During the southern hemisphere winter of 1998, the "ozone hole" over Antarctica covered 26 million square kilometers (10 million square miles), an area larger than North America and the largest recorded since the gap in the ozone layer was first observed in the early 1980s.


Global atmospheric models can also include chemical processes. The figures below show the ozone concentrations in the stratosphere (at 55 hPa, or 25 km height) in August and October. During austral spring up to two thirds of the ozone is destroyed, and the "ozone hole" appears. The hole disappears again during austral summer, primarily due to an influx of ozone from equatorial regions. Worldwide, however, ozone is decreasing, with superimposed regional and pronounced seasonal variations.

Graphics courtesy of: Max Planck Institute for Chemistry, Mainz

Our rising emissions of "greenhouse gases," such as carbon dioxide, carbon monoxide, methane, and nitrous oxide, trap heat in the atmosphere, which drives the trend of increasing average global temperature that will last well into the next century. While the temperature increase is expected to be 1 to 3.5° C (1.8-6.3° F), this "small" change will be faster than any other climate changes in the last 10,000 years. It will likely cause dramatic changes in sea levels, oceanic and atmospheric circulation patterns, and regional climates.

Already, climate scientists have determined that northern hemisphere temperatures over the last century have been the hottest of the past six hundred years (as inferred by a wide range of proxy climate indicators). Indeed, the years 1990, 1995, and 1997 were hotter than any others since approximately 1400 AD. Moreover, the increases in temperature during the past century have been due to human-produced carbon dioxide emissions, as opposed to changes in solar irradiance or volcanic gases. Finally, the month of July 1998 was recently documented as the warmest month ever recorded.