February is one of the first months since before months had names to boast carbon dioxide concentrations at 400 parts per million.* Such CO2 concentrations in the atmosphere have likely not been seen since at least the end of the Oligocene 23 million years ago, an 11-million-year-long epoch of gradual climate cooling that most likely saw CO2 concentrations drop from more than 1,000 ppm. Those of us alive today breathe air never tasted by any of our ancestors in the entire Homo genus.
Homo sapiens sapiens—that’s us—has subsisted for at least 200,000 years on a planet that has oscillated between 170 and 280 ppm, according to records preserved in air bubbles trapped in ice. Now our species has burned enough fossil fuels and cut down enough trees to push CO2 to 400 ppm—and soon beyond. Concentrations rise by more than two ppm per year now. Raising atmospheric concentrations of CO2 to 0.04 percent may not seem like much but it has been enough to raise the world's annual average temperature by a total of 0.8 degree Celsius so far. More warming is in store, thanks to the lag between CO2 emissions and the extra heat each molecule will trap over time, an ever-thickening blanket wrapped around the planet in effect. Partially as a result of this atmospheric change, scientists have proposed that the world has entered a new geologic epoch, dubbed the Anthropocene and marked by this climate shift, among other indicators.

We aren't done yet. Greater concentrations will be achieved, thanks to all the existing coal-fired power plants, more than a billion cars powered by internal combustion on the roads today and yet more clearing of forests. That's despite an avowed goal to stop at 450 ppm, the number broadly (if infirmly) linked to an average temperature rise of no more than 2 degrees C. More likely, by century's end enough CO2 will have been spewed from burning long-buried stores of fossilized sunshine to raise concentrations to 550 ppm or more, enough to raise average annual temperatures by as much as 6 degrees C in the same span. That may be more climate change than human civilization can handle, along with many of the other animals and plants living on Earth, already stressed by other human encroachments. The planet will be fine though; scientists have surmised from long-term records in rock that Earth has seen levels beyond 1,000 ppm in the past.
The current high levels of CO2 have spurred calls, most recently from the National Academy of Sciences, to develop technologies to retrieve carbon from the atmosphere. The U.N. Intergovernmental Panel on Climate Change relies for that on growing plants, burning them instead of coal to produce electricity, capturing the resulting CO2 in the smokestack and burying it—or in the argot: BECCS, bioenergy with carbon capture and storage, a few examples of which are scattered around the globe. Other schemes range from artificial trees to scour the skies of excess CO2 to fertilizing the oceans with iron and having diatoms do the invisible work for us.
Climate change is inevitable and, if history is any guide to what can be expected, so, too, may be regime change. A few years of diminished rainfall and attendant bad harvests have been enough in the past to fell empires, such as in Mesopotamia or China. The world's current roster of nations struggles to hash out a global plan to cut the pollution that causes climate change, which currently stands at 90 pages of negotiating text. In addition, one nation has submitted its individual plan (or "individual nationally determined contribution," INDC in the argot) to accomplish this feat—Switzerland.
The plans of China, the European Union and the U.S. are already broadly known, if not formally submitted. Together, they are both the biggest steps ever taken to address global warming and likely insufficient to prevent too much climate change, scientific analyses suggest. The E.U., U.S. and China remain reliant on fossil fuels and the world is slow to change that habit thus far. In fact, China has become the world's largest polluter and millions of Chinese have lifted themselves out of poverty with the power from burning more and more coal, a trick India hopes to follow in the near future.
For the Swiss, the bulk of pollution comes from driving cars and controlling the climate inside buildings. Their long-term plan is "to reduce per capita emissions to one–1.5 tonnes CO2-equivalent," the INDC states. "These unavoidable emissions will have to be eventually compensated through sinks or removals." In a world that spews more and more CO2 but needs to get to below zero emissions, bring on those sinks and removals. In the meantime the sawtooth record of rising atmospheric CO2 levels moves ever upward and March 2015 will likely be the name of the next month to boast levels above 400 ppm.

*Correction (3/16/15): This sentence was edited after the original posting to correct an error.