Comments by Isaac Asmiov, from a lecture in 1974

This is taken from (about 1/2 way down). Its from a transcription of an audio tape of a lecture.

Note: this is not a scientific reference. Its here as an example of the mistake that a well-read non-expert can (and did) make.

This is (as far as I can see) the only relevant section of the text. CO2, warming and iceage are not mentioned: his context is immediate food security. Read what he says: then I'll comment.

The very thing that makes it possible for us to use more and more energy is our industrial technologized world. And another thing that our industry produces is dust. And the air is dustier now than its ever been before in human history. Except perhaps very temporarily after a large volcanic eruption.

This means that the Earth's albedo, the percentage of light from the sun that it reflects back into space before it hits the ground, has been going up slightly because dusty air reflects more light than clear air does. And...well, not very much more, but enough. It has been making the temperature of the Earth drop since 1940. It's been going down steadily. Again, not very much. You're probably not aware that the summers are cold, or that the winters are extraordinarily icy, they're not. The drop in temperature may be one degree. But it's enough to cut down on the growing season in the northern climates. It makes the weather a little bit worse. It sends the storm tracts further south, so that the Sahara Desert creeps southward, so that the monsoon rains in India fail a little bit. Just enough so that the harvests aren't as good as they used to be, and the Earth's reserve supply of food sinks to it's lowest in recent history.

And just as this is happening...and it's going to continue happening because the air isn't going to get un-dusty unless we stop our industrial activity. And if we stop our industrial activity, that's going to be because we've suffered some complete disaster.

So, the weather isn't going to turn better. The air is going to stay dusty, and it's going to continue getting a little colder.

OK, so my comments: well, he was wrong. He was wrong because although dust/aerosols produce cooling, CO2 produces a warming which outweights the cooling.

Can he be forgiven for this in the context of the state of knowledge of the time? No. It was clear then (see references from main page) that whether CO2 or dust/aerosol would predominate was not known. To mention just dust is wrong. Asimov was very very well read.

Note also that calling the air "dusty" is misleading. He may be doing it for the sake of a general-public audience. Most of the forcing for cooling from dust/aerosol came fom aerosol not dust.

WMC. 21/12/2001.