Global Warming Fact and Fiction
Some Critical Findings • Global temperatures have increased 0.6 0C the past 100 years • In some areas, like the southeast United States, there has been a decrease in temperatures since the late 19th century • There has been a cooling of the lower stratosphere which is due to the trapping of greenhouse gases in the upper troposphere
Layers of the atmosphere
Stratosphere Evidence of Cooling
Source: http://www.ncdc.noaa.gov/oa/climate/globtemp.html
Some Critical Findings • Pre-Industrial Revolution Carbon dioxide levels were 280 ppm (.012%) CO2 in the atmosphere • Today the level is 388 ppm, which demonstrates a rapid increase which has not been seen for at least 420,000 years ago.
Increase in carbon dioxide levels between 1960 and 1990. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com).
Past Evidence • Measurements from this period have been made on air trapped in ice cores, drilled mainly from the Antarctic and Arctic, which have extended back as far as 160,000 years with the "Vostok" ice core (Gray, 1998).
Extinctions(1)end Ordovician. (2)late Devonian. (3)end Permian. (4)end Triassic. (5)end Cretaceous
Are Ice Cores Accurate? • It is difficult to believe that a chemically active gas such as carbon dioxide can remain unaffected by burial in ice for as long as 160,000 years. There are questions whether the carbon dioxide can diffuse through the snow, react with dust particles, or form clathrate compounds under pressure The technique of drilling, removal and preservation of the ice core is very difficult, and there are many things that can go wrong (Jaworski, 1996, 1997).
Are Ice Core Samples Accurate? • Most of these objections have now been overcome, with a recent study on the Law Dome ice cores by Etheridge et al (1996, 1998).
Indirect Evidence • Indirect indicators of warming such as borehole temperatures, snow cover, and glacier recession data, are in substantial agreement with the more direct indicators of recent warmth. • Large-scale measurements of sea-ice have only been possible since the satellite era, but through looking at a number of different satellite estimates, it has been determined that Arctic sea ice has decreased between 1973 and 1996 at a rate of -2.8 +/- 0.3%/decade
Twenty glacier length records from different parts of the world all show a decline in lengths through the World Glacier Monitoring Program
Findings • The period since 1972, when the increase has been linear despite an increase of over 45% in emissions, suggests that there are new carbon sinks being established in the ocean and in the terrestrial biosphere to absorb the increases (Gray, 1998).
El Nino • El Niños are not caused by global warming. • However, it has been hypothesized that warmer global sea surface temperatures can enhance the El Niño phenomenon, and it is also true that El Niños have been more frequent and intense in recent decades.
Sea Level Rise • Global mean sea level has been rising at an average rate of 1 to 2 mm/year over the past 100 years, which is significantly larger than the rate averaged over the last several thousand years. Projected increase from 1990-2100 is anywhere from 0.09-0.88 meters (depending on the severity of the warming)
Ocean Currents? Illustration by Jack Cook, Woods Hole Oceanographic Institution
The Future • Due to the enormous complexity of the atmosphere, the most useful tools for gauging future changes are 'climate models'. • The Intergovernmental Panel on Climate Change (IPCC), was established to study global change • IPCC projects a global temperature increase of anywhere from 1.4 - 5.8°C from 1990-2100 (based upon region of the world).
The Future (continued) • Precipitation is also expected to increase over the 21st century, particularly at northern mid-high latitudes, though the trends may be more variable in the tropics. Snow extent and sea-ice are also projected to decrease further in the northern hemisphere, and glaciers and ice-caps are expected to continue to retreat.
References Etheridges, D.M., L.P. Steele, R.L. Langenfelds, R.J. Francey, J.-M Barnola, V.I. Morgan. 1996. "Natural and anthropogenic changes in atmospheric CO2 over the last 1000 years from air in Antarctic ice and firn" J. Geophys. Res. 101 (D2) 4115-4128 Etheridges, D.M., L.P. Steele, R.L. Langenfelds, R.J. Francey, J.-M Barnola, V.I. Morgan. 1996. "Natural and anthropogenic changes in atmospheric CO2 over the last 1000 years from air in Antarctic ice and firn" J. Geophys. Res. 101 (D2) 4115-4128 Gray, V.R., 1998. "The IPCC future projections: are they plausible" Climate Research 10 155-162 http://palaeo.gly.bris.ac.uk/Palaeofiles/Permian/PALIntro.html http://www.ncdc.noaa.gov/oa/climate/globalwarming.html#Q11 Jaworowski, Z. 1996 "Reliability of Ice Core Records for Climatic Projections" in "The Global Warming Debate", (John Emsley, Ed.) European Science and Environment Forum , London, 95-105. Jaworowski, Z., 1997. "Ice Core Data Show No Carbon Dioxide Increase" 21st Century Science and Technology 10 , (1) 42-52
