Now, let's see, Setanta said:
It has been known for more than a century now, though. that greenhouse gases exist in the atmospher and that they trap infraredradiation and cause temperature to rise, and it is known furthermore that human activity has caused the rise in greenhouse gas concentration in the atmosphere. There is a prettyt straightforward connection there.
Those were natural causes in effect. CO2 is now somewhat above 380 ppm, and the temp is rising, and we're the ones overriding natural causes this time around. We weren't there and able to effect the natural state in previous cycles.
Krumple is justified in his response, because MJ is claiming that man is responsible for the current round of climate change. He's working without a net, and he has no business making this claim.
No, set, what I was talking about was the effect of CO2, not climate change in general. bAnd I stand by what I said about CO2. There are obviously a whole host of things that affect climate and can cause it to change in a number of different ways, as it has often in the past.
A number of posts back now, I cited the evidence that say Krumple's claims about what happened with CO2 millions of years ago (he talks later on about climate change 50K years ago--that was in the middle of the last ice age and there were no great extinctions then--I think he's talking about 50 million years ago, there was more CO2 then, and it was hotter--natural result and what you'd expect), but CO2 declined precipitously then and has not been that high in the 50 (actually more than that) million years since, so that argument has no effect on present conditions. Probably an effect of the appearance of flowering plants which uptake vastly more CO2)have no bearing on what's going on today.
Keumple poopoohs the greenhouse effect. It's a METAPHOR. No one says it's the same process as a glass greenhouse which works by containing convective cooling with glass panes. The atmospheric greenouse effect occurs because IR radiation from the sun is at certain wavelengths which don't interact with atmospheric gases. It's absorbed by the earth and the seas and is them re-emitted at different wavelengths which DO interact with certain gases. The greenhouse gases, notably H20 vapor, CO2, methane, and nitrous oxide absorb that IR and re-emit it in all directions. The re-emitted IR that is emitted upward may not encounter other greenhouse molecules (concentrations are low) and escape to space, or it may meet other molecules and go thru the same process again. AS the concentration of greenhouse gases increase, more and more IR will be reflected back earthward and raise temps. That's why it's called a greenhouse effect. There's no glass panes, because the process is different. But the effect is similar.
Now, setanta, H2O vapor is in fact the main greenhouse gas. No one disputes that. However no one can demonstrate that it's changing much, due to human or other activity (actually water vapor theoretically will increase as temp rises, but it's a dependent variable, not an independent one--the temp has to go up for the water vapor to increase, and then that will amplify the effect, but something has to cause the temp to rise in the first place, and that's what CO2 and the other gases cause). But CO2 acts on wavelengths that H2O does not, and increases the temp. And CO2 is demonstrably changing in the atmosphere, and the science shows that we are the ones changing it.
There are two main lines of evidence. nSimple calculations of how much fossil fuel we use every year indicate how much carbon and carbon dioxide we introduce into the atmosphere every year (Oil and coal industries keep records of how much they produce. Combustion product amounts are simple engineering). We know carbon sinks take up and remove (at least long-time temporarily, sometimes for millions of years) about half of the CO2 we produce. The other half is somewhat more than the amoutn of CO2 increase in the atmosphere every year. No one has been able to show that anything else exists that takes up any significant part of the remaining half except the atmosphewre.
Now that CO2 we produce from fossil fuels is OLD CO2. It's been out of the atmosphere for millions of years--that's what the carbon sinks existing millions of years ago took up--the ancient plants that made up the biota then, which is why it's called fossil fuel. The CO2 naturally occurring in the atmosphere contains three isotopes of carbon, c12, c13, and c14, in essentially stable ratios to each other. But ancient CO2 contains different ratios, C14 is radioactive and decays slowly, but after millions of years underground, it has all decayed to other carbon isotopes. Plants differentially absorb C12 over C13. As a result, CO2 from old plant life has a significantly different isotopic signature from naturally occuring CO2. Scientists have analyzed changing isotopic ratios over the last century, and found they are in fact changing, in line with the increasing amounts of CO2 in the atmosphere being due to fossil fuel burning (and also, as a secondary cause, the significant, tho much smaller, increase in fossil CO2 due to concrete production, which buiklds most of our modern infrastructure and comes from the burning of limestone, which is made up of millions of year old depositions of the shells of marine microorganisms).
And that, Set, is why I, and the science, say that CO2, which is the largest effect causing a warming effect, is mostly anthropogenic. Methane, which also has a large human contributi0n to it, and is indeed stronger in effect than CO2 or H20 but is present in much lower concentrations also has an effect.
There are also other factors that affect temperature, but as the worldwide research the IPCC summarizes indicate, their effect at present is quite a bit less than anthropogenic causes NOW. Solar output has been declining over the last two nominally-11-year cycles, while temperatures have seen their strongest rise. It is estimated to be no more than about a quarter to possibly a third of the total (and the latest research reduced the figure a bit, I believe, after the end of the last solar cycle a couple years ago).Aerosol effects can be either cooling or warming, depending on what and where they are. They can be either anthropogenic or natural. they are, in any case, factored into the results the IPCC summarizes (but is, I reiterate, generated by other sources than the IPCC, which means the IPCC conspiracy theorists are wacked).