Economic activity and energy use are closely coupled. Today the yearly increase in economic activity is larger than the totality of world economic activity of 200 years ago; the population is huge compared to then and will continue to increase; and the energy we now use affects the world's entire environment in many ways. This is the source of the global warming problem.
Large scale, anthropogenic environment problems have happened before and governments have responded collectively to the dangers. More than 30 years ago Rachel Carlson's famous book, "Silent Spring," awoke us to the dangers of DDT, and DDT was phased out. More recently, scientific evidence showing depletion of ozone over the Antarctic (the ozone hole) resulted in the Montreal Treaty phasing out chlorofluorocarbons. The response to these two environmental problems was relatively easy because the economic impact of the required response was limited.
We now face a more complex problem, Global Climate Change. Response to this problem will be much more difficult because its source is the carbon-based energy systems (oil, gas and coal) that drive our economy. This issue first leaped into the consciousness of governments at the 1992 World Summit in Rio de Janeiro, although it had been worrying the scientific community for 40 years. We know that energy use is coupled to economic development. A growing population in the developing world aspires to a standard of living approaching that of the rich nations, and this requires that energy use increase.
The greenhouse gases emitted in energy production drive global warming, and limiting global warming requires that the use of carbon based fuels decrease at the same time that energy use increases. This can be done, in principle, by using a combination of conservation and efficiency and carbon-free energy sources; renewables (hydropower, wind, geothermal, biomass, solar), fusion, and nuclear. However, the nations of the world have yet to make a real start on the necessary changes. The not yet ratified Kyoto Protocol is only the barest of beginnings. Here I want to discuss the problem, the numbers, the options, and conclude with some recommendations.
The picture of the earth taken by the Apollo astronauts on their way to the moon (Figure 1) has, I believe, had a profound effect on thinking about global ecology. This picture shows our world hanging in a black void, our nearest neighbor a dead moon 240,000 miles away, and no signs of life anywhere else in our solar system. We live on a thin skin on our world about 13 miles thick from the top of the highest mountain to the depths of the deepest ocean, tiny compared to our world's 8000-mile diameter. It is what we put into this thin skin that is responsible for global climate change.
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The scientific evidence for climate change is clear. The last 100 years has seen a rapid increase in temperature (Figure 2) that is unprecedented and which tracks the increase in greenhouse gases that we have put into our atmosphere mainly from carbon-based fuels. The evidence comes from actual temperature data, growth rings in trees, gas bubbles trapped in glaciers, coral reefs, etc. The 1990's were the warmest decade in recorded history, and there is more carbon dioxide in the atmosphere now than has been there in the last 400,000 years.
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After the Rio de Janeiro World Summit, governments set up the Intergovernmental Panel on Climate Change (IPCC) to analyze the problem. The scientific community, led by the IPCC, has been working to predict the consequences of the increasing level of greenhouse gases. Modeling the world climate system is complex because of the interaction of the atmosphere, landmasses, and the oceans, but the models continue to improve and now give a quite reasonable agreement with what has happened in the past (Figure 3). …