The latest issue of Scientific American has a informative article on the current state of climate science: why we know the earth is warming, and why we know human activity is partly to blame.
The authors are William Collins of UC-Berkeley; Robert Colman, an Australian; James Haywood of the UK's Met Office; Martin Manning of NOAA; and Philip Mote, the climatologist for the state of Washington.
Unfortunately it'll cost you $5 to read the article online. I'll summarize the key points here, but if you want to read the whole article you'll need to buy a copy or go to the library.
The main points:
Atmospheric concentrations of carbon dioxide, methane and nitrous oxide have been stable for 10,000 years — until they began growing rapidly about the time the Western world industrialized.
1. 11 of the past 12 years are the warmest since reliable records began around 1850. That's a pretty short time frame, geologically speaking, but the probability of that happening by chance are very small.
2. Measurements from ice cores and tree rings provide a longer time line, showing that the current climate is warmer than it has been for at least 1,300 years.
3. While natural variability occurs, temperature extremes have changed in accordance with the warming trends. Frost days and cold days have become less common, while heat waves and hot days have become more common.
4. The oceans are warming as well, more so at the surface than in the depths, a sign that the warming source is at the surface.
5. Overall, the planet's average temperature has risen .75 degrees Centigrade (about 1.5 degrees Fahrenheit) in the last 100 years — and the pace is accelerating.
Rising Sea Levels
1. The oceans have absorbed more than 80 percent of the added heat. This has warmed the water, which expands, causing sea levels to rise. Melting glaciers and ice sheets add to the effect.
2. The oceans have been measured rising an average of 3.1 millimeters a year. Over 50 years, that would mean a total increase of 155mm, or about 6 inches. The process is expected to accelerate, however, for a total rise in the 21st Century of maybe 40 centimeters (400mm, or about 16 inches) and possibly as much as 60 centimeters (about two feet).
3. With rising sea levels comes inundation of low-lying coastal areas, a higher water table, increased flooding, erosion, salinization of coastal waterways and wetlands, and greater danger from storms. An EPA study of the effects of various levels of sea rise suggests (while admitting it is an underestimate) that even a 6-inch increase would cost the United States alone something like $100 billion if we wanted to protect developed coastal areas and prevent inland flooding. That cost would be spread over 100 years, so the annual cost isn't too bad and assumes coastal development all but ceases, and that sea levels stop rising. The costs rise fairly rapidly with additional increases in sea levels.