Global warming -- what's the worst-case scenario?

Great Debates
41

[QUOTE=Mosier]

More water means more evaporation, right? More evaporation means more rain, right?
[/QUOTE]

It’s not quite so simple. It is true that one expected effect is an increase in the intensity of heavy rain events (and, in fact, I think such a trend has already been detected). However, the increased temperature also means stronger drying of soils in some areas particularly during the summer months. And, there are also simply predictions that weather patterns will shift in ways that will tend to make some areas wetter and some areas (like the Southwest U.S.) drier.

42

[QUOTE=jshore]
It’s not quite so simple. It is true that one expected effect is an increase in the intensity of heavy rain events (and, in fact, I think such a trend has already been detected). However, the increased temperature also means stronger drying of soils in some areas particularly during the summer months. And, there are also simply predictions that weather patterns will shift in ways that will tend to make some areas wetter and some areas (like the Southwest U.S.) drier.
[/QUOTE]

I’ve heard this before but I’m not sure I get it. Wasn’t the average global temperature much higher in the past…say before the mass extinction of the ‘dinosaurs’ (at various times)? I seem to recall that during several of those periods there were huge inland sea’s in the US, and that much of the South West and the great plains were either under water or pretty lush habitat…much more so than today. And in the north there were vast tracks of very good habitat under what is basically snow today.

I don’t know what the sizes of deserts were then, but I know that, say, the Gobi was ALSO pretty lush habitat at one point when the world was much warmer…and as I said the south west in the US was pretty good habitat (when it wasn’t under water I suppose :)) in the past as well. IIRC, the Sahara and Northern Africa ALSO was pretty good habitat at one time…as well as Siberia.

My guess is that my mistake is that these places weren’t all good habitat at the same time (i.e. they were good at different times in the past)…and that this is just the tip of the ice berg of what I DON’T understand about all this climate changing stuff. Could you explain why it will be different this time than it was in some of these past (much warmer) climates?

-XT

43

They’ve recently said that Bangkok will be under water. Given that’s we’re about 30 miles upriver, that’s pretty amazing. (Fortunately, we’re on an upper floor. :D)

But at least they’re finally acknowledging there will be a problem. Earlier this yerar, some Thai “scientists,” in an attempt to please the government, came out publicly to say that even though the sea level would rise elsewhere in the world, it would not along Thai coasts.

44

Desertification is something that is already occuring in drier climates because of land degradation resulting from human activities like agriculture. The prediction is that global warming will cause less rainfall in drier climates, thereby exacerbating desertification.

The IPCC states that in Latin America, for example, “In drier areas, climate change is expected to lead to salinisation and desertification of agricultural land.”

And:

I think that, when it comes to desertification, the difference between what happened in the past and what’s happening now is us.

45

[QUOTE=xtisme]

My guess is that my mistake is that these places weren’t all good habitat at the same time (i.e. they were good at different times in the past)…and that this is just the tip of the ice berg of what I DON’T understand about all this climate changing stuff. Could you explain why it will be different this time than it was in some of these past (much warmer) climates?

[/QUOTE]

I’m not sure what the answer to your question is but I think that your guess is one reasonable one. Also, you have to remember that once you go back 10s to 100s of millions of years, you are talking about continents being in different places and mountain ranges being different and such. All of these differences can have important climatic effects.

46

The part that concerns me the most is rapid sea level rise.

It’s not just a matter of moving everyone back a mile or two from where the coast used to be. Who’s going to pay for all the reconstruction of coastal infrastructure should that become necessary? Whose wallet are all the rebuilt ports and sewage treatment plants and major coastal highways going to come out of? What will be the price of goods and services in this country if current ports are rendered inoperable and there are major negative effects from global climate change in China and India?

If there is not permanent coastline change, just increased seasonal coastal flooding, how long will it take for erosion to provide drainage for new water deposits, and how will contagious disease vectors be affected in the meantime? And who’s going to bear the cost of the accompanying increased medical spending?

Plus, a sea level rise of a few tens of feet will put coastal reef systems that much farther from shore and that much further away from sunlight. The IPCC report also indicates that the warmer temperatures and changes in ocean pH could cause widespread coral bleaching and die-off in any event, and impair the marine animal shell development that leads to new coral development. We could be talking about temporary or permanent collapse of some major fisheries in that case.

Very worrisome.

47

[QUOTE=xtisme]
I’ve heard this before but I’m not sure I get it. Wasn’t the average global temperature much higher in the past…say before the mass extinction of the ‘dinosaurs’ (at various times)? I seem to recall that during several of those periods there were huge inland sea’s in the US, and that much of the South West and the great plains were either under water or pretty lush habitat…much more so than today. And in the north there were vast tracks of very good habitat under what is basically snow today.

I don’t know what the sizes of deserts were then, but I know that, say, the Gobi was ALSO pretty lush habitat at one point when the world was much warmer…and as I said the south west in the US was pretty good habitat (when it wasn’t under water I suppose :)) in the past as well. IIRC, the Sahara and Northern Africa ALSO was pretty good habitat at one time…as well as Siberia.

My guess is that my mistake is that these places weren’t all good habitat at the same time (i.e. they were good at different times in the past)…and that this is just the tip of the ice berg of what I DON’T understand about all this climate changing stuff. Could you explain why it will be different this time than it was in some of these past (much warmer) climates?

-XT
[/QUOTE]

Hunting around for something related to a fact that surprised me in my college geology course, I found this page which explains some things pretty well.

Deserts are not randomly distributed. Current deserts across the world are centered at about 30 degrees latitude north and south of the equator. The reason for that is that global air circulation is currently in resonance in such a manner that hot air rises from the equator and cycles back downward at those latitudes. As it rises, it cools, and the moisture it contains (you will notice on the same map you looked at to verify the desert pattern that there ain’t a whole lot of land at the equator) precipitates out. When the air is cool enough to descend at 30 degrees, it is dry as a bone, and then gets warmed by the earth as it descends. Voila! Desert.

There are a lot of factors that go into making atmospheric circulation resonate the way it currently does, but as my linked page shows, 8,000 years ago it must have been circulating differently, because the Sahara was lush back then.

It’s a combination of temperature patterns, ocean currents, the specific location of major mountain ranges, etc. And since the Earth’s crust is just a bunch of big rocks bobbing around on top of the mantle, rocks which rise, fall, bend and tilt over time, and the continents are just the parts of the thicker areas of crust that happen to be sticking out above the waterline, the distribution of major landforms is much much different now than it was in the time of the dinosaurs. This affects ocean and air circulation both, and means that it was literally a different world back then. Our current world just happens to be made of some of the same rocks the old one used, and they tell the tale.

48

[QUOTE=xtisme]
I’ve heard this before but I’m not sure I get it. Wasn’t the average global temperature much higher in the past…say before the mass extinction of the ‘dinosaurs’ (at various times)? I seem to recall that during several of those periods there were huge inland sea’s in the US, and that much of the South West and the great plains were either under water or pretty lush habitat…much more so than today. And in the north there were vast tracks of very good habitat under what is basically snow today.

I don’t know what the sizes of deserts were then, but I know that, say, the Gobi was ALSO pretty lush habitat at one point when the world was much warmer…and as I said the south west in the US was pretty good habitat (when it wasn’t under water I suppose :)) in the past as well. IIRC, the Sahara and Northern Africa ALSO was pretty good habitat at one time…as well as Siberia.

My guess is that my mistake is that these places weren’t all good habitat at the same time (i.e. they were good at different times in the past)…and that this is just the tip of the ice berg of what I DON’T understand about all this climate changing stuff. Could you explain why it will be different this time than it was in some of these past (much warmer) climates?

-XT
[/QUOTE]

Huh. One cannot do a single-post job of correcting the inferences in this. Without being insulting, would you allow me to suggest that the approach you are taking here is akin to Days of Yore when cave men discovered fire and the wheel, Moses led the Israelites out of Egypt, Roman legionnaires conquered the world, King Arthur’s knights went a-questing, the Pope tried Galileo for heresy, and les Trois Mosquetaires (avec D’Artagnan) fought for France and the Right – all at the same time?

On an appropriate time scale – say a sample every 10 million years, with 460 such samples since Earth’s formation – we’re in the middle of an Ice Age. More shallow sea is above surface as coastal plain, more land covered by permanent snow/ice cover, than is SOP for the planet. Unfortunately, everything we know about living on this planet is geared to an environment where the shallow seas are coastal plains, places like Anhwei, Saskatchewan, and Kansas are fertile temperate plains suitable for crops, etc. Switching to a lowlands-are-scarce scenario might be problematic.

As for desertification, it occurs whenever evaporation exceeds enhydration (i.e., the total water supply to the area from either precipitation, available groundwater, or river inflow). Humans alter this with canals and irrigation – and it goes plumb chuck to Hell when war destroys such systems, as happened in Iraq in the 1200s. L.A. was desert until the 20th Century – and will be again if the aqueducts were to be abandoned.