[Eric A. Taylor (OP)]

I'm wondering if anyone has compared the levels of atmospheric carbon to levels emitted in the past? I here the media spitting out big numbers, such as 45 gigatons of CO2 emitted. This is admittedly a really big number on the face of it. 45 billion (metric?) tons is a lot. However nature produces 30 times this amount. How? Well organic decay is a big contributor. True plants absorb CO2 but they re-emit it when they die. An even bigger one is geologic activity, mostly volcanic. The State of Hawaii produces much more carbon dioxide than all the rest of the United States combined, when considering both man made and natural sources.

  It seems to me that it would be very easy to compare man made sources with increased CO2 levels for the last 200 years. Even if accurate measurements were not made at the time records of what businesses where doing what and where are surly still around. From these records it should be fairly easy to estimate how much carbon was being emitted and then compare those numbers to ice core samples. This would go a long way to convincing me that climate change is man caused. That is if the numbers match up. If they don't I think it would go a long way in convincing everyone else that climate change is a natural proses over which humans have little influence.

  I would like to point out here that there are many historical account of climate change long before the industrial revolution. There are parts of Alexandria, Egypt that are flooded by the sea and have been thus for hundreds, if not thousands of years. Surly the ancient Egyptians didn't build their buildings under water. They were flooded after they were built, perhaps hundreds of years after. Even in the middle part of the last millennium there are hundreds of accounts of glacial advance and retreat throughout the Alps in Europe. Unfortunately many American historical records from before the 1600's were destroyed so we may never have detailed records of climate in the Americas but accounts of Washington's crossing of the Delaware river had men pushing ice out of the way. That river doesn't freeze nowadays.

  Is climate change real. YES! is it man caused? I don't think so.

[Bored chemist]

The CO2 in the air from the decay of (recently dead) plants is different from the CO2 from burning oil or coal. You can tell them apart by radiocarbon dating.
When they look at ice cores the isotopic data tallies with mankind being the big source of increased CO2.
Also, volcanic emissions of CO2 are relatively easy to spot- they are localised near volcanos.

[litespeed]

EAT: Atmospheric carbon is not solely a human creation. However, the natural carbon cycle seems to have been in balance for some time, leaving the increase in recent times suspiciously related to human activity.

However, human contributions are not always properly attributed. For instance: "In 1997, Indonesian peat fires were estimated to have released between 13% and 40% of the average carbon emissions caused by the burning of fossil fuels around the world in a single year.[9][10][11]." http://en.wikipedia.org/wiki/Carbon_dioxide_in_Earth's_atmosphere

Further, it is clear the climate has routinely oscillated between warmer and colder eras independent of atmospheric carbon content. For instance, within historical times there is The Roman Warming. I believe the excess agricultural production provided by this warming is almost entirely the explanation of how Rome could support both vast military and civil engineering projects. They could tax grain production.

The fall of Rome, so to speak, is almost the entire reverse. First, the climate cooled resulting in less taxible grain production. Worse yet, the Northern Tribes of Barbarians were forced South by the colder weather. One two punch on Rome.

This cooling era is coincident with the near total demise of contiguous Western Civilization in the early Middle Ages. Nearly the entirety of Western Europe, including Britain, was reduced to little more then small scale gang warfare between tiny kingdoms, with occasional larger unification such as provided by Alfred The Great and Charlemagne.

Still, the subsequent Midieval warming from about 800 to 1300 is often considered a golden age. For instance, Viking migrations extended to both Iceland and Greenland. However, subsequent cooling exterminated the Viking colonies in Greenland and reduced the populations in Iceland.

The five centuries from 1300 to 1800 are often termed 'The Little Ice Age'. It was a bad time. The plaques of the colder era killed an estimated 1/3 the entire population of Europe. It got even colder during the Maunder Minimum [of sun spots] from about 1645 to 1715. At any rate, the London Frost Fair was held from 1607 to 1814 on the frozen Themes.

Things have gotten warmer since then. Some say as warm as the Midieval Warming. None-the-less we have large numbers of citizens who believe warming, whatever the cause, is a bad thing. I believe they are now being tested across the entire Northern Hemisphere. And speaking of sunspots. Cycle 24 is missing and may be soon presumed dead.

The next couple of years could very well settle the matter. My motto is 'warm is good, cold is bad'. Perhaps this coming Summer season will be agriculturally productive, and Next Winter will be better then this year. I certainly hope so.....

[Mazurka]

I consider it unlikely that the question of anthropogenic climate change will be settled in the next couple of years – the “losing side” will always be able to argue that the timescales are wrong or that the data has been cherry picked etc.  Fascinating as written historical records are, they tend to have little additional bearing on the science because, as noted, they only really relate to particular civilizations, so there applicability to a global questions is limited.  There are also considerable difficulties in interpretation based upon the assumptions of the day, for example, historically, alpine glacial advance and village engulfing avalanches were ascribed to witchcraft and decorated eggs were buried to ward off such witchery  - actions few would consider likely to succeed now.

I would also suggest that the reason why arguments relating to mankind’s influence on climate remains unresolved is that the processes involved are tremendously complicated.  No one would seriously dismiss solar and milankovitch cycles as being major influence on climate/ weather (albeit on differing timescales).  Nor would anyone say that the vast majority of carbon cycling around is anything to do with mankind at all.  However, the question is one of equilibrium.  Has the wholesale release of geologic carbon from the use of fossil fuel (and to a lesser extent the burning of limestone for cement) upset the natural balance?
Or put another way, to borrow the term from chemistry, who much “buffering” can natural systems provide to this unprecedented (in the terms of the life’s history on earth) release of CO2?

With respect to volcanos, I feel it essential to correct an oft repeated misapprehension.

According to USGS

Comparison of CO2 emissions from volcanoes vs. human activities.
Scientists have calculated that volcanoes emit between about 130-230 million tonnes (145-255 million tons) of CO2 into the atmosphere every year (Gerlach, 1991). This estimate includes both subaerial and submarine volcanoes, about in equal amounts. Emissions of CO2 by human activities, including fossil fuel burning, cement production, and gas flaring, amount to about 27 billion tonnes per year (30 billion tons) [ ( Marland, et al., 2006) - The reference gives the amount of released carbon (C), rather than CO2, through 2003.]. Human activities release more than 130 times the amount of CO2 emitted by volcanoes--the equivalent of more than 8,000 additional volcanoes like Kilauea (Kilauea emits about 3.3 million tonnes/year)! (Gerlach et. al., 2002)

Now if you had suggested that the methane from cows destined to be Mcburgers was greater than that of the rest of the economy I would have been right behind you []

[litespeed]

Maz

I am with you on all those planetary ungulates. They make one heck of a mess in more ways then one. Sheep seem of particular concern. I read someplace they roughly equal, in number, the entire population of humans. Assuming sheep have always been roughly equal in number to people, that is a rather frightening observation!

Perhaps someone has graphed planetary methane against CO2 over time? This is actually more important then it seems, but not because of sheep, though that would be interesting. Some investigators have implicated sudden large releases from sea bottom methane-hydrates in mass extinctions.

How bad would THAT be? All of us getting croaked by a giant ocean fart!