Raze said:
Because clearly a rise in temperature (due to solar activity) would release methane, CO2, etc that is trapped in the ocean or in ice, so one would expect increases in temperature to precede increases in greenhouse gases in the atmosphere (ETA- holding non "naturally" caused changes in greenhouse gases out of the equation).
OK, so by this theory we expect temperature rises to precede CO
2 increase. And the data shows that to be the case. Q.E.D.
No, it is not that simple. We expect INITIAL temperature rises to precede CO
2. We could then have that energy linger, while more energy is pumped into the system. The problem, of course, is that we cannot know to what degree continued input of energy versus retarded release of energy due to the increases in greenhouse gases in the atmosphere direct the change in energy flux.
That is why we must look at the amount of time it takes to return to thermodynamic equilibrium (i.e. no more large changes in temperature over the examined time interval), and compare it to what we would expect if human activity was negligible. Further, the rate of change OF the rate of change of the temperature will be a function of the preceding considerations (that is, again, how fast the system returns to equilibrium after the initial increase in energy due to solar activity). From this, we could, in principle, glean how important emissivity was to the actual temperature vs time curve, and from that we could, in principle, glean how important human activity was. Not so simple in practice, of course- and this is with using the Stefan-Boltzmann law, which is clearly more of an idealization.
But just to sum up again, rises in temperature are not what are important. What is important is how fast the system, after the initial increase, returns to equilibrium.
The way it works with a gray body is this:
Heat comes in, heat is radiated out.
But the flux of that radiation is proportional to the forth power of the temperature, the geometry of the object, to Boltzmann's constant, and to the emissivity of the body.
If there is a change in how the body radiates heat over some time interval, than either there has been a change in temperature (higher temperature = higher rate of radiation by for powers) or a change in emissivity.
Greenhouse gases are related to emissivity, as are several (many) other things.
So basically, no the jury isn't in, I don't think, at least when looking at it from such a broad, general perspective. Because in order to know how much of an effect WE have, we also have to know how the emissivity is changed by our activity. I don't know how we can know that by experimental data, since we've been releasing these gases for such a tiny fraction of Earth's history.
ETA- but yes, looking at the data over the long term, there should be, at least initially, always a rise in temperature before a rise in CO
2, assuming things like volcanic activity, etc are held constant. No, that doesn't mean that CO
2 or other greenhouse gases have no effect on global temperature. It is
absurd to say that they don't. What matters is the degree in which they do, and more pertinently, what matters is if what WE add to the atmosphere has a significant effect.