Friday, October 08, 2010

Clearing up climate confusion from today's Al Stahler Union column on Venus

If you perused today's The Union science column about Venus, "Many Ways To Shine"(no link), by Union columnist and KVMR science host Al Stahler, you might have come away thinking that the CO2 we're spewing into the air here on Planet Earth isn't so important.
- which is false, so in this post I'll explain how the column could mislead someone, and how the reality differs.

Here's the passage that could misdirect. Read it carefully, think about the message it sends:
"Orbiting closer to the sun than Earth, Venus long ago lost her oceans to evaporation, loading the air with a powerful greenhouse gas. Water vapor. Venus grew hot.

Without oceans, Venus was unable to sequester her carbon dioxide. If not as powerful as water vapor, carbon dioxide [CO2] is, too, a greenhouse gas.

Venus remains hot today, her surface averaging some 860 degrees Fahrenheit."
OK, quiz time. Based on this passage -

1. Which greenhouse gas makes Venus hellaciously hot - water vapor, or CO2?
2. Which greenhouse gas should we be more concerned about here on earth - water vapor, or CO2?

To me, the passage suggests both answers would be "water vapor" (not CO2) - which just ain't so.

From RealClimate's post Lessons from Venus -
"...the atmosphere of Venus has as much mass as about 100 Earth atmospheres, and it is almost pure CO2. This accounts for its very strong greenhouse effect."
How to reconcile this with the Union article passage above - which talks about the oceans of Venus evaporating into water vapor, and about water vapor being a more powerful greenhouse gas than CO2 - and each sentence of which, AFAIK, is accurate?

RealClimate explains the larger picture:
"Venus succumbed early to a "runaway water vapor greenhouse"...much of the ocean evaporated into the atmosphere.
[as the Union article mentions.]

Once this happens, it is easy for the water vapor to decompose in the upper atmosphere...
the Union article mentions, but many paragraphs later, in an entirely different context.]

Once water is lost, the reaction that turns carbon dioxide into limestone can no longer take place,
[as the Union article mentions.]

so CO2 outgassing from volcanoes accumulates in the atmosphere instead of staying bound up in the rocks.
[as the Union article implies.]

The end state of this process is the current atmosphere of Venus... essentially no water in the atmosphere and essentially the planet’s whole inventory of carbon in the form of atmospheric CO2."
[ which the Union article does not mention at all.]
This omission would be fine - you can't convey every nuance in a column, after all - if there weren't an important lesson for us humans in the parallels between the atmosphere of Venus (packed to the gills with carbon dioxide) - and the changes we're making to the atmosphere of Earth (packing it with carbon dioxide).

Which is not to say that we're facing runaway global warming that'll yield another Venus, the RC hosts clarify:
"The runaway greenhouse that presumably led to the present Venus is an extreme form of the water vapor feedback that amplifies the effect of CO2 increases on Earth. Is there a risk that anthropogenic global warming could kick the Earth into a runaway greenhouse state? Almost certainly not. ..."

OK, on to our second quiz question, "Which greenhouse gas should we be more concerned about here on earth?"

The Union article's [untangled] statement, "Carbon dioxide [CO2] is not as powerful a greenhouse gas as water vapor", implies that the answer is "water vapor". But this is misdirection, since with water vapor vs. CO2, "more powerful" does not translate to "more important" (as the excellent explains here). Even though CO2 is a less powerful greenhouse gas in and of itself, it's more important than water vapor because of the processes it drives.

So the reader's being misled if you just mention the "more/less powerful" relation; you're telling her something that's literally true but that paints a false picture; it's not the right metric for grasping the problem.

(It's kind of like the 1960s nuclear power PR folks telling us that the amount of nuclear waste per person per year would be equivalent - in mass - to a couple of aspirin in your medicine cabinet; really not a helpful metric, if these "aspirin" could sicken everyone in the neighborhood.
(And no, I don't want to discuss nuclear power here; I probably support it more than you do.)

The so-called skeptics (who aren't true skeptics) ignore the huge difference in how long extra water vapor vs. CO2 stays up in the atmosphere - added water vapor rains back out within days, while added CO2 takes centuries to come out. And CO2 is the climate change driver, the "control knob" of climate, that - by the warming it causes by itself - causes the atmosphere to *hold onto* more water vapor, which amplifies the just-CO2-only-caused warming.
(all of which the article will explain better than I've done here.)

Did that help?
(Was it clear, or clear as mud?)

I want to keep doing these "corrective" posts, and I want them to be useful...

1 comment:

Don Pelton said...


Thanks for this excellent and -- yes -- very clear post. I appreciate the considerable effort you put in to deconstructing what is, after all, a nuanced misdirection in The Union article.

I hope you will do more of this.

Very useful.