Laura Rose & Lisa Ayers Lawrence, Virginia Sea Grant, Virginia Institute of Marine Science
Global warming refers to an increase over time of the average temperature of the Earth’s atmosphere and oceans. The majority of qualified scientists believe that most of the warming observed over the last 50 years is due to the continued emission of greenhouse gases produced by industry and agriculture. Greenhouse gases are so named because they trap heat in the atmosphere by allowing sunlight through but preventing some heat from escaping into space, thus acting like the glass in a greenhouse. The majority of this greenhouse effect is natural, keeping the Earth's average temperature at a pleasant 60° F (15° C), as opposed to the frigid 0° F (-18° C) we would experience otherwise. However, the atmospheric concentrations of several greenhouse gases have been rising as a result of human activity. Levels of carbon dioxide, which is released primarily by the burning of fossil fuels such as coal, oil and natural gas, have increased by nearly 30% since pre-industrial times. Levels of methane—emitted during the production and transport of coal, natural gas and oil, and released from the decomposition of organic wastes in municipal solid waste landfills and the raising of livestock—have more than doubled, and levels of nitrous oxide—emitted during agricultural and industrial activities, as well as during combustion of solid waste and fossil fuels—are increasing, too.
If average global temperatures continue to rise, they would, at some point, be expected to cause changes in precipitation frequency and intensity patterns, changes in soil moisture, and a rise of global sea level. Sea level would rise as a result of warmer air temperatures because ocean waters expand when heated, and many mountain glaciers would melt. Significant sea level rise would eliminate beaches and plague coastal towns and cities with flooding. Certain islands and low-lying countries such as Bangladesh would be particularly at risk. In addition to the loss of property and historically and culturally significant landmarks that would be caused by flooding, mosquito-borne illnesses and other diseases would increase in incidence. Coastal marine ecosystems would be severely affected by a combination of sea level rise and warmer temperatures. The potential impacts of global warming are numerous.
It has recently been discovered that the polar ice caps have been thinning and shrinking, and that the Earth’s permafrost is thawing. Most scientists believe that the chances of the ice shrinkage being due to natural cycles are slim. If Arctic ice continues to melt at its present rate, in a few decades it could be nonexistent during summer months. The Arctic would become a huge heat collector, absorbing 80% of the sunlight that reaches it, rather than reflecting it back into space as it does now. Major ocean currents that exchange energy from the tropics to the poles would be altered, as would world weather patterns.
In the past 100 years, Earth's average temperature has increased by 1° Farenheit. When deciding what to wear in the morning, this seems trivial; however, consider the fact that during the last Ice Age, the planet was only 9° F cooler than it is now. It doesn't take much to seriously affect climate patterns and ecosystems. If greenhouse gas emissions continue to rise, projections for temperature increases in the next century range from 1.8° F to 6.3° F (assessments by the U.S. National Academy of Sciences and the United Nations' Intergovernmental Panel on Climate Change (IPCC)). During that same period, sea level is projected to rise six inches to as much as three feet. If future climate change occurs at this magnitude, 21st century Earth would experience the fastest warming in the history of civilization and the warmest temperature since the evolution of modern humans. What does this mean for our existence? We cannot possibly know. We are conducting an experiment in real time.
The longest continuous record of atmospheric carbon dioxide measurements in the world dates back to 1958 and comes from a site in Mauna Loa, Hawaii. This site is considered one of the most favorable locations for measuring undisturbed air because possible local influences of vegetation or human activities on atmospheric CO2 concentrations are minimal, and any influences from volcanic vents may be excluded from the records. Because of the favorable site location, continuous monitoring, and careful selection and scrutiny of the data, the Mauna Loa record is considered to be a precise record and a reliable indicator of the regional trend in the concentrations of atmospheric CO2 in the middle layers of the troposphere.
Various ideas exist for dealing with the pollution which may be causing climate change. Many of us could take steps in our daily lives to reduce our consumption of energy. There are also good reasons for switching to renewable energy sources. These energy sources are rapidly replaced, unlike fossil fuels, and are generally less polluting. Examples of renewable energy sources are solar power, wind
For more activities and resources, check out the Bridge's Climate & Atmosphere page, as well as the following sites: