Despite the best efforts of the Trump administration to ignore or contradict scientific reality, carbon dioxide levels continue to soar far outside the bounds of what Homo sapiens have ever experienced.
This is worrisome for several reasons. First, CO2 is the primary heat-trapping greenhouse gas humans spew into the air, mainly by burning fossil fuels. The higher CO2 levels are, the greater the warming.
Second, CO2 levels or concentrations in the atmosphere will keep rising until the world has reduced global CO2 emissions by more than 80 percent from current levels. CO2 concentrations are like the water levels in a bathtub, and annual emissions are like the flow from the faucet. The water going down the bathtub drain is like CO2 sinks such as the oceans, forests, and soils.
Third, the annual rise in CO2 levels has been speeding up, as long predicted by climate science. Indeed 2015 and 2016 were the two biggest annual jumps in CO2 levels on record.
The fourth thing to worry about these record CO2 levels is that some of the Earth’s carbon sinks appear to be turning into CO2 sources, most notably the defrosting permafrost, which contains twice as much carbon as the atmosphere does today.
This thawing creates a dangerous amplifying feedback, as rising CO2 warms the planet, which thaws the permafrost, releasing carbon that further warms the planet, releasing more CO2, and so on.
The fifth thing to worry about is that, historically, record CO2 levels are accompanied by record temperatures and record sea level rise. We haven’t hit the temperature levels we can expect from current CO2 levels, and by the time we do, CO2 levels will be even higher. Sea level rise can take even longer to catch up but the latest science says we are headed towards worst-case scenario levels, 3 to 6 feet (or more), by century’s end.
The sixth reason for concern is that CO2 levels (and temperatures) were relatively flat for the past 10,000 years — during which time modern civilization and agriculture developed capable of sustaining a population of billions of people.
But now CO2 levels have surpassed those seen not just during modern civilization, but during all of human evolution. Indeed, current levels haven’t been seen for many millions of years.
The final thing to worry about is that by exiting the Paris climate deal, President Donald Trump has made it all but impossible to achieve the lower range of projections in the chart above (graph on far right). We are now exceedingly unlikely to stay below 500 ppm — and could go far, far higher if Trump were able to persist in his self-destructive policies over two terms.
The last time the Earth sustained CO2 levels near the 400 ppm range, a few million years ago, the Arctic was 14°F warmer, and “the West Antarctic Ice sheet did not exist,” according to a 2013 study in the journal Science. Sea levels were about 80 feet higher.
A 2009 analysis in Science found that when CO2 levels were sustained in the 400 to 500 ppm range some 15 to 20 million years ago, it was 5°F to 10°F warmer globally, and seas were also 75 to 120 feet higher.
That’s why a rational and moral society would be scrambling to strengthen Paris, not destroy it.