Freshman Seminar: Introduction to the Science of Climate Change Prof. Jordi Miralda-Escudé, F 9:30

Lecture 9: Solutions to Global Warming.

To mitigate global warming in the future, what we need to do is to reduce the radiative forcing that is causing the warming. At present, about half of the anthropogenic greenhouse radiative forcing is caused by carbon dioxide, and another half by methane, nitrous oxide, and halocarbons. In addition, particles of black carbon (or soot) released to the atmosphere when fossil fuels or biomass is burned can also cause warming by absorbing sunlight (reducing the albedo of the Earth). Efforts should be made to reduce the emissions of all these agents.

The emission of carbon dioxide is associated with the burning of fossil fuels that provide most of the energy used by our society today. Carbon dioxide is made by the reaction of carbon in the fossil fuels with oxygen during the burning. It can therefore not be eliminated by using ``clean burning'' technologies: the amount of carbon dioxide produced is fixed for any given mass of coal, oil, or natural gas that is burned. The only ways to reduce carbon dioxide emissions are to burn fewer fossil fuels (especially less coal, which produces more carbon dioxide than oil and gas per unit of energy obtained), or to capture the carbon dioxide and store it underground instead of letting it go in the air.

To reduce carbon dioxide emissions, we have these options available:

• Energy efficiency : We can work at making the production and consumption of energy more efficient. With improved efficiency, people can obtain the same services while consuming much less energy, so that less fossil fuels need to be burned.

  Examples: Using electrical appliances that perform the same function consuming less energy, in homes and in the industry (such as using modern flat computer and television screens instead of the old monitors, more efficient refrigerators, compact fluorescent instead of incandescent light bulbs, eliminating phantom loads, etc.). Increasing fuel efficiency of cars to improve mileage. Redesign our cities and provide energy-efficient transportation by trains and subways to reduce the need for people to drive and fly. Insulating our buildings better to consume less energy for heating and for air conditioning. Improving the efficiency of electricity production at power plants.

  Improvements in energy efficiency can reduce our emissions by a lot in the short term. But there is still a minimum amount of energy our society needs to use even with ideally good efficiency, and eventually population and economic growth will increase the demand, so energy efficiency can only be part of the solution.

• Nuclear energy : Electricity generated in nuclear power plants does not produce carbon dioxide (since no fossil fuels are used). Present nuclear power plants use fission of uranium to obtain energy, and they generate about 15% of electricity consumed in the world.

  Nuclear fission faces a number of problems: the electricity produced is rather expensive, the problem of nuclear waste disposal has not been solved, there are new fears related to terrorist attacks, the technology related to nuclear fission plants has been used by many nations to acquire the capability for making nuclear weapons. In addition, if we wanted to generate most of the energy demand over the next century from nuclear fission, we would probably run out of uranium; so nuclear fission will only be able to provide a small fraction of our energy needs anyway.

  Nuclear fusion would be a very different story. In nuclear fusion, we fuse nuclei of deuterium (an isotope of hydrogen) to make helium. Nuclear fusion has only been obtained so far in hydrogen bombs. The efforts to obtain controlled nuclear fusion by confinement of deuterium to very high densities and temperatures have not succeeded so far, and it is uncertain whether this will be achieved in the future. Even the most optimistic estimates are that the first fusion nuclear power plants might start working in 2030.

• Renewable energies : these include electricity generated from wind turbines, solar thermal collectors and solar photovoltaic panels, geothermal energy, hydroelectric plants, and wave and tides energy from the ocean.

  Hydroelectric power plants have been operating for a long time, but the large dams required often result in massive forced rellocation of people. The lakes that are created can also be an important source of methane emission, sometimes causing more greenhouse emission than what is saved from not emitting carbon dioxide to generate the electricity that is produced.

  Wind energy has recently become sufficiently economic to start competing favorably with coal. Solar photovoltaics are still expensive, but their price has been coming down and there are more potential technological improvements that can make them cheaper. Solar and wind energy still account for only 0.1% of all the energy generated in the world, but they are growing faster than any other form of energy generation. In principle they can provide all of our energy needs. For example, covering all paved areas in the United States with solar photovoltaic roofs would provide all the present energy consumption, and the wind potential over the United States and adjacent sea is also more than enough to provide all our energy needs, but a very fast increase. Because these renewable sources of energy are variable and unpredictable, they would require a way to store the energy for use at night or when it is cloudy and the wind is not blowing, before they can become an important part of our total energy generation. This energy storage could be provided by batteries or hydrogen fuel cells.

  Biomass energy is obtained from burning plant tissue. The carbon dioxide released by biomass burning does not contribute was previously taken from the atmosphere by photosynthesis when the plant was growing, so it does not contribute to the increase of atmospheric carbon dioxide. Vehicles running with ethanol and wood-burning furnaces for heating are examples of biomass energy. At present, we are already using most of the land and water resources dedicated to agriculture to produce food for humans. At present, humans use much more energy from fossil fuels than from the food they eat, so it is doubtful that agriculture could be expanded enough to produce all the biomass we would need for generating our energy. Moreover, the production of ethanol involves growing corn, and the operation of agricultural machinery and the manufacture of fertilizers needed to grow the corn often ends up emitting about as much carbon dioxide as is emitted by using oil instead of ethanol. Biomass energy can only contribute a small part of the solution to reduce greenhouse emissions if agricultural waste and sustainably produced wood is used for generating energy.

• Carbon sequestration : There are techniques to sequester the carbon dioxide after coal is burned in a power plant, and transport it to coal and oil deposits where it can be injected underground and used to recover more oil. The problem at present is that the capture and transportation of carbon dioxide is far too expensive to make it economical. Future technological improvements might lower the cost of carbon capture, which would need to be added to the price of electricity generated from fossil fuels.

  Sequestration of carbon dioxide can also be achieved through vegetation and agricultural soils. Better agricultural practices can help soils absorb more carbon dioxide from the atmosphere. This can help reduce the atmospheric carbon dioxide over the short term (until 2050), but not over a longer term because there is a maximum carbon reservoir that soils and vegetation can retain.

There are also strategies for reducing other greenhouse gases and black carbon. Some of these have other benefits as well: for example, reducing methane and black carbon emissions can also reduce tropospheric ozone, smog and pollution in cities. A particularly interesting strategy for the overall reduction of radiative forcing has been put forward by Dr. James Hansen, explained in his Scientific American article of March 2004 .

International Treaties on Emissions.

The United Nations Framework Convention on Climate Change was a document agreed to in 1992 whereby the signatory nations commit to the ultimate objective of stabilization of greenhouse gas atmospheric concentrations at a level that would prevent dangerous anthropogenic interference with the climate system.

The Kyoto Protocol was proposed in 1997 as an international treaty by which nations would agree to gradually reduce their emissions. The treaty asks nations to account for their emissions of all greenhouse gases, and to reduce them by a certain amount in whichever way is most economically feasible (for example, a nation can choose to pursue a greater reduction of carbon dioxide, or of methane, or other gases depending on which is cheaper to do). Nations are also allowed to trade permits for emissions, so one country could emit more than its commitment if it purchases emission permits to another country that cuts its emissions below its commitment. Initially only developed nations are required to reduce their emissions by a specified amount before 2012. Developing nations, which at present still have much lower per capita emissions, will only be required to reduce emissions after 2012 under new negotiation.

At present the Kyoto Protocol has an uncertain future because the United States, Russia and Australia have not agreed to sign it. The Kyoto Protocol would achieve a reduction of world emissions relative to the situation with no treaty of about 5% by 2012, and the cuts can be increased under new negotiation after 2012.

A case study: The Ozone Problem and the Montreal Protocol.

In the late 1970s and early 1980s scientists realised that some chemicals containing chlorine (chlorofluorocarbons) used by industry and released to the atmosphere were reducing the protective layer of ozone in the stratosphere through chemical reactions catalyzed by chlorine. The stratospheric ozone layer absorbs ultraviolet light from the Sun, so its reduction implies an increase of sunburns, skin cancers and cataracts on humans and other negative effects on plants and agriculture due to increased exposure to ultraviolet light. Concern increased when it was discovered in 1985 that a large ozone hole appeared over Antarctica every spring, where conditions were particularly favorable for the destruction of ozone by chlorine. In 1987 the was approved, to reduce emissions of chlorofluorocarbons. The original 1987 Montreal Protocol would have led to only small decreases in the rate of emission of chlorofluorocarbons. The signing of the protocol led to investments into finding alternative technologies for industrial processes that could avoid the release of the chemicals threatening the stratospheric ozone layer. This made it possible to agree to much larger emission reductions in later ammendments to the Montreal protocol. At the present time, emissions are much smaller than before the Montreal protocol was brought into force. Thanks to this rapid reduction in emissions, the concentration of chlorine in the stratosphere has now stopped increasing. Because the chlorine that is already in the stratosphere takes a long time to be naturally removed, ozone levels are still low and it is thought that they will only gradually recover over the 21st century.

The Montreal protocol on stratospheric ozone is therefore an example of a successful international treaty to solve an environmental problem, but it also shows how the impacts of altering the atmosphere by the human society can persist for a long time in the future after remedial action is taken, and be increasingly dangerous as the necessary remedial actions are delayed.

Proposals to compensate greenhouse warming by artificially increasing sunlight reflection

There have been several ideas to compensate the global warming effect of greenhouse gases by the deployment of structures that would increase reflection of sunlight to space. These ideas include: releasing a lot of specially designed aluminum dust in the stratosphere; launching a large number of tiny hydrogen balloons with reflecting metal surfaces on their tops to the stratosphere; or building a 1000 kilometer diffracting grid located between the Sun and the Earth at a special place called the Lagrangian point where objects remain stationary.

These ideas sound rather fictional because of the enormous scale they involve. To compensate for the warming from greenhouse gases over the next century, we would need to block about 2\% of the sunlight reaching the entire planet Earth. Nevertheless, they have been shown to be feasible in a report by the scientists E. Teller, L. Wood and R. Hyde Lawrence Livermore National Laboratory . There are serious ethical and political concerns about attempting to directly manage the climate of the Earth. Nevertheless, if we realise at some point during the next century that climate change and sea-level rise induced by global warming due to greenhouse gases are going to be too severe to allow for an adaptation strategy, by that time reducing greenhouse emissions alone may no longer be a solution, because it takes more than 100 years for carbon dioxide to be absorbed from the atmosphere after emissions are stopped. In that case, this type of large-scale engineering of planet Earth would be the only solution left.