Hurricane Patricia, the most intense tropical cyclone ever observed in the Western Hemisphere and the strongest storm ever recorded in terms of sustained winds, is now headed for the coast of Mexico. Normally, strong hurricanes develop over a period of a week or more; meteorologists track such storms as they move across the Pacific and Atlantic Oceans and warn island and coastal populations days before the storm actually hits. In this case, Patricia has exploded in less than three days. At 5 AM EST on Thursday, Patricia had sustained winds of 85 miles per hour. By 5 AM on Friday, the storm had reached 200 mph sustained winds.
Meteorologists took these measurements by flying into the hurricane itself, and the storm’s path is now considered locked-in. Barring a miracle, the most violent storm on record is going to smash into central Mexico into areas with limited infrastructure and little early warning capability. As for how this happened, the storm began in water that’s already warmer than usual, thanks to the ongoing El Nino cycle. Water temperatures in the area are 1-2C above average, as shown in the chart below:
The atmosphere is also warmer than normal (ocean and air temperatures are always related), which created the right conditions for Patricia to gain strength very quickly. Adding to the problem is the fact that not many cyclones have developed in the same geographical area as Patricia, which means there was a tremendous amount of untapped energy waiting to be unleashed. One thing that may confuse some readers is that while Patricia is intensely powerful, it’s also relatively small — much smaller than Super Typhoon Haiyan or Hurricane Katrina.
Climate change and extreme weather
One question that arises every time a severe or unusual storm strikes is whether or not the storm is caused by global warming. Patricia’s sudden appearance is particularly illustrative of both the risks of unchecked anthropogenic climate change and the futility of attempting to blame any single storm or unusual weather pattern on these trends.
Climate change generally contributes to extreme weather in two ways. First, we see increased variation in temperature. This was captured neatly last year, as various parts of the United States saw record highs, while others were crushed with record lows. As a resident of Buffalo NY, let me promise you: Last winter was brutal unless you lived in Boston, in which case everyone else had the easiest winter of all time. In Alaska and the Pacific Northwest, winter was unusually warm. 2014-2015 was the second winter in a row in which the Arctic jet stream dipped lower than it typically does, blasting the Eastern US into an icy hellscape, while locking hot air over the western half of the country (more, if you count Alaska).
The second way that climate change causes problems is that it shifts the scale from its old default towards a newer default warmer state, thereby creating conditions that are both warmer than before and more prone to deviate from the norm. This is captured by the graph below, which shows climate trends that are both more variable (the curve is more shallow) and right-shifted (temperatures are generally warmer).
One of the complexities inherent to the topic of global climate change is that people tend to instinctively evaluate the idea based on the weather in the place they live. If you lived on the East Coast during the winters of 2013-2014 and 2014-2015, the idea that temperatures are rising might seem farcical. That’s why it’s important to evaluate both the way in which the weather varies in any given place and the long-term overall trends across the entire planet.
How an El Nino demonstrates the danger of small temperature increases
One of the common arguments from people who think the threat of climate change is generally overblown is that we’re fighting to hold the average temperature increase across the entire planet to just 2 C, or 3.6F. A 4F difference (let’s round up for simplicity) scarcely seems like much of a much; the outside air temperature can vary by 20-30F during the course of an ordinary day.
Let’s say, for the sake of argument, that Hurricane Patricia would have formed in exactly this fashion whether anthropogenic climate change is real or not. We’re still left to contend with the existence of an El Nino, a well-established periodic phenomenon in which a band of warmer-than-usual ocean water develops in the central and east-central equatorial Pacific. Both El Nino and La Nina, its counterpart, are associated with changes in global temperatures and rainfall.
Refer up to the beginning of this story, however, and you’ll note that the water fueling this incredibly powerful hurricane is only 1-2C warmer than average. Small changes in temperature + already optimal conditions are therefore demonstrably capable of having a much larger impact than is immediately obvious.
Of course, we have the luxury of discussing whether Patricia is or isn’t driven by a confluence of anthropogenic global warming and El Nino — we’re not the people sitting squarely in its path. No matter what caused it, Patricia is going to devastate the Pacific coast when it arrives later today.