Climate Science: An Update
Some impacts of a changing climate are increasingly evident: more severe storms (as in hurricanes and tornados), more intense rainfall and flooding (as in the Mid-West this spring), more drought and forest fires (as in California). Others are more subtle: gradually warmer temperatures, rising sea levels, changing fisheries, starving polar bears (as polar ice melts).
The underlying causes of these changes are well known and well documented—if also frequently denied by, among others, the President of the United States. What warms the Earth is radiation from the sun. Much of that radiation is re-radiated from Earth’s surface to space, but as longer wavelength, infra-red radiation. So-called greenhouse gases in the atmosphere—especially carbon dioxide and methane—absorb that radiation, trapping the resulting heat and warming the atmosphere. As concentrations of these gases increase, principally from combustion of coal, oil, and natural gas, but also from growing livestock herds (who emit methane) raised for meat, so will the warming. For more than 60 years, scientists have documented a steady growth in greenhouse gas concentrations in the atmosphere and rising atmospheric temperatures.
The atmospheric warming is most pronounced in the polar regions, hastening the melting of the Arctic sea ice, the Greenland ice cap, and the massive south polar ice cap—all of which drive sea level rise. The warmer atmosphere affects weather patterns, leading to more frequent intense storms such as hurricanes and to increased rain and flooding in some regions and increased drought in others. A serious, persistent drought in parts of Central America that has made it impossible for many small farmers to feed their families is a major cause of increased migration from that region to the U.S. Likewise, sustained drought has dried out the forests of the western U.S., leading to more numerous and intense forest fires—which in turn release more carbon dioxide to the atmosphere.
The warmer atmosphere also leads to warming of the upper layers of the ocean and to higher concentrations of carbon dioxide in the seawater, making the marine environment more acidic. Warmer ocean water both expands (adding to sea level rise) and impacts marine life, since warmer water contains less oxygen. (Yes, fish and other marine animals need oxygen to survive, just like people). Warmer water also evaporates more rapidly, adding to the moisture in the atmosphere and hence to the likelihood of intense rainfall and flooding. A more acidic ocean may impair the photosynthetic ability of algae and microbes to produce oxygen (half of atmospheric oxygen we breathe comes from the oceans).
Natural processes such as the growth of trees can remove carbon dioxide from the atmosphere, but only slowly; at present the average life of a carbon dioxide molecule in the atmosphere is at least 100 years, and we are adding carbon dioxide much faster than it can be removed. That means we (and our descendants) are already committed to some significant amount of additional warming and sea level rise. Already, the costs for protecting coastal urban areas against rising seas are estimated at $5-$10 billion per city, just for sea walls (not counting the costs of redoing water and sewer systems or re-locating whole neighborhoods). Experts think most smaller coastal communities, and perhaps those along flood-prone rivers, will have to be abandoned.
Climate skeptics point out that models can’t yet predict the timing and impacts of climate change in specific areas with any accuracy. That’s not surprising; even daily weather predictions are often wrong, let alone predictions months or years in advance. At the level of the entire Earth, however, there is virtually no doubt that human activities have set in motion significant—and for the most part unwelcome—changes to the climate. Moreover, the scientific consensus is that we have only a couple of decades to take major steps—such as shifting the majority of our energy needs to renewable energy sources—before we are committed to changes that will significantly alter life on earth for generations to come.
Common Sense for the Eastern Shore
