Climate Climate & Energy

‘Historically, CO2 never caused temperature change’–Not so

(Part of the How to Talk to a Global Warming Skeptic guide)

Objection: In the geological record, it is clear that CO2 does not trigger climate changes. Why should it be any different now?

Answer: Given the fact that human industrialization is unique in the history of planet earth, do we really need historical precedent for CO2-triggered climate change before we accept what we observe today? Surely it is not far-fetched that unprecedented consequences would follow from unprecedented events.

But putting this crucial point aside, history does indeed provide some relevant insights and dire warnings.

From the U. of Arizona

The U. of Arizona put together an impressive seminar series on climate change this past fall. There were seven talks by different U of A professors, covering almost all important aspects of the "climate change problem." The talks are now online.

I have a video iPod, and I downloaded the seminars and watched them during my recent trip to the AGU meeting. It's a worthwhile way to pass a 4-hour plane trip. If you want to learn more about climate change, I recommend you check them out. (They also have audio-only versions.)

‘Geological history does not support CO2’s importance’–Just not true

(Part of the How to Talk to a Global Warming Skeptic guide)

Objection: Over the last 600 million years, there hasn't been much correlation between temperatures and CO2 levels. Clearly CO2 is not a climate driver.

Answer: While there are poorly understood ancient climates and controversial climate changes in earth's long geological history, there are no clear contradictions to greenhouse theory to be found.

‘CO2 doesn’t lead, it lags’–Turns out CO2 rise is both a cause and an effect of warming

(Part of the How to Talk to a Global Warming Skeptic guide)

Objection: In glacial-interglacial cycles, CO2 concentration lags behind temperature by centuries. Clearly, CO2 does not cause temperatures to rise; temperatures cause CO2 to rise.

Answer: When viewed coarsely, historical CO2 levels and temperature show a tight correlation. However, a closer examination of the CH4, CO2, and temperature fluctuations recorded in the Antarctic ice core records reveals that, yes, temperature moved first.

Nevertheless, it is misleading to say that temperature rose and then, hundreds of years later, CO2 rose. These warming periods lasted for 5,000 to 10,000 years (the cooling periods lasted more like 100,000 years!), so for the majority of that time (90% and more), temperature and CO2 rose together. This remarkably detailed archive of climatological evidence clearly allows for CO2 acting as a cause for rising temperatures, while also revealing it can be an effect of them.

What do the climate scientists think?

No Se Nada had an interesting post last week claiming climate scientists are starting to worry that they've oversold climate change:

What I see is something that I am having a hard time labeling, but that I might call either a "hangover" or a "sophomore slump" or "buyers remorse." None fit perfectly, but perhaps the combination does. I speak for (my interpretation) of the collective: {We tried for years - decades - to get them to listen to us about climate change. To do that we had to ramp up our rhetoric. We had to figure out ways to tone down our natural skepticism (we are scientists, after all) in order to put on a united face. We knew it would mean pushing the science harder than it should be. We knew it would mean allowing the boundary-pushers on the "it's happening" side free reign while stifling the boundary-pushers on the other side. But knowing the science, we knew the stakes to humanity were high and that the opposition to the truth would be fierce, so we knew we had to dig in. But now they are listening. Now they do believe us. Now they say they're ready to take action. And now we're wondering if we didn't create a monster. We're wondering if they realize how uncertain our projections of future climate are. We wonder if we've oversold the science. We're wondering what happened to our community, that individuals caveat even the most minor questionings of barely-proven climate change evidence, lest they be tagged as "skeptics." We're wondering if we've let our alarm at the problem trickle to the public sphere, missing all the caveats in translation that we have internalized. And we're wondering if we've let some of our scientists take the science too far, promise too much knowledge, and promote more certainty in ourselves than is warranted.}

I was also at the AGU meeting, and here's my take:

There is no proof in science, but there are mountains of evidence

(Part of the How to Talk to a Global Warming Skeptic guide)

Objection: Correlation is not proof of causation. There is no proof that CO2 is the cause of current warming.

Answer: There is no "proof" in science -- that is a property of mathematics. In science, what matters is the balance of evidence, and theories that can explain that evidence. Where possible, scientists make predictions and design experiments to confirm, modify, or contradict their theories, and must modify these theories as new information comes in.

Water vapor is indeed a powerful greenhouse gas, but there is plenty of room for CO2 to play a role

(Part of the How to Talk to a Global Warming Skeptic guide)

Objection: H2O accounts for 95% of the greenhouse effect; CO2 is insignificant.

Answer: According to the scientific literature and climate experts, CO2 contributes anywhere from 9% to 30% to the overall greenhouse effect. The 95% number does not appear to come from any scientific source, though it gets tossed around a lot.

Warning: techno-engineering speak ahead

Amory Lovins is rightfully admired by environmentalists. But nobody is right all the time, and the hydrogen path is one of his few mistakes. He summarizes his argument for hydrogen in Twenty Hydrogen Myths (PDF). More extensive discussion is embedded in his book Winning the Oil Endgame (book-length PDF).

His basic proposal:

‘Climate scientists dodge the subject of water vapor’–No, they really don’t

(Part of the How to Talk to a Global Warming Skeptic guide)

Objection: Climate scientists never talk about water vapor -- the strongest greenhouse gas -- because it undermines their CO2 theory.

Answer: Not a single climate model or climate textbook fails to discuss the role water vapor plays in the greenhouse effect. It is the strongest greenhouse gas, contributing 36% to 66% to the overall effect for vapor alone, 66% to 85% when you include clouds. It is however, not considered a climate "forcing," because the amount of H2O in the air basically varies as a function of temperature.

‘We are just recovering from the LIA’–Why should we expect this to happen?

(Part of the How to Talk to a Global Warming Skeptic guide)

Objection: Today's warming is just a recovery from the Little Ice Age.

Answer: This argument relies on an implicit assumption that there is a particular climatic baseline to which the earth inexorably returns -- and thus that a period of globally lower temperatures will inevitably be followed by a rise in temperatures. What is the scientific basis for that assumption?