In the wake of Climategate, common sense deniers like to say that there is lots of other evidence for global warming, in addition to that which has been debunked by the East Anglia whistleblower. Actually, however, the scientific evidence for AGW is remarkably weak. At Icecap, Lee Gerhard, geologist and reviewer for the Intergovernmental Panel on Climate Change, sums up the key scientific evidence with admirable brevity:
It is crucial that scientists are factually accurate when they do speak out, that they ignore media hype and maintain a clinical detachment from social or other agendas. There are facts and data that are ignored in the maelstrom of social and economic agendas swirling about Copenhagen. Greenhouse gases and their effects are well-known. Here are some of things we know:
• The most effective greenhouse gas is water vapor, comprising approximately 95 percent of the total greenhouse effect.
• Carbon dioxide concentration has been continually rising for nearly 100 years. It continues to rise, but carbon dioxide concentrations at present are near the lowest in geologic history.
• Temperature change correlation with carbon dioxide levels is not statistically significant.
• There are no data that definitively relate carbon dioxide levels to temperature changes.
• The greenhouse effect of carbon dioxide logarithmically declines with increasing concentration. At present levels, any additional carbon dioxide can have very little effect.
We also know a lot about Earth temperature changes:
• Global temperature changes naturally all of the time, in both directions and at many scales of intensity.
• The warmest year in the U.S. in the last century was 1934, not 1998. The U.S. has the best and most extensive temperature records in the world.
• Global temperature peaked in 1998 on the current 60-80 year cycle, and has been episodically declining ever since. This cooling absolutely falsifies claims that human carbon dioxide emissions are a controlling factor in Earth temperature.
• Voluminous historic records demonstrate the Medieval Climate Optimum (MCO) was real and that the “hockey stick” graphic that attempted to deny that fact was at best bad science. The MCO was considerably warmer than the end of the 20th century.
• During the last 100 years, temperature has both risen and fallen, including the present cooling. All the changes in temperature of the last 100 years are in normal historic ranges, both in absolute value and, most importantly, rate of change.
Contrary to many public statements:
• Effects of temperature change are absolutely independent of the cause of the temperature change.
• Global hurricane, cyclonic and major storm activity is near 30-year lows. Any increase in cost of damages by storms is a product of increasing population density in vulnerable areas such as along the shores and property value inflation, not due to any increase in frequency or severity of storms.
• Polar bears have survived and thrived over periods of extreme cold and extreme warmth over hundreds of thousands of years extremes far in excess of modern temperature changes.
• The 2009 minimum Arctic ice extent was significantly larger than the previous two years. The 2009 Antarctic maximum ice extent was significantly above the 30-year average. There are only 30 years of records.
• Rate and magnitude of sea level changes observed during the last 100 years are within normal historical ranges. Current sea level rise is tiny and, at most, justifies a prediction of perhaps ten centimeters rise in this century.
The present climate debate is a classic conflict between data and computer programs. The computer programs are the source of concern over climate change and global warming, not the data. Data are measurements. Computer programs are artificial constructs.
Public announcements use a great deal of hyperbole and inflammatory language. For instance, the word “ever” is misused by media and in public pronouncements alike. It does not mean “in the last 20 years,” or “the last 70 years.” “Ever” means the last 4.5 billion years.
For example, some argue that the Arctic is melting, with the warmest-ever temperatures. One should ask, “How long is ever?” The answer is since 1979. And then ask, “Is it still warming?” The answer is unequivocally “No.” Earth temperatures are cooling. Similarly, the word “unprecedented” cannot be legitimately used to describe any climate change in the last 8,000 years.
SCOTT adds: The direct link to Gerhard’s piece is here.