Fossil Fuels and Climate Change

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Climate change, and especially global warming, is receiving much attention and is considered as one of the most pressing and severe global environmental problems facing humanity. Its significance has been widely reported to the general public by the media, always eager to emphasize the possible catastrophic consequences of global warming and link it even to claimed "extreme" weather experienced in the recent years. The Hollywood film The day after tomorrow, an environmental catastrophe movie in which a new ice age sets in over the northern hemisphere in a matter of days, gave many people the impression that an increasing greenhouse effect will have practically instant, drastic, apocalyptic consequences on our climate. It adds to the fear that global warming could result in the short-term destruction of ecosystems, cause more powerful and devastating storms and hurricanes as well as melting of the polar ice caps followed by flooding of low-lying coastal areas in Bangladesh, The Maldives, The Netherlands, and Florida. To understand whether such fears have solid foundations we have to look at the facts. The most reliable and internationally accepted and trusted source of information about global climate change is in the International Panel on Climate Change (IPCC) reports. The IPCC was jointly established in 1988 by the World Meteorological Organization (WMO) and the United Nation Environmental Program (UNEP). Its reports are the reference on global climate change for most policymakers, scientists, and experts. The third assessment report published in 2001 shows that the Earth's average surface temperature has increased by about 0.6 + 0.2 °C from 1861 to 2000 [41] (Figs. 7.1 and 7.2). Closer analysis reveals that most of the warming occurred, without a clear explanation, during two periods, from 1910 to 1945, and from 1976 to 2000. The 1990s has been the warmest decade and 1998 the warmest year since 1861, based on the systematic and global use of thermometers (although measuring the average surface temperature of the Earth is still a complex and difficult task). Temperatures before this date have to be determined indirectly employing so-called proxy data obtained from objects sensible to temperature and still present and measurable today, such as tree rings, ice cores, or corals. The collected data, even if less accurate than direct measurements, indicate that the increase in temperature in the 20th century was probably the largest in the past 1000 years. As a consequence of higher temperatures, there has been a widespread retreat of mountain glaciers in the non-polar regions as

Figure 7.1 Variations of the Earth's surface temperature for the past 140 years. (Source: IPCC, Third Assessment Report, Climate Change 2001: The Scientific Basis.)
Figure 7.2 Variations of the Earth's surface temperature for the past 1000 years. (Source: IPCC, Third Assessment Report, Climate Change 2001: The Scientific Basis.)

well as a 10-15% decrease in the sea-ice extent during spring and summer in Arctic since the 1950s. The global average sea level rose between 0.1 and 0.2 m during the 20th century, and the global ocean heat content has increased since the 1950s. However, some parts of the globe, mainly in the Southern hemisphere, have not warmed in recent decades and no clear trends in the sea-ice extent of Antarctica are apparent since the end of the 1970s. Furthermore, no significant trends or changes in storm activity, frequency of tornadoes, thunder or hail were noticed over the 20th century. It should also be recognized that, long before human activity on Earth, there were many ice-age periods followed by warming. Thus, human activity caused climate change, although significant, must be considered as superimposed on that caused by natural cycles.

Considering the variations from the past, the question that must be raised is, can we predict climate changes for the future? First, the reasons for past warming periods must be explained. Global warming is now recognized as being based significantly on the greenhouse effect caused by heat-absorbing gases that are present in the atmosphere; these trap some of Earth's reflected infrared radiation of the sun and act like a giant blanket around our planet. These so-called "greenhouse gases" include water vapor, CO2, methane, nitrous oxide, ozone, and some others. More recently, it was established that man-made chlorofluorocar-bons (CFCs) contributed to the depletion of the ozone layer, which protects the Earth from excessive damaging ultraviolet (UV) radiations from the sun. The damage was most pronounced in polar regions, where holes were detected in the Earth's protective ozone layer. Without naturally occurring greenhouse gases such as CO2, water vapor and methane in the atmosphere, the Earth's average temperature would be much cooler, comparable to the atmosphere on Mars. At the expected -18 °C on average, most of the water would be frozen all year long and the emergence and evolution of life as we know it would have been much more difficult, if possible at all. On the other hand, too much of the greenhouse effect is also detrimental. Such a situation is encountered on Venus, which has an atmosphere rich in CO2, inducing temperatures above the melting point of metallic lead and making it as hostile to life than the cold Mars. The mankind-caused increased greenhouse effect is real, and of concern. It is important to be concerned about the greenhouse gas concentrations in our atmosphere in order to keep the temperature of the Earth under the control of human effects and to maintain life as we know it. If the concentration of CO2 or other greenhouse gases in the atmosphere continues to increase substantially, the effect would most certainly lead to further increases in global average temperature. As early as 1895, the Swedish chemist Svante Arrhenius, calculated that a doubling in CO2 concentration, through human action, would result in an increase of 5-6 °C in the Earth's average surface temperature [42]. He even estimated the amount of coal that would have to be burned, and how long such a process would take. Of course since then we have also burned large amounts of other carbon-based fossil fuels, such as oil and gas. In fact, CO2 concentrations in the atmosphere have been increasing steadily for more than a century. During several thousand years before the industrial era, the CO2 concentration was relatively

Co2 Hawaii
Figure 7.3 Atmospheric CO2 concentration measured at Mauna Loa, Hawaii. (Source: CDIAC, Carbon Dioxide Information Analysis Center.)
Figure 7.4 Global carbon cycle. Based on data from IPCC.

stable around 280 ppm, but since 1750 the atmospheric concentration of CO2 has increased by 31% to reach some 370 ppm today (Figs. 7.3 and 7.4). The present CO2 concentration has not been exceeded in the past 420 000 years, and the current rate of increase is unprecedented in at least the past 20 000 years. It is now widely accepted that the observed increase in CO2 concentration is significantly due to anthropogenic source - that is, due to human activities. The combustion of fossil fuels is by far the largest contributor to man-made anthropogenic CO2 emissions, the remainder being mainly a result of land-use change, especially deforestation (Figs. 7.5 and 7.6). About half of the anthropogenic CO2 emissions is absorbed again by the oceans and vegetation of land areas, whereas the remainder is added to the atmosphere, increasing CO2 concentration. It should be remembered that the overall concentration of CO2 in the air is only about 0.037% (370 ppm), but this plays an essential role in maintaining life on Earth.

So far, most of the concerns about greenhouse gases have been focused on CO2, which represents about 60% of the human-caused greenhouse gases present in the atmosphere [21]. Less attention has been given to other greenhouse gases, the concentrations of which have also been increasing, especially methane, nitrous oxide and, more recently, chlorofluorocarbons. Atmospheric methane concentrations have risen by 150% since 1750, and continue to increase, being now at the highest in the past 420000 years. Methane has both natural and human-related origins. Decaying plant matter in wetlands and rice paddies ac-

Fossil Fuels Cement

fuel burning, cement production, and gas flaring for the period 1750 until 2002. Source: Marland, G., TA. Boden, and R. J. Andres. 2005. Global, Regional, and National CO2

Emissions. In Trends: A Compendium of Data on Global Change. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tenn., USA.

Figure 7.5 Global CO2 emissions from fossil fuel burning, cement production, and gas flaring for the period 1750 until 2002. Source: Marland, G., TA. Boden, and R. J. Andres. 2005. Global, Regional, and National CO2

Emissions. In Trends: A Compendium of Data on Global Change. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tenn., USA.

Figure 7.5 Global CO2 emissions from fossil

Figure 7.6 The world's largest energy-related CO2 emitters in 2002. Source: IEA.

counts for some three-fourths of natural methane emissions. Other sources include oceans, gas hydrates releasing methane due to changes in temperature or pressure, and termites which produce methane as a part of their normal digestive process. Similarly, in the digestive system of domesticated animals such as cattle, buffalo, sheep, goats or camels, cellulose from plant material is broken down by microbial fermentation in their digestion process, producing also significant amounts of methane as a byproduct. This constitutes a major source of human-related methane emissions besides wet rice agriculture, oil and gas production, and landfills. Methane generated in landfills, as waste decomposes under anaerobic (oxygen-lacking) conditions, is increasingly used as an energy source and is not allowed to escape into the atmosphere. In total, about half of the current methane emissions are anthropogenic. Even with a concentration increase of only 1060 ppb in the atmosphere (much less than that of CO2), methane contributes to 20% of the increased greenhouse effect [21]. Methane is a more effective greenhouse gas because it has a higher Global Warming Potential (GWP). The GWP is a measure of the relative heat absorption capability of a given substance compared to CO2 and integrated over a chosen time. Over a 100-year period methane, has a 23-fold higher GWP than CO2.

The atmospheric concentration of nitrous oxide (so-called "laughing gas"; N2O) has also increased by about 16% during the industrial era to levels not seen in the past thousand years. Because of its high GWP factor of 296, N2O contributes to 6% of the increased greenhouse effect [21].

Chlorofluorocarbons (CFCs) destroy the Earth's ozone layer and also absorb infrared radiations. The latter also contributes to global warming. Due to their ozone-depleting properties, CFCs have been phased out by the Montreal Protocol and their concentrations in the atmosphere are now diminishing, or at least increasing more slowly. Substitutes for CFCs may be less harmful for the ozone layer, but some compounds such as hydrochlorofluorocarbons (HCFC) and hydro-fluorocarbons (HFC) still have GWP factors reaching up to 12 000. The concentration of HCFC and HFC in the atmosphere is increasing. All halocarbons combined represent today some 14% of the increased greenhouse effect [21].

Atmospheric aerosols are small airborne particles and droplets produced by a variety of processes that can be natural (such as volcanic eruptions or sand dusts), or anthropogenic (mainly through fossil fuel and biomass burning). Sulfate aerosols from fossil fuel burning and other aerosols from volcanoes and biomass burning reflect and scatter solar energy before it can reach the Earth's surface, and thus have a cooling effect on the atmosphere. Aerosols can also enhance the condensation of water droplets and consequently favor cloud formation, increasing the reflection of incoming sunlight back into space. Whereas aerosols are cooling the atmosphere, the magnitude of this effect does not compensate for the heating induced by greenhouse gases. Furthermore, aerosols have a much shorter lifetime than greenhouse gases in the atmosphere.

Table 7.1 Global warming potentials (GWPs) of some greenhouse gases.

Gas

Formula

Global warming potential3

Atmospheric lifetime (years)

Carbon dioxide

CO2

1

Methane

ch4

23

12

Nitrous oxide

n2o

296

114

Hydrofluorocarbons (HFC)

12-12 000

0.3-260

Examples:

HFC-23

chf3

12 000

260

HFC-32

CH2F2

550

5

HFC-134a

CH2FCF3

1300

14

Fully fluorinated species

5700-22 200

2600-50000

Examples:

Perfluoromethane

CF4

5700

50000

Perfluoroethane

c2f6

11 900

10000

Sulfur hexafluoride

sf6

22 200

3200

a Over a 100-year time horizon. Based on data from IPCC, Third Assessment Report, 2001.

a Over a 100-year time horizon. Based on data from IPCC, Third Assessment Report, 2001.

Figure 7.7 Relative contributions of green- 2001: The Scientific Basis, Table 6.1. Total house gases to the increased greenhouse ef- forcing change between 1750 and 1998 is 2.48

fect induced by human activity. Source: IPCC W/m2. Third Assessment Report. Climate Change

Figure 7.7 Relative contributions of green- 2001: The Scientific Basis, Table 6.1. Total house gases to the increased greenhouse ef- forcing change between 1750 and 1998 is 2.48

fect induced by human activity. Source: IPCC W/m2. Third Assessment Report. Climate Change

When considering the question of global temperature change, it must be remembered that the greenhouse gas of overwhelming concentration is the moisture in the air, and that we have only extremely limited control of this parameter. Nature, therefore, has its own major controlling effect on the climate, including the cycle of celestial alignment of the Earth relative to the Sun [43]. Although temperature and the CO2 content of the air are clearly related, some point out that increasing temperature would cause increasing CO2 levels, but not necessarily vice versa [44].

By using the vast amount of data collected about greenhouse gases and other elements able to influence the Earth's atmosphere, computer simulations have been created to investigate the causes of climate changes and, most importantly, the observed warming trend of our time. These models have become more sophisticated over the years, but some aspects can still not be effectively simulated due to the extreme complexity of climate systems. Nevertheless, they now provide a reasonably accurate model of climate variations that have occurred during the past 150 years. Over the past 50 years, the rate and increase of warming seems to be directly correlated to the increase in greenhouse gas concentration in the atmosphere. This led the IPCC to state in its third assessment report that "...there is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities". Whereas there is no question that the human activities of a growing population on Earth will continue to affect our climate, the degree to which the human effect is superimposed on Nature's own cycles remains to be questioned. By continuing to emit greenhouse gases, humanity will continue to influence the atmospheric composition well into the 21st century. CO2 emissions from fossil fuel combustion especially are expected to remain a major factor for coming trends in global warming. However, as our fossil fuels reserves are being steadily depleted, this trend will not go on indefinitely as fossil fuel will not last significantly for more than a century or two. Based on mathematical models similar to the ones used to describe the past, projections for future climate changes have been made. Of course they are highly dependent upon assumptions such as future greenhouse gas emissions, and therefore a large number of potential scenarios can be envisioned. Nevertheless, they all project a global average temperature increase, from 1.4 to 5.8 °C over the remainder of this century, with atmospheric CO2 concentrations ranging from 540 to 970 ppm. Realistically however, a rise of 3 °C or less is more likely than a 6 °C increase. Nonetheless, such a temperature change would have widespread repercussions on the Earth. Initially, it would affect the sea level, which is expected to rise up to 0.88 m during the next century, primarily due to thermal expansion and water added from melting glaciers and ice caps. Even if the overall greenhouse gas concentrations were to be stabilized, the local warming of Greenland for example, if sustained, could lead to a further meltdown of the ice sheet with a resulting increase of sea level. This would certainly be very bad news for low-lying islands and countries such as The Netherlands, Bangladesh, and The Maldives. Globally, due to warming of the oceans and increased evaporation more intense and heavy precipitations can be expected with increased risks of flooding. At the same time, more cloud formation and precipitation could mitigate atmospheric warming.

As a result of higher temperatures, not only sensitive ecosystems but also agricultural productivity in many regions would be drastically affected. The consequences will differ greatly between the industrialized world and developing countries. Globally, industrialized countries in temperate climates will gain longer growing seasons, while the higher CO2 concentrations will act as a fertilizer, increasing crop growth and yield [45]. Higher temperatures could also extend the growing range of some crops such as wheat further north in Canada or parts of Siberia. At the same time, crop yields in other areas may be reduced by more frequent droughts. Improved irrigation, changes in farming methods or selection of more adapted crops would be necessary.

Overall, it is likely that the adverse impact of global warming will be the greatest for lower-income populations, particularly in tropical countries where fewer resources are available to adapt to the negative effects of climate change. But with the advantages that can also be expected from a moderate temperature increase, the overall balance of the global change would be difficult to predict. It is clear that man's contribution to climate change should be of great concern to all of us, and it is important that steps be taken as soon as possible to mitigate greenhouse gas emissions and their consequences. It is also necessary to point out that, in the longer time scale, the man-made causes of climate change (primarily considered as global warming) will in many instances be only of a temporary nature. As the world's fossil fuel reserves are finite and not renewable, and there is a leveling of the world's population, then excess CO2 release will by necessity decrease. It is not only Nature's own technology but also effective CO2

chemical recycling technologies (see Chapters 10 to 14 on the methanol economy) that will tend to keep CO2 levels balanced.

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