Last week, with very little attention, our fragile globe cruised quietly past what some news sources called a "milestone": On May 10, the atmospheric concentration of the heat-trapping gas carbon dioxide reached an average daily level of just over 400 parts per million.

The New York Times called this an "odometer moment," meaning, I guess, that it's an event we note casually, like when our car reaches 100,000 miles. And then we keep our foot on the gas and start on the next 100,000.

Four-hundred ppm doesn't sound like that much, but, according to The Times, it's the highest level since the Pliocene Epoch at least 3 million years ago, a time characterized by warmer temperatures, much smaller ice caps, and sea levels 60 to 80 feet higher than they are today.

For nearly a million years, the carbon dioxide level has fluctuated within a relatively narrow range, from around 180 parts per million during ice ages to 280 ppm during warmer periods. A higher level is associated with warmer temperatures, and during the relatively warmer geological-time eye blink represented by the period of human civilization, carbon dioxide ppm has hovered around 280.

Since the Industrial Revolution, however, carbon dioxide ppm has climbed steadily, reaching the milestone this month and, according to some scientists, heading for 450 within less than 25 years.

All reputable scientists agree that a high ppm implies tough times ahead in terms of climate, and, in fact, it's hard to open a newspaper without finding indications that they've already started. Only a few days after the 400 ppm milestone, New York Times columnist Thomas Friedman reported on dramatic weather changes in Yemen and Saudi Arabia. The growing season has been disrupted -- with grim political implications for Yemen -- and 13 Saudis died in the most violent rainstorms in 25 years.

And on May 15, at least 13 tornadoes, some with winds as high as 200 mph, struck the region around Granbury, Texas, killing at least six.

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Even though we're careful not to connect any particular weather event with global climate, one needn't be a genius to figure out that what's been happening in the last few years is precisely in line with what scientists have predicted for decades: higher carbon dioxide ppm corresponds with weather extremes.

Is there any good news on the climate front? On May 14, the International Energy Agency produced a five-year outlook for the global energy market. The "good news" is that the threat of oil shortages has essentially disappeared and that the U.S.

will continue to depend less and less on Middle Eastern oil. Part of the transformed market is declining oil consumption in the developed world.

But the other part is increased oil and gas production, especially in the U.S. and Canada, thanks to better technology and driven by higher oil prices. Middle Eastern oil will flow increasingly to the burgeoning Asian market, where citizens covet a lifestyle like ours, which can be achieved only with hydrocarbons. In short, as long as hydrocarbons are out there, we will find them and burn them, and carbon dioxide levels will continue to rise.

Of course, nothing I've said so far is particularly new or surprising. Still, probably we occasionally need to be reminded of the most surprising thing of all: the denial and obliviousness with which we are allowing this to happen.

Then there's the worst climate news so far: the so-called Benghazi scandal, the I.R.S. pseudo-scandal, the putative Associated Press scandal. The wounds were largely self-inflicted, but blood is in the water, nevertheless. The frenzy will go on until new scandals can be found, undermining and distracting the only administration in some time that's shown even half-hearted interest in taking on climate change.

This is the real scandal. Thus, Columbia University scientist Maureen Raymo, referring to the news that the globe had finally reached 400 ppm, says: "It feels like the inevitable march toward disaster."

John M. Crisp teaches in the English Department at Del Mar College in Corpus Christi, Texas.