This month we reached a tragic milestone: Carbon dioxide levels hit 400 parts per million (ppm) in our atmosphere (Scientific American, May 9). For hundreds of thousands of years, CO2 levels have not risen above 300 ppm. The last time CO2 was at 400 ppm was about 3 million years ago, before humans existed, and sea levels were at least 50 feet higher than they are today.

While already dangerously high, we can expect CO2 levels to continue rising 2-3 ppm each year on our current course. The 350 ppm level, which a number of scientists regard as the safe limit, is growing smaller and smaller in our rearview mirror. How high will we allow this number to go before we decide to take significant action to curb greenhouse gases?

We know that higher carbon dioxide levels result in higher temperatures, and, not surprisingly, our global average temperature rose by 1.4 degrees Fahrenheit in the past century (http://climate.nasa.gov/news/649). If we do nothing to reduce carbon emissions, scientists predict that global temperatures will increase by 7 degrees by the end of the century.

If many Americans fail to hear alarm bells, it may be due to the fact that a well-orchestrated campaign has been waged to create the illusion that there is significant disagreement in the scientific community about climate change. A recent survey of more than 12,000 peer-reviewed articles on climate change, however, shows such disagreement is virtually nonexistent. Published in the journal Environmental Research Letters, the survey found this consensus among climate scientists: 97 percent agree that global warming is happening because of human activities.

If the science is settled, what does this mean for us here in Kansas?

In their 2008 report, “Climate Change Hits Home, The Risks to Kansas,” Drs. Nathaniel Brunsell and Johannes Fedemma, et al, predict that Kansas’ average temperature will increase 2 to 4 degrees by the end of the century, and southwest Kansas will face an average increase of 8 degrees. We will also experience fewer frost days, more heat waves, more intense storm cycles, a higher probability of flooding and decreases in soil moisture.

This does not have to be our future. We can take action to preserve a livable world for future generations.

One solution, championed by Republican and former Secretary of State George Shultz, is a revenue-neutral carbon tax. In an op-ed appearing in the Wall Street Journal, Shultz wrote, “Clearly, a revenue-neutral carbon tax would benefit all Americans by eliminating the need for costly energy subsidies while promoting a level playing field for energy producers.”

Citizens Climate Lobby, a nonprofit, nonpartisan organization also working to pass a revenue-neutral carbon tax, recommends returning the revenue to all households on an equal basis, which would offset increased energy costs arising from the carbon tax.

Hopefully, Sens. Jerry Moran and Pat Roberts and Rep. Lynn Jenkins will join Shultz and support this innovative solution. In lieu of congressional action, President Obama will turn to Environmental Protection Agency regulation to curb greenhouse gases. Which would our Republican members of Congress prefer: The regulatory approach or the free market approach?

Reaching 400 parts per million is our wake-up call on climate change. It’s time to choose the path of heat resistance.

— Lynate Pettengill is the director of field development for Citizens Climate Lobby. She resides in Lawrence.