I'm a professor at U Michigan and lead a course on climate change problem solving. These articles often come from and contribute to the course.
By: Dr. Ricky Rood , 10:58 PM GMT on February 24, 2011
Cold and Snowy and Warm and Wet
Yes it is, again, a cold and snowy winter in the eastern parts of the U.S. (Master’s Wunderblog) You might recall that it was very cold and snowy in Europe at Christmas time. In the middle of Asia, January was very cold. Of course those whose opinions on global warming are anchored in the political arguments use the cold and snowy winter to substantiate their position that global warming is not real. I do not write to convince you.
Others become sensitized to the weather and start to think about climate and changing climate and what such a cold and snowy winter means.
A lot of scientists start out explaining the cold and snowy winter by making the statement that there are certain weather patterns, for example, the Arctic Oscillation. (see this blog in Washington Post for a different take) These patterns are part of dynamical or internal variability, and when the Arctic oscillation is in one phase of the pattern it is cold and snowy in the eastern U.S. and northern Europe. It should also be warm in Greenland. It’s been cold in central Asia and warm in northern Siberia. (Master’s Wunderblog: Near Record Warmth in Canada and Siberia) Hot-Cold-Hot-Cold = natural variability. It's just part of what we have to live with. All of this is true, accurately stated, but it does not strike me as a terribly intuitive explanation for those who just lost their crops in northern Mexico or central Florida. I am going to try to develop a more broadly intuitive framework to think about a cold and snowy winter in a warming world. I have written a number of previous blogs on this, one of which is reproduced at the end of this one. Also, I just finished lecturing on dynamical variability in class, and I have put those lectures on line - Lecture 11 and Lecture 12. There are a lot of links in these lectures.
An Intuitive Approach to the Cold and Snowy Winter: I will write from the point of view of the gardener or someone who likes to be outdoors and pays attention to the season and the weather.
In the winter the Sun becomes low in the sky because of the tilt of the Earth’s orbit. At polar latitudes, the Sun is below the horizon. There is no solar heating. It is dark at the pole.
During winter at the pole, the Earth continues to emit energy to space. This energy is emitted as infrared radiation. It gets cold.
It is worth remembering that if there is no solar energy to heat the Earth, the Earth will get very, very cold. It would start to approach the background temperature of outer space. At the pole, in the winter, it gets cold, say, – 40 degrees below zero. (The cool thing about 40 degrees below zero is that this is where Fahrenheit and Celsius are equal.)
Here in the U.S. it is intuitive to the gardener that the winter is cold, and dark, and it gets colder and darker the farther north you go. It’s right there on the back of the seed packet.
The atmosphere responds to this cooling at the pole; whenever and wherever there is a hot-cold contrast, a temperature gradient, there is motion. The wind blows.
A fact of the Earth is that it rotates. That rotation strongly determines the winds; the motion of the air aligns with the rotation of the Earth. (Here are two neat movies from MIT’s Climate Modeling Initiative Geophysical Fluid Dynamics Laboratory: .mpg format (large ones) non-rotating fluid, … rotating fluid )
Something of a river of air, the polar jet stream, forms around the pole. (perhaps a home boy’s figure) Most outdoor people have gotten pretty familiar with the jet stream, and that the jet stream is sometimes wavier than at other times and that that influences the weather – a lot.
Now here is something that is important, that is not quite as intuitive. The jet stream that forms around the pole largely isolates the air in the polar region from air outside the polar region. Here is how I would develop some intuition, imagine you are next to a rapidly flowing stream and you put a leaf in the stream. Does it flow across the stream to the other side, or is it rapidly carried downstream? It is carried downstream, and therefore, one side of the stream is effectively isolated from the other. The jet stream around the pole, this river of air, effectively isolates the pole. Therefore, not a whole lot of heat is carried to the pole; the sun is down; it gets cold at the pole.
This isolation of the pole during the winter occurs, whether or not there is global warming. The Sun goes down for a long period of time. Without transport of heat to the pole, the pole can get as cold now as it did 50 years. It might take a few days longer, but if it is isolated long enough then it gets just as cold. So we have a store of cold air at high latitudes.
Here is another, perhaps less intuitive fact. For the rotating atmosphere of the Earth, the hot-cold contrast, the temperature gradient, represents a source of energy for atmospheric motion. The atmosphere does not like these gradients. It wants to mix them up. If it as cold at the pole as it used to be, and warmer outside of the pole, then there is MORE energy for that mixing. So when the mixing occurs it is, likely, more vigorous, more energetic.
With this more energetic mixing, then it is possible that when the jet stream is wavy, it is very wavy compared to history. It is possible that the cold polar air goes farther south than it used to go. And more warm middle latitude air finds itself at the pole. Previously isolated polar air is pushed off the pole. It sits over Asia, Europe – North America. For a time in the middle of the winter, it can stay cold for a long time. And up at the pole it is warm. And if that cold polar air is pushed just a little bit farther south than historical, it can be damaging record cold.
And that is what January looked like. Here it is:
Figure 1: Observations of temperature in December of 2010. The temperatures are represented as a difference (anomaly) from a 30 year average. See more from (Master’s Wunderblog: Near Record Warmth in Canada and Siberia)
I don’t know if that helps. I apologize not being able to draw some new figures. There are some things that are worth thinking about for the sake of consistency.
Do we see these episodic record cold temperatures in unusual places in the middle of the winter, when we would have stronger temperature gradients, perhaps more vigorous mixing?
Do we see it taking a little longer for the pole to get cold in the transition from fall to winter?
Does the temperature at the pole bottom out at about the same temperature as it always has, but the temperature in middle latitudes gets a little warmer?
Is spring coming earlier?
Is it possible that midwinter risk to crops at southern middle latitudes increases, at the same time the spring growing season starts earlier?
Is it snowier in the middle of winter, but less snowy in the spring?
What does it mean when the United States is as cold as it has ever been for a month in the middle of winter, but the planet as a whole is still the 17th warmest on record?
Relevant Blog from 2010 linked here and repeated below.
Warm Cold Warm Cold
You may remember that early last winter it was cold in the eastern half of the United States. There was a lot of press about what the cold weather implied about global warming. I wrote a series of blogs last year that are:
Cold in a Warm World
Cold in the East
Last Year and This Year
Last Year and This Year – and the Next Big Story?
I have started teaching again. One of things we do in the beginning of the class we talk about what people already know about global warming. Two of the students raised the issue of “what’s in name?” That is, if it is called “global warming,” then people are confused when it is not, always, uniformly warmer all the time. (Might remember this discussion as well.)
As I stand in front of these students prattling on, I am always thinking of ways to explore, challenge, and expose ideas. Early on, we talk about the role of greenhouse gases in the natural climate of the Earth. We have known since, at least, 1800 that water vapor and carbon dioxide are greenhouse gases that make the Earth “warm.” That is, if you take away these gases which act like blankets and hold the Sun’s energy near the surface of the Earth for a while, then the Earth would be MUCH colder – say, about zero degrees Fahrenheit. Restating this, without the atmosphere the surface of the Earth would be cold. (Spencer Weart’s great history) Water is about two thirds of the greenhouse warming.
One could take from this fact, and it is not often I use the word “fact,” – one could take from this fact, that there is a strong physical reason that works to take the Earth towards this “equilibrium” temperature. Think of it this way, suppose you have a pot of boiling fresh organic chicken broth on the stove. Once you get the pot boiling, if you want to keep it boiling then you have to keep adding a little heat to the bottom of the pot. If you turn off the heat, then the pot stops boiling. This loss of energy which works to stop the boiling is always occurring, and you are always adding energy through the burner to counter this loss. For the Earth, the Sun is the burner, the source of energy, and the Earth is always cooling to get rid of this energy. It’s a little like a spring trying to pull the Earth’s temperature to, on the average, about zero degrees Fahrenheit. (A question for the reader: what is the impact of putting a top on the pot?)
If you were to turn off the Sun, then the Earth would get cold fast. That is what happens when winter comes to the poles. In the north, throughout October and November, the North Pole starts to cool. The Earth emits radiation to space. Since the heating from the Sun is totally absent at this time, it can get far colder than that equilibrium temperature of zero degrees Fahrenheit. The atmosphere and the oceans continue to transport heat to the north, but they can’t keep up. This process of cooling at the poles in the winter is a fact of the planet that will continue even as greenhouse gases build up.
This is where weather comes into play. We have this cold air up towards the North Pole. The atmosphere and the ocean have many different types of - I will call them features - features that have characteristic types of motion associated with them. An example of such a feature is a hurricane, which has closed circulation around an eye. The hurricane then moves around, but pretty much no matter how it bounces around for a week or two, after a while the hurricane heads out to the north. Really they head off to the pole, and north or south depends on which hemisphere. What the hurricane does is transport heat from the tropics to the pole, and that is what the atmosphere and oceans do all the time. They are trying to reduce the contrast between warm and cold.
The hurricane is an example of a dynamical feature. There are many more dynamical features and many of them behave like waves. A hurricane behaves more like a spinning top; it’s a vortex. The atmosphere is full of waves, and professors like me torment students of meteorology with mathematical descriptions of these waves. There are many ways that waves come into being, but one way is because of air flowing over mountain ranges. You can imagine, more intuitively, a stream of water flowing over a rock. I have tried to convey this idea of a wave in the figure below.
Figure 1: A schematic picture that represents a wave in temperature. There are hot and cold parts of the wave. Do other climate bloggers draw such compelling figures?
What I have drawn with the dashed line is a “small” wave, perhaps a wave that would form in October. Then I draw, with the solid line, a bigger wave, perhaps a wave of December or January. These waves are always growing and decaying, sometimes moving a little bit to the east and the west. If we label the graph so that the bottom is the south, the top is the north, the left hand side is west and the right hand side is east, then we can imagine North America siting under this wave. If the left hand side is the Pacific Ocean and the right hand side is the Atlantic Ocean, then it sets up the story. If the wave grows in the west, the warm air pushes up to the north towards the pole, and the cold air is displaced south into the United States. This is not some random, made up thing, because 1) there are the Rocky Mountains that help make the wave, 2) the way the Earth rotates makes the air flow from west to east, 3) northern part of North America, we call it Canada here in the South, gets cold because the Sun is down, and 4) the Pacific Ocean starts to look warm as the continent starts to get cold.
If I hear people talking about how cold it is in the east of the U.S., I ask them to, using Wunderground.com of course, to look at what is going on in California and Alaska. If it is cold in the East, then usually it is warm in the West. And if this wave gets big enough, then it pushes up towards to pole, and it looks warm in the north, and the air that is displaced to the South, off the pole, looks cold. And to weak-kneed academics from Florida State University, it might look VERY cold. (What’s going on at Florida State? Must be all of that money that goes to cushy climate scientists.)
Even if there is a lot of carbon dioxide it still gets cold when the Sun goes down at the poles, and that cold air can get pushed down away from the pole, and there is still winter. In fact, if that push of air towards the pole is especially vigorous, then the cold air can get pushed to new places, and we have a record cold. If you are going to play the “record game,” look for new highs that might be paired with the new lows. (Jerry Meehl and colleagues did this recently, many, many more new highs. They concluded that it’s getting warmer.)
OK …. Let’s look at last December. It’s from the usual place the National Climatic Data Center.
Figure 2: Observations of temperature in December of 2009. The temperatures are represented as a difference (anomaly) from a 30 year average.
I recall Boulder, Colorado being really cold in December, as well as a blizzard in Baltimore. The map shows two cold centers over North America and Siberia. It’s pretty warm in Greenland and Alaska, and you can study the map more. Here is a link to the excellent discussion at the National Climatic Data Center. In the northern hemisphere this map shows a distinctive wave pattern. (There are good reasons that these waves appear as 1, 2, or 3 , but I will make you take dynamics on your own.)
I deliberately did this without referring to the Arctic Oscillation. I was driving around this afternoon thinking about that. If the pole has spent the last few years with its cold phase at the pole, and that cold phase was, by historical standards, not so cold, does that mean something? Just thinking on the way to Sprayberry's.
I posed the question at the end of a recent blog about what a record December blizzard in Baltimore might or might not say about climate change. Since then there have been record snow storms all over the northern hemisphere. At a very real level, a set of storms in one winter says NOTHING about global warming. Nothing. It surely does not say that global warming is abated, or of no concern. In fact, as a couple of comments pointed out, if the atmosphere is warmer, and the air is moister, if it is cold enough to snow, then there is a lot of snow. Others say that cold is cold.
There is still cold weather. Fact is, when the entire surface of the globe is considered, December 2009 was a warm month, in a warm year, of the warmest decade we have measured. (see this write up) Prepare in the next week for a bunch of storms to hit California. (Of course, that’s just a model prediction.) I wonder how many people will attribute those storms to El Nino, based on the science, but at the same time dismiss the far more certain science of global warming. I’ll be at the American Meteorological Society Annual Meeting in Atlanta. Our group has eight talks, so there is student stress and faculty worry. More and more climate at the meeting as we start to think about a National Climate Service.
And here is
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