What would it take to turn Earth into a global desert?

[S.Kin]

Hello. I am a fiction novelist and a new member here at PF. I write mostly futuristic sci-fi stories so I'll probably be poking my head in from time to time with new questions for you guys. I'm very anal and a stickler for scientific accuracy (or at least as close to accurate as I can get and still write fiction); and I'm especially concerned with receiving scrutiny from the scientific community because I penned something completely implausible.

Having said all that: I'm currently working on a story in which I propose a scenario where Earth has been transformed into a global desert, and I’m looking for information on whether this is even plausible, and what sort of events might facilitate such a drastic change to our climate.
How exactly might this be achieved? I've looked at multiple theories concerning global warming, the effects of nuclear soot on the atmosphere, and even theories surrounding subduction zones and the loss of ocean water; but I still have concerns that any of these events could eventually produce the sort of environment that I'm looking for.
I’d also like to know how long it would take for these sorts of changes to take place. Depending on the catalyst, is this something that would take a billion or more years to transpire, or could something like this potentially occur over the course of several hundred years?
How long could life continue on this planet as temperatures began to rise and the world dried up? Would mankind even live to see a desert (or at least mostly desert) Earth? At what point in the process would it become impossible for life to continue on the planet?

One of my biggest concerns are the oceans. It seems to me that as long as oceans still exist, the rain cycle will continue and completely negate any possibility of the planet going arid. But what would have to take place in order for the oceans to disappear? Or is their disappearance irrelevant?

I’m appreciative of any advice that you guys can give me and open to all ideas and theories. Thank you in advance.


- S. Kincaid

 

[Andre]

Welcome to PF, S

It has been thought that this may happen in another billion or so years, global desertification. There are two different -speculative- scenarios possible, the first, the depletion of water as it seeps into the mantle, touched upon http://eurjmin.geoscienceworld.org/cgi/content/abstract/21/3/637. But that seems a long shot, considering that there are no indications that the volume of oceans was significantly greater in the geologic past

Another scenario, perhaps much more plausible, is the depletion of useful carbon in the carbon cycle. There are many long and short sub cycles in the global carbon cycle; one of them may be off balance, that's the interaction with the Earth lithosphere. The http://eurjmin.geoscienceworld.org/cgi/content/abstract/21/3/637 constantly transforms carbon dioxide and silicate minerals into limestones where it stays put, acting as a near permanent sink, unless the carbon is reduced back to CO2 very locally and sporadically, due the heat associated with geothermal features.

So if the constant weathering process outweights the volcanic counter action in this cycle, the useful carbon in the carbon cycle may continue to deplete until a very low equilibrium when virtual all carbon is in the limestone rox (assuming an abundance of silicates), and without a certain minimum of carbon dioxide no plants (photosynthesis) and ultimately no life.

It is -for instance- assumed that the weathering associated with forming of the Himalayas starting in the Eocene, caused a drop of CO2 in the atmosphere, which is speculated to be responsible for the Pleistocene Ice ages. see this.

Apart from that the soil/peat/coal forming with plant remains also depletes the available amount of carbon for the total biomass

Therefore I wrote some 15 years ago that at least one positive element of the use of fossil fuels, is the restoring of disappeared carbon via CO2, back into the carbon cycle and thus increase the total biomass again that way. Obviously this would put some question marks to what we are doing, considering climate carbon concerns

 

[dorlomin]

What do you mean by 'global desert'. Devoid of life or merely arid? The first thing that springs to mind is that it is much drier during the glaciation phases of the current ice age. Give it IIRC its about 50 000 years till we are ready for the next glaciation, anthropogenic CO2 should have been cleared from the climate by then.

 

[Xnn]

Ice ages don't result in global deserts, although the climate is drier than it is now.

On the other hand, if atmospheric CO2 levels were to fall to <20 ppm, then the Earth would cool dramatically and eventually the oceans would freeze completely. This has actually happened in the past and is called "Snowball Earth". Technically, this would also be an Earth wide desert since there would be no significant evaporation.

 

[Andre]

Snowball Earth is claimed to be debunked

http://news.bbc.co.uk/2/hi/uk_news/scotland/1857545.stm

 

[russ_watters]

I'm wondering if a large increase in global temperature (say, when the sun starts getting to its red giant phase) would cause the oceans to start to evaporate and cause a hot, humid earth? I guess since the oceans are colder than the air on average, the water vapor in the air will always lag the saturation point, keeping average humidity down.