Your Opinion: Human contribution to climate change

Dear Editor:

In his April 27 commentary George Will dismissed global warming concerns with his old argument that climate has always been changing.

This followed an April 24 letter by local writer Keith Davis where he made the point that during the past 542 million years, climate stability has been rare. The point both miss is that Earth’s climate past provides an alarming perspective on how much humans are influencing climate stability by burning fossil fuels.

For the past million years, on 100-thousand-year cycles, earth has wobbled in its orbit around the sun. This changed the intensity of the sun just enough to cause the planet to start cooling. As oceans cooled they drew carbon dioxide out of the atmosphere, which added to cooling. As the earth’s orbit wobbled back to warmer, the oceans released carbon dioxide back into the atmosphere, which added to warming.

The earth’s wobbles by themselves wouldn’t have caused significant global temperature changes, but with the resulting changes in atmospheric carbon dioxide, together they were major drivers of significant global cooling and warming. So yes, we can all agree that climate has always been changing.

But now we have the human contribution. Based on the Earth’s wobble cycle, we should be cooling, actually headed to a period of much colder temperatures and glacier advances by about year 3500. But we’ve added enough carbon dioxide to our atmosphere to reverse that trend. Our great-great-great grandchildren in the year 3500, if they exist, are far more likely to be too warm than too cold.

Understanding climate change throughout earth’s past supports warnings by climate scientists that if we fail to quickly reduce carbon-dioxide emissions, we’ll likely see highly disruptive global warming by 2050 and catastrophic changes by 2100.

If humans unknowingly through the industrial revolution added enough carbon dioxide to the atmosphere to prevent the next ice age, we should be optimistic that with more informed science and modern clean-energy technology, we can avoid pushing global warming to dangerous limits this century.

The website skepticalscience.com is highly recommended by climate scientists and provides an excellent discussion about Milankovitch cycles, more commonly known as Earth’s orbital wobble.