Hank Green made a video blaming this on changing regulations on shipping fuel. We were essentially geohacking by sending clouds of particulates into the air when burning the fuel, they blocked the sun temporarily but made global warming worse in the long term.

So by changing fuel standards, we basically pulled forward some warming to minimize the total amount of warming. Which is good that we are reducing the total warming, but obviously jarring in the short term.

If that is an accurate read, it isn’t going to go back down. Hopefully it spurs us into action so it doesn’t get much worse.