Ezra Klein: In 2005, when “An Inconvenient Truth” came out, I remember that the hope was we could keep the carbon load in the atmosphere to 350 parts per million, and the fear was we would hit 400ppm. Now we’ve hit 400ppm and people are hoping to avoid 450ppm. This seems to be getting out of hand, and fast.

Al Gore: We have already crossed the 400 parts per million mark. We crossed it earlier this year. The question now is how high it will go before we begin bending the curve. But in spite of the continued released of 90 million tons of global warming pollution every day into the atmosphere, as if it’s an open sewer, we are now seeing the approach of a global political tipping point.

The appearance of more extreme and more frequent weather events has had a very profound impact on public opinion in countries throughout the world. You mentioned my movie back in the day. The single most common criticism from skeptics when the film came out focused on the animation showing ocean water flowing into the World Trade Center memorial site. Skeptics called that demagogic and absurd and irresponsible. It happened last October 29th, years ahead of schedule, and the impact of that and many, many other similar events here and around the world has really begun to create a profound shift.

A second factor is the sharp and unexpectedly steep decrease in prices for electricity produced from wind and solar and the demand destruction for fossil fuel energy from new efficiency improvements. The difference between 32 degrees fahrenheit and 33 degrees fahrenheit seems larger than just one degree. It’s the difference between water and ice. And by analogy there’s a similar difference between renewable electricity that’s more expensive than electricity from coal and renewable electricity that’s less expensive. And in quite a few countries in the world and some parts of the United States we’ve crossed that threshold and in the next few years we’re going to see that crossed in nations and regions containing most of the world’s population.

Another way to think about this is that back when mobile telephones first appeared, the market projections for how quickly they would increase market share turned out to be not just wrong but way wrong. This is a point made by Dave Roberts at Grist, but the projections made 5-10 years ago for the installation of solar and wind technologies were, similarly, not just wrong but way wrong. We’ve seen a dramatic increase that’s far more rapid than anybody projected and it’s accelerating — not just in the United States but even more rapidly in developing countries.

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