The facts about global warming are as follows: We know exactly how much carbon dioxide has increased during the last century in the Earth's atmosphere. The increase is very substantial, from a pre-industrial level of 270 parts per million to the present value of 375 parts per million. There is no way this increase could be due to natural causes, it is instead consistent with its origin in human activities. Carbon dioxide remained practically constant for the 10000 years before the industrial era, and it is now increasing at unprecedented levels. There has not been as much carbon dioxide in the atmosphere as there is now for at least the last four hundred thousand years. There is nothing that is uncertain about these facts.
Carbon dioxide accounts for 60% of the human-induced global warming, the other 40% being due to methane, nitrous oxide, and hydrofluorocarbons. The increase of all these gases over the last two centuries are due to human activities. While it is important to reduce all the greenhouse emissions, carbon dioxide has the largest effect and therefore reducing global warming requires reducing carbon dioxide emissions.
How does global warming work? The temperature of the Earth is determined by an equilibrium, a balance between the energy that is received from the light of the Sun and is absorbed by the Earth, and the energy that is emitted as infrared radiation from the Earth to space. In order to keep the temperature constant, the energy that comes in from the Sun and the energy that goes out in infrared radiation need to balance each other. How does the carbon dioxide (and the other greenhouse gases) alter that balance? Carbon dioxide absorbs infrared light. As its abundance in the atmosphere increases, more of the infrared light emitted from the ground is absorbed by the carbon dioxide in the atmosphere, and sent back to the surface. The atmosphere becomes more opaque to the infrared light, and therefore acts like a blanket covering the Earth, preventing the heat from escaping, and warming up the Earth.
There is no scientific uncertainty whatsoever about the fact that human activities have increased the atmospheric carbon dioxide, and that carbon dioxide is sending back to the surface the heat that the Earth radiates, therefore increasing the temperature. We know that this has the potential of dramatically changing the weather patterns of the Earth. The uncertainties start when we try to predict exactly what the climate changes will be in various local areas of the Earth, and what the effects of clouds will be in determining the rate at which the mean temperature will increase. There are also uncertainties on other consequences of a warmer planet: sea-level rise, spread of certain diseases out of their usual geographic range, the effect on agricultural production, increased strength and frequency of storms, extreme heat events...
I think these uncertainties on the impact of global warming make it more imperative that we take immediate action to stop our dependence on fossil fuels. The fact that we are not certain about the exact consequences of global warming means that we are doing an experiment with the Earth . We are doing an experiment because we are altering the Earth with our activities, and we cannot safely predict what the outcome will be. However, it must be added that this is a reckless experiment . A change in the global climate could bring catastrophic consequences for agriculture in some countries, spread of disease, and sea-level rise causing as many as 100 million environmental refugees. Different countries may suffer from an increased occurrence of floods, hurricanes, or drought. When such disasters happen, nobody can say with certainty that they were caused by global warming (as in the case of hurricane Mitch in Honduras and Guatemala, which killed 10000 people), even though global warming likely increases their rate of incidence. When the poorest nations of the Earth are affected, are the rich nations that are causing the problem with their carbon dioxide emissions going to pay the bill? If the forecasted rise in sea level and increased storm intensity renders large parts of Bangladesh or other countries uninhabitable, or unusable for agriculture, will these countries receive sufficient reparations from the Western world to make up for their losses? History suggests that the rich nations will continue to be as selfish (and irresponsible) as ever.
Surely, all of these events are uncertain. However, one thing we know is that human civilization has appeared over the last few thousand years during a period of unusually good climate conditions for our society. This should come as no surprise. While the Earth was not highly conducive to the development of agriculture, it was difficult for humans to increase their population, migrate to new lands, and develop new technologies. So civilization arose when the climate was ideal for us. It does not take a lot of common sense to understand that, if we start changing the conditions of the Earth, any changes in the climate caused by our activities are likely to bring many more disasters than benefits, even if our science is not advanced enough to predict everything that will happen.
If it is considered unethical to do medical experiments with human beings (with good reason!), even when these experiments might result in medical advances that could help save other people's lives, then isn't it much more unethical to do an experiment with the Earth, when this experiment might result not just in the death of one human being, but in the demise of entire countries?
The problem of global warming is a sufficiently severe one that it demands an immediate mobilization of the citizens and, especially, the scientists, who have an additional responsibility to warn about the danger and to demand responsible action to politicians. During World War II, scientists were mobilized to build a nuclear bomb out of fear that the Nazis would build it first (a fear which turned out to be unfounded). Thousands of scientists left whatever work or research they were doing to concentrate on the building of the nuclear bomb. Now that the threat is coming from ourselves instead of an external aggressor, now that the objective is to preserve the natural climate of the Earth instead of building a weapon of mass destruction, are we not going to mobilize? Are we going to remain passive?
Taking action to stop global warming does not imply a threat to our economy. It is only a threat against some specific corporate interests, like those of the big oil companies and those who would like the society to continue to be dependent on a continuous supply of oil. The solutions lie in increased energy efficiency and increased investment in renewable energy sources. Rather than damage the economy, the demand for technological development that will come with such investment should boost the economy.
We do not actually need to eliminate completely our greenhouse emissions to guarantee a stable atmospheric composition and climate in the future. We only need to reduce the emissions and maintain them at a fraction of present emissions in the future. The ocean has a certain capacity to absorb the carbon dioxide we produce (at present it is absorbing about one third of our carbon emissions); the problem we have now is that our rate of emissions are exceeding the capacity of the biosphere to regulate the climate.
One argument that is often heard against solar energy is: in order to supply our current energy needs with solar energy, we would need to cover 1 per cent of the surface of the United States with solar panels, which is unrealistic. That sounds very persuasive until you realise that 1 per cent of the surface of the United States is already paved over! If we could install roofs with solar photovoltaics in every highway, road, parking lot, driveway and building, all our energy needs would be taken care of and we would never need to burn fossil fuels again. Why do we have so little solar energy today? Because of the huge government subsidies for fossil fuels, and because investment in research and technology has not been directed to renewable energy.
Of course, solar energy is not the only thing we should rely on: there is wind, geothermal, tidal, and biomass, there are hydrogen fuel cells that can be used to store energy, and there is the reduction in demand that can be achieved by using more efficient cars and electric appliances. The way forward should be based on energy efficiency and a diversity of renewable energy sources. If we believe that ensuring a safe environment for our future is more (or at least as!) important than being able to drive anywhere in the country, then it will surely not be difficult to take the necessary actions to stop global warming.
The Union of Concerned Scientists
Energy Innovation Analysis by the Union of Concerned Scientists
Global Change Electronic Edition
Intergovernmental Panel on Climate Change
Greenhouse gases online , a website with lots of information on global warming, and links to recent news and scientific papers.
The webpage of Environmental Defense .
Read more about President Bush Energy Report, and the reality of Global Warming .
Various links to news about global warming.