By Robert Hazen, George Mason University
We all have read about global warming. Increased concentrations of carbon dioxide, and a few other atmospheric gases, are leading to an increase in global temperature, causing a greenhouse effect. We have two facts: temperatures are going up and CO2 concentrations are going up. However, in spite of these two facts, we don’t yet know for sure if they are linked, if this is a cause-and-effect relationship.
Rise in Temperature
Let’s first understand global warming. It is conceivable that the slight rise in temperature might be due to increased solar energy output. We know that the Sun fluctuates slightly and in ways that we’re not sure of; we haven’t had measurements of the Sun’s energy output for long enough to be sure.
However, solar variations have certainly occurred. For example, there was a short period of global cooling during what was called the Mini Ice Age, from about 1645 to 1715. During that period, sunspots all but disappeared, and the Sun is estimated to have been about one percent cooler. That’s a huge difference, and it caused this period of 50 years or so when climate was quite different.
It is essential to have better long-term measurements of the Sun, as well as atmospheric CO2, and temperatures, and so forth. It is also absolutely essential to document the complex global cycles of carbon and oxygen. Where are these atoms stored? How do they shift from one reservoir to another? We really don’t understand these geochemical cycles fully yet.
This is a transcript from the video series The Joy of Science. Watch it now, on Wondrium.
Evidence from GCMs
From the political point of view, two questions rise above all the others. The first question: Are CO2 concentrations leading to an increase in global temperatures? The most compelling evidence for this greenhouse effect comes from global circulation computer models, the GCMs. They invariably predict warming associated with increased atmospheric carbon dioxide.
It is possible that increased CO2 might change the atmospheric-temperature profile in such a way as to increase the cloud cover, and therefore cool parts of the Earth’s surface, even though we have increased CO2. There are lots of other variables, too: vegetation, the rate at which polar ice is melting, carbon dioxide uptake by the ocean, etc. There are also mitigating effects of sulfates and other aerosols.
But every model, no matter how we run it, predicts warming. In a recent report that summarized more than 10,000 different computer simulations, the Environmental Protection Agency concluded that ocean levels are going to rise by an additional half-foot by the year 2050, and by at least a foot by the year 2100. This is as a result of an estimated 4° Fahrenheit increase in temperature by that year 2100.
The second of the questions we have to ask is: How much is it going to cost, in social and economic terms, to wean ourselves from fossil fuels?
Any effort to drastically reduce the consumption of fossil fuels is going to cost consumers money, and it might require significant changes in our lifestyle as well. Following are some of the different ways we use fossil fuels: burning wood, gasoline in our car, natural gas and heating oil. Most of the power plants are run by burning coal.
We have a tremendous infrastructure that’s based on burning fossil fuels, and it’s certainly true in the rest of the world as well. Moreover, some politicians, from regions rich in fossil fuels, or those strongly dependent on their use, discount the significant effect of the greenhouse effect.
Opinions on Global Climate Change
We should consider how society should deal with these global issues. We don’t know how much global warming is going to take place during the next half century, but all models indicate that it’s taking place. We can’t predict the consequences of widespread species loss, the elimination of rainforest ecosystems, but we do know that such loss is irreversible.
In the face of such environmental projections, supported by the preponderance of evidence, and endorsed by the vast majority of researchers working in the field, it’s only common sense to protect the environment as much as we can.
Scientific research on the environment is essential to address the magnitude of the problem. Environmental scientists can model the complex interplay of the economic and the social and the physical factors that place limits on human survival. But the most troubling unanswered question about human population explosion and environmental change lies outside the domain of science.
Some politicians call global climate change scientific nonsense. They say it’s, at best, unproven and at worst, claptrap.
It’s difficult to respond to such extreme claims with purely scientific arguments, because uncertainties are always going to remain. However, we must remember that we have only one Earth with which to perform this experiment, and we’re living that experiment right now. We can make a choice. Do we to want to be conservative and try to save the Earth? Or, do we want to just let the Earth run its course and see what happens?
Common Questions about Global Warming
The Mini Ice Age was a short period of global cooling, from about 1645 to 1715. During that period, sunspots all but disappeared, and the Sun is estimated to have been about one percent cooler. That’s a huge difference, and it caused this period of 50 years or so when climate was quite different.
Following are some of the different ways we use fossil fuels: burning wood, gasoline in our car, natural gas and heating oil. Also, most of the power plants are run by burning coal.
The most compelling evidence for CO2 concentrations leading to an increase in global temperatures comes from global circulation computer models, the GCMs. They invariably predict warming associated with increased atmospheric carbon dioxide.