Xref: utzoo talk.politics.misc:8304 sci.misc:1013 Path: utzoo!mnetor!uunet!lll-winken!lll-tis!ames!husc6!tut.cis.ohio-state.edu!bloom-beacon!athena.mit.edu!jfc From: jfc@athena.mit.edu (John F Carr) Newsgroups: talk.politics.misc,sci.misc Subject: Re: the "greenhouse effect" theory Message-ID: <3862@bloom-beacon.MIT.EDU> Date: 18 Mar 88 04:24:32 GMT References: <22138@bbn.COM> <3851@bloom-beacon.MIT.EDU> <22277@bbn.COM> Sender: daemon@bloom-beacon.MIT.EDU Reply-To: jfc@athena.mit.edu (John F Carr) Followup-To: sci.misc Organization: Massachusetts Institute of Technology Lines: 81 (I think the political flaming has settled down enough that I am directing followups to sci.misc) In article <22277@bbn.COM> eli@BBN.COM (Steve Elias) writes: >In article <3851@bloom-beacon.MIT.EDU> I wrote: [Re: greenhouse effect] : but detailed models of any long-term atmospheric effect : just aren't around yet. you are a planetary scientist, right? : do you admit that we don't have enough data to really be able : to predict any planetary atmosphere? : as a computer dude who has studied astronomy, i'll say that even if : we did have enough data to learn how to predict atmospheres, we : don't have .001 the processing power available to do the job. It depends on what level of detail you want. I mentioned an article I read in Scientific American which discussed computer simulations of the Ice Ages. Today's computers, as far as I know, do a good (but not great) job of predicting gross effects (like the Ice Ages and approximate global temperature distributions). They do an acceptable job of calculating details. In both cases the models can probably be improved, especially as more computer power gives more accurate models. In all cases, more power will help as long as we have the observational detail to get data accurate enough (which means, there is a lot of room for improvement). The statement above is just too general. JFC: However, chemical plants also produce carbon dioxide which does the real JFC: harm to the heat balance by trapping IR radiation. : thermal pollution could do real harm to the heat balance, too. : especially if someone ever puts 'solar power stations' in orbit. JFC: My impression is that in extreme quantities either CO2 or heat can cause JFC: the effect, but that it is much harder to do with heat alone. Think of JFC: CO2 as a catalyst, very small quantities of which can produce JFC: great effects. : you bet. enough heat could start thermal runaway, just as enough : CO2 could. i read in today's paper that the current guess about : the extinction of the dinosaurs involves 3x to 5x increase in : atmospheric CO2 levels around the time they disappeared. The point is, enough heat is vastly more than we are producing now (another article said 10^-7 of the Earth's energy budget is man-made). Enough CO2 seems not to be much more than we are producing now. JFC: (Thermal energy is spent heating up the earth, which would then cool on JFC: a timescale of days if it were removed. : i think John is doing some big time speculation here. : massive amounts of thermal energy would not dissipate in a : matter of days. (i mean thermal energy produced from power plants: : if we produced 10x or 100x the power we do now.) the Earth can : only radiate energy at a specific rate -- sigma T^4, cloud cover, : CO2 levels, and other stuff determines that rate. Timescales to consider: The atmosphere heats and cools in hours (now that I think about it, I seem to remember deriving a cooling time for atmospheres in a course I took on planetary science. I'll try to find this). Looking at daily temperature curves I have estimated a time constant of no more than a day. (i.e. the atmosphere effectively follows man-made inputs with no lag). The surface is a trickier matter, as is the ocean. I would guess the time constant from the lag of seasons behind the driving force: the Earth's axial tilt. The lag is slightly less than 3 months; this would make the best-fit timescale [i.e. if one treated the earth's temp. as a driven 2nd order system] about the same. (I hear the flames coming now: what is this! someone is threatening to have a rational discussion in talk.politics.misc!) John Carr "No one wants to make a terrible choice jfc@Athena.MIT.EDU On the price of being free"