650 ppm isn't easier than 450 ppm

Global warming is largely a bathtub problem. It's not enough to slow the flow of emissions into the atmosphere. The level of pollution would still be rising. We need to stabilize and decrease carbon pollution already in the atmosphere. That requires much more radical steps than even the typical MIT graduate student realizes and poses some real challenges to climate straight talk.

It also leads to some highly uncomfortable conclusions: stabilizing emissions at 650 ppm, a level of concentration that approximates any climate scientist's nightmare scenario of doom and gloom, isn't any easier than 450 ppm, what many see as a reasonable target (albeit still one that likely means rising temperatures and sea levels for generations).

The reason is laid out clearly in the latest report on The Costs of Delay courtesy of the ClimateWorks Foundation, a $300 million venture with the goal of stabilizing concentrations in the atmosphere much closer to 450 ppm than the doomsday scenario of 650 ppm.

The reason is simple: Not just concentrations—the water levels in the bathtub—but also emissions—the flows into the tub—keep going up: The longer we delay, the more fossil-dependent infrastructure will be built in the meantime, and the greater the eventual adjustment necessary:

We can compare these effects to driving on an icy road. It's easier to slow to 20 miles per hour when you're motoring along at 40 mph than when you're doing 60. By the same token, if we wait to reduce emissions, it will be harder to achieve a 650-ppm equilibrium than if we start now and aim for 450 ppm.

This fundamental logic is at the heart of the bathtub analogy and perhaps the most important reason why global warming is one of the toughest problems to wrap our minds around.