The physical processes that underlie global climate systems are complex and not fully understood. In addition their are scientific data, such as that used to show why temperatures are rising.
According to a recent report of the UN-sponsored Intergovernmental Panel on Climate Change (IPCC), global warming is “unequivocal,” or a fact; and “very likely,” mankind is largely to blame. Some who differ with this conclusion, especially in regard to the human factor, concede that cities may be heating up because they are growing in size. Moreover, concrete and steel readily absorb the sun’s heat and tend to cool down slowly at night. But urban readings, skeptics say, do not reflect the trend in rural areas and can distort global statistics.
On the other hand, Clifford, a village elder who lives on an island off the coast of Alaska, says he has seen changes with his own eyes. The people of his village travel across sea ice to the mainland to hunt caribou and moose. Rising temperatures, though, are making the traditional lifestyle impossible. “The currents have changed, ice conditions have changed, and the freeze-up of the Chukchi Sea has . . . changed,” says Clifford. The sea used to freeze up at the end of October, he explains, but now it does not freeze until late December.
In 2007, warming was also evident in the Northwest Passage, which was fully open for the first time in recorded history. “What we’ve seen this year fits the profile of lengthening melt seasons,” said a senior scientist for the National Snow and Ice Data Center in the United States.
The Greenhouse Effect—Vital for Life
A reason given for such changes is an intensification of the greenhouse effect, natural phenomena vital for life on earth. When energy from the sun reaches the earth, about 70 percent is absorbed, heating air, land, and sea. If it were not for this mechanism, the average surface temperature would be about zero degrees Fahrenheit (-18 degrees Celsius). Eventually, the absorbed heat is released back into space as infrared radiation, thus preventing the earth from overheating. But when pollutants change the composition of the atmosphere, less heat escapes.
Gases that contribute to the greenhouse effect include carbon dioxide, nitrous oxide, and methane, as well as water vapor. The atmospheric concentration of greenhouse gases has increased markedly over the past 250 years, since the start of the industrial revolution and the increased use of fossil fuels, such as coal and oil. Another greenhouse-enhancing factor seems to be the rising population of farm animals, whose digestive processes produce methane and nitrous oxide. Some researchers point to other causes of warming that they say occurred before humans could have influenced climate.
Just Another Fluctuation?
Skeptics of human-induced warming point out that earth’s temperature has undergone substantial fluctuations in the past. They point to the so-called ice ages, when the earth was supposedly much cooler than it is now; and in support of natural warming, they cite evidence that cold regions, such as Greenland, at one time supported vegetation that prefers warm areas. Of course, scientists concede that the further back they go, the more their certainty about climate diminishes.
What may have caused temperatures to vary significantly before human influence was a factor? Possible causes include sunspots and solar flares, which correlate with fluctuations in solar energy output. Additionally, earth’s orbit moves in cycles that take many thousands of years and that affect our planet’s distance from the sun. There is also the influence of volcanic dust and changes in oceanic currents.
Climate Modeling
If earth’s temperature is rising—no matter what the cause or causes—how will it affect us and the environment? Precise predictions are hard to make. Nowadays, though, scientists have access to powerful computers, which they use to create digital simulations of the climate system. Incorporated into their models are the laws of physics, climate data, and natural phenomena that influence climate.
Simulations enable scientists to experiment with climate in ways that are otherwise impossible. For instance, they can “change” solar output to see how this affects polar ice, air and sea temperatures, evaporation rates, atmospheric pressure, cloud formation, wind, and rainfall. They can “create” volcanic eruptions and examine the effects of volcanic dust on weather. And they can examine the effects of human population growth, deforestation, land use, changes in the emission of greenhouse gases, and so on. Scientists hope that their models will progressively become more accurate and reliable.
How precise are present models? Much, of course, depends on the accuracy of the data and the amount of it fed into the machines. Hence, climate projections vary from the mild to the catastrophic. Even so, says
Science, “surprises could spring from the [natural] climate system.” And some already have, such as the unusually rapid rate of Arctic melting, which has amazed many climatologists. Still, even if policymakers had only a rough idea of the consequences of present action or inaction, they could make decisions today that might reduce problems tomorrow.
With that possibility in mind, the IPCC examined six different sets of computer-simulated scenarios—ranging from unrestricted greenhouse-gas production to business as usual to severe restraint—each producing different climatic and environmental results. In the light of the predictions, analysts urge a variety of measures. These include mandatory limits on fossil-fuel emissions, penalties for offenders, more nuclear power generation, and the introduction of more environmentally friendly technologies.
Are the Models Reliable?
Present forecasting methods “oversimplify poorly understood climate processes” and “simply ignore others,” say critics. They also point to the inconsistencies in computed projections. One scientist who participated in the IPCC discussions said: “There are some of us who remain so humbled by the task of measuring and understanding the extraordinarily complex climate system that we are skeptical of our ability to know what it is doing and why.”
Some would argue, of course, that using an element of doubt as justification for doing nothing is gambling with the future. “How would we explain this to our children?” they say. Whether the climate models are accurate or not, we can be certain that the earth is in serious trouble. Its life-sustaining environment is being assaulted by pollution, deforestation, urbanization, and the extinction of species, to name just a few factors that no one can successfully dispute.
In view of what we know, can we expect mankind as a whole to make an about-face so as to spare our beautiful home—and us too? What is more, if human activity is causing global warming, we may have only years, not centuries, to make the needed changes. At the very least, making such changes would mean promptly addressing the root causes of earth’s problems—human greed, self-interest, ignorance, inept government, and apathy. Is such a prospect probable or just wishful thinking? The question will be answered in short
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