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Bios: Megafauna (Second Edition)» Forums » General

Subject: Biom becomming a desert causes less water in atmosphere? rss

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Petr Míka
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I imagine desert (excluding polar deserts) as a place without water. So first thought is that when a biom becomes a desert, the volume of water in atmosphere (or in clouds) should increase. But in this game it decreases. I am just curious if there is any scientific reasoning behind this. I definitely see why is this done this way for gameplay purposes.
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Niko
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Pemik wrote:
I imagine desert (excluding polar deserts) as a place without water. So first thought is that when a biom becomes a desert, the volume of water in atmosphere (or in clouds) should increase. But in this game it decreases. I am just curious if there is any scientific reasoning behind this. I definitely see why is this done this way for gameplay purposes.
As you said, a desert is a dry place. The water doesn't just change state, it moves to a different biom entirely.
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Petr Míka
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Well, in this game the water moves from the atmosphere.
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Niko
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Pemik wrote:
Well, in this game the water moves from the atmosphere.
Bad wording on my part, sorry. Should have said "doesn't just change state", a desert has a very low humidity in addition to lack of water on the ground.
If something becomes a desert that means the water has left the location entirely, i.e. the atmosphere has less water in it not more.
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Petr Míka
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But in this game the atmosphere means global atmosphere, not just mass of air above one biom. If the water is not in the biom it should be somewhere else unless it dissociates to hydrogen and oxygen which I doubt it does in this case.
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Roel van der Hoorn
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Pemik wrote:
I imagine desert (excluding polar deserts) as a place without water. So first thought is that when a biom becomes a desert, the volume of water in atmosphere (or in clouds) should increase. But in this game it decreases. I am just curious if there is any scientific reasoning behind this. I definitely see why is this done this way for gameplay purposes.


I haven't played the game, but could it be that the desert is not a cause, but a consequence of the planet losing water as a whole?
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David Fenton
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Pemik wrote:
But in this game the atmosphere means global atmosphere, not just mass of air above one biom. If the water is not in the biom it should be somewhere else unless it dissociates to hydrogen and oxygen which I doubt it does in this case.

There's lots of area over the oceans or in high altitude that the "atmospheric water" could be in. I always viewed water in biomes to be either on the ground or in low level clouds (falling as precipitation).
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davey yaved
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The question is one of causation. Neither causes the other as such, both are manifestations one might expect under a climate with less precipitation. But as to the actual expectations from climate science... I don't know, it's complex seems a safe response. but I think the above is reasonable rationale for gaming purposes at least. Great question though. I wonder what other people will say.
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Phil Eklund
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Pemik wrote:
I imagine desert (excluding polar deserts) as a place without water. So first thought is that when a biom becomes a desert, the volume of water in atmosphere (or in clouds) should increase. But in this game it decreases. I am just curious if there is any scientific reasoning behind this. I definitely see why is this done this way for gameplay purposes.


You are absolutely right, and this was where I cheated. White disks in the game represent water in the water cycle. Each white disk is 12000 gigatonnes of water vapor or clouds if in the atmosphere. There are a fixed number of white disks in the game, so each disk in the air means one less on the ground. Therefore, white disks on the ground should be places with sequestered water, not dry deserts.

White disks on the ground normally represent ice sheets, i.e. sequestered water. This is really the same as carbon or oxygen sequestered into limestone or oil deposits, etc. During an ice age, the air is bone dry due to all the water sequestered into ice, and is unusable by the biota.

So this use of white disks for the water cycle works great! If the ice caps melt, the white disks go into the atmosphere and the air becomes moist (and greenhouse and sea levels rise). If the ice advances, the air becomes cloudless and dry. And the ground is covered in white disks, more barren & dryer than the Sahara.

But then I wanted to use disks to represent deserts, principally for CO2 deserts, rainshadow deserts, and barren lands before terrestrial plants developed roots and other innovations allowing them to colonize continental interiors. I contemplated a new color disk for this purpose, yellow disks, to represent such deserts. But introducing another color started overcrowding information on the event cards, and also was strange because it was not associated with a cycle.

I finally decided to use black disks, which are mountains in the game, to represent CO2 deserts as well. This made sense, because the less CO2 in the air, the more deserts form on the Earth from plants dying from a combination of lack of water and CO2. Its important to understand that plant adaptations to low CO2, as CO2 becomes a trace gas, are water intensive, so CO2 deserts first form in low water areas. Sahara and Gobi are examples of CO2 deserts. This also worked thematically, because deserts are great to store carbon because dead things don't rot there, instead eventually getting buried. This all worked great, but still left rainshadow and Ordovician barrens.

Both of these deserts are of rather marginal use in the game, so I decided to use white disks to represent them. This works great to represent uninhabitable barrens, but (as you point out) does not represent the water cycle well. So its a cheat, a concession to playability.

I should mention that, in the Mars and Venus scenarios, white disks represent actual seas, and sea levels, so this also works great for simulating the water cycle.
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Petr Míka
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Thank you Phil for explanation and honesty. Now when I will be explaining the rules and somebody asks about this I will know what to answer... It's because Phil cheated.

Although I would like this game to be more accurate regarding this topic I see how much more complexity would it add without any benefits for gameplay. So I am overall happy with current rules regarding this.
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davey yaved
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I'm so looking forward to playing this game!
I'm a science teacher. one of my teaching aspirations is to get some kids in my high schools game club to get into this game!

Here's a few questions your thoughtful response raised for me:

I realize this is a game we are meant to play for the fun of it and not a detailed scientific climate model, but I'm wondering about two claims in this explanation.
1: Deserts increase during ice ages. I think this must be correct, however we also hear that desertification will be a major phenomenon with continued global warming brought on by increasing co2 levels in our atmosphere. so could it be that the atmosphere over the past 12,000 years or so is situated in a low desert sweet spot and that a shift to either higher or lower co2 levels will 'precipitate' expansion of deserts across the globe???
2: Is it really true that deserts are environments in which organic matter doesn't decay and instead forms carbon reservoirs? That seems unlikely to me... Bacteria, like rust, never sleeps...
Thanks,
Davey
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Alexandre Santos
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tsbrez wrote:

1: Deserts increase during ice ages. I think this must be correct, however we also hear that desertification will be a major phenomenon with continued global warming brought on by increasing co2 levels in our atmosphere. so could it be that the atmosphere over the past 12,000 years or so is situated in a low desert sweet spot and that a shift to either higher or lower co2 levels will 'precipitate' expansion of deserts across the globe???

Warmer temperatures will increase the amount of liquid water (melting of ice caps), and more atmospheric activity. So some places will have more rain, but some places may remain deserts, because it just doesn't rain enough.
It's not just the quantity of rain, it's also about where it rains.

Quote:

2: Is it really true that deserts are environments in which organic matter doesn't decay and instead forms carbon reservoirs? That seems unlikely to me... Bacteria, like rust, never sleeps...

Without water there is no organic activity. So there is no rotting. That's why dried foods can last.
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Phil Eklund
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tsbrez wrote:
I'm so looking forward to playing this game!
I'm a science teacher. one of my teaching aspirations is to get some kids in my high schools game club to get into this game!

Here's a few questions your thoughtful response raised for me:

I realize this is a game we are meant to play for the fun of it and not a detailed scientific climate model, but I'm wondering about two claims in this explanation.
[q="tsbrez"]1: Deserts increase during ice ages. I think this must be correct, however we also hear that desertification will be a major phenomenon with continued global warming brought on by increasing co2 levels in our atmosphere. so could it be that the atmosphere over the past 12,000 years or so is situated in a low desert sweet spot and that a shift to either higher or lower co2 levels will 'precipitate' expansion of deserts across the globe???


It is a somewhat recent discovery that, when CO2 levels drop to parts per thousand, or even to parts per million as per today, plants must open their stomata as wide as possible to avoid asphyxiation. This causes water loss. As the CO2 levels have fallen throughout the Cenozoic (i.e. the last 40 million years), plants have had to adapt to water loss as well as not being able to breathe. This explains well the rise of cactus and water-conserving plants, and the rise of plants able to thrive in ultra-low CO2 levels, especially grasses using C4 photosynthesis.

Saying desertification is the result of global warming is a fallacy. The desertification of the last 40 million years (in which vast swaths of forests were converted into prairies, grasslands, savannas, and sandy wastelands) occurred during global cooling, not warming. This includes much of Africa, heartland USA, Argentina, and the Sahara and Gobi deserts, all of which are more or less CO2 deserts. This global cooling gradually plunged the Earth from hothouse to icehouse conditions, to use the language of Bios:Megafauna. We live today in an Ice Age. There is actually ICE that can be found, which although common in the outer solar system, is a novelty on Earth!

Sometimes one thinks of deserts as being "hot". But for the Earth, hotter temperatures mean more ocean evaporation, and more humidity and rainfall. And the driest deserts, as far as life is concerned, are in Antarctica. During the last glacial maximum, which humans somehow survived, most of Europe and North America became such a desert, buried under a kilometer of sequestered frozen water.

tsbrez wrote:
2: Is it really true that deserts are environments in which organic matter doesn't decay and instead forms carbon reservoirs? That seems unlikely to me... Bacteria, like rust, never sleeps...


This one is a bit personal: I was an observer in an experiment by the University of Arizona Agricultural and Biosystems Engineering in Tucson, Arizona. On land plots (that happened to be within walking distance of my house), areas of desert were gridded off with various control plots and plots with leaves and other organic material. There were various sunscreens applied. The idea was to see how important the desert was for sequestering carbon from vegetation that gets buried instead of rotting. Of course, the results were important for the funding & very existence of the Agricultural and Biosystems Engineering Dept., so we were under some pressure.
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Alexandre Santos
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phileklund wrote:
Of course, the results were important for the funding & very existence of the Agricultural and Biosystems Engineering Dept., so we were under some pressure.


So what were the results? the cliffhanger is unbearable
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Alexandre Santos
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phileklund wrote:

Saying desertification is the result of global warming is a fallacy. The desertification of the last 40 million years (in which vast swaths of forests were converted into prairies, grasslands, savannas, and sandy wastelands) occurred during global cooling, not warming. This includes much of Africa, heartland USA, Argentina, and the Sahara and Gobi deserts, all of which are more or less CO2 deserts.


This needs to be qualified: the Sahara was humid and green from a period of 15.000 to 5.000 years ago, a time when monsoons penetrated deeply into the heart of the continent, and despite the gradual loss of CO2 from the last million years. The loss of vegetation in the Sahara is directly correlated to changing patterns of rain, which are also probably related to changing global temperatures.

Not to deny the effect of CO2 loss, but weather patterns also have a deep impact.
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Phil Eklund
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AlexFS wrote:
phileklund wrote:

Saying desertification is the result of global warming is a fallacy. The desertification of the last 40 million years (in which vast swaths of forests were converted into prairies, grasslands, savannas, and sandy wastelands) occurred during global cooling, not warming. This includes much of Africa, heartland USA, Argentina, and the Sahara and Gobi deserts, all of which are more or less CO2 deserts.


This needs to be qualified: the Sahara was humid and green from a period of 15.000 to 5.000 years ago, a time when monsoons penetrated deeply into the heart of the continent, and despite the gradual loss of CO2 from the last million years. The loss of vegetation in the Sahara is directly correlated to changing patterns of rain, which are also probably related to changing global temperatures.

Not to deny the effect of CO2 loss, but weather patterns also have a deep impact.


I quite agree Alexandre, the Sahara has been influenced by monsoon weather patterns, and has appeared and disappeared, and within the memory of human herders it was rather habitable. I tried to simulate this in Origins, and am still struggling with this in Bios:Origins.

I don't know the desert sequestration results, maybe he wanted a decade test?, and it still has a couple of years to run? But the last I looked the plots with various shades were still installed, so it is still running. It is right next to the ARID demonstrator, (Algal Raceway Integrated Design), and the GONG solar telescope (Global Oscillation Network Group).
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