I was watching a show on National Geographic Channel this weekend and they were talking about the Sun (the show was called Naked Science). One of the things they mentioned was that the sun was getting hotter…its (according to the show) 30% ‘brighter’ than it was when it first formed, and rises about 10% every billion years. Does ‘brighter’ equal ‘hotter’? If so, how does this factor into the whole Global Warming issue…or does it not factor in at all? If it is getting hotter how long does the earth have until its basically uninhabitable? Would 10% more heat in a billion years do it for the earth pretty much?
It is getting brighter, and that does imply hotter (though the relationship is not linear). But timescales in the billions of years are completely irrelevant to global warming: Most global warming studies look at timescales from about a hundred years to perhaps tens of thousands. On those scales, changes in the Sun itself are only just barely detectable by the most sensitive measurements.
The steady increase in the Sun’s brightness during its main-sequence lifetime (as its helium core gets bigger) is too slow to be relevant to global warming.
However, other short-term variations in solar output (e.g. the Maunder Minimum occur on a more relevant timescale (e.g. the Maunder Minimum appears to correspond to the “Little Ice Age”).
Like Chronos said though, it’s negligable in a global warming sense, far outweighed by other current processes and an extrodinary long time before appreciably realized. What I found amusing was when they’d talk of the effects this rise in temps would have on man in a billion or two years. I’d rate the notion we’ll be here as applaudably optimistic.
I was told by my astronomy professor that I didn’t have to worry about the Sun becoming a red giant. The steady increase in solar output would push the Earth into thermal runaway, like Venus, well before that happened. We’re doomed.
Well, according to the show I mentioned in the OP its 10:45am (the sun being born at 6am and dieing at 6pm)…and the planet will be uninhabitable by 11:30am. So…we actually have less than an hour (which I think translates into less than one billion years) before the average surface temperature is something like 170 degrees F. :eek: If the show is right of course.
Or a lot of time. I recall one claim from a scientist a while back that you could do it just by carefully moving an asteroid into repeated, constant near misses of the Earth. Do it right for enough millions of year and the repeated tiny tugs will move the planet. OTOH sunshades are rather less likely to smash the biosphere if you make one tiny mistake over those millions of years.
Anyone know what a hotter sun will do to the outer planets in the solar system? What will, say, Mars be like when the earth is toasting at 170 degrees F on average? How about the gas giants?
You’d have to get the asteroid to steal energy from some other planet (say, Mars) at the other end of each orbit, by dragging that planet down toward the sun a bit, otherwise it would need constant boosting to keep it going, the energy for which would be equivalent to the total amount needed to move the Earth.
Yes, or a solar sail. Yes it still would take energy, but the energy involved is there for the taking anyway. Or, you could use a sail powered by Mercury-mounted solar powered lasers if you want more push.
Anything you do is going to take energy, including the sunshade idea ( it has to be built, set up and maintained, after all ). Therefore the practical question is one of energy density; in other words, how much energy do you need at any one time ? The asteroid idea involves a reasonable amount of energy.
