Humans have little or nothing to with recent temperature changes, says atmospheric scientist William M. Gray of Colorado State University. The doubling of the amount of greenhouse gases in the atmosphere over the past century, principally carbon dioxide (CO2) from burning fossil fuels, could only have caused insignificant amounts of global warming.

The reason is that the dominant natural greenhouse gas is water vapor and its cloud derivatives. The evidence indicates rising levels of human-released greenhouse gases either reduce levels of water vapor and cirrus cloudiness, or have no affect at all.

• But advocates of human-induced (anthropogenic) global warming assume that as greenhouse gases increase, water vapor and upper-level cloudiness will also rise and lead to accelerated warming -- a positive feedback loop.

• It is this hypothesized positive feedback loop -- extra water vapor and cloudiness -- that is supposed to cause significant warming, not the greenhouse gases themselves.

• However, the global general circulation models which simulate significant human-induced warming are incorrectly structured to give this positive feedback loop -- thus their assumptions are not realistic.

No significant human-induced greenhouse gas warming can occur under such circumstances.

The small warming that has occurred is likely a result of natural alterations in global ocean currents -- as yet little understood -- which are driven by variations in the salinity of seawater. "Our global climate's temperature has always fluctuated back and forth and will continue to do so," says Gray, "regardless of how much or how little greenhouse gases we put into the atmosphere."

Source: William M. Gray, "Get Off Warming Bandwagon," BBC News Online, November 16, 2000.