Climate in the Spotlight
There has been much discussion in the media and in the political realm about the evidence for climate change in connection with the greenhouse effect and the expected global warming that goes with it. In fact, no other environmental issue has garnered more attention in our nation’s capitol than climate change and the associated debate over global warming. This issue has been the topic of countless hearings over the past several years, most of which have been essentially economic in focus, although some have dealt directly with climate change science.
The list of calamities that come with continued global warming is by now known to everyone: sea level rise, hot spells in summer, drought, floods, hurricanes, and perhaps even blizzards, among others. Each time there are unusually bad weather conditions the question arises whether perhaps global warming is to blame. Perhaps it is indeed at fault. Or perhaps there was an equal abundance of bad weather before global warming set in. Or perhaps the weather would have gotten worse without global warming. Or perhaps the weather is in fact no worse than it has been in the past, and we just notice things more now since we have more people, better instruments, and better communication. Another possibility is that perhaps global warming does not exist, and it is an illusion.
Full media attention to the issue first arose in the summer of 1988, which brought the worst drought in decades to the US. For many this was proof that the man-made greenhouse effect had finally brought the expected global warming. In fact, during the 1980’s one temperature record after another was broken. And then the same happened again in the 1990’s. Has global warming arrived?
Carbon Dioxide (CO2) Increase
Although it is only a trace gas having concentrations much less than 1% in our atmosphere, carbon dioxide’s tremendous increase from the combustion of fossil fuels since the mid-1800’s has had scientists worried about its potential to exacerbate what is called the greenhouse effect. The greenhouse effect is a phenomenon whereby atmospheric gases with special physical properties (like carbon dioxide, methane and even water vapor) help trap heat received from the sun, making our planet warmer than it would be otherwise. To its credit, the greenhouse effect has been around long before humans began to burn fossil fuels, and it is a “natural” phenomenon in that makes life habitable for all living things. The problem lies in the possibility that human activities over the past 150 years may result in an increase of this greenhouse effect that could, in turn, cause large-scale changes in the climate system. It is this potential for human-induced change in the greenhouse effect that we refer to as global warming. Since carbon dioxide has the highest concentration of all the greenhouse gases and is the most likely to cause us problems in the very near future, it is the greenhouse gas that has received the most attention in the debate over global warming. However, as we shall learn in later chapters, increased emission of other gases, especially methane, also pose a strong threat to the stability of Earth’s climate.
The rise of carbon dioxide gas in our atmosphere has been measured continuously since 1958 and follows an oscillating line known as the "Keeling Curve," named after Dr. Charles David Keeling, professor at Scripps Institution of Oceanography. A renowned expert on the way carbon cycles itself on our planet, Keeling was the first to measure carbon dioxide in the atmosphere. He demonstrated its annual fluctuations (the little squiggles in the curve) and was the first to report that global atmospheric concentrations of carbon dioxide were rising. The concentration of carbon dioxide is given in units of parts per million by volume, also abbreviated ppmv. (For the more scientifically inclined: ppmv is the same as what chemists call the “mixing ratio” of a mixed gas, in this case the ratio of carbon dioxide molecules with all other air molecules, because equal volumes of gas at equal pressure hold equal numbers of molecules) Before the industrial era, circa 1800, atmospheric CO2 concentration was between 275 and 280 ppmv for several thousand of years (that is, between 275 and 280 molecules of CO2 for every one million molecules in the air); this we know
from the composition of ancient air trapped in polar ice. Carbon dioxide has risen continuously since then, and the average value when Dr. Keeling
ted his measurements in 1958 was near 315 ppmv. By the year 2000 it has risen to about 367 ppmv (that is 367 molecules of CO2 for every one million molecules in the air). Thus, it is higher than pre-industrial values by one third of the pre-industrial era. (You can check the math on your calculator.)
A graph of Dr. Keeling
’s now famous curve of increasing CO2
concentration. The measurements are made at a station on top of Mauna Loa in Hawaii. Note carefully the magnitude of the increase from 1958 until present. We’ll discuss the seasonal variations (the squiggles) in Chapter 4. To link to the scientific article by Dr. Keeling
and Dr. Whorf go to : Carbon Dioxide Information Analysis Center
Global Temperature Increase
While this increase in carbon dioxide has occurred, temperatures in the northern hemisphere have risen by between 1°F and 2°F (almost 1°C) since A.D. 1850, as recorded by measurements. The record only goes back 150 years because direct measurements before 1850 are hard to find. The ten warmest years on record have occurred since 1983, seven of them since 1990. Global temperature in 1998 was the hottest in the historical record. This amount of overall increase in temperature is approximately equal to the amount of increase that is predicted by raising the abundance of carbon dioxide by one third of pre-industrial values – exactly what has happened in the last 150 years.
This is a time series graph showing the combined global land and marine surface temperature record from 1856 to 2001. The temperature is plotted as the difference (called an “anomaly ”) from the long-term average (a value calculated from the years 1961-1990). It is being compiled jointly by the Climatic Research Unit
and the UK Meteorology Office Hadley Centre and continually up-dated and improved. The purpose of these measurements is to detect climate change due to global warming
by measuring an increase in temperature in the records of thermometers. Increased concentrations of greenhouse gases in the atmosphere due to human activities are the underlying cause of global warming. (From: Jones, P.D., New, M., Parker, D.E., Martin, S. and Rigor, I.G., 1999: Surface air temperature and its changes over the past 150 years. Reviews of Geophysics, 37,