st Edition. 1983.
5. Solomon, S. et al. Irreversible climate change due to carbon dioxide emissions.
Proceedings of the National Academy of Sciences, Vol. 106 no. 6. February 10, 2009.
6. Rutledge, D. Hubbert’s Peak, The Coal Question, and Climate Change. Association for the
Study of Peak Oil and Gas. October 19, 2007.
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Impacts. Proceedings of Workshop on Carbon Dioxide Capture and Storage. IPCC
Working Group III: Mitigation of Climate Change. 2002.
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Atlantic CO2 trends on multidecadal timescales. Nature Precedings. 2011.
10. Hansen, J. et al. Global temperature change. Proceedings of the National Academy of
Sciences, Vol. 103, no. 39. September 26, 2006.
11. International Energy Agency. Key Energy Statistics 2010.
http://www.iea.org/textbase/nppdf/free/2010/key_stats_2010.pdf