I disagree with George Mathews’ evaluation of the anecdotal evidence involved in various studies of global warming cited in his letter, “Global warming is a hoax” (July 25).

1. Carbon dioxide is a gas that traps heat in the troposphere. It occurs naturally and also as a result of burning carbon fuels (coal and oil).

2. A carbon dioxide balance in the troposphere is necessary for the Earth to maintain a temperature that is livable for inhabitants. Not too hot, not too cold. The troposphere (part of the planet’s atmosphere closest to Earth) controls this natural function, capturing heat from the sun and the Earth.

The troposphere is, in effect, a thermostat for human survival. Higher levels of carbon dioxide in the troposphere intensify the heat on the Earth. Carbon dioxide levels that are too low could result in an ice age.

3. The history of the carbon dioxide content of the troposphere is best measured by the air bubbles in core samples taken from glaciers. Cameron Wake, a climatologist at the University of New Hampshire, has examined samples going back 800,000 years.

Since the late 1800s and extending into this century, the carbon dioxide parts-per-million content of the troposphere has increased from 301 parts to 390 parts. During the previous millennia, the average parts per million were in the 265 range.

People can draw their own conclusions on whether the Earth is in a warming situation.

I totally agree with Mathews that people should be “better stewards of this planet and should try to limit personal consumption of everything.”

Robert Moorehead, Paris