Well, the subject of climate change has comes up from time to time. Often in denial.
A recent cite of evidence (Shrinking Artic summer ice.) has come up at:
http://economistsview.typepad.com/economistsview/2011/09/the-lack-of-ice-age.html#comments. Follow the comments for more references. I think I’ll also give some references in a later entry.
Climate change may seem to be a little off the path for an economics blog, but the economics of winter is very different from that of summer. So also the economics of a changed climate as well.
Now I’m not one of those climate change deniers. But neither am I quite in the camp of the global warmers, either. Global heat retention, yes, but that’s not quite the same thing.
The main problem is that we are dealing with a non-linear system, here, and non-linear systems are, well, non-linear, full of curves and unexpected changes. And reversals.
Most particularly, from the point of view of climate change, for the past million years or so, whenever it has warmed up- enough, we have an ice age: God turns on the air conditioner, to cool things down. NOTE: Ice ages work the reverse of how you might think they do. They do not start cold, and then warm up until all the ice melts. They start warm, and cool down until they stop, because... well, the air conditioner shuts down: Evaporation in the Pacific is no longer sufficient to drop more snow in Canada than melts in the summer.
Now some theorize that this is driven by external forces: changes in the orbital parameters of the earth. My own idea is that it is strictly internal, brought about by the peculiar nature of the ocean circulation of the earth, these days. (It may be phase locked by orbital parameters, but that is much different from saying the change in orbital parameters is the cause.)
Ice ages have only been happening for the last million and a half years or so. What about the ocean circulation could have changed?
Drake Passage 41 mil yrs ago: This created the Antarctic current, which just goes around Antarctica, and which basically cut off Antarctica from the rest of the oceanic circulation.
Isthmus of panama 3mil yrs This cut off direct flow from the Pacific to the North Atlantic, which would help cool the Pacific.
Bering straits got narrow about 1.5 million years ago, when they were probably in the neighborhood of 200km wide. A pretty gradual transition, admittedly, but there is a definite critical point in the transition, when the straits were narrow, and shallow, enough to block sufficient flow to the Artic from the Pacific to keep the North Pacific from overheating.
The theory runs like this: Because the earth is warmer, but the pole is still cold, there is increased heat transport from the equator to the North pole. The main transporter of heat is the circulation of the ocean. But because of the peculiarities of modern geography, for the Pacific, the North Pacific, to cool off this way , water must circulate through the Indian ocean and up the South and North Atlantic to the North pole. It can’t just go to the South pole to cool, as this is blocked by the Antarctic Current. Neither can it just go through the Bering Straits, which is too narrow and shallow to support a sufficient rate of flow. Because this current is so long, it is not strong enough in itself to equalize the temperatures in the ocean, in particular, to keep the North Pacific cool, and the Arctic relatively warm.
Meanwhile, what comes down must first go up. For snow to accumulate in Canada, it first has to evaporate, off the North Pacific Ocean. Ordinarily, evaporation in winter is less than the melting rate in summer, so the snow melts each year. But evaporation increases exponentially with temperature, while melting only increases linearly, (I got this from an old Dover book on glaciers.) so there is a crossing point, when the evaporation rate off the ocean goes above the melting rate for snow in Canada. See Diagram.
Note the Temperature and Quantity scales are rather qualitative. (Quantity is quantity of water.) The point is just to suggest that with increasing temperature, an exponential curve will eventually rise above any straight line.
And then you have to figure in the wind, which increases during ice ages, to an average 30km/hr or so. But that increases both melting and evaporation rate, so it would give an upward curve to both lines.
However, there is another feature about increased wind velocity, which we might dub “Quantum Earth.” What we mean by heat retention is that the average energy content of the atmosphere will increase. As the energy content of the atmosphere increases, so will the average wind velocity. As the wind velocity increases, so will the Coriolis force, which will cause more cyclones and such. This will happen. But if wind velocity increases enough, it might also cause an increase in the bandedness of the atmosphere. (This is a speculative thought: So instead of two, there would be three jet streams in each hemisphere, and four climatic zones. Basically a new one would appear at the equator, as the others migrated north. But, this would render the climatic gradient from North to South steeper, so the present temperate zone would take on qualities of artic air.
But of course, this bandedness idea is not necessary to the rest of the theory, as it is so far developed.
So ice ages are caused by warm ocean, particularly the Pacific. During ice ages, oceans start warm, and slowly cool, about 10 degrees C. And during the interglacial periods they increase that same 10 degrees C., much quicker than they cool, by the way. And indeed, since the end of the last ice age, oceans have warmed by about 10 degrees C. Check out, eg, “Vostok core data images.” Note CO2 levels also peak, prior to ice ages.
So the issue becomes, or the question is, are we headed for an ice age, or are we going to blow right by the conditions necessary for one by having such a massive quantity of greenhouse gases in the atmosphere, if that makes the difference.
And which ever one, how fast?