Wednesday, May 02, 2018

On Edith Foote's Experiment

There is a sort of  simmering discussion on Twitter and Facebook whether Edith Foote found the basis of the greenhouse effect before John Tyndall.  Eli is here to tell you what was done.  The TL:DR is no, she did not.

Her report can be found on the net in as a Google book,

Katherine Hayhoe describes it this way
In 1856, Mrs. Eunice Foote presented the results of a simple experiment at the annual meeting of the AAAS - The American Association for the Advancement of Science.

She filled up glass jars with different types of gases, including water vapour and carbon dioxide, and put them out in the sun. She then measured how much each jar heated up.

In her own words, "the highest effect I have found to be in carbonic acid gas" - that's what they used to call carbon dioxide back then.

She went on to say, "an atmosphere of that gas would give our earth a high temperature; and if as some suppose, at one period of its history the air had mixed with it a larger proportion than at present, an increased temperature from its own action must necessarily have resulted" - in other words, if there were more carbon dioxide in the atmosphere, then it would trap more heat, and the earth would be warmer.

When Eunice did her experiment, average carbon dioxide levels were about 290 parts per million in the atmosphere. She probably never dreamed that by 2016, they'd be over 400 parts per million.

Next year, I'm attending the annual meeting of the American Association for the Advancement of Science. There will be plenty of talk about the latest, cutting-edge research. But the coolest thing is this: that the basic science connecting carbon dioxide to a warming planet is 160 years 
Eli's analysis of Foote's experiment and observations rests on three platforms.  First the observation of the solar spectrum at the surface of the Earth
The absorption of water vapor and CO2 in this spectrum are what are called combination and overtone absorption bands where there is a change of multiple vibrational quantum numbers as a result of absorbing  visible (380 - 800 nm) or NIR (near IR > 800 nm) photons.  For example if the three vibrational modes ν1, the symmetric stretch, ν2,the bend, and ν3, the asymmetric stretch are (0,0,0) in the ground state, a transition to (0,2,0) would be an overtone and to (1,0,1) a combination band.  As a general rule overtones and combination bands are about a factor of 100 to 10000 weaker than single quantum transitions.

Readers of Rabett Run also know that there is very little flux in the solar spectrum in the IR, particularly where the CO2 bending mode is active

The bunnies need one more piece of information, the transmission of glass

Got it?  OK, let's go

Foote used glass cylinders.  Glass cannot pass IR light beyond 4 microns.  The solar spectrum is weak beyond 2 microns.  Foote was not looking at absorption of thermal radiation from the warm surface.  She was measuring absorption in the overtone and combination bands of CO2 and H2O and a bit from the H2O stretching bands at 2.66 and 2.74 microns .

One further point, why did Foote observed a stronger effect from CO2 than H2O?  The answer is that she had a much higher partial pressure of CO2 in her containers than H2O because water vapor is condensible at 25-30 C, about 30 Torr.


Russell Seitz said...

Poor Mrs Foote- a few years later , volatile hydrocarbons became commonplace, and she might have beaten Tyndall to the punch. If she invented salt optics. Too bad she didn't, but Bill Nye shoud read her stuff so as to get the experiment right the next he tries

Barton Paul Levenson said...

Besides, she was just a girl. An icky, icky girl, with cooties.

magmacc said...

I read Foote's note after first hearing the claim a couple of years ago that she had conducted pioneering experimental measurements of the greenhouse effect.

Then, and now, my conclusion was that her experimental methods were far too flawed to isolate and detect the very small effects that might be caused by different gases on this scale. Compare this to the extremely careful experimental work by Tyndall and it's clear that his were the first actual measurements of the greenhouse effect.

Something I hadn't noticed before: the preceding paper in the volume is On the Heat in the Sun's Rays by Elisha Foote, Eunice (Newton) Foote's husband.

Elio Campitelli said...

While I agree that her methods were probably flawed, it seems to me that she did predate Tyndall in proposing the main idea of studying the interaction between gases and light. Refuting the basis of her experiment, in my mind, doesn't take that away. There are countless pioneering experiments that now we can see as fundamentally flawed, but they still count.

jb said...

Eunice Foote is also noteworthy as one of the signers of the 1848 Declaration of Rights and Sentiments at the Seneca Falls, NY, Convention. The Seneca Falls Convention is often described as the first women's rights convention and was organized by women "to discuss the social, civil, and religious condition and rights of woman".

EliRabett said...

Didn't know that

JoeT said...

We know that the greenhouse effect exists because of the temperature gradient in the troposphere. Tyndall brilliantly measured the absorption of infrared by carbon dioxide and water vapor. If he had looked for a temperature change in his apparatus during his absorption experiments, would he have found one?

Russell Seitz said...

No, JoeT, I'm afraid Tyndall would have not.
The iron tubes of his steampunk apparatus had > 10,000 times the thermal mass of the gases whose absorption he measured, and this thermometers and bolometers had only 100 millidegree resolution.

CF :

JoeT said...

Thanks for the response. We know there are problems in many of the experiments that allegedly show the radiative greenhouse effect --- especially the one Russell cites in the comment above about Bill Nye. One of the problems is separating out the convective contribution to the observed warming.

I'll rephrase my question then. Is it even possible to devise an experiment in a laboratory that would clearly indicate a warming due to the radiative greenhouse effect --- or would such a demonstation require a temperature gradient as it does in the atmosphere?

Barton Paul Levenson said...

JoeT -- the radiative greenhouse effect is shown empirically by measuring the back-radiation from the sky, with attention to the wavelengths in which it is found.

Hank Roberts said...

Thanks for sorting this one out, Eli.