29.3:
Global Climate Change
The earth has undergone period of warming and cooling throughout its history. However, for the last few centuries, there has been a drastic increase in global temperatures, outside of the earth's cyclic norms. Warming occurs when atmospheric greenhouse gasses, like carbon dioxide become trapped between the earth and the ozone layer. Carbon dioxide can absorb solar energy of long infrared wavelengths, preventing it from traveling back into outer space, thus increasing atmospheric temperatures.
Although this is a natural process called the greenhouse effect the sharp increase in the amount of carbon dioxide present in the earth's atmosphere caused by the burning of coal and petroleum, is not. The results of this temperature increase can be see around the globe.
For example, in the Arctic, polar ice caps are melting resulting in sea level rise and island submersion. This not only threatens coastal cities, but also can increase the occurrence of extreme meteorological events, like droughts, hurricanes, and severe storms.
Also migration and breeding patterns of many animals are occurring earlier in the year than they did decades ago and the size of species distributions are decreasing.
As global warming becomes recognized by more skeptics, the increase in environmentally friendly practices by industries may provide opportunities to reverse human impact and help to avoid severe consequences of global climate change.
29.3:
Global Climate Change
Throughout its ~4.5 billion year history, the Earth has experienced periods of warming and cooling. However, the current drastic increase in global temperatures is well outside of the Earth’s cyclic norms, and evidence for human-caused global climate change is compelling. Paleoclimatology, the study of ancient climate conditions, provides ample evidence for human-caused global climate change by comparing recent conditions with those in the past.
Past Periods of Warming and Cooling
In the last 650,000 years alone, there have been seven cycles of glacial advance and retreat. Over 11,000 years ago, the most recent ice age abruptly ended—marking the beginning of our modern climate era, the Holocene geological epoch. Most historical climate changes are associated with small variations in earth’s orbit that changed the amount of the solar radiation received by the Earth.
Paleoclimatology
Paleoclimatology is the study of climatic conditions and their causes and effects throughout the Earth’s geologic past. Paleoclimatologists employ a variety of scientific methods to deduce the past conditions of Earth’s climate and atmospheric system.
Ice Core Data
Ice core samples taken from thick mountain glaciers and polar ice sheets can reveal information about global climate change. Seasonal pauses in ice accumulation can lead to observable layers in ice cores. These layers can be used to establish a chronology, with the lowest layers being the oldest. Researchers can then analyze properties of the ice and the material trapped inside it (e.g., air bubbles and ratios of oxygen and hydrogen isotopes) to reconstruct the Earth’s ancient climate. The European Project for Ice Coring in Antarctica analyzed volcanic ash trapped in ice cores from Antarctica to provide a detailed record of Holocene volcanic history. This record revealed 96 eruptions during the Holocene, with 33 of those eruptions occurring during the last 2,000 years.
Dendroclimatology
Scientists can also study past climate by examining annual tree rings—a field called dendroclimatology. Essentially, tree rings are wider under favorable conditions and narrower during harsh times. Tree rings can be accurately dated by matching rings from sample to sample—even samples from archaeological digs. Although dendroclimatology has limitations, tree rings are useful climate proxies that can be used to create high-resolution climate records for specific geographic locations.
Suggested Reading
Castellano, E., S. Becagli, M. Hansson, M. Hutterli, J. R. Petit, M. R. Rampino, M. Severi, J. P. Steffensen, R. Traversi, and R. Udisti. “Holocene Volcanic History as Recorded in the Sulfate Stratigraphy of the European Project for Ice Coring in Antarctica Dome C (EDC96) Ice Core.” Journal of Geophysical Research: Atmospheres 110, no. D6 (2005). [Source]
Yang, Bao, Chun Qin, Jianglin Wang, Minhui He, Thomas M. Melvin, Timothy J. Osborn, and Keith R. Briffa. “A 3,500-Year Tree-Ring Record of Annual Precipitation on the Northeastern Tibetan Plateau.” Proceedings of the National Academy of Sciences 111, no. 8 (February 25, 2014): 2903–8. [Source]