Based on everything we know about climate science, the basic game plan is that if we want to limit global warming below 2 degrees Celsius (so as not to risk the most dangerous and unpredictable impacts), we’ll need to prevent the amount of carbon-dioxide in the atmosphere from rising above roughly 450 parts per million. Currently, we’re at about 392 parts per million. So we’ve got some wiggle room, right?

(Tim Wimborne/Reuters)

And, as the IEA found, we’re about five years away from building enough carbon-spewing infrastructure to lock us in and make it extremely difficult — maybe impossible — to avoid 450 ppm. The point of no return comes around 2017. Here’s a chart to visualize it:

As the IEA report notes, “Delaying action is a false economy: for every $1 of investment in cleaner technology that is avoided in the power sector before 2020, an additional $4.30 would need to be spent after 2020 to compensate for the increased emissions.” Right now, hitting that 450 ppm target will require a clean-energy investment of about 1.1 percent of GDP per year, says the IEA (that’s not a pure “cost,” since there are a lot of efficiency savings in there). But the longer we delay, the more expensive it gets. Delays can quadruple the cost.

Granted, if Europe vaporizes in the next few months and the global economy plunges into yet another depression, this could change. Energy use will drop, emissions will sag, and we’ll get a little more space to act. Maybe the point of no return moves out to 2020 or 2022. But, as we saw after the last downturn, the world doesn’t tend to take advantage of these reprieves. When the economy’s bad, few countries want to bother with newfangled energy technologies or carbon taxes or figuring out how to curb oil use, and when things recover the world roars back closer and closer to that 450 ppm mark.