Ask Mr. Science
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The ozone hole

The ozone hoe came up as I started to answer a question about global warming. Clearly these are two subjects which get mixed up a lot, so I decided to talk about the ozone hole first.
The ozone layer is near the top of the atmosphere, far above the troposphere, where all weather phnomena occur. Ozone absorbs UV radiation from the sun, thereby protecting plants, animals and people.
Ozone gets destroyed by certain chemicals, most imortantly CFC's. CFC's are mostly used in refrigerators, airconditioners and spraycans. They were used there because they were very non-reactive and stable. Unfortunately they are so stable that they can survive for decades as they slowly diffuse throughout the atmosphere all the way up to the ozone layer. There they react with the ozone, if the temperatures are very low. This occurs in the winter over the south pole, and to a lesser extent over the north pole.

It is no longer legal to produce these CFC's worldwide, and gases in new spraycans, fridges and airconditioners are replaced by others. This means that in a few decades, all the CFC's in the world's atmosphere should be gone and the ozone hole should be a thing of the past. However, there is an emerging illegal trade in CFC's, and this may delay the restoration of the ozone layer by a decade or more.

4 Nov 98


 

Global warming

I first talked about this in 1998, and have brought it up yearly since then. The world has taken precious little action, and the outlook becomes grimmer every year.

Recently (2015) I heard about 2 demos related to the greenhouse effect, and I tried to replicate them.


CO2 bottle (in safety enclosure), a 4-foot tube closed with clingwrap on both ends, candle on one end, camera on the opposite end.
Here is first one, following a YouTube video from the BBC, showing absorption of IR radiation from a candle by a tube filled with CO2.
I have a CO2 bottle, so I started building this setup shown on the right →

Next I made a little holder for a tealight candle, which makes it easier to line things up. (It is made from foam-core board)
← click on the picture

The infrared camera: I don't have one, but I know that CCDs are sensitive to IR. So I made an IR-pass filter out of 5 layers of (over)exposed color film, and a holder for my little camera and the filter.

This seems to work: 5 layers of black film are completely opaque to visible light, but the image shows what the camera sees without (left) and with (right) the filter in place.

So here is the result: on the left the view down the tube - you can see the tealight candle on the left, and on the right the image with the IR-pass filter in place.
However, when I fill the tube with CO2, I see no change at all.
My interim conclusion: besides the IR-pass filter that I built, there is an IR-blocking filter inside the camera. I'm guessing that the IR absorption of the CO2 is in a part of the spectrum that is blocked by the camera's filter, and not in the bit of the spectrum passed by my pass filter.

So I have to get another camera so I can hack it and remove the IR-blocking filter, and then try again.


The second demo was easier to set up. This is one I had heard on BBC radio, and I found these YouTube videos:
WARNING: turns out, the following 2 demos are fake!
  from Eric Christensen
  from Dr. Maggie Aderin-Pocock

The demo consists of 2 bottles, one with air, one with CO2, and a big lamp. There is a thermometer in each. You turn on a big lamp, and after a while the temperature in the bottle with CO2 has risen substantially more than in the bottle with air.

.. By 'fake' I mean that if you duplicate these experiments, you get no difference at all. Why is this? First of all, when you turn on the lamp, what gets warmed up is the plastic of the bottle, and the thermometer, and this in turn warms the air/CO2 inside. Even in the main absorption bands of CO2 the mean free in CO2 is many meters so the amount of energy absorbed by the CO2 is tiny, and would not result in an observable temperature difference.

So I'm still looking for a good demo...

Some dates and names from the history of climate change studies, mostly from this article:

1856 Eunice Foote reported that an atmosphere containing CO2 warms up more than an atmosphere without. (more...)
1859 John Tyndall studied the same problem, in more detail
1896 Svante Arrhenius calculated that halving atmospheric CO2 would cause an ice age, and that doubling it would cause global temperatures to rise by 5-6 °C.
1938 Guy Steward Callendar connected the dots between the temperature rise he observed and the burning of fossil fuels
1958 Charles David Keeling starts an unbroken series of CO2 measurement in the air
1967 Syukuro Manabe and Richard Wetherald developed a computer model that contained the major processes that drive climate
2001 Michael Mann and colleagues published the now-famous hockeystick curve, updated
... ...
2022 Antonio Guterrez once again raises the alarm
2022 Remaining carbon budget

10 Nov 98, and ever since...
 

Meteorites

Meteorites were the hot topic this week with the much-publicized arrival of the Leonid meteor storm. We talked about how this is dust left behind by the recent passage of come Temple-Tuttle, and that these are just tiny grains, but that they could do damage to sattelites, and to the people aboard Mir. All the details are in the links below:

17 Nov 98






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