Regardless of the scientific basis of climate change, what can be done about it is a political and economic problem. What makes money is what will happen, but this can be influenced to some extent by laws and subsidies enacted by a savvy government. This well-publicized subject falls outside of the scientific tenor of this book, and only a brief summary is given here. Since the ways to combat global warming depend so much on the way of life and the political setup of each country or community, even the IPCC Working Group 3’s voluminous report [16] on miti­gation gives few substantive conclusions or recommendations. There is disagree­ment about the predictions of the IPCC report. Some say that it is too pessimistic, and we need not over-react to the forecasts; others say that the report is not strong enough, and we should act faster than we are doing now. In any case, it is known that the anthropogenic climate change (the only part we can control) is mostly due to GHG emission, particularly of CO2, and that much of this will persist in the atmosphere for hundreds of years. We can hope to slow down the increase in warming potential, but we cannot expect to recover from our profligate habits for at least half a century.

Mitigation consists of three steps: adaptation, conservation, and invention. Adaptation means taking immediate steps to protect ourselves from impending disasters, such as sea-level rise and violent storms. This means building sea­walls, raising bridge heights, strengthening and raising structures near the shore, and so forth. Conservation requires no new technologies or expenses, and many organizations are already promoting this. Lights can be turned off by infrared or motion detectors when no one is in the room. Electronic equip­ment can be made to draw no current when off. Gasoline can be saved by driving slowly, by carpooling, and by bicycling, for instance. Thermostats can be turned higher in summer and lower in winter. Recycling programs are already in place to save fossil energy used in mining and refining. Everyone is familiar with this list, and many books have been written on “green” living. Along with conservation is efficiency: switching to more energy-efficient appliances which have already been invented. The change from incandescent lamps to fluorescent and LED is being widely implemented. Every time an appliance like a refrigerator has to be replaced, it should be a new, efficient model. Gas-electric hybrid cars and upcoming plug-in hybrids will cut fossil fuel usage, but unfortunately their popularity rises and falls with gasoline prices. The worldwide use of computers has become a large consumer of elec­tricity from fossil fuels. Energy efficiency of computers are increasing all the time, but computers cannot be recycled. New computers all have a large fossil footprint. Houses can be built with better insulation and use of solar energy. Power plants can greatly increase efficiency by co-generation, in which waste heat from electricity generation is recaptured for heating and cooling. Conservation and efficiency are relatively easy to implement, and there is a public will to do this.

The third step in mitigation is the invention of new devices, a longer-term objective. Foremost among these are new ways to generate energy that do not emit CO2, and these are the subject of Chap. 3. Controlled fusion, the topic of this book, fits into this category of long-term solutions. Shorter-term needs are, for instance, the invention of better batteries or new chemistries for making synthetic fuels. Energy storage is a problem both for transportation and for inter­mittent energy sources such as solar or wind power, and there has so far been no great breakthrough on batteries. Paradigm-changing inventions may require going back to basics. Forward thinking in the US Department of Energy’s Office of Basic Energy Sciences led to a series of ten workshops on Basic Energy Needs such as electrical energy storage, solar energy utilization, and catalysis for energy. The resulting Energy Challenges Report New science for a secure and sustainable energy future summarizes the basic scientific advances needed in the long term.13

The magnitude of the long-term problem — controlling or reversing global warming in the next 50-100 years — can be seen from the following graphs. We have seen at the beginning of this chapter that anthropogenic forcing of global warming comes mainly from the emission of GHGs, of which CO2 is the main culprit. Figure 1.25a shows that the major part of this comes from the burning of fossil fuels, so that we must either develop new energy sources or find ways to eliminate the CO2 pollution. Figure 1.25b shows the distribution of GHG emissions from various human activities worldwide. These activities are so var­ied among different countries that general methods of mitigation cannot be applied.

From 1970 to 2004, the CO2 concentration grew by 80%, and the total GHG warming potential increased by 70%. About half of this comes from highly developed nations representing only 20% of the world population. Aggravating the problem is the growth of both population and production. Figure 1.26 shows predictions of population and gross domestic product (GDP) growth and calculations in different scenarios, some 400 in all, without intervention by mitigation techniques. A large divergence of results can be seen, since human behavior has to be assumed in addition to the physics effects considered in climate simulations. Pre-2000 computations are shown by the blue shading, while more recent ones, using different methods, are shown by the lines. Population growth rate has slowed recently, so that the lines give a more opti­mistic view. Third-world countries will increase their GDPs rapidly as they become industrialized. China has already overtaken the USA as the world leader in CO2 emissions.

When mitigation is added to the scenarios, different assumptions have to be made for each economic sector in each country or region, and even larger diver­gence of results is produced. To make sense of the mass of data from some 800 different scenarios, the IPCC has grouped them according to the GHG concentra­tion level or, equivalently, the radiative forcing that each scenario ends up with and has plotted the range of mean global temperature increase above the preindustrial level as predicted by all these models. This is shown in Fig. 1.27. Each category

Fig. 1.25 (a) Major constituents of anthropogenic GHGs; (b) GHG emission by various sectors. Here, F-gases are the ozone-depleting fluoiinated gases [16]

from I to VI lumps together scenarios resulting in an increasing range of GHG levels, and the curves show the range of temperature rises that the scenarios in that group predict. The results are also shown in Table 1.1. Here, it is seen that the CO2 level can be made to peak at some time in the next century and then go down. The larger the CO2 level, the later this peak will occur. Category IV has the most sce­narios; apparently, this is the most anticipated range.

b

As complicated as these computations are, they do not tell us how to achieve the stabilization levels specified. No one method of mitigation will do the trick. A simple and attractive way to analyze the problem has been given by Socolow and Pacala [17-19]. They address the intermediate term of the next 50 years, relying on existing methods of conservation and efficiency enhancement but not counting on any new inventions which may come later. Since CO2 is the dominant GHG, only
that gas is considered here to simplify the problem. In Fig. 1.28, the wiggly line shows the data for yearly carbon emissions measured in billions of tons (gigatons) per year (GtC/year). The dashed line is the current path that we are on, and it will lead to a tripling of our current level of about eight GtC/year by the end of the century. The horizontal line is the desired goal of maintaining emissions at the present level. The yellow triangle between these lines represents, then, the reductions in emissions that we have to make to achieve this goal. This triangle is enlarged in Fig. 1.29.

Equilibrium global mean temperature increase above pre-industrial (°С)

101

GHG concentration stabilization level (ppm C02 eq)

Fig. 1.27 Range of predictions for global temperature rise according to scenarios sorted into Groups I-VI according to the GHG concentration level achieved with mitigation methods [16]

Table 1.1 If the target CO2 level in column 3 (or the equivalent CO2 level of ah GHGs in column 4) is achieved, the year in which the GHG peaks is given in column 5, and the percentage change in emissions is in column 6 [16] Category Additional radioactive forcing (W/m2) CO2 concentration (ppm) CO2-eq concentration (ppm) Peaking year Change in global for CO2 emissions in emissions 2050 (% of 2000 (year) estimations) (%) No. of scenarios I 2.5-3.0 350-400 445-490 2000-2015 -85 to -50 6 II 3.0-3.5 400-440 490-535 2000-2020 -60 to -30 18 III 3.5-4.0 440-485 535-590 2010-2030 -30 to +5 21 IV 4.0-5.0 485-570 590-710 2020-2060 +10 to +60 118 V 5.0-6.0 570-660 710-855 2050-2080 +25 to +85 9 VI 6.0-7.5 660-790 855-1130 2060-2090 +90 to +140 5 Total 177

Fig. 1.28 Socolow-Pacala diagram showing the amount of mitigation (yellow triangle) needed to keep CO2 emissions constant at the present level [17-19]

Fig. 1.29 Division of the stabilization triangle into wedges, each representing a cut of one billion tons of carbon emission per year. (Design originated by the Carbon Mitigation Initiative, Princeton University, and replotted from the data in refs. [17-19])

The triangle can be divided into eight “wedges,” each representing the contribu­tion of one stratagem to these carbon reductions. Each wedge represents a reduction of one GtC/year in carbon emissions. Together, these wedges would hold carbon emissions to eight GtC/year instead of the 16 GtC/year expected by 2058. Looking at this way, the problem is not so overwhelming. Each sector simply needs to focus on that amount of reduction in its activities. The lines, of course, are not exactly straight; they have been straightened to simplify the idea and make it understand­able to all. In fact, the idea is now so simple that the authors have made it into a game that can be played in the classroom, with each student or group of students responsible for finding out how to achieve the goal in one sector. There are numer­ous ways to make a wedge, but these may overlap. For instance, building 700 fewer coal plants in the next 50 years is one wedge, and so is building 2.5 times more nuclear plants than exist now; but these are the same wedge if the coal plants are replaced by nuclear plants. The wedges in Fig. 1.29 are a few examples chosen so as not to overlap.

From top to bottom: one wedge can be gained if cars averaged 60 miles per gal­lon (3.9 liters/100 km) instead of 30 mpg (7.8 liters/100 km). Hybrid technology already exists for this. Driving 5,000 miles per year instead of 10,000 would give another wedge. Bicycling, ride sharing, and public transportation could achieve this, but at the expense of personal time. Buildings use 60-70% of all electricity produced, and much of this is unnecessary. Cutting this in half can yield two wedges. Requiring 800 coal plants to sequester their CO2 output would yield one wedge. Building more renewable energy sources such as wind and solar could give one wedge without inventing new technologies. Replacing coal plants by nuclear plants up to 2.5 times their current number would yield one wedge. Cutting in half the area of forests destroyed per year yields one wedge. With so many ways to tackle the problem, this way of dissecting it makes the problem not as mind-bog­gling as it first seems. It is easier to evolve a strategy. Holding the line is achievable with effort and government incentives. As under-developed countries increase their use of electricity and fuels for cooking, the number of wedges needed will increase, but only by one-fifth of a wedge [17-19].

You may wonder how billions of tons of carbon can get into the air when it goes up as CO2, which is just a gas weighing no more than the bubbles coming out of a carbonized beverage. Box 1.3 explains how.

Most nations have taken action to do their share in reducing its carbon emis­sions. With Chancellor Angela Merkel (a physicist) at the helm, Germany leads the way, and other nations have followed. It is the largest market for solar cells and is the third largest producer, behind China and Japan. A feed-in tariff of about 0.5 euro per kilowatt-hour is paid for electricity fed back into the grid. Germany is also a major user of wind power. Its renewable energy sources pro­duce 14.2% of its power, compared with the European Unions’ target of 12.5% by 2010.14 The program is funded by adding 1 euro to monthly electric bills, and the worry is that this will increase with the rapid growth of solar energy deploy­ment. Tony Blair has set emissions goals of a 50% cut by 2050 for the UK. In the USA, California leads the way under Governor Arnold Schwarzenegger, who has introduced ambitious legislation to reduce CO2 emissions to 1990 levels by 2020 and to 80% below 1990 levels by 2050. The USA, however, has a history of dragging its feet on energy and environment issues since it has more fossil

Box 1.3 How Can CO 2 Weigh So Much?___________________________

Here, we are talking about billions of tons of CO2, a gas as light as the air we breathe. Can our cars and factories actually emit that much weight in a gas? Indeed they can, and here is how. First, a billion is such a large number that it is hard to visualize even though we know that it is a thousand million in the USA and a million million in the UK [A gigaton (Gt) is a US billion.] So let us bring it down to something more palpable. There are about a billion cars in the world, so each car emits about a ton of pollutants a year, or almost the car’s own weight, on average. That is still an unbelievable amount.

The weight of gasoline is mostly in carbon, since gasoline molecules are hydrocarbons with a ratio of about two hydrogen atoms (atomic weight 1) to one carbon atom (atomic weight 12). So 12/14th of the weight of gasoline is the weight of the carbon in it. Gasoline is lighter than water; one liter of it weighs 0.74 kg, compared with the standard weight of 1 kg per liter of water. Of the 0.74 kg, 0.63 kg (six-seventh of it) is carbon. How much does a tank­ful of gasoline weigh? Say it takes 45 liters (12 gallons) to refill a tank. The weight of a tankful is then about 45 x 0.74 = 33 kg (73 lbs), containing 45 x 0.63 = 28 kg of carbon. When the gasoline is burned, the carbon and hydrogen combine with oxygen from the air to form CO2 and H2O, respec­tively. Since oxygen’s atomic weight is 16, a molecule of CO2 has atomic weight 12 + (2)(16) = 44, and the weight of the carbon is multiplied by 44/12 = 3.7 by picking up O2 from the air! So when a whole tankful of gaso­line is burned, it emits 28 x 3.7 = 104 kg (228 lbs) of CO2 into the air. Suppose a car refuels once every two weeks or 26 times a year, its CO2 emis­sion is then 26 x 104 = 2,700 kg of CO2. This is 2.7 metric tons per year or about 3 US tons! The carbon footprint of driving is even larger, since it takes a lot of fossil energy to make the gasoline in the first place.

The discussion about wedges used units of gigatons of carbon, not CO2, per year. To get back to carbon, we have to divide by 3.7, so our example car can emit 2.7/3.7 = 0.73 tons or almost a ton of carbon a year. If we increase miles per gallon by a factor of 2, we would save 0.5 ton per year per car or 0.5 GtC/year for one billion cars. By 2059, we expect to have two billion cars and that doubles the savings back to one GtC/year. Hence the top wedge in Fig. 1.29. While we are merrily driving along the highway, the car is spewing out this odorless, colorless gas in great quantities the whole time!

reserves than most countries outside OPEC. The USA did not sign the Kyoto Protocol because it would have cost too much. The 2008 climate-change strate­gic plan by the Department of Energy called for $3 billion in energy research, which is the same amount as in 1968 in adjusted dollars. Under the Bush administration, the USA failed to live up to its commitment to ITER for two years. ITER is the international project to develop fusion power and is described in Chap. 8. President Obama has appointed Steve Chu as Secretary of Energy and John Holdren (formerly a plasma physicist) as Science Adviser. This admin­istration has already taken steps to move forward aggressively in protecting the environment. For instance, $777 million has been allocated to establish 46 Energy Frontier Research Centers in US universities and laboratories, and a new ARPA-Energy program has been started in the Advanced Research Projects Agency to stimulate new ideas for energy efficiency and curbing of carbon emissions.

The first step that is usually taken for economic reasons is to install a Cap and Trade system, in which companies with large carbon emissions can buy credits from other companies that have emissions below the legislated level. This does not directly reduce overall emissions unless low-carbon companies are new ones using clean energy. Coal plants will find it cheaper to buy carbon credits than to install equipment to capture and sequester their CO2. A carbon tax would be about $100- $200 per ton of carbon emitted, equivalent to $60 per ton of coal burned or $0.25 per gallon of gasoline [17-19]. Perhaps in anticipation of this tax, which will raise electricity bills, it is encouraging that large companies like Walmart and Google have installed solar panels on their roofs.

Enlightened legislation has succeeded in protecting the environment in the past: CFCs have been eliminated to cure the ozone-hole problem, and lead has been taken out of gasoline, paints, and plumbing. We can succeed again with global warming.

Legislation is also necessary because mitigation involves entire communities, not just individuals. “Greener than thou” is not the right attitude. Here is an example. There was a television program showing the construction of a “green” skyscraper in New York. It was noted that the high building intercepts 40 times as much sun­light as would normally fall on that area. By using partially reflecting windows, the heat load on the building could be reduced, with substantial savings in the energy required for air conditioning. Erecting a building, however, does not change the amount of heat that the sun deposits on each square meter of the earth. What hap­pens is that the building throws a shadow, thus cooling the buildings behind it. This benefit accrues regardless of window design. Reflecting windows would heat the buildings in front, thus increasing their air-conditioning energy. Thus, whether total energy is saved or not depends on the energy efficiency of the neighbors’ equipment. Market-driven savings are necessarily selfish, and one has to be wary of such profits.

This discussion of mitigation is about the near term of the next 50 years. In the latter half of the twenty-first century, the world will be quite different. New tech­nologies will exist that we cannot imagine now. We went from the Wright brothers to the Boeing 747 in only 67 years.

In 2050, the remaining supplies of oil and gas will be prohibitively expensive. Local power by solar and wind will be commonplace. Coal and nuclear will supply base power in spite of the problem of storing their wastes and the cost of mining. Controlled fusion, which has neither problem, will be coming online as the primary power source. Much of the expense of developing and commercializing new energy technologies can be spared if we finish the development of fusion sooner.

Notes

1. Subsequent letters and rebuttals published in this journal and in APS News showed that a number of physicists believed that variations in solar radiation could have caused the earth’s temperature rise. Their proposal to mitigate the American Physical Society’s strong statement that climate change is caused by humans was overwhelmingly rejected by the Society.

2. http://www. ipcc. ch or just google IPCC AR4.

3. Note that this is not the half-life of CO2 concentration in the atmosphere, which is 30 years. CO2 molecules go in and out of the ocean, and four years is the recycling time. Courtesy of R. F. Chen, University of Massachusetts, Boston, who read this chapter critically.

4. For instance, Hegerl et al. [10], countered by Schneider [11]. Also, Scafetta and West [4] who elicited seven letters to the editor in Physics Today, October 2008, p. 10ff.

5. Not exactly, since fresh water is about 2.5% less dense than seawater.

6. National Geographic News, December 5, 2002.

7. A. Gore, An Inconvenient Truth, DVD (Paramount Home Entertainment, 2007).

8. The eastward motion is the result of what physicists call the Coriolis force. The earth rotates west to east (making the sun move east to west daily), and the air picks up the large “ground speed” near the equator. As the air moves northward, it goes into a region of lower ground speed and moves faster eastward than the ground does.

9. What this IPCC graph (FAQ 3.2, Fig. 1.1) means in detail is too complicated to explain and is shown here only to illustrate the large local variations in rainfall data.

10. An impressive graph of the changes in several species appeared in Audubon Magazine, March/April 2009, p. 18.

11. The Ocean Conservancy newsletters, Spring 2008 and Winter 2009.

12. National Geographic Video Program, Six Degrees Could Change the World (2009).

13. http://www. sc. doe. gov/bes/reports/list. html.

14. New York Times, May 16, 2008.