(John Brock) wrote in message ...
In article ,
Jaak Suurpere wrote:
(Nick Maclaren) wrote in message ...
In article ,
(Jaak Suurpere) writes:
| (pete) wrote in message ...

| The air density in such a basin, that near the equator, would make the
| conditions unthinkably intolerable. You would have rivers flowing
| down into the basin and evaporating, yielding a blistering hot
| desert which would be very high humidity were it not for its high
| temperature and pressure.

| Pressure would not do anything for humidity.
| If there is open water to evaporate, the air does get near saturated,
| even if the water is boiling hot. Which probably would not have been
| the case in Messinian times. It was still not that deep.

By which I assume that you mean that air flow through the basin
was significant? The "open water - saturation" effect is
conditional on the air movement not counteracting it.

Correct.
If you have archives extending to mid-December, I discussed it
before...
Basically, Mediterranean deep basin would be in a bad situation
regarding air movement.
It would be 3 or 4 kilometres above

Sorry - below, of course!

any surrounding area.
Any wind descending into basin would have to heat at the dry adiabatic
lapse rate. Which, IIRC, is about 10 degrees per kilometre. Over that
height, it would be 30 to 40 degrees.

In summer, it would mean heating from 25 degrees to around 60. If the
basin is only ventilated by winds of over 60 degrees, any cooling of
air inside the basin, whether through evaporation or radiation, would
tend to form cooler air mass, which would be stable and therefore
stagnant. And this would mean thatr it will reach saturation.

This is very interesting, and I want to make sure I understand it:

About 5 million years ago the Mediterranean not only went dry but
turned into a desert far hotter and more hostile to life

This I discussed before. I'll repeat it below for those who do not
have archives.

than anything on Earth today. The reason it was so hot was that as air
descended 3 or 4 kilometers into the basin (someone else said 3
miles -- which is right?)

Both are right, kind of.
The current deepest spots of Mediterranean are at a depth of around 5
kilometres - approximately 3 miles.

But this is on a small area. If there was any water remaining in the
Mediterranean, it could be expected to fill the deepest spots.

But it does seem likely that the remaining water levels could have
been around 3 or 4 kilometres below ocean.

it heated about 10 degrees per kilometer
due to increasing air pressure (is that what the "dry adiabatic
lapse rate" refers to?). In the summer the temperature would reach
60 degrees (Celsius I assume; = 140 Fahrenheit). The air didn't
circulate much, being at the bottom of a basin, and if there were
any significant standing bodies of water at the bottom (and I guess
there had to be, since a number of rivers empty into the Mediterranean)
they would cool the air just slightly, and this air would form a
hot, stagnant air mass with humidity at 100 percent that was
basically nailed to the bottom of the basin.

Is that a reasonable summary?

Summary of what was recently said; but there is more to this.

Synoptic-scale winds, the only thing that could have ventilated the
air in the bottom and kept it dry in the presence of standing water,
would have had to heat at the dry adiabatic lapse rate, 10 degrees per
kilometre, leading to summer temperatures in 60s of Celsius.

However, the air was humid. I have argued that if there was no
large-scale wind capable of blowing the steam away from basin bottom,
the vapour buildup would have favoured radiative heating of basin
bottom since steam is powerful greenhouse gas. Eventually, the vapour
would have caused wet convection - in other words, rainfall probably
in form of thunderstorms.
The wet adiabatic lapse rate is much lower than the dry adiabatic
lapse rate. I have not found out how much lower, especially in the
temperature range I am interested in. Does anyone in s.g.m know?

Thus, it seems likely that the temperatures may have been below 60-s
and accompanied by some rainfall.

Now regarding hostility to life:
Yes, a man whose body temperature is in low 40-s is in mortal peril. A
man whose body temperature is in upper 40-s is a corpse.

The absolute maxima of temperature on modern Earth have occurred in
Azizija - 58 Celsius - and Death Valley - 56,7 degrees.

Death Valley has July averages of 34 degrees, IIRC, and Azizija has
July averages of 28 degrees.

Now if you go to Death Valley or Azizija, in both places you will find
fairly diverse plant life. Part of the plants vegetate throughout
thesummer.

Plants cannot flee heat like animals. Nor can plants, especially
desert plants, cool themselves very much by evaporation like mammals
do, because they cannot afford the water.

It follows that many plants now growing in Azizija, or their
ancestors, have heated to 58 degrees and lived. Actually, sunlight
ground and plants on it could heat to higher temperatures than air in
shadow!

Now, both in Death Valley and Azizija, the extreme heat is usually
accompanied by low humidity. Mammals enjoy it, since it helps
evaporative cooling.

However, plants are not helped much by evaporation. On the contrary -
it tends to dry them up.

It would seem likely that plants which can endure 58 degrees and low
humidity could also endure 58 degrees and high humidity.

Now, the area with currently the highest dewpoint temperatures -
southern Red Sea region - does not really have that great absolute
temperature maxima. What makes the heat troublesome for men - not
intolerable, since they do live there, and long have - is the fact
that there are consistent high temperatures with high humidity.

I don't remember the exact data. But I imagine that in summer of Red
Sea region, you could have night temperatures of upper 20-s and day
temperatures of upper 30-s, with high humidity - whereas in Death
Valley or so, you'd encounter night temperatures of lower 20-s and day
temperatures in lower 40-s, with low humidity, and with occasional
temperatures in 50-s.

Now try to imagine a region where night temperatures are in lower 40-s
and day temperatures in upper 40-s, with high humidity. Occasional
maxima might be somewhere in 50-s, with high humidity...

Men would not endure. On the other hand, many plants might.

Not all the plants, though. I wonder which plants would choose to grow
in such conditions?

One more thing: these conditions might be unfavourable to many
animals, including herbivores.

This is really quite bizarre -- like
something on another planet. If this situation still existed the
worst parts would be as hostile as the South Pole. Worse even,
since extreme cold is easier to deal with than extreme heat. It's
interesting to think about what the history of exploration into
this region might have looked like had it existed until today!

We could expect some seasonality, since the Mediterranean basin is far
from equator. The heat would be less in winter. How much less is very
unclear to me!

In article ,
(Jaak Suurpere) writes:
|
| It follows that many plants now growing in Azizija, or their
| ancestors, have heated to 58 degrees and lived. Actually, sunlight
| ground and plants on it could heat to higher temperatures than air in
| shadow!

They do, as I can witness. Thermophilic bacteria can take much
higher temperatures, too.

| It would seem likely that plants which can endure 58 degrees and low
| humidity could also endure 58 degrees and high humidity.

Not so. Inter alia, high humidity permits fungi to flourish. Few
USA plants would last a month in the humid tropics, and none from
outside the deep south would. But there would be plants that could
adapt, given long enough.

| Now, the area with currently the highest dewpoint temperatures -
| southern Red Sea region - does not really have that great absolute
| temperature maxima. What makes the heat troublesome for men - not
| intolerable, since they do live there, and long have - is the fact
| that there are consistent high temperatures with high humidity.

Fairly high. Not very high. Nowhere near the tropical jungles.

| Now try to imagine a region where night temperatures are in lower 40-s
| and day temperatures in upper 40-s, with high humidity. Occasional
| maxima might be somewhere in 50-s, with high humidity...
|
| Men would not endure. On the other hand, many plants might.

It is unclear, given enough water. I don't know whether mammals'
requirements are for a bound on the relative humidity dependent
on temperature, or for a margin in water vapour pressure between
ambient and maximal (i.e. dew point).

If the latter, mammals would survive. And we are fairly typical
in this respect.

| Not all the plants, though. I wonder which plants would choose to grow
| in such conditions?

Nothing current, but some of them could adapt.

| One more thing: these conditions might be unfavourable to many
| animals, including herbivores.

Yes, they would be.


Regards,
Nick Maclaren,
University of Cambridge Computing Service,
New Museums Site, Pembroke Street, Cambridge CB2 3QH, England.
Email:
Tel.: +44 1223 334761 Fax: +44 1223 334679

Sorry.

In article ,
(Nick Maclaren) writes:
|
| It is unclear, given enough water. I don't know whether mammals'
| requirements are for a bound on the relative humidity dependent
| on temperature, or for a margin in water vapour pressure between
| ambient and maximal (i.e. dew point).

I meant:

ambient (i.e. dew point) and maximal (i.e. water vapour
pressure at the ambient temperature).

Upon thinking about it, it is probable that the requirement is
for the dew point to be sufficiently low - preferably well below
37 Celcius ....

Engage brain before posting, Nick.

However, that is cooling by perspiration. My points about relative
humidity and fungal attack remain true, though it can also be other
organisms that thrive.



Regards,
Nick Maclaren,
University of Cambridge Computing Service,
New Museums Site, Pembroke Street, Cambridge CB2 3QH, England.
Email:
Tel.: +44 1223 334761 Fax: +44 1223 334679

(Jaak Suurpere) wrote:

[ when the Mediterranean was mostly empty ]
However, the air was humid. I have argued that if there was no
large-scale wind capable of blowing the steam away from basin bottom,
the vapour buildup would have favoured radiative heating of basin
bottom since steam is powerful greenhouse gas. Eventually, the vapour
would have caused wet convection - in other words, rainfall probably
in form of thunderstorms.

Eeek! Thunderstorms forming in a saturated 40 deg. C. airmass,
plus an /extra/ 3 km headstart before they rise up to sea-level
(then another 18 km before they finally hit the tropopause.)

So, would the Mediterranean Basin be Convective Hell on Earth,
with nonstop F5 tornadoes, basketball-sized hail, and lightning
utterly destroying any attempts at plant life and removing all
of the topsoil down to the bedrock?


(Note to self: if Mediterranean ever dries up again, do not visit)

;K

(Nick Maclaren) wrote in message ...
In article ,
(Jaak Suurpere) writes:
|
| It follows that many plants now growing in Azizija, or their
| ancestors, have heated to 58 degrees and lived. Actually, sunlit
| ground and plants on it could heat to higher temperatures than air in
| shadow!

They do, as I can witness. Thermophilic bacteria can take much
higher temperatures, too.

| It would seem likely that plants which can endure 58 degrees and low
| humidity could also endure 58 degrees and high humidity.

Not so. Inter alia, high humidity permits fungi to flourish.

At which temperatures?

Jakarta, one of the best-known places in humid tropics, has absolute
maximum of 37 degrees. We can fairly guess that some parts of humid
tropics would have absolute maxima a bit higher. But how much heat can
live fungi endure?

Few USA plants would last a month in the humid tropics, and none from
outside the deep south would. But there would be plants that could
adapt, given long enough.

| Now, the area with currently the highest dewpoint temperatures -
| southern Red Sea region - does not really have that great absolute
| temperature maxima. What makes the heat troublesome for men - not
| intolerable, since they do live there, and long have - is the fact
| that there are consistent high temperatures with high humidity.

Fairly high. Not very high. Nowhere near the tropical jungles.

| Now try to imagine a region where night temperatures are in lower 40-s
| and day temperatures in upper 40-s, with high humidity. Occasional
| maxima might be somewhere in 50-s, with high humidity...
|
| Men would not endure. On the other hand, many plants might.

It is unclear, given enough water. I don't know whether mammals'
requirements are for a bound on the relative humidity dependent
on temperature, or for a margin in water vapour pressure between
ambient and maximal (i.e. dew point).

If the latter, mammals would survive. And we are fairly typical
in this respect.

| Not all the plants, though. I wonder which plants would choose to grow
| in such conditions?

Nothing current, but some of them could adapt.

Really?
What I suppose is that there are plants which are preadapted. For
example, desert plants are adapted to great heat with low humidity.
Some of them might flourish with great heat and humidity.
I suppose that some fungi adapted to great humidity and moderate heat
might not be troubling with great heat. Of course, others might be
trouble.

Then again, if there are places with wet conditions, some plants
adapted to wet conditions and moderate heat might make do with wet
conditions and great heat - and be well rid of some of their
competitors as well as some herbivores.

| One more thing: these conditions might be unfavourable to many
| animals, including herbivores.

Yes, they would be.

In article ,
Jaak Suurpere wrote:

| It would seem likely that plants which can endure 58 degrees and low
| humidity could also endure 58 degrees and high humidity.

Not so. Inter alia, high humidity permits fungi to flourish.

At which temperatures?

Anything above freezing and below whatever their maximum is. We have
this problem very badly in the UK during the winter, and I go into
great lengths in the uk.rec.gardening climate FAQ I am writing.

Jakarta, one of the best-known places in humid tropics, has absolute
maximum of 37 degrees. We can fairly guess that some parts of humid
tropics would have absolute maxima a bit higher. But how much heat can
live fungi endure?

Dunno. What I am certain is that some would adapt to higher temperatures,
just like plants. The key here is that many of the destructive ones are
effectively single celled organisms, and will grow only when their cells
don't dry out. Hence the plant rots in the UK, and all sorts of nasty
and interesting plant and animal rots in places like Jakarta and Port
Harcourt.

What I suppose is that there are plants which are preadapted. For
example, desert plants are adapted to great heat with low humidity.
Some of them might flourish with great heat and humidity.

Experience is that most don't. They can often take great heat and
moderate humidity, but have few defences against fungi and bacteria
(not surprisingly).

I suppose that some fungi adapted to great humidity and moderate heat
might not be troubling with great heat. Of course, others might be
trouble.

Yes. I doubt that many of the species of either plant or fungus would
be quite the same as any we see today.

Then again, if there are places with wet conditions, some plants
adapted to wet conditions and moderate heat might make do with wet
conditions and great heat - and be well rid of some of their
competitors as well as some herbivores.

Again, they would need to adapt. MOST such plants are a bit temperature
sensitive, but not all.


Regards,
Nick Maclaren,
University of Cambridge Computing Service,
New Museums Site, Pembroke Street, Cambridge CB2 3QH, England.
Email:
Tel.: +44 1223 334761 Fax: +44 1223 334679

Mad Bad Rabbit wrote in message ...
(Jaak Suurpere) wrote:

[ when the Mediterranean was mostly empty ]
However, the air was humid. I have argued that if there was no
large-scale wind capable of blowing the steam away from basin bottom,
the vapour buildup would have favoured radiative heating of basin
bottom since steam is powerful greenhouse gas. Eventually, the vapour
would have caused wet convection - in other words, rainfall probably
in form of thunderstorms.

Eeek! Thunderstorms forming in a saturated 40 deg. C. airmass,
plus an /extra/ 3 km headstart before they rise up to sea-level
(then another 18 km before they finally hit the tropopause.)

However, when the convective cloud reaches the height of 3 kilometres
and approaches the sea level, it would encounter the dry etesian winds
shearing off its top.

Humid air rising only 3 kilometres can definitely reach condensation.
But would such clouds produce thunder?

So, would the Mediterranean Basin be Convective Hell on Earth,
with nonstop F5 tornadoes, basketball-sized hail,

Lack of freezing in clouds would prevent hail.

and lightning
utterly destroying any attempts at plant life and removing all
of the topsoil down to the bedrock?

If there is a bedrock, and some place below to carry th soil.
I suppose that there would be at least some gently sloping plains not
far above the erosion base level.



(Note to self: if Mediterranean ever dries up again, do not visit)

;K

Conrad Hodson wrote in message ...
On 15 Dec 2002, Jaak Suurpere wrote:

I remembered that the evaporites had been seen by seismic reflections,
but this would not tell much about the precise conditions of deep or
shallow brine.

So, a lot of evaporites have actually been brought to surface?

Drilled cores, going back at least to one of the GLOMAR ships in the '70's
IIRC. The evaporites--thick beds of water-soluble stuff like halite on
what is, after all, the floor of a sea was unexpected, to say the
least. Then the seismic mapping you mention showed just how extensive the
evaporite deposits are. Putting this together with ground-based work that
showed how valleys such as the Nile and Rhone are sediment-filled cuts in
bedrock that go far deeper than modern sea level is what led to the
realization that Gibraltar has been intermittently closed (and the Med
dried up) ever since Africa got close enough to Spain to apply the
squeeze. The Med is a Tethys Sea relict of course--but it's since it got
pinched off at both ends that things have gotten really interesting!


Compare it with the Gangetic Plain!

You could expect cold air to build up over the large plateaux and
basins of Tibet and then spill into the gorges of the numerous rivers
passing through the Himalayas.

And the effects? None that I know of. Gangetic Plain in winter has
quiet, clear weather, except for feeble cyclones arriving from the
west.

Good point. And "winter" is the hot dry season there, at least away from
the coasts. There may be a difference, though, in that the Med is a
winter rainy season area--at least today, and the extensive and
distinctive ecosystem suggests that that's been true for quite a while.

Siberian air isn't any kind of moisture source--mP air spilling over
Europe from the North Atlantic is.

I am not sure if all the air in Tibet comes from Siberia.
Part of the air comes from the west, Atlanic Ocean, and arrives the
western edge of Pamir, Hindu Kush and Karakoram as source of
snowfalls.

But if it tries to continue east across Pamirs and Tibet, apparently
it suffers adiabatic heating. And if it attempts to turn south towards
the Gngetic Plain, it apparently is even more unable to descend.

A possible difference? Now _I'm_
speculating beyond my knowledge... :-)


Apparently the descent of the 4 or so kilometres from Tibet to India
precludes any cold air from getting through. The Mediterranean could
have had similar relief.

Or take the Colorado Plateau. Again, do cold air outbursts often
trouble Phoenix?

Don't know about Phoenix, but I've been in the Los Angeles Basin while
katabatic winds from the high deserts were blowing the roofs off houses in
Glendale. Adiabatic heating warms the air up, and a good thing, too, if
your roof is gone.


Yes.

And the barrier between Los Angeles and high desert has several gaps
around 1000 metres.

My impression is that strong katabatic winds exist downwind of gaps
that are either on the same level or include barriers of up to one
kilometre.

But descents of over two kilometres, like the western slope of Sierra
Nevada, southern slopes of Colorado Plateau and Alps et cetera
apparently force any cold air not only to heat up but also to break
off the surface before reaching the bottom.


Adiabatic heating of the cold air mass is only part of
the story, because the cT air in the temporarily humid basin is
solar-heated as well, powerfully.

But its temperature would have upper constraints set by wet convective
instability, whereas the cold air mass has to undergo dry adiabatic
heating.

Agree. Aren't we talking about something akin to the difference between
local and frontal thunderstorms in a place like the Mississippi Valley,
though? The "upper contraints" you talk about serve to recycle moisture
locally, in afternoon thunderstorms of essentially local origin. But it's
when a cold air mass blows in from outside the area that all hell breaks
loose. Instead of being diffused over a large area, that moist-air
potential energy gets concentrated and organized into a violent contact
zone. That's the sort of thing I wonder about happening along the
air-drainage routes into the basins.

Again remember that Mississippi Valley has no high barriers to cold
air and thus no adiabatic heating.

Even without adiabatic heating, take the modern mistral. It follows
the Rhone gap and crosses relief of at most 300 metres in Burgundy.

But mistral is usually accompanied by clear weather and sunshine -
however cold and strong the wind is.

Yo could expect the wintry Mediterranean to have a lot of moisture
from warm water surface. But where are the violent rainfalls mistral
migh cause?

The cold front remains a cold front all
the way to the bottom of the basin. There's also more going on than air
responding instantly and passively to the gas laws. Moving air has
momentum, and violent katabatic winds in the real world go for long
distances even after adiabatic heating has done its bit. If that air mass
hits the unyielding basin floor and its momentum goes to work lifting
already unstable humid air--well, it would be fun to watch, especially
from the mouth of a cave in the side of a hill. In a canyon bottom, or
lighting-riddled hilltop, or on a plain where tornadoes came to dance, it
might be less fun.

So this still seems plausible to me, but I've called you on the subject of
ground truth, and here _I_ am speculating. Does anyone here know of
geological evidence that's relevant? Flash-flood deposits from
now-submarine canyons, perhaps? Fossils or pollen from plants (if
any) growing in the basins? If your steamy supertropical lakes and swamps
of fresh water really existed, stuff probably lived there. If my "Venus
Lite" suggestion is more accurate, there might not have been much down
there but thermophilic bacteria digesting flood debris when they could
come up with the moisture to do so.

Now let us think of the physiological constraints on plant life.

The hottest places on Earth are Azizija and Death Valley.

Both have reasonably obvious and diverse plant life. Part of it is
perennial.

Which is no wonder. Death Valley receives over 40 mm of rain per year.
Azizija gets over 200 mm.

But we must conclude that many of the plants who grow at Azizija, or
their ancestors, endured heat of 58 degrees one day.

Given that most of the desert plants, even perennial ones, do not have
constant plentiful water supply for evaporative cooling, the plants
must have heated to 58 degrees - or more, if they themselves were
heated by sunlight and hot ground.

They lived.

Now, plants do not like drying. We can conclude that if these plants
endured 58 degrees with low relative humidity, they would also have
endured 58 degrees with high humidity.

From what I have heard, the Red Sea coasts don't have particularly
high temperature extremes.

So, an area could have absolute maximum temperature of 57 degrees over
the average of 34 degrees with low humidity, (Death Valley) or
absolute maximum of 58 degrees over the average of 28 degrees with low
humidity (Azizija) and be settled by plants. But what if there is an
area that has absolute maxima of 58 degrees over a July average of 45
degrees and high humidity? Would plants endure?

Not all, of course. There are plants that have trouble occasionally
enduring 30 degrees.

I'd like to crosspost to sci.bio.botany for opinions and drop
sci.geo.oceanography for that goal.

Microfossil studies might be really relevant here, if cores have hit the
right places and researchers have asked the right questions of the cores.

Conrad Hodson

(John Brock) wrote in message ...
In article ,
Jaak Suurpere wrote:
(Nick Maclaren) wrote in message ...
In article ,
(Jaak Suurpere) writes:
| (pete) wrote in message ...

| The air density in such a basin, that near the equator, would make the
| conditions unthinkably intolerable. You would have rivers flowing
| down into the basin and evaporating, yielding a blistering hot
| desert which would be very high humidity were it not for its high
| temperature and pressure.

| Pressure would not do anything for humidity.
| If there is open water to evaporate, the air does get near saturated,
| even if the water is boiling hot. Which probably would not have been
| the case in Messinian times. It was still not that deep.

By which I assume that you mean that air flow through the basin
was significant? The "open water - saturation" effect is
conditional on the air movement not counteracting it.

Correct.
If you have archives extending to mid-December, I discussed it
before...
Basically, Mediterranean deep basin would be in a bad situation
regarding air movement.
It would be 3 or 4 kilometres above

Sorry - below, of course!

any surrounding area.
Any wind descending into basin would have to heat at the dry adiabatic
lapse rate. Which, IIRC, is about 10 degrees per kilometre. Over that
height, it would be 30 to 40 degrees.

In summer, it would mean heating from 25 degrees to around 60. If the
basin is only ventilated by winds of over 60 degrees, any cooling of
air inside the basin, whether through evaporation or radiation, would
tend to form cooler air mass, which would be stable and therefore
stagnant. And this would mean thatr it will reach saturation.

This is very interesting, and I want to make sure I understand it:

About 5 million years ago the Mediterranean not only went dry but
turned into a desert far hotter and more hostile to life

This I discussed before. I'll repeat it below for those who do not
have archives.

than anything on Earth today. The reason it was so hot was that as air
descended 3 or 4 kilometers into the basin (someone else said 3
miles -- which is right?)

Both are right, kind of.
The current deepest spots of Mediterranean are at a depth of around 5
kilometres - approximately 3 miles.

But this is on a small area. If there was any water remaining in the
Mediterranean, it could be expected to fill the deepest spots.

But it does seem likely that the remaining water levels could have
been around 3 or 4 kilometres below ocean.

it heated about 10 degrees per kilometer
due to increasing air pressure (is that what the "dry adiabatic
lapse rate" refers to?). In the summer the temperature would reach
60 degrees (Celsius I assume; = 140 Fahrenheit). The air didn't
circulate much, being at the bottom of a basin, and if there were
any significant standing bodies of water at the bottom (and I guess
there had to be, since a number of rivers empty into the Mediterranean)
they would cool the air just slightly, and this air would form a
hot, stagnant air mass with humidity at 100 percent that was
basically nailed to the bottom of the basin.

Is that a reasonable summary?

Summary of what was recently said; but there is more to this.

Synoptic-scale winds, the only thing that could have ventilated the
air in the bottom and kept it dry in the presence of standing water,
would have had to heat at the dry adiabatic lapse rate, 10 degrees per
kilometre, leading to summer temperatures in 60s of Celsius.

However, the air was humid. I have argued that if there was no
large-scale wind capable of blowing the steam away from basin bottom,
the vapour buildup would have favoured radiative heating of basin
bottom since steam is powerful greenhouse gas. Eventually, the vapour
would have caused wet convection - in other words, rainfall probably
in form of thunderstorms.
The wet adiabatic lapse rate is much lower than the dry adiabatic
lapse rate. I have not found out how much lower, especially in the
temperature range I am interested in. Does anyone in s.g.m know?

Thus, it seems likely that the temperatures may have been below 60-s
and accompanied by some rainfall.

Now regarding hostility to life:
Yes, a man whose body temperature is in low 40-s is in mortal peril. A
man whose body temperature is in upper 40-s is a corpse.

The absolute maxima of temperature on modern Earth have occurred in
Azizija - 58 Celsius - and Death Valley - 56,7 degrees.

Death Valley has July averages of 34 degrees, IIRC, and Azizija has
July averages of 28 degrees.

Now if you go to Death Valley or Azizija, in both places you will find
fairly diverse plant life. Part of the plants vegetate throughout
thesummer.

Plants cannot flee heat like animals. Nor can plants, especially
desert plants, cool themselves very much by evaporation like mammals
do, because they cannot afford the water.

It follows that many plants now growing in Azizija, or their
ancestors, have heated to 58 degrees and lived. Actually, sunlight
ground and plants on it could heat to higher temperatures than air in
shadow!

Now, both in Death Valley and Azizija, the extreme heat is usually
accompanied by low humidity. Mammals enjoy it, since it helps
evaporative cooling.

However, plants are not helped much by evaporation. On the contrary -
it tends to dry them up.

It would seem likely that plants which can endure 58 degrees and low
humidity could also endure 58 degrees and high humidity.

Now, the area with currently the highest dewpoint temperatures -
southern Red Sea region - does not really have that great absolute
temperature maxima. What makes the heat troublesome for men - not
intolerable, since they do live there, and long have - is the fact
that there are consistent high temperatures with high humidity.

I don't remember the exact data. But I imagine that in summer of Red
Sea region, you could have night temperatures of upper 20-s and day
temperatures of upper 30-s, with high humidity - whereas in Death
Valley or so, you'd encounter night temperatures of lower 20-s and day
temperatures in lower 40-s, with low humidity, and with occasional
temperatures in 50-s.

Now try to imagine a region where night temperatures are in lower 40-s
and day temperatures in upper 40-s, with high humidity. Occasional
maxima might be somewhere in 50-s, with high humidity...

Men would not endure. On the other hand, many plants might.

Not all the plants, though. I wonder which plants would choose to grow
in such conditions?

One more thing: these conditions might be unfavourable to many
animals, including herbivores.

This is really quite bizarre -- like
something on another planet. If this situation still existed the
worst parts would be as hostile as the South Pole. Worse even,
since extreme cold is easier to deal with than extreme heat. It's
interesting to think about what the history of exploration into
this region might have looked like had it existed until today!

We could expect some seasonality, since the Mediterranean basin is far
from equator. The heat would be less in winter. How much less is very
unclear to me!

In article ,
(Jaak Suurpere) writes:
|
| It follows that many plants now growing in Azizija, or their
| ancestors, have heated to 58 degrees and lived. Actually, sunlight
| ground and plants on it could heat to higher temperatures than air in
| shadow!

They do, as I can witness. Thermophilic bacteria can take much
higher temperatures, too.

| It would seem likely that plants which can endure 58 degrees and low
| humidity could also endure 58 degrees and high humidity.

Not so. Inter alia, high humidity permits fungi to flourish. Few
USA plants would last a month in the humid tropics, and none from
outside the deep south would. But there would be plants that could
adapt, given long enough.

| Now, the area with currently the highest dewpoint temperatures -
| southern Red Sea region - does not really have that great absolute
| temperature maxima. What makes the heat troublesome for men - not
| intolerable, since they do live there, and long have - is the fact
| that there are consistent high temperatures with high humidity.

Fairly high. Not very high. Nowhere near the tropical jungles.

| Now try to imagine a region where night temperatures are in lower 40-s
| and day temperatures in upper 40-s, with high humidity. Occasional
| maxima might be somewhere in 50-s, with high humidity...
|
| Men would not endure. On the other hand, many plants might.

It is unclear, given enough water. I don't know whether mammals'
requirements are for a bound on the relative humidity dependent
on temperature, or for a margin in water vapour pressure between
ambient and maximal (i.e. dew point).

If the latter, mammals would survive. And we are fairly typical
in this respect.

| Not all the plants, though. I wonder which plants would choose to grow
| in such conditions?

Nothing current, but some of them could adapt.

| One more thing: these conditions might be unfavourable to many
| animals, including herbivores.

Yes, they would be.


Regards,
Nick Maclaren,
University of Cambridge Computing Service,
New Museums Site, Pembroke Street, Cambridge CB2 3QH, England.
Email:
Tel.: +44 1223 334761 Fax: +44 1223 334679

Sorry.

In article ,
(Nick Maclaren) writes:
|
| It is unclear, given enough water. I don't know whether mammals'
| requirements are for a bound on the relative humidity dependent
| on temperature, or for a margin in water vapour pressure between
| ambient and maximal (i.e. dew point).

I meant:

ambient (i.e. dew point) and maximal (i.e. water vapour
pressure at the ambient temperature).

Upon thinking about it, it is probable that the requirement is
for the dew point to be sufficiently low - preferably well below
37 Celcius ....

Engage brain before posting, Nick.

However, that is cooling by perspiration. My points about relative
humidity and fungal attack remain true, though it can also be other
organisms that thrive.



Regards,
Nick Maclaren,
University of Cambridge Computing Service,
New Museums Site, Pembroke Street, Cambridge CB2 3QH, England.
Email:
Tel.: +44 1223 334761 Fax: +44 1223 334679

(Jaak Suurpere) wrote:

[ when the Mediterranean was mostly empty ]
However, the air was humid. I have argued that if there was no
large-scale wind capable of blowing the steam away from basin bottom,
the vapour buildup would have favoured radiative heating of basin
bottom since steam is powerful greenhouse gas. Eventually, the vapour
would have caused wet convection - in other words, rainfall probably
in form of thunderstorms.

Eeek! Thunderstorms forming in a saturated 40 deg. C. airmass,
plus an /extra/ 3 km headstart before they rise up to sea-level
(then another 18 km before they finally hit the tropopause.)

So, would the Mediterranean Basin be Convective Hell on Earth,
with nonstop F5 tornadoes, basketball-sized hail, and lightning
utterly destroying any attempts at plant life and removing all
of the topsoil down to the bedrock?


(Note to self: if Mediterranean ever dries up again, do not visit)

;K

(Nick Maclaren) wrote in message ...
In article ,
(Jaak Suurpere) writes:
|
| It follows that many plants now growing in Azizija, or their
| ancestors, have heated to 58 degrees and lived. Actually, sunlit
| ground and plants on it could heat to higher temperatures than air in
| shadow!

They do, as I can witness. Thermophilic bacteria can take much
higher temperatures, too.

| It would seem likely that plants which can endure 58 degrees and low
| humidity could also endure 58 degrees and high humidity.

Not so. Inter alia, high humidity permits fungi to flourish.

At which temperatures?

Jakarta, one of the best-known places in humid tropics, has absolute
maximum of 37 degrees. We can fairly guess that some parts of humid
tropics would have absolute maxima a bit higher. But how much heat can
live fungi endure?

Few USA plants would last a month in the humid tropics, and none from
outside the deep south would. But there would be plants that could
adapt, given long enough.

| Now, the area with currently the highest dewpoint temperatures -
| southern Red Sea region - does not really have that great absolute
| temperature maxima. What makes the heat troublesome for men - not
| intolerable, since they do live there, and long have - is the fact
| that there are consistent high temperatures with high humidity.

Fairly high. Not very high. Nowhere near the tropical jungles.

| Now try to imagine a region where night temperatures are in lower 40-s
| and day temperatures in upper 40-s, with high humidity. Occasional
| maxima might be somewhere in 50-s, with high humidity...
|
| Men would not endure. On the other hand, many plants might.

It is unclear, given enough water. I don't know whether mammals'
requirements are for a bound on the relative humidity dependent
on temperature, or for a margin in water vapour pressure between
ambient and maximal (i.e. dew point).

If the latter, mammals would survive. And we are fairly typical
in this respect.

| Not all the plants, though. I wonder which plants would choose to grow
| in such conditions?

Nothing current, but some of them could adapt.

Really?
What I suppose is that there are plants which are preadapted. For
example, desert plants are adapted to great heat with low humidity.
Some of them might flourish with great heat and humidity.
I suppose that some fungi adapted to great humidity and moderate heat
might not be troubling with great heat. Of course, others might be
trouble.

Then again, if there are places with wet conditions, some plants
adapted to wet conditions and moderate heat might make do with wet
conditions and great heat - and be well rid of some of their
competitors as well as some herbivores.

| One more thing: these conditions might be unfavourable to many
| animals, including herbivores.

Yes, they would be.

In article ,
Jaak Suurpere wrote:

| It would seem likely that plants which can endure 58 degrees and low
| humidity could also endure 58 degrees and high humidity.

Not so. Inter alia, high humidity permits fungi to flourish.

At which temperatures?

Anything above freezing and below whatever their maximum is. We have
this problem very badly in the UK during the winter, and I go into
great lengths in the uk.rec.gardening climate FAQ I am writing.

Jakarta, one of the best-known places in humid tropics, has absolute
maximum of 37 degrees. We can fairly guess that some parts of humid
tropics would have absolute maxima a bit higher. But how much heat can
live fungi endure?

Dunno. What I am certain is that some would adapt to higher temperatures,
just like plants. The key here is that many of the destructive ones are
effectively single celled organisms, and will grow only when their cells
don't dry out. Hence the plant rots in the UK, and all sorts of nasty
and interesting plant and animal rots in places like Jakarta and Port
Harcourt.

What I suppose is that there are plants which are preadapted. For
example, desert plants are adapted to great heat with low humidity.
Some of them might flourish with great heat and humidity.

Experience is that most don't. They can often take great heat and
moderate humidity, but have few defences against fungi and bacteria
(not surprisingly).

I suppose that some fungi adapted to great humidity and moderate heat
might not be troubling with great heat. Of course, others might be
trouble.

Yes. I doubt that many of the species of either plant or fungus would
be quite the same as any we see today.

Then again, if there are places with wet conditions, some plants
adapted to wet conditions and moderate heat might make do with wet
conditions and great heat - and be well rid of some of their
competitors as well as some herbivores.

Again, they would need to adapt. MOST such plants are a bit temperature
sensitive, but not all.


Regards,
Nick Maclaren,
University of Cambridge Computing Service,
New Museums Site, Pembroke Street, Cambridge CB2 3QH, England.
Email:
Tel.: +44 1223 334761 Fax: +44 1223 334679

Mad Bad Rabbit wrote in message ...
(Jaak Suurpere) wrote:

[ when the Mediterranean was mostly empty ]
However, the air was humid. I have argued that if there was no
large-scale wind capable of blowing the steam away from basin bottom,
the vapour buildup would have favoured radiative heating of basin
bottom since steam is powerful greenhouse gas. Eventually, the vapour
would have caused wet convection - in other words, rainfall probably
in form of thunderstorms.

Eeek! Thunderstorms forming in a saturated 40 deg. C. airmass,
plus an /extra/ 3 km headstart before they rise up to sea-level
(then another 18 km before they finally hit the tropopause.)

However, when the convective cloud reaches the height of 3 kilometres
and approaches the sea level, it would encounter the dry etesian winds
shearing off its top.

Humid air rising only 3 kilometres can definitely reach condensation.
But would such clouds produce thunder?

So, would the Mediterranean Basin be Convective Hell on Earth,
with nonstop F5 tornadoes, basketball-sized hail,

Lack of freezing in clouds would prevent hail.

and lightning
utterly destroying any attempts at plant life and removing all
of the topsoil down to the bedrock?

If there is a bedrock, and some place below to carry th soil.
I suppose that there would be at least some gently sloping plains not
far above the erosion base level.



(Note to self: if Mediterranean ever dries up again, do not visit)

;K