The climate over the tropical Pacific is in an extreme state at the moment. That explains some of the extreme anomalies affecting the United States right now. It also gives us a window through which we can glimpse how even more dramatic and long-term climates of the distant past might have worked, and – in the most radical scenarios, unlikely but impossible to rule out entirely – how much more extreme future climate changes could occur.
Now that Typhoon Chan-Hom has blown over Shanghai, then past Seoul before fizzling out, and Typhoon Nangka now heads north towards Japan, there are four other tropical cyclones further east in the Pacific. None of them is particularly powerful yet, but there’s time. Two of the current storms are in the Central North Pacific, in the general vicinity of Hawaii, where another one, Ela, has just fizzled out. This is an incredibly strong burst of tropical cyclone activity for the Central Pacific, and unprecedented for how early in the season it has come.
What is going on? The El Niño event currently ongoing in the eastern and Central Pacific is strengthening. The only question is whether it will be just a significant event, or a huge one. While those of us who were in New York City for the blizzard of late January 2015 have learned that we shouldn’t apply the word “historic” to weather or climate events before they actually happen, this El Niño has at least the potential to become the biggest one since the onset of modern records. It’s already at least competitive with the current record holder, the “super El Niño” of 1997-1998. Strong tropical cyclone seasons in the Central and Eastern Pacific often occur during El Niño events, when the ocean surface becomes anomalously warm along the equator there. That pattern is firmly in place now.
Around a week ago, the most commonly used indicator of the Madden-Julian oscillation (MJO) reached a value in excess of four standard deviations, breaking the record since the start of modern observations in the 1970s. The MJO is the most important atmospheric phenomenon you’ve never heard of, a tropical weather disturbance with global ramifications broadly similar to those El Niño, except that the MJO evolves faster, over a month or two, while El Niño takes months to years. The current extreme MJO happened as its disturbed weather conditions temporarily locked into phase with the anomalously high sea surface temperatures and rainy weather already in place in the Central Pacific due to the El Niño. The combination of the two helped to spawn the current flock of tropical cyclones there…
…the other potential benefit of the El Niño is that if it holds together into the winter — as is very likely — there is good reason to hope it could deliver some heavy rain events to California. This would have the potential to make a dent in the severe and protracted drought there, though unlikely enough to end it entirely.
On the other hand, it’s not good news for the Pacific Northwest, where El Niños tend to lead to warm, dry winters. Oregon, Washington and British Columbia are already experiencing serious drought and wildfire, after a winter where precipitation fell as rain even in the high mountains, leaving no snowpack to provide summer’s water supply.