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Are We Having a Heat Wave?

Yes — it's the global warming you've heard discussed and debated. You may wonder why I haven't written about it here before since it's supposed to be a major scientific and technological problem facing the world. But it isn't easy to write a short piece about it. The basic science is simple, but the whole problem is not simple because the earth's climate system is very complicated. Furthermore, the question of what to do about global warming doesn't have easy answers. Still, let's give it a try.

The Scientific Facts
First, consider the basic science. The earth receives radiant energy from the sun, the surface temperature of which is roughly 6,000 degrees Celsius. In turn, the earth reradiates energy into space. A basic law about radiation says that the hotter a body is, the shorter the wavelength at which it emits the most energy. (As a piece of metal is heated it changes from dull red to orange to white hot.) Solar radiation is at a maximum in the visible part of the spectrum, and visible light passes easily through our atmosphere. But because the earth is much cooler than the sun, it emits longer infrared waves, and some of that radiation can be absorbed by gases such as carbon dioxide, CO2.

The presence of those gases in the atmosphere thus results in the earth's surface being warmer than it would be in their absence. A balance will be reached when enough energy can get to the top of the atmosphere and be radiated away to match the amount received from the sun. This is called the greenhouse effect, though the analogy isn't perfect.

It is important to realize that this conclusion — that a planet will be warmed if there is CO2 in its atmosphere — is a consequence of noncontroversial science. It does not violate common sense like quantum mechanics does. It is reasonable to think that if we burn carbon-based fuels, the earth's temperature might rise.

We have good global thermometric measurements for about the past century and a half, which corresponds roughly with the time during which we have been adding to the "natural" atmospheric CO2 by burning large amounts of fossil fuels. These indicate that the average temperature of the earth increased by about one Fahrenheit degree during the twentieth century. The earth has indeed warmed since we began burning large amounts of fossil fuels.

Other Factors
That's the easy part. Now we have to ask if the rise in temperature is significant and if there might be additional causes, such as changes in the sun's energy output, that could have contributed to the change. We need to know how the CO2 content of the atmosphere has varied over that time and where that CO2 has come from. There are also other greenhouse gases such as water vapor and methane that have to be taken into account. We need to consider all the causes of global warming and decide how much has been caused by human activity.

We can track the variations in atmospheric CO2 over recent centuries. In fact, we can trace both temperature and composition of the air back several hundred thousand years. One way is to carefully examine the compositions of ice cores and the air bubbles they contain. These data show a general correlation between the earth's temperature and the amount of CO2 in its atmosphere. In recent decades the proportion of CO2 has risen precipitously and is now considerably higher than it has been for millennia.

We cannot immediately assume that human activity has caused the current situation; we have to evaluate other influences. There are possible contributions to warming besides greenhouse gases, such as changes in the earth's orbit or solar activity, but these cannot account for the current temperature rise. There are other sources of CO2, such as volcanoes, but the increase in this gas is consistent with estimates of the amounts of coal, oil, and natural gas that have been burned over the past couple of centuries. Other greenhouse gases, such as methane from herds of cattle and rice paddies, have an effect, but these also originate in human activity.

The situation is complex, and there isn't room even to sketch all the relevant data here. The publications mentioned at the end of this column go into much greater detail. The kinds of evidence and arguments that I have mentioned briefly have convinced the great majority of climate scientists that global warming is real and that human activity has played a major role in bringing it about.

Choices and Consequences
Global warming will continue for a while whatever we do because CO2 stays in the atmosphere for years, and it will get worse if our present output of greenhouse gases continues. A change in temperature of a few degrees, though seemingly small, would have important climatic effects, such as melting of polar ice with consequent rise in sea levels. These could have deleterious effects on humanity and other species. The 2006 film An Inconvenient Truth, though not totally objective, pictures phenomena that probably already result from global warming.

It is hardly surprising that there has been controversy about global warming. Earth's climate system involves interactions of sun and earth, the atmosphere, oceans, land, plants, and animals. Well-informed people could until recently argue that we just don't understand this well enough to say what has been causing a temperature increase. But the debate extends beyond the boundaries of science. Anything we do to stop or slow global warming will have economic impact, and it is hard to be objective when jobs and stock prices are affected.

What should we do? Attention is being given to sequestering CO2 in the earth or oceans and reforestation to remove it from the atmosphere, but serious efforts have to be made to reduce emissions from our vehicles and power plants. Here I won't speculate about economically and politically feasible ways of doing that. But we should think about what the Christian community can contribute.

We can try to reduce our own use of fossil fuels and at least set good examples. Beyond that, we need to do some serious theological reflection. One source of resistance to taking the problem seriously is the idea that God can't let anything really bad happen to the world because God has promised to take care of us. That is not the message of texts like Deuteronomy 11:13–17 or Jeremiah 4:23–28! God has called us to care for creation, and disobedience has consequences. The divine promises will be fulfilled, but perhaps in spite of devastation that we bring about.

At the same time, we cannot ignore concerns about the state of economies and people's jobs. Leviticus 25 makes it clear that both caring for the earth and doing justice among human beings are important and necessary for us.

Finally, global cooperation on a new scale will be called for if we are to deal effectively with global warming. Americans will need to make significant changes in their lifestyles, but that alone will not solve the problem. This is an opportunity for the body of Christ to provide a practical vision of what true community can be.

Richard Wolfson's Earth's Changing Climate lectures (The Teaching Company, 2007) is a good resource. Reports from the Intergovernmental Panel on Climate Change are at www.ipcc.ch.

George L. Murphy, an ELCA pastor and physicist living in Tallmadge, Ohio, is an adjunct faculty member at Trinity Lutheran Seminary in Columbus and a pastoral associate at St. Paul's Episcopal Church in Akron. His e-mail address is gmurphy@raex.com.