April 2011 Archives

Debunk your skeptic 101

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Last week I attended in UQAR a long presentation given by a climate modeler from the OURANOS consortium on regional climatology and adaptation to climate change, based in Montréal, Québec. I picked among the wealth of information provided a survival kit to use in any occasion you face a so-called skeptic. They are inconveniently widespread now, even among your family, friends or neighbors, the federal government, and worse, they are spreading outside of the US into Canada as I'm writing this blog entry...


So, skeptics cherish a handful of "arguments", which are not (only) bad or misunderstood science, but are essentially outdated science, and when you'll face it you'll have to debunk it! The skillful skeptic will probably not deny the global increase in atmospheric CO2 since the beginning of industrialization (Documented first by Callendar in 1938), as Andy recently pointed out, but rather deny its impacts on climate through a short list of arguments, some of them being:


"Climate changes are forced by the sun (not my SUV)"

This argument is incomplete and out of date. This was a legitimate scientific hypothesis formed by Milankovic in the 40's. He thought that the intricate interplay of the precession, obliquity and eccentricity of the earth altered the radiative forcing from the sun, and thus the climate. However as early as the 70's with the help of the first ice cores (some made by Milankovic himself...), it was proven that this effect would essentially modify the seasonality of the sun forcing, and not the total quantity of radiation reaching the earth which is what is important in the radiative balance of the planet. Moreover it could not explain a number of fast historical climate changes events, nor the warming trend of the last 30 years.


The more subtle skeptic will try to ensnare you in some apparently complex issues like:

"H2O vapor already blocks infrared wavelengths, so an increase in CO2 (by my SUV) won't change the earth's radiative balance"

This argument is of the oversimplified type, and is actually wrong. To better get the importance of infrared absorption by gases, please refer to this pages for a quick introduction of radiative balance of the planet and greenhouse effect. Basically, H2O doesn't absorb at all the infrared wavelengths that CO2 can absorb. So despite water vapor being overwhelmingly abundant, there is still room for an increase in heat in the atmosphere solely due to increased infrared absorption by increased atmospheric CO2. Plass realized this in the early 50's after a careful study of infrared wavelengths absorption by water vapor and other gases. He published as early as 1956 all of the major figures now confirmed by measurements and advanced numerical models in the most recent IPCC science reports: temperature increase by year 2000, temperature increase if doubling of CO2, etc. Plus, as Andy has just shown, an increase in heat due to CO2 will lead to an increase in water vapor, ad hence a positive (more warming) feedback...


And about feedback and climate numerical models, what about:

"Models are oversimplified, don't take in to account water vapor (!) and overlook feedback."

Well nowadays climate models are FAR from simple, and beyond their physical and numerical structure, the way they are used presently (ensemble approach, with powerful statistical methods to get meaningful confidence interval etc.) are far more advanced than usually thought. There is a widespread misconception equating the problem of predicting weather (a chaotic monster) and climate (the statistical resultant of many weather events)...

For water vapor, it was first modeled in 1967 by Manabe & Wetherald, and there is simply NO modern model that overlook it. Finally, most climate models now incorporate feedback from land (including vegetation, wild fires, volcanoes etc.), the ocean and the cryosphere (ice).


I leave you with a very nice animation presenting the current state-of-the-art climate modeling. This animation was made for the Pierre-Simon Laplace Institute of France, so the comments are in French, but I can assure you it's a great piece of climate modeling for the layman!


Time lapse

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How can it be that a month has passed since the last entry?  Indeed, a poor showing by the seascapers.

Speaking of lapsing time...

Somehow, lost in my slurry of scientific ideas, I forgot to post this video last summer after our cruise.  Here it is: an afternoon's worth of sampling, collapsed into a minute of time-lapse imagery.

-Nick Record, signing off

Time lapse sampling near Mount Desert Island

Water Vapor Feedback and Global Wetting

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Even the most ardent climate change denier acknowledges that CO2 concentrations in the atmosphere have increased.  Most will even admit that CO2 does indeed absorb heat energy, making it a greenhouse gas.  However, many of the denier arguments start from the assumption that the heat absorbed by the extra CO2 is not enough to drive changes in the Earth's climate.  In once sense, they're right.  The expected increase in CO2 in 2050 would only lead to 0.5°C of warming by 2050.

Of course, that last sentence leaves off the key phrase: "if nothing else changed."  The 0.5°C number, which I poached from Hansen's book, assumes that nothing else changes.  In reality, if you change one part of the climate system, in this case, by adding a little bit of extra heat, that change will cause other changes in the atmosphere and ocean.  If these other changes lead to more heating, then we have a positive feedback loop that will take a little bit of warming by CO2 and turn it into a  larger heating.  Climate scientists have identified many feedbacks in the climate system (atmosphere, ocean, and ice).  Some of these feedbacks are positive (they amplify warming), while some are negative (they counteract warming).  The earth's "climate sensitivity" is then the sum of all of these feedbacks.  Many lines of evidence suggest that the climate sensitivity is strongly positive, that is that a small increase in CO2 leads to a larger amount of warming.    

My favorite climate feedback is the water vapor feedback.  Like CO2, water vapor (H2O) is a greenhouse gas.  If the amount of water vapor in the atmosphere increases, then the atmosphere will trap more heat and the planet will warm.  The basic idea behind the water vapor feedback is

1. The atmosphere contains a mixture of gases.  The ability of these gases to absorb heat is represented by the gray haze in the image:
wv_001.jpg
2. CO2 in the atmosphere increases.  Now, the atmosphere absorbs more heat (more gray haze),  leading to a small amount of warming in both the atmosphere and the ocean:
wv_003.jpg
3. The warming increases the rate of evaporation over the ocean (blue arrows), leading to more H20 in the atmosphere:
wv_005.jpg
4.  The water vapor absorbs more heat (more haze), and the Earth gets warmer:
wv_007.jpg
Of course, the warming from water vapor isn't any different than that from CO2, so the new warming will lead to more water vapor and more warming, etc, but I'm sick of making pictures.

While the warming from the water vapor feedback is important, warmer temperatures are only one consequence.  Water vapor in the atmosphere tends to move from warm areas like the tropics, where there is a lot of evaporation, to cooler areas, like our own temperate latitudes.  At these latitudes, the additional water vapor leads to more rain and snow, meaning that global warming will lead to wetting over large parts of the globe.  

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