People often talk as if warming temperatures are the only evidence of human-induced global climate change. But the amount of carbon dioxide in the atmosphere also has increased dramatically.

For most of the past 800,000 years, atmospheric carbon dioxide concentrations ranged from about 180 to 280 parts per million. Today, it is 387 parts per million, and growing.

Carbon dioxide levels have been higher, but not recently. A newly published study estimates that you’d have to go back 15 million years to find a sustained period when CO2 levels were this high. That was during the Middle Miocene Period.

Global temperatures at that time were warmer by between 5 degrees and 10 degrees Fahrenheit. Sea levels were 75 feet to 120 feet higher. There was no Arctic Ocean ice cap or large ice sheets in Greenland and Antarctica.

Something else was missing from the Earth as we now know it: Humans.

The study is the first to link changes in sea levels with atmospheric concentrations of carbon dioxide for the period between 20 million and 800,000 years ago.

Earlier studies measured carbon dioxide levels in air bubbles trapped in Arctic ice. But the latest research used a chemical analysis of the shells of ancient sea creatures to calculate atmospheric carbon dioxide levels.

The study comes as Congress is debating legislation aimed at capping the amount of carbon dioxide we emit into the atmosphere.

The so-called cap-and-trade bill would create a market that would put a price on carbon dioxide emissions from power plants, oil refineries and large industrial facilities. That would encourage development of new technologies.

But even if that bill were approved, big polluters and industry groups have mobilized in opposition, CO2 concentrations probably will continue to grow.

That uncomfortable reality underscores the importance of international negotiations set to resume in early December in Copenhagen, Denmark. Negotiators will try to shape a new climate agreement to replace the Kyoto Treaty, which expires in 2012.

With the clock ticking, it now appears unlikely that negotiators will finish the new treaty. But they can, and they must, continue working to find common ground.

Carbon dioxide stays in the atmosphere for years. Some scientists say the amount of CO2 could reach more than 600 parts per million unless restrictions are put in place. That level of CO2 in the atmosphere would be disastrous.

Scientists think that massive volcanic eruptions finally cooled global temperatures at the end of the Middle Miocene Period. We have to hope for something less catastrophic this time.

The above editorial was originally published Nov. 3 by the St. Louis Post-Dispatch. Content was made available by MCTCampus.