Global Warming Fact-Sheet

Via NASA’s Earth Observatory mailing list my attention was drawn to their newly freshened Global Warming fact sheet, written by Holli Riebeek (dated 11 May 2007), and I wanted to take this space to draw more attention to it.

As most of my readers will know, there’s a great deal of misleading disinformation and obfuscation in our current global-warming “debate” here in the US, a concerted effort by some business and political forces to confuse the public into thinking that there is no scientific consensus on anthropogenic climate change, i.e., global warming because of carbon-dioxide (and other greenhouse gas) emissions being pumped into the atmosphere from human sources.

There is consensus among scientists working in the field; how and why and what it all means is nicely summarized in this short, succinct, and accurate fact sheet. Without being patronizing and without distorting the information, it’s a clear and understandable presentation of what we (the science “we”) know about global warming, the trends, the causes, and the likely or possible consequences.

In particular, the author addresses this question:

But why should we worry about a seemingly small increase in temperature? It turns out that the global average temperature is quite stable over long periods of time, and small changes in that temperature correspond to enormous changes in the environment.

It keeps popping up as a joke, especially during wintertime or a cool day in the summer, when people casually say “I wouldn’t mind a bit if it were a degree or two warmer”.

What is missing in this superficial understanding is a realization that, overall, the Earth’s temperatures are quite stable on average, and that very small changes in average temperatures can have very, very large effects on weather patterns and that those changes in weather patters lead to subsequently surprisingly large shifts in the weather we get at any particular location. In other contexts this is sometimes called “the butterfly effect”: consequences can be out of all proportion (i.e., nonlinear) to the causes. Ice ages have been accompanied by changes in the average global temperature of only about 5°C — which doesn’t sound all that big.

This is discussed quite well in the fact sheet, and summarized (in part) this way:

Potential Effects

The most obvious impact of global warming will be changes in both average and extreme temperature and precipitation, but warming will also enhance coastal erosion, lengthen the growing season, melt ice caps and glaciers, and alter the range of some infectious diseases, among other things.

For most places, global warming will result in more hot days and fewer cool days, with the greatest warming happening over land. Longer, more intense heat waves will become more frequent. High latitudes and generally wet places will tend to receive more rainfall, while tropical regions and generally dry places will probably receive less rain. Increases in rainfall will come in the form of bigger, wetter storms, rather than in the form of more rainy days. In between those larger storms will be longer periods of light or no rain, so the frequency of drought will increase. Hurricanes will likely increase in intensity due to warmer ocean surface temperatures.

It’s a good piece and a few minutes invested in reading through it will arm the reader with better understanding that will help cut a confident path through the thicket of opinions and misinformation that have clogged the information superhighway on the issue lately.

Exponential Growth

Here’s a quick question with a pedagogical purpose. Would you buy a battery from this man?

“The energy capacity of batteries is increasing 5 percent to 8 percent annually, but demand is increasing exponentially,” Mr. Cooper[, vice president for business development of PolyFuel Inc., a company working on battery technology,] said.

[Damon Darlin and Barnaby J. Feder, "Need for Battery Power Runs Into Basic Hurdles of Science", New York Times, 16 August 2006.]

Forget basic hurdles of science, the basic hurdle here would seem to be an executive in a technical industry who doesn’t understand what exponential growth is.

In short: growth of something that is proportional to the current size of that thing is exponential growth. Thus, demand for batteries that grows 5% to 8% annually — i.e., 0.05 to 0.08 times current demand — is exponential growth.

The constant that governs how fast something grows exponentially is the “growth rate”. Small growth rate = slow growth; large growth rate = fast growth. In symbols, an exponential function of time, t, is

f(t) = A × e^st

where A is a constant amplitude and s is the growth rate. If s is relatively large, f(t) changes values rapidly; is s is very small, f(t) changes values slowly. If s happens to be a negative number, f(t) disappears over time, quickly or slowly depending on the size of s. The letter ‘e’ represents the base of natural logarithms. Why it shows up in the exponential function takes some explanation; for now, just think of it as a constant number nearly equal to 2.17 and don’t lose any sleep over it.^*

Many people think “exponential growth” means “grows really, really quickly”, but this is a misconception. It is true that power-law growth is generally faster than algebraic growth (for instance, multiplying a number over and over again by some number, say, 47) all other things being equal, but any particular exponential function will grow slowly or quickly depending on its growth rate. Think of a $0.15 deposit in a bank account that pays compound interest; the account grows exponentially but it’s going to be awhile before you’re a millionaire.

So please, please can we stop saying things like “Wow! That growth is so exponential! It’s huge!”

And if I were you, I don’t think I’d buy a battery from Mr. Cooper, either.
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^* In fact, ‘e’ is irrational (not expressible as the fraction of two integers, or whole numbers) and transcendental (not the solution to an algebraic equation, which is to say a polynomial with rational coefficients and integer powers). But that’s a lot of other story that we needn’t go into right now.

Don’t Need no Science

Is Bob Park’s What’s New for 11 May 2007, this quick summary of the Republican presidential-candidate field, demonstrating that science is not a conservative, traditional-family value and that Ars Hermeneutica has its work cut out for it:

BELIEFS: SCIENTIFIC ILLITERACY REACHES CLEAR TO THE TOP.
Last week at the Republican presidential debate, moderator Chris Matthews asked whether any of the wannabes did not believe in evolution. Sam Brownback, Mike Huckabee and Tom Tancredo raised their hands. John McCain waffled: “I believe in evolution, “he said, “but I also believe when I hike the Grand Canyon that the hand of God is there also.” The Sunday Washington Post pointed out that they weren’t that far from mainstream. In an ABC poll a year ago, 61% thought Genesis is literally true.

The Brightest Supernova Ever

Here’s the lead from the NASA release about an observation with the Chandra X-Ray [orbiting] Observatory of “the brightest supernova ever“:

May 7, 2007: The brightest stellar explosion ever recorded may be a long-sought new type of supernova, according to observations by NASA’s Chandra X-ray Observatory and ground-based optical telescopes. This discovery indicates that violent explosions of extremely massive stars were relatively common in the early universe, and that a similar explosion may be ready to go off in our own galaxy.

“This was a truly monstrous explosion, a hundred times more energetic than a typical supernova,” said Nathan Smith of the University of California at Berkeley, who led a team of astronomers from California and the University of Texas in Austin. “That means the star that exploded might have been as massive as a star can get, about 150 times that of our sun. We’ve never seen that before.”

Astronomers think many of the first stars in the Universe were this massive, and this new supernova may thus provide a rare glimpse of how those first generation stars died. It is unprecedented, however, to find such a massive star and witness its death. The discovery of the supernova, known as SN 2006gy, provides evidence that the death of such massive stars is fundamentally different from theoretical predictions.

The photographs accompanying the release are extraordinary, showing that the supernova was as bright as the core of its galaxy — that’s bright! It seems this one was bright enough that some light even reached the mainstream press, as in this story from the L.A. Times.

As additional background, may I point out my own posting called “A Star Explodes in Slow Motion“, which feature an informative excerpt from Galileo’s Finger: The Ten Great Ideas of Science, by Peter Atkins.

Noctilucent Clouds

For those who fear that there may be nothing left in the world to discover (hardly a chance!), consider this item from Space Weather News for April 25, 2007:

NIGHT-SHINING CLOUDS: NASA’s AIM spacecraft left Earth Wednesday on a two-year mission to study mysterious noctilucent (night-shining) clouds. Hovering at the edge of space, these clouds were first noticed in the 19th century; they are remarkable for their electric-blue color and sharp, wavy ripples. In recent years noctilucent clouds have been growing brighter and spreading. What causes them? Theories range from space dust to global warming. For the next two years, AIM will scrutinize the clouds from Earth orbit to learn what they may be telling us about our planet. Visit http://spaceweather.com for more information about the AIM mission, pictures of noctilucent clouds and observing tips.