Sen. Orrin Hatch doubts human activity has much effect on climate ("Hatch explains," Opinion, Oct. 20). He cites 400,000-plus years of ice core data indicating that atmospheric temperature changes preceded changes in atmospheric CO2 by several hundred years, then concludes that global warming causes an increase in CO2, not the reverse.

The Vostok ice core data do indicate a close correlation between atmospheric CO2 and temperature; but a correlation does not tell the causal story.

Here's a hypothesis consistent with the data: Periodic changes in Earth's wobble and orbit determine the solar radiation that reaches Earth. More sunlight produces an initial temperature rise, which causes a release of CO2 from oceans, which amplifies the warming. These two factors increase plant biomass, which removes CO2 from the atmosphere and dampens both effects, producing homeostasis until a prolonged decrease in solar radiation reverses the whole process.

Contra Hatch, three incontrovertible facts nearly prove that human activity is swiftly affecting climate: (1) atmospheric CO2 has doubled in the past 150 years due to human activity, (2) CO2 traps heat that would otherwise be radiated back into space, and (3) nearly all the ice on Earth is rapidly melting.

Kirk Robinson

Salt Lake City