Bill McKibben writes:

It’s Earth Day +51, as we near the end of President Biden’s first hundred days, and forty world leaders are scheduled to join him for a virtual summit on climate change. “For those of you who are excited about climate, we will have a lot more to say next week,” the White House press secretary, Jen Psaki, said last Thursday, which is a sweet way to think about it—better than “for those of you who are existentially depressed about climate.”

But, amid the blizzard of numbers that will come this week (such as a new report from the Lawrence Berkeley National Laboratory showing that America is “Halfway to Zero” in cutting the carbon from its electricity sector, as long as you don’t count the methane that all those new gas-fired power plants produce), it’s possible to discern the single, unlikely number that is really driving action at the moment, and it’s important to recall how it came to enter the debate. That number is 1.5 degrees Celsius, which is enshrined in Article 2 of the 2016 Paris climate accord as the world’s official goal for how much we will let the planet warm.

In the early decades of the climate era, government negotiators used two degrees Celsius as a target—that number has a tangled history, tracing back to at least the mid-nineteen-nineties, when Angela Merkel, then Germany’s environment minister, and other European officials seized on it as a benchmark. But there was never much hard science behind it, and by the mid-two-thousands the rate of damage already observable around the planet had begun to spook researchers, not to mention the residents of the most vulnerable countries. Even though the temperature had risen less than one degree Celsius, we were already seeing extensive Arctic ice melt, for instance. So the Alliance of Small Island States, with a lot of leadership from the Caribbean nations, and some of the African countries most vulnerable to drought, began to talk about a lower target. I first remember hearing chants of “1.5 to Stay Alive” at the Copenhagen climate talks, in 2009, and the Barbadian poet Adisa Andwele performed a song of that name for the assembled delegates. But those negotiations were such a mess that the short final document that the summit produced reiterated the old target of two degrees, merely mentioning the new number as a “consideration.” [Continue reading…]