Models and Books

Working as a summer student continues to be rewarding. I get to spend all day reading interesting things and playing with scientific software. What a great deal!

Over the weekend, I ran the “Global Warming_01” simulation from EdGCM, which is an old climate model from NASA with a graphical user interface. Strangely, they don’t support Linux, as their target audience is educators – I doubt there are very many high school teachers running open-source operating systems! So I ran the Windows version on my laptop, and it took about 36 hours. It all felt very authentic.

Unfortunately, as their Windows 7 support is fairly new, there were some bugs in the output. It refused to give me any maps at all! The terminal popped up for a few seconds, but it didn’t output any files. All I could get were zonal averages (and then only from January-March) and time series. Also, for some reason, none of the time series graphs had units on the Y axis. Anyway, here are some I found interesting:

CO2 concentrations increase linearly from 1958 to 2000, and then exponentially until 2100, with a doubling of CO2 (with respect to 1958) around 2062. (This data was output as a spreadsheet, and I got Excel to generate the graph, so it looks nicer than the others.)

Global cloud cover held steady until around 2070, when it decreased. I can’t figure out why this would be, as the water vapour content of the air should be increasing with warming – wouldn’t there be more clouds forming, not less?

Global precipitation increased, as I expected. This is an instance where I wish the maps would have worked, because it would be neat to look at how precipitation amount varied by location. I’ve been pretty interested in subtropical drought recently.

Albedo decreased about 1% – a nice example of the ice-albedo feedback (I presume) in action.

I also ran a simulation of the Last Glacial Maximum, from 21 thousand years ago. This run was much quicker than the first, as (since it was modeling a stable climate) it only simulated a decade, rather than 150 years. It took a few hours, and the same bugs in output were apparent. Time series graphs are less useful when studying stable conditions, but I found the albedo graph interesting:

Up a few percent from modern values, as expected.

It’s fairly expensive to purchase a licence for EdGCM, but they offer a free 30-day trial that I would recommend. I expect that it would run better on a  Mac, as that’s what they do most of the software development and testing on.

Now that I’ve played around with EdGCM, I’m working on porting CESM to a Linux machine. There’s been trial and error at every step, but everything went pretty smoothly until I reached the “build” phase, which requires the user to edit some of the scripts to suit the local machine (step 3 of the user guide). I’m still pretty new to Linux, so I’m having trouble working out the correct program paths, environment variables, modules, and so on. Oh well, the more difficult it is to get working, the more exciting it is when success finally comes!

I am also doing lots of background reading, as my project for the summer will probably be “some sort of written something-or-other” about climate models. Steve has a great collection of books about climate change, and keeps handing me interesting things to read. I’m really enjoying The Warming Papers, edited by David Archer and Ray Pierrehumbert. The book is a collection of landmark papers in climate science, with commentary from the editors. It’s pretty neat to read all the great works – from Fourier to Broecker to Hansen – in one place. Next on my list is A Vast Machine by Paul Edwards, which I’m very excited about.

A quick question, unrelated to my work – why do thunderstorms tend to happen at night? Perhaps it’s just a fluke, but we’ve had a lot of them recently, none of which have been in the daytime. Thoughts?

The Best Analogies Ever

An analogy is a powerful tool in science communication. Here are two of my favourites to do with climate change.

The first is of my own creation (although it isn’t too original) and came about after I had presented to high school students a few times. As anyone taking high school physics learns pretty quickly, when using the formula F=ma, to find the net acceleration (the actual, observable result) you must always use the net force. If three people are pushing a box three different directions, you can’t just take one person into account. You have to look at all of them to see which way the box will move, and how fast.

Similarly, to analyze observed climate change, you can’t just take one forcing into account. You can’t only look at greenhouse gases and expect that they will track perfectly with the global temperature. You have to look at what the sun is doing, what aerosol levels are doing, where the ENSO cycle is. Climate is influenced by a combination of factors, and it will never track perfectly with any one. But if only one is changing significantly, and the others are staying pretty much steady, it’s obvious which way the box is going to move.

I found the second analogy in David Archer’s book Global Warming: Understanding the Forecast. I’m only two pages in and already I found something that I want to share here!

[The energy budget/climate equilibrium] is analogous to a sink with water flowing in from a faucet. The faucet fills the sink at some constant rate, while outflow down the drain depends on the water level in the sink. The sink fills up until water drains out as fast as it comes in.

It is possible to change the average temperature of the Earth by altering the energy flow either coming in or going out. In our sink, one way to raise the water level is to turn up the faucet and wait a few minutes. The water will rise until it finds a new equilibrium water depth. We can also alter the water level by partly constricting the drain. Egg shells and orange peels work well for this purpose. If the drain is partly obstructed, the equilibrium water level will rise.”

Brilliant, no? I think that Greg Craven had a similar analogy (the “bathtub”) in his book.

What are your favourite analogies – of your own creation or that you heard elsewhere? Share them in the comments below.