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Do we contribute? Perhaps. Are we THE cause? History would say NO. Can WE stop it? History would say NO.
The Little Ice Age gave us the Dark Ages and the Plague as I recall.
Well said, even if it's to illiterate for Proof! ;-)
That's been one of my problems all along: They are comparing ice coverage 150 years after the end of a 400 year ice age, to the ice coverage right after that ice age ended, and telling us how bad that is, as if that heavier coverage were normal for none ice-age-like conditions.
Just like with the Northwest Passage possibly becoming open every summer: How do we know that it wasn't open before the Little Ice Age too?
Science is being used every day to challenge the man made global warming hysteria and the warmers continue to ignore the data. The credibility of this AGW movement is losing ground little by little. Unfortunately our politicians smell tax revenue so it will never be resolved with integrity.
Of course, there are all those 'computer models' which activists tout. :)
The problem with human attribution to global warming is that one needs to invoke a theoretical, completely unproven mechanism, the so-called CO2-water vapor feedback mechanism to get enough warming from CO2 to explain the temperature increase from 1980-2002.
Recent downward trends in temperature are problematic for that argument because, if you can have natural variations that are large enough to swamp the anthropogenic signal to cause a net cooling, then the opposite is almost certainly true as well: Likely part of the warming we say 1980-2000 was natural, in which case the C02 climate sensitivity is less extreme than some people have been claiming.
If you are left with the classic effect being the only mechanism at play, the net warming for a doubling of CO2 is small enough that it would undermine the global warming alarmist narrative.
Basically they're assuming a worse case scenario and tweaking their models to work with that. At the same time they ignore any historical evidence that the Earth can warm up and cool off on it's own accord.
According to the fossil record, CO2 levels rose shortly AFTER a period of global warming rather than BEFORE.
This is a commonly accepted, yet untrue aspect of the global warming argument.
However, that is an average. There are cases where the CO2 increase comes first (e.g, volcanic eruption). But in general, not only is the lag negative, but the changes in CO2 concentration are minute (e.g., changes from 200-300 ppm) compared to the temperature swings (which are of order 8 C):
<img src="http://www.ncdc.noaa.gov/paleo/globalwarming/images/temperature-change-small.jpg">
Whistler you are exactly right about ignoring potential negative feedback loops. See for example Roy Spencer's web site for details on his proposed "iris mechanism", in which he proposes (and finds evidence for) a negative feedback mechanism in the tropics that tends to stabilize the Earth's temperature against large changes in CO2 concentration. We know such a mechanism has to exist, because otherwise a large increase in CO2 would lead to a run-away greenhouse gas effect, and there is evidence that the CO2 concentration has been twenty times it's current value, yet... life still goes on (we haven't turned into Venus yet).
However, that is an average. There are cases where the CO2 increase comes first (e.g, volcanic eruption). But in general, not only is the lag negative, but the changes in CO2 concentration are minute (e.g., changes from 200-300 ppm) compared to the temperature swings (which are of order 8 C):
<img src="http://www.ncdc.noaa.gov/paleo/globalwarming/images/temperature-change-small.jpg">
Whistler you are exactly right about ignoring potential negative feedback loops. See for example Roy Spencer's web site for details on his proposed "iris mechanism", in which he proposes (and finds evidence for) a negative feedback mechanism in the tropics that tends to stabilize the Earth's temperature against large changes in CO2 concentration. We know such a mechanism has to exist, because otherwise a large increase in CO2 would lead to a run-away greenhouse gas effect, and there is evidence that the CO2 concentration has been twenty times it's current value, yet... life still goes on (we haven't turned into Venus yet).
All gases retain heat in certain conditions.
Remember the argument isn't whether there is enough heating from CO2 to produce the recent global warming, but whether CO2 is an important greenhouse gas. You can have the latter be true ("classic greenhouse gas effect") without the former being true (hypothetically dominant process, the "CO2 water vapor feedback cycle").
The mechanism is very basic, there are "windows" in the infrared portion of the absorption spectrum of the Earth's atmosphere that get filled by CO2 excitations at 5.3 and 14.8 microns. When the Earth radiates heat, part of that heat gets traped by CO2. That's pretty close to an unassailable argument.
A bit better picture of the absorption spectra via WIKI:
<img src="http://upload.wikimedia.org/wikipedia/commons/thumb/7/7c/Atmospheric_Transmission.png/595px-Atmospheric_Transmission.png">
We know this happens because we can measure both the absorption properties of CO2 and other gases, and because we can measure the transmitted infrared radiation that makes it into space via satellites. So it is an empirical fact that CO2 traps heat radiated from the Earth.
On the face of it, the portion of the infrared radiation trapped by CO2 is small (I think the number is 9% of the total heat trapped via the classic greenhouse gas effect), and further the CO2 absorption is heavily saturated even at the trace levels that CO2 is found in our atmosphere, meaning that increasing the amount of CO2 changes how much heat gets absorbed logarithmically. A doubling of the CO2 does not double the greenhouse gas effect from CO2.
Having a water vapor feedback loop be important, amplifies the classic greenhouse gas effect from CO2, but the strength of the effect still varies logarithmically with CO2 atmospheric concentration.
So the question for anybody who wants to argue this point, is to find a scientist who disagrees that the classic CO2 greenhouse exists and disagrees that the CO2 greenhouse gas significantly contributes to atmospheric heating.
Again the question isn't whether there is a classic greenhouse gas effect related to CO2, but whether an exotic mechanism, the CO2-water vapor feedback mechanism provides enough amplification of the classic greenhouse gas effect to produce significant warming effects from a 25% increase in CO2.
Notice the price of food recently? Part of that is due to crop failures related to colder weather.
Actually Mr. Spencer's work was why I mentioned the possibility that there is a negative feedback effect.