Global warming - natural or manmade?

[Philly_SWAT]

Talk in another thread got me to thinking about this. Opinions differ about the "causes" of global warming. Here are a couple of thoughts I have on this. Whether global warming is actually "caused" by man's activities, I think it is safe to assume that even it our activities are not the cause, they certainly help to exacerbate the natural occurance. Whatever tasks would need to be performed to help insure humankinds longterm survival (for example, learning how to, and creating the instruments of, being able to travel beyond the solar system) would benefit from longer time between ice ages. With our seeming inability to co-operate, and not constantly wage war against our fellow man, our very nature puts enough obstacles in our way or progress, without us adding another problem to it, i.e., making the period of time we have to come up with solutions shorter. Therefore I submit that it is in the collective best interests of the human race to not hasten the effects of global warming, whether it is mam made, a natural occurance, or a combination of them both. I remember something interesting after reading the book by Stephen Hawking, a brief history of time. As someone generally regarded as one of the, if not THE, smartest person on the planet, he attempts to explain the mysteries of the universe by conveying complex theoretical physics concepts in layman's terms (and even then, I still found some of the concepts somewhat confusing). I dont think he even addresses the issue of global warming at all, it is not a function of his book. But he casually mentions something that I always remember. It is a very minor, brief comment, that has no bearing on any great overriding idea, he just mentions it in the course of telling something. He mentions something that over long periods of time, that the orbit of the earth around the sun shifts, bringing it a little closer/little further away from the sun. "Little" is a relative term here, as the earth is approx 93 million miles away from the sun, so a little in this context would be enough to have a major effect on the planet. I think he made this comment in some type of reference as to why there was an ice age, that the relative small distance that the orbit took was enough to drastically change the environment here on earth. Again, he was not trying to directly or indirectly make any comment about the issue of global warming (the book came out in 1988) but if what he says is true, that lends some support to the idea that global warming would be a natural occurance, and that there would be nothing we could do to stop it. As I said, I think the only thing we could do is not to lessen the time available before the next ice age by irresponsible actions, in order to accomplish as much as we could before then.

[MoonSylver]

Yeah, I'd agree. Don't think we're 100% the cause, but certainly exacerbating the problem. Just the sheer number of people, the energy needs to support all oue infrastructure, the production of food, etc, etc, etc. The History Channel had a great program on "The Little Ice Age", a period of cooling that occurred approximately from the 16th to 19th centuries, which detailed all the many & wide reaching effects the extended period of even moderately cooler global temperatures had. Fascinating stuff. http://en.wikipedia.org/wiki/Little_Ice_Age

[Mike70]

He mentions something that over long periods of time, that the orbit of the earth around the sun shifts, bringing it a little closer/little further away from the sun. evan, at first glance i think you might be talking about the sun getting hotter and brighter as it ages. i'll look it up in my copy of brief history but i think that maybe what hawking was referring to. the predictions of the earth's orbit, even out to several billion years render it stable, the earth has very little eccentricity in it's orbit (the amount that it differs from a perfect circle around the sun is only .016). mars (.093) and mercury(.205 - this is huge in astronomical terms, it means that mercury has a 20% variance in it's perihelion and aphelion) on the other hand have eccentricities that are growing over time to the point that in a few billion years, mars might be on an earth crossing orbit and mercury could be ejected from the solar system entirely due to interactions with venus and the earth. neither of these is anything to worry about, in a few billion years the sun will be 30 to 40% hotter and brighter than it is today. humans would frizzle fry on earth's surface. to break this orbital thing down further (because i am both ultra interested in this sort of stuff and ultra bored because it is cold as a frost giant trying to chat up a vestal virgin here with snow and ice everywhere): mercury: aphelion: 69. 8 million km perihelion: 46.001 million km earth: aphelion: 152.097 million km perihelion 147.098 million km mars: aphelion: 249.209 million km perihelion: 206.669 million km see the relationship? the earth only varies by about 5 million km in its orbit, where as mars and esp. mercury have huge differences in how they orbit the sun. this also means that the distance between the earth and mars and the earth and mercury will slowly decrease over time. 4.6×10 to the 9th years Today. Sun remains a main sequence star, continually growing warmer and brighter by ~10% every 10 to the 9th years. 6×10 to the 9th years Sun's habitable zone moves outside of the Earth's orbit, possibly shifting onto Mars' orbit. 7×10 to the 9th years The Milky Way and Andromeda Galaxy begin to collide. Slight chance the Solar System could be captured by Andromeda before the two galaxies fuse completely. this change in the sun over time, even though it is 10% every billion years or so, will render the earth a very different and very inhospitable place for humans in a much shorter time. he could've also been referring to the fact that the earth's orbital axis is subject to what is called precession. it wobbles back and forth over time, something like 25,600 years or so.

[Philly_SWAT]

at first glance i think you might be talking about the sun getting hotter and brighter as it ages. i'll look it up in my copy of brief history but i think that maybe what hawking was referring to. No, I am not referring to him talking about the sun getting hotter as it ages. I got the book from the library, so if you have a copy, you could try to find it, although that could be a challenge, because it was a minor point. In fact, I dont think he was even making a point one way or the other about the Earth's orbit in the comments I am talking about, it was abuot something else. To try to give an analogy...if you were to ask me what is the worst day of your life, and I started out "I remember it well. It was a Sunday, and ...(insert horrible circumstance here)" Even though I say it was a Sunday, that has nothing to do with what I am talking about. Hopefully this makes sense. As far as the Earth's orbit goes, I dont remember him as trying to say that it was unstable, just that is changes slightly. But in the grand scheme of things, even a slight difference (which would take many thousands, or 10's of thousands, or whatever, of years to occur) could make a drastic effect on the earth. I am pretty sure he was referring to why the last Ice Age occured, and that it was because at that point in time the earth was slightly farther away from the sun than normal, but that slight difference accounted for the drastic conditions here. Since you are so interested in this topic, and presumably a lot more familiar with the book than I am, perhaps you will be able to find the section in question easily. I would be interested if you could in fact find it and let me know exactly what he said, and provide your thoughts on his words.

[LoneCrusader]

Natural. It's happened hundreds of times before. It's just a cycle of the earth.