The Climate in Emergency

A weekly blog on science, news, and ideas related to climate change


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How Do You Know?

We’re in the deep freeze, thanks to a destabilized polar vortex, and predictably, certain people are publicly complaining that the cold disproves climate change, not realizing that this weather pattern is, in fact, a symptom of change.

Old news.

In the meantime, I’ve been thinking about uncertainty, and how climate deniers sometimes use the fact that climatologists don’t know everything to argue that they don’t know anything.

Actually, it’s a fair question. While no one could fairly expect any expert to literally know everything in their field, how can climatologists be so sure of some things and so unsure of others? When a climate denier makes a wild claim (for example, that climate change on Earth can’t be due to carbon dioxide emissions because other planets are warming, too–which, by the way, they mostly aren’t), how can the rest of us be sure it is wild?

I thought of an analogy.

Imagine someone says to you “I just saw someone walk by the window, but I can’t be sure who it is.”

So, you start asking questions–what gender, what age, what clothing–and the person isn’t sure. “I think it was a man, but I’m not sure. Dark hair, blue clothing? I really didn’t get a good look.”

You then ask “OK, what about skin color? Was the skin purple?”

Even though your informant knows very little, the question is ridiculous, because humans can’t have purple skin. Three nipples, sometimes. Four kidneys, occasionally. But not purple skin, and we’re all familiar enough with our own species that we never ask if barely-glimpsed people have purple skin.

Knowledge comes in different levels–for any topic, some types of information are superficial, while others are fundamental. If you know those fundamentals, and a claim violates those fundamentals (as any suggestion that rising carbon dioxide levels aren’t causing warming does) then you don’t need to do any research on the specifics to know the claim is false.

Now, most of us don’t know the fundamentals about climate–it’s not difficult to study up, but not everybody has the energy or the time. If that’s your position, then you can’t identify wild claims as balderdash on your own–but you can trust that the genuine experts are not being arbitrary when they call foul.

This trust is important. I do not mean thoughtless trust, I mean informed trust, based on a carefully-developed capacity to identify which people have the fundamental knowledge and the understanding that such knowledge isn’t universal. There are things we really do need experts for–like performing surgery, flying airplanes, and sorting out real science from hooey.

Such trust makes us smarter, not dumber, because it means we don’t have to make sense of the world alone.

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Nor’easters

Last week, I spent three days huddled inside because of high winds rattling the house and ripping dead branches off of swaying trees–and I live in Maryland, where the storm (“Winter Storm Riley,” officially) was relatively minor. What we saw was nothing, compared to what the people in coastal Massachusetts experienced.

Now we’re preparing for another one (“Quinn”). And some meteorologists expect another storm after that.

What Are Nor’easters?

This week’s storms are nor’easters. They’re not unusual, although the recent one was an extreme example. Like hurricanes, they are very large low pressure systems that bring wind and rain (or snow) and last for several days. Unlike hurricanes, they draw their power, not from warm water (there wasn’t any under Riley) but from the interaction between warm and cold air masses. They generally form in winter. In the case of Riley, a storm system moved east across the US, then drove the rapid development of a very intense low pressure area just off the coast, which then moved north and gradually east. On satellite images, the thing looks like a hurricane, a massive pinwheel of swirling cloud off the coast. While too far out in the Atlantic now to influence my weather directly, Riley still exists. It’s busy causing damaging surf on Puerto Rico from thousands of miles away.

Nor’easters seldom approach hurricane force winds. Typically, these storms are gusty, not windy, a serious inconvenience, but not a danger, unless you have bad luck (such as an unusually weak tree limb right above your car). Rily was the most intense I’ve seen, and around here it was only in the high tropical storm-force range.

The lesser winds do not make these storms mild.

For one thing, nor’easters have much larger peak wind fields than hurricanes do. While a hurricane might have sustained winds of 90 miles an hour near its center, most of the area the storm passes over will get much weaker winds, say 50 or 60 miles per hour. A strong nor’easter will blast the same 50 or 60 miles per hour over the same large area, it just lacks the 90 mph core.

Second, wind is not the most destructive aspect of a hurricane, it’s just the easiest way to compare storms to each other. The size of the wind field, the speed the storm travels (and hence how long it spends in any one place), the size of its storm surge, and how much it rains are all much more important in terms of its destructive power–and above all, there is the question of what it hits. A low-lying, heavily populated area where the people lack both money and political power is where the disaster happens. And nor’easters have large wind-fields, heavy precipitation, sometimes heavy coastal flooding, and can persist for days.

And, as with hurricanes, when we get a bad one (or several) people start asking about climate change.

Nor’easters and Climate Change

Meteorologists can be quick to point out that individual storms can’t be linked to climate change, which both is and is not true. One recently referred to efforts to draw the link as “witch-craft.” That’s at best disingenuous.

We can absolutely prove that climate change is making nor’easters worse, for the same reason that climate change is making hurricanes worse. First, the single most dangerous aspect of either storm is coastal flooding, which is unquestionably worse now that the sea level is several inches higher than it was when most existing infrastructure was built and when the data used to define flood zones for insurance purposes were gathered. The apparent sea-level rise varies from place to place, because geological forces are also in play making the ground rise in some places and fall in others, but climate change can claim about eight inches of it world wide, due to a combination of thermal expansion (things, including oceans, expand when they heat up) and glacier melt. That means every coastal flood event, including all hurricanes and all nor’easters, are  eight inches worse than they would otherwise have been.

Eight inches doesn’t sound like much, until you imagine them inside your living room.

Also, a warmer planet means more humid air, which means wetter storms. In the winter, as long as the air temperature is below freezing (which isn’t really very cold), that means more snow–more closed roads, more fallen trees and snapped power lines, more collapsed roofs, more car accidents, more missed days of school. All of this should sound very familiar to some readers right about now. All that white stuff? Yup, it’s a symptom of climate change, not a negation of it. In warmer weather, wet storms means rain which means flooding. That’s ruined houses, damaged roads, washed-out bridges, soaked earth–leading to toppled trees and snapped power lines–and drownings.

We’ve been through this already with hurricanes; climate change does not have to cause individual storms, or even make a certain type of storm more likely or more intense, in order to directly cause more storm damage.

But can climate change cause nor’easters? Yeah, it kind of looks like they can.

Connecting the Dots

To tell this story, we have to cover a bit of atmospheric anatomy.

Remember the polar vortex? It was all over the news a few years ago, but I haven’t heard of it of late. It still exists, though. Actually, there’s two of them. Or sometimes three.

The polar vortex is not a type of storm, but rather either of two long-term atmospheric features–this sounds a little different than the last time I explained it, because the two features tend to get mixed up in public discussion, and I only recently learned that they are distinct.

Originally, “polar vortex” meant a circular pattern of winds that forms in the stratosphere around the pole in winter. It’s also called the polar night jet, because the sun does not rise in the winter at its latitude. The winds blow from west to east and divide cold polar air from warmer air at lower latitudes–the stratosphere is a layer that begins several miles up, above where weather happens. But in recent years, the term has also been applied to the jet stream, a circular pattern of winds in the troposphere–a much lower layer–also at a boundary between warm and cold air, but much farther south. The jet stream meanders, across the latitudes covered by the United States and southern Canada. The jet stream exists winter or summer, and its shape and location help determine whether any given area gets warm, tropical air or cold, arctic air this particular week.

Ok, so, definitions taken care of, what does either polar vortex have to do with climate change or Winter Storm Riley?

A lot of the strange weather we’ve had in recent years has been caused by extreme waviness in the jet stream. Because the jet marks the boundary between warm air and cold air, an extreme meander means that warm air flows much farther north than normal over here, while cold air flows much farther south than normal over there. At the same time, weather systems tend to persist longer and move slower than normal. Rainy weather becomes catastrophic floods. Dry, hot weather becomes killer heat waves and droughts. The extra waviness is likely caused by global warming, especially the loss of Arctic sea ice. As the planet warms, the polar regions warm faster than the rest of the planet, decreasing the contrast between the warm and cold regions and weakening the jet stream that lies at their boundary. Weak jets are slow and wavy.

So climate change doesn’t cause snowstorms in Florida by some magical method of “global weirding,” but instead through a fairly straight-forward form of atmospheric messiness, a weakened and wobbly boundary between warm and cold caused directly by the warming Arctic.

The next bit is less certain, as in not all scientists agree, but a weak and waving jet stream could be one of the mechanisms able to put pressure on the polar vortex and cause it to temporarily break down and allow warm air in over the pole. Such an event is, sensibly enough, called a Sudden Stratospheric Warming, or SSW. Although the stratosphere itself doesn’t have weather in the normal sense of the word, it can influence the weather of the troposphere, resulting in odd weather several weeks later–such as cold snaps, warm periods, or violent storms. SSWs appear to be natural (we have only been measuring stratospheric temperatures for a few decades, now, so it is hard to be sure), and their frequency has not increased, but some computer models suggest an increase could happen, and the extra-wavy jet stream could make it happen–or could already be making it happen. It takes a while to gather enough data to document a change in events that don’t happen every year.

Riley (and presumably its sibling-storms, to some extent) was triggered by a particularly severe SSW, one which ripped the polar vortex in two and triggered a bizarre winter heat wave in which parts of the Arctic rose above freezing for days on end. There’s no sun up there, remember, yet the ice started melting instead of growing–a bad sign. That triggering is not in doubt. And the SSW could have been triggered by a weak and wavy jet stream, which is itself caused by melting sea ice (notice the ominous cycle implied there?). Melting sea ice is, rather unambiguously, a symptom of global warming.

That “maybe” in the middle of the causal chain remains, but this is very close to a linkage between climate change and a single storm. Anyone who claims differently is going to have to marshal a much better argument than claiming “witchcraft” to convince me otherwise.

 


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It’s *%@$ing Cold

Actually, no it isn’t, at least not where I am. I’ve just been outside and the air is definitely brisk, I’d want a coat if I stayed out long, but it’s not unpleasant and the day looks beautiful and bright. But it is noticeably colder than it was yesterday, and I understand almost all of the United States is in a cold snap right now.

Predictably, the Internet is chattering about a “polar vortex” again, as if the term simply meant an unusually severe cold snap. It doesn’t–the polar vortex is not a weather event but a current within the atmosphere. There is always a polar vortex; it is the southern boundary of the polar air mass. It’s basically another name for the familiar jet stream. Sometimes the jet stream is almost straight, a circle drawn around the northern part of the globe. Sometimes it is wavy, bringing cold air farther south in some places and warmer air further north in other places. Right now, the boundary between polar and non-polar air is extremely wavy, and it is colder in Texas than in Alaska. What this is, really, is a good old fashioned cold-snap, albeit one that extends unusually far south.

There are signs that this year the media may shift to “arctic outbreak” as their buzzword of choice.

The current cold-snap is a little different than last year’s, where the cause of the extremely wavy boundary was debatable but might have been related to melting sea-ice in the arctic. Right now, we’re looking at the effects of the former Super Typhoon Nuri, which formed in the Western Pacific, became one of the most powerful storms of the year, and then weakened and recurved, heading northeast. By the time it reached Alaska it had lost its tropical characteristics (meaning its structure and the way energy moves through the system were no longer hurricane-like) but retained much of its power. Last week, the air mass formerly known as Nuri was among the most powerful storms in the Bering Sea ever recorded. Pacific storms can and do interact with the jet stream, causing weather changes hundreds of miles away. In this case, Nuri caused the boundary to become extremely wavy, freezing Texas.

Probably, some climate skeptics are wondering about global warming about now, and while I haven’t seen it yet, I expect some deniers are going to advance this cold-snap as proof against climate change. In writing this post, I’m being preemptive.

Yes, cold weather can be a symptom of global warming. A warmer atmosphere is generally more active, more prone to extremes of all kinds. A destabilized, extremely wavy polar vortex specifically could well be more common now that the arctic ice is melting, and Nuri, like all tropical cyclones, has a link to to global warming through the rising temperature of ocean water. This year’s Western Pacific typhoon season has not been startlingly intense (except for the monstrous Super Typhoon Vonfong, which fortunately weakened before it hit anyone), but it has been stronger than average. The sea has also been exceptionally warm.

But there are a couple of other points worth bearing in mind:

  • It isn’t cold everywhere. Yes, the weather is unusually cold today in the eastern half of the United States, but there are other parts of the world and some of those parts are unusually warm. An unstable polar vortex doesn’t actually make the average temperature of the world drop, it just redistributes cold air. Last year, while the Eastern U.S. was freezing and questioning the existence of climate change, the same weather patterns were causing record-breaking heat in California, Alaska, and parts of Europe. The hot weather exacerbated the California drought and caused a dangerous avalanche in Alaska that completely cut off one town’s road access. For the people there, global warming was not in doubt.
  • Coldness is relative and we have been spoiled by warm weather in recent years. Although the current “arctic blast” may break some local temperature records, it feels a lot colder than it really is because we’ve gotten used to the new normal of warm temperatures. Much of what we saw last winter would have been quite normal twenty or forty years ago (yes, I did just cite the cartoon, XKCD, but the cartoon in question does cite its sources and its author is an actual scientist).
  • Global warming means cold weather is rare, not that it never gets cold anymore. Yes, there are going to be genuinely cold years going forward, probably including some record-breakers where the entire planet is colder than it has been since record-keeping began. The weather on Planet Earth is extremely variable, and that isn’t going to change. What we are seeing, and will continue to see, is that the cold snaps are fewer and less severe than the warm spells. On average, we’re going up. 

This year, we have been especially far up. May, June, August, and September each broke global heat records. I am not certain, from the wording of my sources, whether May, June, and August were each in turn the hottest month ever, or simply the hottest May, June, and August ever. In either case, the records were based on a global average, meaning that they included measurements from places experiencing Fall or Winter at the time. September was definitely the hottest of any month ever recorded. 2014 is likely to be the planet’s hottest year on record, cold snaps in the U.S. notwithstanding. This is a big deal.

Weather.com put the situation in startling perspective:

Earth hasn’t set a monthly record for cold since December 1916, but all monthly heat records have been set after 1997.