To the editor:
In his columns for May 23 and May 29, Brian Watson treats the subject of global warming. Unfortunately, some of his statements are wrong and his columns do not provide a framework for thinking about the problem. Below are some points that may help to structure a meaningful discussion:
1. The phenomenon often referred to by descriptors such as “greenhouse gas warming” is real. Without it, the temperature at the surface of the Earth would be cooler than it is by about 30 K (54 F). Water vapor is by far the most important greenhouse gas, but carbon dioxide (CO2) also plays an important role.
2. Since 1850, the average temperature at the surface of the Earth has increased by about 0.8 K (1.4 F). However, for the last decade or so, the global average temperature has been essentially constant.
3. The concentration of CO2 in the atmosphere has increased from a value of about 280 ppm in 1850 to about 400 ppm today. The source of this CO2 is clearly anthropogenic.
4. Sea level has been rising at about 2mm to 3mm a year (an inch per decade or a foot per century) throughout the period of about 200 years for which data are available. There has been no obvious change in rate during this period. It is therefore clear that change was underway long before there was any change in the concentration of CO2.
5. It is misleading to state that greenhouse gases “trap heat.” The earth is in approximate energy balance, i.e. it radiates to space virtually all of the energy that it receives from the sun. No energy is trapped.
6. Emission of energy to space occurs from the troposphere and predominantly from a height on the order of 5 km (16,000 ft) and at an emission temperature of about 250 K.
7. Tropical storms, droughts, heat waves, and other aspects of sensible weather are not easily connected to any long-term changes in climate. It is best to ignore weather when trying to assess the extent of global warming.