Heat Waves (4) A Climate Case Study:
Heat Waves (4) A Climate Case Study:
In the last article I wrote that the extreme events of 2011 were providing us with the opportunity to think about climate and how to cope with a warming world. The U.S. is experiencing an extreme heat event this week (Masters @ WU). This heat wave is the consequence of a strong, stationary high pressure system over the central U.S., and it will move to the east over the next few days. Back on July 14th The Capital Weather Gang did a nice write up on the forecast of the heat wave. At the end of this blog are links to my previous blogs on heat waves and human health.
When thinking about weather, climate, and extreme events an important idea is “persistence.” For example, a heat wave occurs when there are persistent high temperatures. Persistent weather patterns occur when high and low pressure systems get large and stuck; that is, they don’t move. In the Figure below, you need to imagine North America and the United States. There is a high pressure center over the proverbial Heartland. With blue arrows I have drawn the flow of air around the high pressure system, and in this case moist air. There is moisture coming from the Gulf of Mexico and, in fact on the date when this was drawn, from the Pacific. This is common in the summer to see both the Gulf of Mexico and Pacific as sources of continental moisture.
Figure 1: Schematic of a high pressure system over the central United States in July. While generic, this is drawn to represent some of the specifics of 2011. The green-shaded area is where there have been floods in 2011. The brown-shaded area represents sustained drought in the southern part of the nation.
At the center of this high pressure system there is a suppression of rain, because the air is moving downward. This sets up a situation where the surface heats from the Sun’s energy. There is not much mixing and cooling, because of the suppression of the upward motion that produces rain. Hence, if this high pressure system gets stuck, then there is persistent heat. This is a classic summer heat wave.
Let’s think about it some more. There is lot of moisture being drawn around the edge of the high pressure system, and this moisture contributes to the discomfort of people. People – just a short aside about people: if we think about heat and health, then we are concerned about people’s ability to cool themselves. It is more difficult to cool people when it is humid because sweat does not evaporate. Suppose that in addition to this moisture, there is a region where the ground is soaked with water from flooding. Then on top of already moist air coming from the Gulf, there is local evaporation into the air being warmed by the Sun. If on the interior of the high, where the rain is suppressed, there is hot, wet air, then it becomes dangerous heat.
It’s not easy to derive a number that describes dangerous heat. But in much of the eastern U.S. a number that somehow combines temperature and humidity is useful. Meteorologists often use the heat index. It’s the summer time version of “it’s 98 degrees, but it feels like 105.” For moist climates, the heat index is one version of the “it feels like” temperature. Jeff Masters tells me that in Newton, Iowa yesterday, July 17, 2011, the heat index was 126 degrees F. (see here, and 131 F in Knoxville, Iowa on July 18)
Another measure of heat and humidity is the dew point; that is, the temperature at which dew forms, and effectively limits the nighttime low. The dew points in Iowa, South Dakota, Minnesota, and Wisconsin are currently very high and setting records. Here is a map of dew point for July 19, 2011.
Figure 2: Exceptionally high dew points centered on Iowa.
Now if I was a public health official, and I was trying to understand how a warming planet might impact my life, then here is how I would think about it. First, the Gulf of Mexico and the Pacific are going to be warmer, and hence, there will be more humid air. This will mean, with regard to human health for the central U.S., heat waves will become more dangerous, without necessarily becoming hotter. It is also reasonable to expect heat waves will become more frequent and last longer, because those persistent, stuck high pressure systems are, in part, forced by the higher sea surface temperatures. If I am a public health official here is my algorithm – heat waves are already important to my life, and they are likely to get more dangerous, more frequent, and of longer duration. But by how much? Do I need to know by how much before I decide on a plan for action?
If I think about the air being more humid, then I might expect to see trends in the heat index. I might expect to see trends in dew points, and trends in the nighttime minimum temperatures getting higher. (That’s where a greenhouse effect really matters.) I worry about persistent heat, warm nights, and the inability of people and buildings to cool themselves. I worry about their being dangerous heat in places where people and emergency rooms are not used to dangerous heat – not acclimated to heat – not looking for heat-related illness.
Let’s go back to the figure. Rain is suppressed in the middle of the high pressure system, but around the edge of the high pressure system it will rain; there will be storms. (see Figure 3 at the end) The air around the edge of high is warm and very wet. Wet air is energetic air, and it is reasonable to expect local severe storms. (See Severe Storm on Lake Michigan) And if the high pressure is persistent, stuck, then days of extreme weather are possible. If this pattern sets up, then there is increased likelihood of flooding. If I am that public health official, then I am alerted to the possibility of more extreme weather and the dangers thereof. But, again, can the increase of extreme weather be quantified? Do I need to quantify it before I decide on a plan of action?
Still with the figure - what about that region of extended drought and the heat from the high pressure system? Dehydration becomes a more important issue. As a public health official, I start to see the relation of the heat event to other aspects of the weather, the climate. I see the relation to drought. I see the flood, and it’s relation to the winter snow pack and spring rains.
So what I have presented here is to look at the local mechanisms of the weather – what are the basic underlying physics responsible for hot and cold, wet and dry – for moist air? If I stick to these basic physics, and let the climate model frame the more complex regional and global picture, what can I say about the future? Do I have to have a formal prediction to take action? Here in 2011, I see drought and flood and hot weather and warm oceans that interact together to make a period of sustained, dangerous heat. It does not have to “set a record” to convey the reality of the warming earth. It tells me the type of event that is likely to come more often, of longer duration, and of, perhaps, of greater intensity. If I am a public health planner, then I can know this with some certainty. The question becomes, how do I use that information in my planning?
r
Figure 3: Radar loop showing precipitation around the edge of the large high pressure system in the middle of the continent. July 19, 2011.
Previous Blogs on Heat Waves
Hot in Denver: Heat Waves (1)
Heat Waves (2): Heat and Humans
Heat Waves (3): Role of Global Warming
Reader Comments
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haha!
Should your rudimentary analogy were to occur in reality we wouldn't be talking about a 100-year event, which is why I said before, we do not have a long enough period of record to actually define a 100-year event. We simply don't. This is why when you begin on this premise of 100-year events it's inherently wrong.
You also make plenty of assumptions. First, I doubt you even know who I am or ever seen me post here before. I see you're rather new here and this is certainly my first interaction with you. So for you to throw around terms like denialist, without even having the slightest clue of my stance on this subject I can already tell that you're going to be rather cumbersome and arrogant. Second, I do believe it was you who made the coy remark about being 'blinded by ideology' so don't sass me about how amusing you find some supposed accusation. You're not going to be able to turn phrases like that with me, buddy.
So, with that in mind, let me answer your query. You don't, in fact, have to convince me that the planet has warmed. So your fingers can save some work there. You will, however, have to convince me that the climate is changing drastically. Hell, convince me that the climate of today is changing more drastically than it has during any other time during the Holocene.
Now Ossymon
How can you post such dribble?
Nobody in this video denounced their belief in God, smacked their lips as they spoke or raised one eyebrow as they spoke.
Yet....the sound of silence is thundering...ain't it?
I did on more than one occasion , and didn't like it!
Can you say ~ snack? :)
The warming problem has been ongoing. The results are the same.
There is no such thing as a long term coastline.
Yup, or back yards in some instances? :)
Tied for 8th place now.
I have been here in the background for a longer while than most, and I do appreciate what you bring to the table.
Fact + Reality = Truth as we currently understand it.
Thanks for the binocular view!
Out >>>
Wednesday, 20 July 2011 22:39
Polar wave has left up to nine feet of snow and possibly 6,500 people isolated.
President Sebastián Piñera declared much of La Araucania disaster areas on Wednesday, as four days of non-stop snowfall have isolated the region’s predominantly rural communities and wreaked havoc on basic utilities.
“The government has resolved to help those affected, especially those living in Lonquimay,” Piñera said on Wednesday. “We declare the zone a disaster area in order to give us greater tools to help our fellow Chileans.”
Lonquimay, the borough with the second most extensive area in Chile, was affected by a polar front that submerged the town of just over 10,000 into chaos.
Intermittent since Sunday, the snowfall has piled as high as nine feet in some areas. Although this part of the country is no stranger to the cold weather, Piñera described the current polar front as the worst the region has seen in 30 years.
Mayor Guillermo Vásquez told local press on Wednesday that temperatures had plunged to -23 degrees Celsius (-9.4 degrees Fahrenheit) in some of the more rural areas.
According to El Mercurio, sub-zero temperatures have frozen pipes, leaving most of the city without water.
Radiators were also reported to be shorting out and even the fuel in some vehicles’ gas tanks was frozen. The same source described the wave as taking a toll on local firewood supplies.
Moreover, help sent from authorities beyond the storm front has been stalled in delivery due to snow-covered roads. La Segunda reported 400 boxes being sent by the regional government to Lonquimay but only 25 reaching their destination.
“In four days we have had four months worth of snowfall,” said Regional Governor Miguel Mellado in an interview with Canal 13. “We’ve got a very difficult situation here.”
With 70 percent of the population living in rural areas, governor Miguel Mellado estimated that 6,500 people were isolated as a result of the storm.
The communities declared as part of the disaster area are: Lonquimay, Curralehue, Melipeuco, Curacautín, Pucón, Cunco, Vilcún and Villarrica.
By Ivan Ebergenyi (editor@santiagotimes.cl)
Copyright 2011 – The Santiago Times
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The term "denialist"--like all similar terms--is simple shorthand for those who a) dismiss the overwhelming evidence in support of AGWT, b) haven't offered their own viable alternate theory to explain the current ongoing climate changes, and c) refuse to even accept the possibility that the climate is changing. It may be true that I don't know who you are, but I've been dealing with this issue long enough that I don't need to read a person's CV to understand how they think; a handful of comments is more than enough to tell me.
Now, my interaction with you began after your statement that extreme weather events were not increasing in either frequency or severity, which is something I had claimed. To me, that fits item 'c'. I've not seen you say anything in support of AGWT, so I think I can safely assume item 'a'. Item 'b' just naturally follows, but if you have, indeed, offered such an alternate theory, and it's been independently tested and is still standing, I'm unaware of it; please forward the particulars, and I promise to retract the "denialist" bit PDQ.
Here's the thing: the claim of increasingly severe events isn't something I or others state lightly. There are decades of solid and rigrous observations by thousands of people behind it. And even if it were true as you state that "we do not have a long enough period of record to actually define a 100-year event."--which it's not; if it were, thousands of scientists and risk management types would be out of work--the long-predicted signals of rapid climate change are unmistakable. If people want to honestly debate about the extent to which our burning of fossil fuels has and is contributing to that change, fine. But to simply dismiss it all as coincidence or nothing out of the ordinary is demonstrably wrong.
In reading your comments here and in your blog, it's evident that your weather knowledge is deeper than that of many WU members. It's just as evident that you've a great command of the written word, which is also something that can't be said of many WU members. Kudos on both.
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While I appreciate your recognition I'm not particularly fond of your interpretation and comprehension of my comment. The point of my comment was the following: "...there are hundreds of examples of extreme weather of varying nature for various places at various stable lengths of time that can be compared against each other." So while there may be short-term changes in the nature of the extreme weather events, the overall number of extreme weather events remains fairly constant. And by fairly constant I mean despite all the ups and downs the filtered values don't leave a predictable range of values, as shown in this graph of US climate extremes.
So while the number of extreme events recently is higher than it was 40 years ago, for the US, it's roughly the same it was 90-100 years ago. There's essentially no way one can determine what the future of this graph will look like based in the information contained therein. This is why my statement was as such: "There isn't one shred of evidence that today's weather is any more extreme than any other period on record in question in any other region of the world" We can compare today's extreme's (1995-present) with extremes from 1910-1935 for the US and the numbers aren't that far apart with any difference easily explained by much improved data collection/increase in reporting stations. We can also look at the period of 1955-1975, a lull in extremes over the US, but should data exist for other areas of the globe that's compiled and analyzed similarly there would be regions where 1955-1975 were above their long term average of extreme weather events while we were below ours. Keeping this in mind, these aren't even 'stable' climatic periods, which is at a minimum 70 years in length to account for well-documented cyclical changes in the state of ocean basins.
Moving on from real data to a hypothetical. Let's say that the climate of Region 'A' for a 100-year period 'a' had 'X' number of extreme weather events, say 253. Meanwhile the climate of Region 'B' for a 100-year period 'b' had 'Y' number of extreme weather events, say 197.
If the following 100-year period Region 'A' has 212 and Region 'b' has 270. . . and the following 100-year period Region 'A' has 235 and Region 'B' has 233, using this example, over the 300 total years both Regions have 700 extreme events a piece, yielding an average of 233 extreme events per 100-year period.
Right now, using NCDC US data as a crutch, we're 17 years into the second 100-year period of Region 'B' and you're looking at the first 100-year period and comparing it against the increase you're seeing in the beginning of the second 100-year period and extrapolating that out to the third, while ignoring Region 'A'. And, in using this example, in the third 100-year period the number of extreme events at Region 'B' falls back to 'normal'. Furthermore, Region 'B' in having only 197 extreme events over the first 100-year period is going to have a smaller sample of events to be able to determine what exactly is a 100-year event. Using this example its still hard to define what a 100-year event would be considered and that's with three separate 100-year periods. This is why using weather events is, in my opinion, short-sighted when trying to win a climate debate. There's endless apples to put up against infinite oranges.
This is why I take issue with your use of the term denialist, which is an insult to those who actually do take the time out to educate themselves about this subject. So you twist my words to fit me into your 'c' category of denialism, which is "refusing to accept the climate is changing." Using my examples above, extreme weather events can change up and down many times over while the climate remains stable, which is why, again, using weather events to promote the theory of human-induced climate change (the greenhouse gas kind) is short-sighted. It's a lazy argument. How much effort does it take to copy and paste a news article about snowfall in the Atacama Desert?
But I shall go on. You say "I've not seen you say anything in support of AGWT, so I think I can safely assume item 'a'" but right I did write the following: "You don't, in fact, have to convince me that the planet has warmed. So your fingers can save some work there." So again, I ask, why throw around the term denialist? What am I denying in that statement?
And what about your 'b' point? Very simply put, AGWT is overstated. It's occurring but not at the rate which is claimed and won't reach the values modeled. I don't know what else you want me to say here because real world data does not fall into line with GCM's. It just doesn't.
So from here on out you may just want to study a person's curriculum vitae before making an absolute fool of yourself through presumptuous comments.
treat anxiety
There is a debate about who is (or are) to blame for this dangerous phenomenon: what are the causes of global warming? Are them the industry CO2 emissions? Are them other gases, maybe made by animals or producted in another natural way, anyway? Is it the whole mankind itself, with its own way of using and abusing the planet Earth?
We think it does not really matter, because the problem exists (yes, global warming is REAL and it is happening) and is useless to look for someone to blame for it: instead, we need to act: everybody should do what is in his/her possibilities to DO something: we as humanity can still slow down the rising of temperature on the planet.
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