10 February 2010

Three feet of global warming

Now that that idiotic line is out of the way, let's do some thinking about what we should expect from climate change. I've been calling it climate change, rather than 'global warming', since at least 1993. A major reason being that there is more to climate than temperature, and changing temperatures affect more than just how hot it gets.

One of the things that temperature affects is how much water can be in the atmosphere. The hotter it is, the more water vapor you can have in the air before it starts to form a cloud. So one very simple expectation that we could have on climate is that warmer = more humid (absolute humidity that is). Since there's more than temperature to climate, we don't really expect it'll work out that simply everywhere, all the time. But it tells us one line of research to take -- look to see what has been happening to atmospheric moisture content.

Jeff Masters has written this up at his blog on the Weather Underground, and I'm relying partly on his notes in my write up.
The research has been done, and you can find a summary of it in chapter 3 of the 4th IPCC report; section is the one you want.  As usual, I prefer and recommend going to the scientific papers that are cited, rather than to rely only on the summary.  One of the papers to look up is Trenberth, K.E., J. Fasullo, and L. Smith, 2005: Trends and variability in column integrated atmospheric water vapor. Clim. Dyn., 24, 741−758. The conclusion being that atmospheric water vapor has increased about 5% over the past century, and 4% since 1970.

In other words, what we expected from a warmer earth is what is observed.  Score (another) one for our understanding of the climate system.

In looking at weather, we also tend to look at water vapor as a severe weather sign.  It takes a lot of energy to evaporate water.  Conversely, if you get it to condense, you release a lot of energy.  The main place the energy can go is to make the air warmer.  Warmer air rises (giving us motion*).  It also makes more water condense.  It is this process that powers hurricanes, or, less dramatically, thunderstorms.  A second expectation we have had is more water vapor = stronger storms.  This was documented for rainfall in Karl, T.R., and R.W. Knight, 1998: Secular Trends of Precipitation Amount, Frequency, and Intensity in the United States. Bull. Amer. Meteor. Soc., 79, 231–241.

*The upwards motion of air in a storm has to be balanced by inwards motion at the bottom -- the air that is going up has to come from somewhere.

So, score a second point for our understanding of the climate system.

It wasn't just rain that was expected to show this kind of tendency.  Snow comes from a similar meteorological setup -- rising air condensing moisture and dropping it as precipitation.  But snow is much more variable.  1 inch* of water equivalent (namely, take the snow and melt it, then see how deep it is) snow can be anything from 3 inches snow (an incredibly heavy/thick snow) to 20 (a very dry, powdery snow).  We normally guess 10:1.  But one thing this means is that 30 inches of snow in one year may not be the same as 30 inches in another year.  This gives even more variability to the numbers than you'd otherwise see.

* replace inch with cm, or meters, if you like.  These are matters of proportion, so it doesn't matter what unit you use.

Nevertheless, people have been researching it since at least the 1990s (
Score a third for our understanding of the climate system.
The thing is, warmer climate does not necessarily mean nicer.  Nor does it necessarily mean worse.  You have to do some thinking about the system, preferably combined with observing it, to discover what the nature of the changes will be.  And then decide whether those changes are nice or not.

The current blizzard (NWS has issued a blizzard warning for my area), and the weekend's major snow, are indeed things expected for this area from climate change.  The power failures, loss of cable tv, people trapped at home while in need of medication, and so on, that are occurring are all, also, expected things for climate.  It being more common is expected from our understanding of climate change.


Hank Roberts said...

Worth a look:
by Kim Stanley Robinson (Author)

Robert Grumbine said...

Thanks for the suggestion. I have the first two books of his Mars trilogy on my 'to read' bookcase. Maybe this will help me to get to reading them. I've heard excellent things about them, and have enjoyed his other writings that I've read.

Andy Harris said...

I've been calling it "Climate Change" ever since whenever. But some folks seem to think it's a new term invented by climatologists to cover their bases now that global average temperatures aren't going up year-on-year. My favorite response is to ask them what the initials IPCC stand for...

Deech56 said...

Glad to see this appear as a lead article on Yahoo. Looks like Jeff Master's article had traction.

Robert Grumbine said...

I think they answer 'climate conspiracy'. At least I've heard that answer a time or two.

Glad to see Jeff's article reaching more widely. He's been doing good work for a long time.

carrot eater said...

Thanks for the links. For now, my only comment is that one should be careful when saying "more of weather event x is consistent with climate change." Use the wrong words, and it can quickly sound like "this specific instance of weather event x happened because of climate change", and that's a statement that can not be supported. I think it's difficult to do anything but look at trends.

I'm also wary of forgetting about regional patterns. Globally, we expect more precipitation, and yet we also expect some regions to have more droughts. This is clearly complicated, and once people figure out the nuances they'll be left confused about why the simple explanations didn't mention the nuance.

John N-G has his own take, which could be of interest. (the URL is messy, but I'm not sure how to clean it up in this format)

Anonymous said...

My question is: If more Water Vapor = More clouds, and more cloud cover = decrease in surface temperatures, then how do you have warming?

Robert Grumbine said...

You're right that we need to be careful. I think I stayed on the accurate side of the line -- that we expect more of this kind of thing from climate change. There's a second line to consider, though. Namely, if we spend too much time talking about how any specific storm can't be directly/solely attributed to climate change, it leaves the impression that this storm had nothing to do with climate change. I discovered this the hard way, as my cautious, conservative nature had put me on the wrong side of this line.

You're also right to be concerned about regional effects. The Chagnon paper is exactly about that. Our region is one of the ones that can expect more severe snows from climate change.

I'll take this up in a full post, since it's worth a longer consideration. The shorter, which you can check by looking at section 3.4.3 of the IPCC report linked to above, is that neither of your linkages are obviously true. More water vapor (indeed observed) has not lead to more clouds. Nor do more clouds necessarily mean decrease in surface temperature. This latter is obvious if you're in a cold weather climate and compare what happens to temperatures on a cloudy day versus a clear day.

There's more to the story than this, which is while it'll be a full post of its own. Thanks for the question.

cms said...

This line of argument certainly would seem to make a certain amount of sense. All the climate models depend on co2 to trigger an increase in water vapor to create any significant warming as co2 in and of itself is not potent enough to explain the apparent warming. Hence the question of the effects of clouds has always been problematic. At any rate I quess the question has to be asked what is special about this winter that makes it stand out from the last 10 winters when the degree of warming was more or less the same. One other question, in a warming world one would not be surprised to see more snow given this theory, but the increased heat that this theory depends on would also suggest fewer snow storms in ratio to rain and movement of the tracks closer to the poles. Would it not?

Robert Grumbine said...

cms: I look at it this way. Snows (and thunderstorms) are touchy things. Among other things, this means you don't have a lot of them. That means the signal of having more of the extreme events is not a simple steady increase -- we only have one big snow in a normal year here, and many years it is zero -- the increase shows up as having more years with one big snow, and, now, having a year with two big snows. A little differently, let's say that we do average 1 big snow a year. A 10% increase in severe snows doesn't mean that we get 1.1 such snows. It means that over 10 years, we get 11 big snows. So this year, in a sense, was our turn for getting the additional big snow storm.

The storm tracks and rain versus snow are the reason for why you want to look to the regional effects of climate change. Some areas can warm enough to seldom get snow storms, for instance. DC is not one of them. And when we do get snow, we can expect to get the severe storms more frequently.

carrot eater said...

I had a look at the Changnon paper, and I think the data are too noisy to say much of anything, in terms of trends. Of course, that's just my eyeball; I didn't do any formal statistics on it.

Maybe some more obvious trend will appear over time, I don't know.

Robert Grumbine said...

Certainly a messy set of data. It's for times when eyeballs might miss something that we invented statistics. Still, more time will give us better data, and more obvious conclusions.