In a June 7 letter "Water vapor, greenhouse gases, and global warming" Peter Byrne complains about the "attack on fossil fuels," citing opposition to fracking because of groundwater contamination. He further argues that since water vapor accounts for 90 percent of the greenhouse effect "which we can do nothing about" we should therefore make no effort to curtail carbon dioxide emissions since CO2 contributes significantly less to the greenhouse effect than water vapor.

While the 90 percent quoted somewhat overstates the actual fraction of water vapor's contribution to the greenhouse effect, the main point is that Mr. Byrne misunderstands the role of both water vapor and carbon dioxide in global warming.

As we have all observed, dew condenses on grass in cool mornings and evaporates as it warms. As humans add CO2 to the atmosphere that additional warming leads to increased evaporation, hence an increase in atmospheric water vapor. This strongly amplifies the warming caused by additional CO2. That's why climate scientists refer to CO2 as the "control knob" of global warming. This water vapor "feedback effect" amplifying CO2 warming is a well-known and observed fact.

There is plenty of room for discussion on what policies for dealing with human-caused climate change make the most sense in our free market economy. But without a factually correct scientific understanding of the problem, such discussions are pointless. I extend an offer to meet with Mr. Byrne and anyone else truly interested in a fact-based understanding of basic climate science.

Dr. Ray Weymann

Atascadero