Arctic's sub-tropical past

[JonClarke]

Hi Steve<br /><br />Yep, solar variability is the BIG unknown. certainly the solar "constant" has been increasing since the maunder minimum, this will have a warming effect. It coincides the anthropogenic increase in CO2 with industrialisation, making disentangling the two effects difficult. <br /><br />For the Cretaceous the assumption is that while solar output may have been different it probably wasn't too different and its effect was overwhelmed by other factors like continental configuration, ocean circulation patterns etc. <br /><br />The sun can't be too variable or we would have frozen or fried long ago. But I find it fascinating that Mars is warming up at the same time that earth is, maybe comparing ice cores from Mars with the terrestrial climate record will help us tie down the solar variability issue. I hope in my life time!<br /><br />Your analogy with the N-body problem is a good one. Almost all geological problems are N-body ones, which is why we geologists look down on mere physicists who can only cope with the simple questions <img src="/images/icons/wink.gif" /><br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[JonClarke]

Hi Steve<br /><br />the rortation of the earth slows down at a rate of 1.6 milliseconds a century, so at 100 Ma the day would have been 1600 seconds shorter than at present, 26 minutes. I doubt if this would have been significant, bu you never know.<br /><br />Cheers<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[Maddad]

Jon<br />The slowing rate itself is slowing, so the day would have been slightly more that 1,600 seconds shorter then. (Unless the calculation is based on the answer, which well might be! In that case the current slowing rate is slower than 1.6 miliseconds per century.) Not much shorter though, so it probably doesn't change the basic answer that the day wasn't short enough to make much of a difference.

 

[rogers_buck]

I wonder what sort of a role space itself might play. For example if the solar system passes through a super nova remnant that increases the particle density around the sun. The particles might form a sun centered torus flattened at the ecliptic with tendrils leading to the terrestrial planets. Perhaps by contriving enough perverse optics the particles could act as an IR light pipe of sorts that channels more IR specifically into the polar regions. <br /><br />Ok, it's a stretch, but you see the point of my question? Maybe it's a better argument for an ice age...<br /><br />

 

[JonClarke]

I Steve<br /><br />As I recall the there were 400 days in a year 400 My. This is cacluated from annual growth rings in corals. This equates with a 22 hour day.<br /><br />The problems with this is that the corals in question were the extinct Rugose family. We don't really know whether they had annual growth rings like modern scleractinian corals. It it is interesting. It gives a rotational slowing rate of 1.8 milliseconds a century, which is of the right order.<br /><br />Cheers<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[newtonian]

Interesting that you all ignored my post.<br /><br />Why?

 

[silylene old]

<i>Interesting that you all ignored my post. <br /><br />Why?</i><br /><br />I interpreted your post was an attempt to wrap science around a Creationite belief. So I ignored it. Perhaps others did too?<br /><br />Did I misinterpret you? <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>

 

[earthseed]

Also, an account of events on the early Earth has no relevance to this discussion, which is about the planetary climate 50 to 100 million years ago. These threads are best if they stay reasonably on topic, which is why off-topic posts often get ignored.

 

[JonClarke]

Hi Newtonian<br /><br />Looking back to see who had ignored your post I was chargrined to note that your comment was in response to a post of mine. My apologies.<br /><br />Some quick responses to your numbered comments.<br /><br />1. From memory if you have liquid water, water rock reactions very quickly remove dissolved CO2 from the water column, which then adborbs more from the atmosphere. As I recall the earliest well preserved sediments, such as those of the ~3.7 Ga Warrawoona supergroup in the Pibara indicate that the ocean was close to or at carbonate saturation, although widespread carbonate deposits are much younger, at ~2.7 Ga for example in the Hamersley Group sediments.<br /><br />2. Depends what you mean by hot. My understanding is that the tungest isotopes argue against a global magma ocean, as does the abence of a widestread anorthositic crust, unlike for the moon.<br /><br />3. As pressure goes up, so does the boiling temperature. If the early earth had a very thick atmosphere one could expect evidence of bioling, for example in hot springs, to occur at higher temperatures than at present. This can be measured from the properties of fluid inclusions, although the complicating factor of water depth has to be allowed for. Again, from memory, the presence of boiling indicators in the earliest shallow hydrothermal systems are consistent with an atmospheric pressure not too different to present. If there was a superdense atmosphere for the early Erath, it has to predate the oldest sediments, and thus 3.7 Ga<br /><br />3. This is a given. The challenge for the historical sciences is to determine which changes were gradual and which were catastrophic.<br /><br />4. In my view people should about using the Bible as a source of scientific information. It was written in a non-scientific era and addresses non-scientific issues. To use it to answer questions for which it was not written is a misuse of it. But this leads us in a different direction to this threa <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[JonClarke]

Fantastic images, thanks very much for posting them.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[earthseed]

Yes, very nice images. Where do they come from?

 

[rogers_buck]

I'd give anything to tape that picture to the porthole of the ISS. (-;

 

[earthseed]

Thanks, eburacum45, there is a lot of good stuff here. I use the Paleomap Project by Chrisopher Scotese, and also THE PALEOGEOGRAPHIC ATLAS PROJECT from the University of Chicago. There seems to be more detail in this site.

 

[newtonian]

See the current Free Space thread on the melting of Arctic Sea Ice.

 

[newtonian]

JonClarke - Now it is me who ignored your response- not deliberately, I clearly got busy with other things and forgot.<br /><br />You have my apology for the delay in responding.<br /><br />As there is a related thread in Free space, I had recalled your reference to the Maunder minimum and others who also posted on this in the missing old SDC threads.<br /><br />Now, I am not as educated as you on the details, so it will take me some research time to respond to your response properly.<br /><br />However, a simple question for starters:<br /><br />How can earth's crust have so many carbonates apparently deposited by the geologic carbon cycle without early earth having the equivalent amount of carbon dioxide in its atmosphere.<br /><br />Note I did not assign dates - that is important but makes it more complex. <br /><br />However, it is relevant to thread theme if ancient carbon dioxide levels were a factor in warmer climate.

 

[JonClarke]

Hi Newtonian<br /><br />No worries, real life intervenes for all of us <img src="/images/icons/smile.gif" /><br /><br />My understanding is that earth has always had a hydrosphere. The oldest mineral grains in detrital rocks on the Yilgarn contain istope signatures of liquid water between 4.2 and 4.6 Ga. This means that CO2 has being extracted from the atmosphere and sequested in the lithosphere via a hydrosphere since this time. While it is likely that atmospheric CO2 was higher in the Hadean ( />4 Ga) earth, the planet probably never had a super greenhouse because of this process of removal. This process happens even in the absence of life, although biota great faciliate it.<br /><br />Cheers<br /><br />Jon<br /><br /> <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[earthseed]

Well, stevehw33, I have a few problems with some of the details in your post. Lets start at the beginning:<blockquote><em>While the earth probably always had a hydrosphere, meaning, oceans, and they were probably larger a billion years ago than now, there is the probable global snow ball effect, seen about 700 M years ago, where most of the earth froze, from very severe glaciations. There might have been some water, but most of it was ice.</em></blockquote><br />I assume you mean surface ice. The Snowball Earth hypothesis says that most of the Earth's oceans were frozen, but water freezes only the surface. Most of the ocean underneath would still be liquid. Even if the Earth was ejected into outer space, it would take hundreds of millions of years to freeze the oceans to the bottom.<br /><blockquote><em>That would have taken water vapor out of the atmosphere, by freezing, just like high mountain ranges take out water and the leeward sides of them there are often deserts, as in the West.<br /><br />With water vapor gone, largely, as it is a green house gas, the earth would have cooled even more.</em></blockquote>Mountains remove water from the air because they force the air to rise, which cools it and causes water to condense. It has nothing to do with how cold they are. There is no net loss of water vapor unless it freezes to form ice caps. Since mountain tops have a very small area relative to the rest of the Earth, this has almost no affect on total water vapor in the air. But as far as Snowball Earth is concerned, you are right to conclude that water vapor would be reduced because of the lower temperature, and this would reinforce the cooling.<br /><blockquote><em>Most greenhouse gas models do not include water vapor and methane effects on global warming. The reason is that 2 factors can be calculated. With 3 the equations become non-linear, chaotic and difficult to use, if not impossible. Even approximations have so many errors it's hard to be sure.</em></blockquote>

 

[earthseed]

The fundamental fact is cold air holds less moisture than warm air. Air temperature decreases with altitude because the air is thinner. So when air rises over a mountain, it loses moisture. That is as true in the tropics as in northern regions - it is the relative temperature difference that matters. If it is cold enough, the moisture falls as snow, and is not recycled. I don't think there is much to debate here.<br /><br />The ice in Antarctica formed over a continent. The weight of the ice may have pushed the land surface below sea level. Thick ice does not form over the ocean (eg. in the Arctic), because circulation of ocean water causes the bottom to melt, and the ice acts as insulation from the colder temperatures above it. So freezing the oceans to any significant depth would take a very long time.

 

[earthseed]

Yes, but the transition between one climate system to another can be very stressful, especially in the short term (ie. our lifetimes), no matter how nice and warm the end point may seem. If the climate changes too quickly vegetation will die off before it can be replaced with plants adapted to the new climate. No plants means no life, particularly on an already overpopulated planet.<br /><br />The lesson in this thread is that Earth can support very different climates than what we have today, and that our climate models cannot account for this. Paleoclimatology tells us that climate changes can occur very quickly, in a decade or two. Our present models may be questionable, but that does not mean there is no risk - we just don't know exactly what it is.<br /><br />I think that messing with the factors that govern our climate is not a wise idea.

 

[Maddad]

earthseed<br />"<font color="yellow">The lesson in this thread is that Earth can support very different climates than what we have today, and that our climate models cannot account for this.</font><br /><br />There is no such discrepancy in our climate models. Our climate is different today as compared to other times because the arrangement of the continents is different, the the sun's output varies, the angle of incidence of sunlight varries, and the ecentricity of our orbit varies. These processes are well understood.

 

[earthseed]

If you believe climate change is caused primarily by solar temperature changes, you would expect climate to change slowly. Most climatologists do not believe that, and the idea of slow steady change is out of date, invalidated by more recent and accurate observations. For example, from the introduction of this paper:<blockquote><em>Until a few decades ago it was generally thought that all large-scale global and regional climate changes occurred gradually over a timescale of many centuries or millennia, scarcely perceptible during a human lifetime. The tendency of climate to change relatively suddenly has been one of the most suprising outcomes of the study of earth history, specifically the last 150,000 years (e.g., Taylor et al., 1993). Some and possibly most large climate changes (involving, for example, a regional change in mean annual temperature of several degrees celsius) occurred at most on a timescale of a few centuries, sometimes decades, and perhaps even just a few years.</em></blockquote><br />The primary driver of quick climate change is thought to be ocean currents. A relatively small climate event could cause an ocean current to reverse, leading to a major temperature change. This and other ideas are detailed in the paper referenced above.<br /><br />There are problems with the currently popular viewpoint on greenhouse warming. The models are crude, the effects are exagerated, and worst of all, it is all so regular and gradual. We add a waming agent, and the Earth gradually gets warmer, helped along by a questionable water vapor accelerator. These models don't deal with unexpected negative feedback, such as an ocean current change. Or more to the point, they do not predict ocean current change, when the paleoclimate evidence shows that it has happened repeatedly.<br /><br />We have been in an era of unprecedented climate stability for the past 10,000 years. The combination of this int

 

[earthseed]

maddad: The general causes of the warmer Cretaceous climate, as you point out, are understood. But as far as I know, we cannot put this information into one of our climate models and get the correct result. As discussed in some of the posts above, the question of how so much heat gets transferred from the tropics to the polar areas is not understood, especially given the evidence (from Jon) that the thermohaline circulation we have in todays oceans was not present at that time.

 

[earthseed]

The effects of a volcanic eruption usually only last for a few years; this is better thought of as weather rather than climate. A volcanic eruption could kick off serious climate change, but there is little evidence from ice cores that this has actually happened.<br /><br />A careful reading of the paper I referenced shows that ocean circulation changes are more than a "hypothesis in search of substantiation." The exact cause of these changes is less clear.<br /><br />Given the history of abrupt cooling events, I would not be so sure the current interglacial period will end gradually. Or it might be punctuated by a brief (ie. human lifetime) rapid cooling event, which would look the same to us.<br /><br />The paper ends with the statement: To paraphrase W.S. Broecker; 'Climate is an ill-tempered beast, and we are poking it with sticks'.

 

[nexium]

Hi Earthseed:"how so much heat gets tranferred from the tropics to the polar areas"? Venus has no oceans, yet the poles are almost as hot as the equitoral location where the Sun is at the zenith. I think that location has a powerful updraft, and a down draft occurs at each pole. Perhaps on Earth, a slight weakening of the polar down draft causes ice age, and a slight strengthening causes interglacial, with ocean currents mainly local in their effect. Neil

 

[Maddad]

steve<br />"<font color="yellow">Any really powerful volcanic eruption can seriously freeze the temperate latitudes within a few months of the eruption. I think this was pretty well understood since Krakatoa and Katmai.</font><br /><br />Good point. The eruption in 1915 of Tambora was responsible for the "year without a summer" in 1816. They think it was about 150 times as explosive as Mt. St. Helens.