Greenhouse gases (GHG) naturally blanket the earth's atmosphere, and keep the planet warm enough for life to survive by allowing sunlight (solar energy) to enter the earth's atmosphere freely. When sunlight strikes the earth's surface, some of it is reflected back towards space as infrared radiation (heat). Greenhouse gases absorb this infrared radiation, keeping our planet warm. The problem we are facing today is that with increased levels of GHGs, additional heat is being trapped in the atmosphere, increasing the temperature of the earth's land and oceans, leading to abrupt climate change .
Naturally occurring GHGs in our atmosphere include water vapour, carbon dioxide, methane, and nitrous oxide that mostly occurr in very small quantities. Over the past couple of centuries humans have also created several other GHGs, such as chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6) that also contribute to the greenhouse effect in the atmosphere.
Studying climate change can be a tough task. Unfortunately, modern climate information (gathered using instruments like thermometers, barometers, etc) only goes back a couple of centuries at best (and usually only a few decades for most places). We can, however, study sources of information such as ice sheets, tree rings, sediments, pollen and spores, and rocks to obtain climate records dating back thousands of years. The ice fields of Antarctica provide one of these sources. As snow falls to the ground it traps air bubbles that become part of the ice. Over time, as snow continues to fall and condense, glaciers form. These small air bubbles provide miniature samples of the atmosphere from the exact time the snow fell, allowing us to make estimates on climate conditions from the past based on the GHGs found in the samples.
Presently in Antarctica, scientists drill down hundreds of meters into glaciers to remove ice cores that are taken back to the lab and examined layer by layer . Back in the laboratory data from ice cores can be translated into information about temperature, ocean volume, precipitation, volcanic eruptions, sea-surface productivity, and what the gas composition of the lower atmosphere was like thousands of years ago.
Ice core samples from glacial fields of Antarctica provide us with GHG data going back to 650,000 years ago . From this information we can take a peek into what the world was like long before our ancestors had even explored much of the land on earth. Globally, carbon dioxide levels have fluctuated greatly over the last 650,000 years, causing atmospheric temperatures to change significantly as well. Alarmingly, throughout this period of time, GHG levels have never been as high as they are today [2, 3].
Although there is some evidence that humans started to alter the gases in the atmosphere as early as 8,000 years ago through agricultural development , most scientists agree that we really began to change our atmosphere at the start of the Industrial Revolution, around the year 1800, when machinery began to replace manual labour . Although carbon dioxide levels have changed often in the past, the extensive burning of fossil fuels associated with new technologies brought about by the Industrial Revolution is likely when human activities started to harmfully impact the atmosphere.
What is most alarming about climate change is how humans have impacted the rate of change over the last 150 years. Since 1850, the amount of carbon dioxide in the atmosphere has increased to levels never before observed in the geological record . Air temperatures around the globe have increased an average of 0.5°C, with ocean temperatures increasing twice as fast . The Intergovernmental Panel on Climate Change estimates that over the next century temperatures will continue to rise between 1.8°C and 4°C . This will have severe impacts on climate and life.
Although GHGs help keep our planet warm, abnormally high levels of them in our atmosphere may disrupt the climatic balance that is so important to the survival of life. Clearly, there are times when having too much of a good thing can produce negative results.
1. Weaver, A.J. and C. Green, Global climate change: lessons from the past - policy for the future. Oceans and Coastal Management, 1998. 39 : p. 73-86.
2. Brook, E.J., Tiny Bubbles Tell All. Science, 2005. 310 : p. 1285-1287.
3. Alley, R., et al., Climate Change 2007: The Physical Science Basis, Summary for Policymakers. 2007, Intergovernmental Panel on Climate Change. p. 18.
4. Ruddiman, W.E., How did humans first alter global climate. Scientific American, 2002. 292 (3).
5. Bratcher, A.J. and B.S. Giese, Tropical decadal variability and global warming. Geophysical Research Letters, 2002. 29 (19): p. 24-1 to 24-4.