Clouds keep drifting over the science of global warming.
New reasons have emerged to doubt the standard assumption that the earth is warming because carbon dioxide is building up in the atmosphere.
The alarmists who want people to burn less fossil energy always cite the coincidence over the past 100 years between an increase in observed temperature and an increase in the atmospheric concentration of CO2. Motivation to do something immediately to preclude catastrophic warming flows from the assumption that the gas buildup caused the warming.
A problem with the cause-effect relationship over that period has long been recognized by global warming doubters. In the past century, recorded temperatures rose by half a Celsius degree, peaked in 1940, fell until the 1970s, then regained 0.2 degree.
More than 80% of CO2 from human sources entered the atmosphere after 1940-after the main part of the century's temperature build. So the coincidence crumbles under a close look at the data. Something is wrong with the cause-effect relationship central to the alarmists' assumption.
The problem now looks more than a century old.
Drilling finished up this year at the Vostok station in East Antarctica, which has yielded ice records of atmospheric chemistry and climate for the past 420,000 years.
The record shows fluctuations between fairly stable bounds of temperature, CO2, and methane, another greenhouse gas. The gas and temperature changes correlate well. And the historic gas concentrations show current levels to be unprecedented over the period.
According to scientists at the George C. Marshall Institute, however, Vostok data reported in the journals Science and Nature show timing dislocations similar to that of the past 100 years.
"The temperature and the carbon dioxide concentrations do indeed vary together," the group says, "but the carbon dioxide changes occur after the temperature changes. When the earth's temperature increases, carbon dioxide also increases, but roughly 1,000 years later.
"Clearly, atmospheric carbon dioxide cannot be the cause of a warming that occurred before this carbon dioxide existed."
The Marshall Institute suggests that the CO2 build-ups are effects, rather than causes, of warming. The ability of oceans to retain the gas diminishes as their temperatures climb.
"Consequently, when the oceans warm they release some of the carbon dioxide into the atmosphere," says the institute.
An advance in scientific understanding of a complex problem thus challenges a popular and simple assumption, however flawed, at the core of a political agenda with lots of momentum.
The issue tests the ability of science to influence human behavior, politically expressed.