Global Warming; A Debate for Today
Although a small minority of scientists argues that there is no global warming at all, that group grows smaller every year. Data assembled by the Environmental Protection Agency (EPA) and others suggest that the global average surface temperature has been rising at roughly 0.4 to 0.6 Celsius degree per century.
In their Climate of 2001-Annual Review Preliminary Report, the National Climatic Data Center (NCDC) add that the last 25 years have seen a dramatic increase in warming to nearly 2 Celsius degrees per century. There are two major theories to explain this global warming; one attributes global warming mainly to human emissions and the other attributes it to mainly natural climatic variability.
The emissions theory holds that greenhouse gases (carbon dioxide especially) generated by human industry (in particular fossil fuel burning) exaggerate the natural greenhouse effect that keeps our planet warm. Although they add caveats about considering other causes as well, the National Oceanic and Atmospheric Administration (NOAA) and the EPA agree human emissions are the main cause of global warming. A NOAA article (21 November 2000) stated “While natural—solar and volcanic—forcings appear to be important factors governing the natural variations of temperatures in past centuries, only human greenhouse gas forcing alone...can statistically explain the unusual warming of the past few decades.”
The solar activity theory says that the sun radiates energy in cyclically varying degrees of intensity and a more active period relates to a warmer climate on earth and visa versa. Aside from the well-known 11-year cycle, there is a 22-year cycle, and a 90-120-year cycle of solar activity. The 11-year cycle is the period between high and low activity levels. The 22-year cycle refers to the full cycle from and back to high activity.
The 90-120 year cycle, the Gleissberg cycle, describes the long-term “ebb and flow” of solar radiative intensity. It modulates the shorter cycles, suppressing or enhancing activity during a maximum or during a minimum. When a Gleissberg cycle suppresses activity during a minimum, it can virtually stop sunspot activity for a period. The Maunder Minimum, associated with a very cold period, is thought to have occurred during a suppressing Gleissberg cycle.
In a conference article published in 1998 scientists stated that increased sunspot activity “might go a long way, even all of the way to explaining the observed pattern of global warming of the Earth in the last decades of the 20th century.” By studying both historical records and a number of natural markers (tree rings, ice cores, etc), scientists have determined that the Spörer Minimum (16th century) and the Maunder Minimum (17th century), both periods of little to no sunspot activity, occurred with cold periods. Evidence of warming after these periods also exists.
There are problems with both theories. Scientists from both groups can point to a huge body of facts and figures that seem to indicate there is a connection to global warming, but neither group has enough proof to categorically rule out any other explanation. Reliable temperature readings, widespread weather reporting and a consistent standard of accuracy are all very recent additions to a data base that is that even yet not comprehensive across the globe.
Information from earlier than the most recent decades is sparse and notoriously unreliable. Carbon dating has recently come under fire as well so even data from ice cores, tree rings and such must now be questioned. Data quality aside, the biggest problem all theories face is the complexity of the system. It is nearly impossible to separate cause and effect links from other surrounding influences.
Although more and more of the scientific community now agrees that man-made global warming is real, there is still a fairly substantial portion that does not. There is considerable proof that the climate has always warmed and cooled in irregular cycles and that for most of its existence, the atmosphere has actually been much warmer than it is now. Experts in the field speculate that, during the long age of the dinosaurs, global temperatures may have been as much as 12 Celsius degrees warmer than it is now.
Evidence that the climate cycles between warm and cold periods is seen in the Medieval Climatic Optimum (a warm period), which followed the last great ice age. During this warm period, the Norse explored far to the north and west through areas now covered in permanent ice. Remains of their outposts are found in coastal areas of Iceland, Greenland, Newfoundland, Canada, and even New England. History books and ancient stories tell of wine produced in vineyards as far north as southern Scotland.
It takes a mild climate to get consistent wine grape crops. Slow cooling after the Medieval Climatic Optimum gradually accelerated and then bottomed out in the Little Ice Age. It, in turn, has been followed by steady, renewed warming. Today, there are credible scientists who predict the onset of another cool phase around 2030.
The impact of global warming is as much up for debate as the cause. Some predict wilder and more frequent swings in the weather ranging from vast, terribly destructive storms to devastating droughts to epic floods and rapidly rising sea levels. Others predict little discernible change: springs that begin earlier and winters that begin later, longer growing seasons farther north, a little more rain in the higher latitudes and a little less in the tropics, and possibly a more favorable climate over a larger portion of the globe.
Depending on political agenda, scientific discipline, and data field under scrutiny, predicted impacts of global warming vary widely. Without conclusive, undeniable proof in support of any one theory, it is too soon to quantify what is really going on with the global climate.
Written by Melody L. Higdon, 14 WS/DOPA