Quick summary -- no one knows yet, but the best evidence I can find
suggests that Peter Ward was basically right, that global warming is pushing us closer than
we would think to "fire and brimstone" -- a rerun of the mass extinctions of the past, where H2S poisoning ("brimstone") and radiation from "ozone holes" ("fire") were high enough to kill
every human on earth.
Peter Ward's important classic, Under a Green Sky, presents us with
some important questions: how close are we to the time when emanations
of H2S to the atmosphere
("brimstone") or radiation induced by a new ozone hole ("fire") start
growing to the point where all higher mammals on earth, including
humans, would be killed? Ward's book (and the paper by Kump which he
cites) proves that these problems have caused mass extinctions many
times in the past, but he doesn't unravel the mechanisms of HOW this
happens well enough to give us any kind of decent early warning. He
argues that a new kind of crossdisciplinary cooperation would be
needed, between people who study the long history of earth and people
who study the relevant types of ocean currents -- "thermohaline
currents" (THC), in order to understand just how bad the problem is
for us today. He does suggest that we are in fact on a road to a new
mass extinction, sooner than we think.
I have done a lot of google scholar search and such, to see whether
anyone on earth has made the right connections to analyze this
situation. Failing that -- I have groped to try to make the
connections myself. Just yesterday, I had a chance to study a paper by
Iris Grossman, of the Carnegie Mellon climate change group, which
explains the relevant THC more clearly than any other paper I have
found as yet. The picture is complicated, but here are..
MY CRUDE INITIAL IMPRESSIONS OF THE BOTTOM LINE
1. There is a very tight coupling between the warming northern Gulf
Stream ("GS") currents and the deep currents ("NDWA"?) which protect
us from a Green Sky event.
2. For the moment, the melting of ice on Greenland reduces the
saltiness (salinity) of water in the North Atlantic, which weakens the
warming current (adding some cold and snow and such to places like
England, France and New England) and the NDWA. However, the AMOUNT of
weakness of these currents is proportional to the RATE of melting of
the Greenland ice; if it keeps melting at the same rate, the cold
storms would not get worse,
and the ocean will not become more stagnant than it is today. It may
even be that this problem peaked at around 1970, when there was a
"Great Saline Anomaly" (low salinity
and a weakening for a few years of the warming GS).
3. Midterm, the situation seems even less threatening. The NDWA seems
to depend on the salinity of the cold North Atlantic and North Pacific
water more than anything else. For now, melting of Greenland ice is a
major factor, but when that is totally gone (just as the Arctic ice is
on path to disappear), this effect goes away. Then we fall back to the
long-term drivers of salinity: rain and evaporation. Thanks to
melting, we know to expect less rain in places like the Himalayas (due
to the "albedo effect"); warming and low albedo should also increase
evaporation. That all should increase saltiness.
4. HOWEVER: this nice NDWA of ours is new. In most of earth's history,
we did not have it at all. In most of earth's history, agricultural
runoff like what we had today, combined with
stagnant flows in the deep ocean, would be enough to cause a "green
sky" effect --
and many times did, killing everyone. What was different about the THC
The obvious answer: the THC now is very sensitive to effects of
salinity when water is in the very special and unique regime between 0
degrees C and 4 degrees C. (Notice how
little the salinity and temperature at the equator seems to change
this story!) Back then, the poles were warmer. Bottom line: there
probably exists a "tipping point" when temperatures at
the North Pole would get high enough to turn off the NDWA, both in
north Atlantic and north Pacific, quite enough to get us all killed.
BOTTOM LINE: It looks as if the Green Sky problem is current reducing;
however, when things get warm enough in the water in the North Pole
area, that will reverse. We do not yet know the critical temperature
which kills us all, but on the whole, the bottom line feels a lot like
Ward's position, even though the logic behind it is quite different.
Needless to say, this cries out for scientific analysis, and
quantitative analysis, far beyond
anything I have done here.
It doesn't help us that the South Pole is in a different regime.
I find myself thinking back to the old movies, AI and Wall-E.
Thoughts about robots and archaea. But the bottom line here really
cries out for more direct follow-ups.
I also remember the line in the Bible about "next tme wikll be fire and brimstone."
And I think about the friendly NASA xenobiologist who guided me a few years ago, when
I was first exploring these questions... and other issues related to archaea.
Of course, none of this represents anyone else. It's all tentative even for me. Just groping
as best I can to understand stuff. (Am sorry how I once thought temperature gradient
would be more important here. Maybe they will be more important in future to THC,
but not quite yet.)
Best of luck... we all need it...