@BaldOldGuy
Here is my argument:
You've gotten the facts wrong. CO2 is about 400 ppm of the atmosphere, which is .04%. The fact that the variance of a few hundredths of a percent correlates that strongly to most of the rises and falls of the temperature of the earth says a lot about how little difference can impact a lot. Here is the chart if you'd like to see by yourself, tons of research has gone into this
http://www.planetseed.com/relatedarticle/co2-and-temperature-change
Secondly, depending on your definition of manmade, humans have had a part in the vast majority of the new CO2 emissions. Sure dead trees and oceanic emissions are considered natural, but deforestation causes more CO2 output than input, in a system that is semiclosed and is supposed to be equal in the long run.
Think about like this, there is a set amount of CO2 that can exist on earth (based on the amount of Oxygen and Carbon in the air.) It cycle through the carbon and oxygen cycles and only during a certain stage does the two exist as CO2. What humans are doing is taking dormant Carbon from the ground and putting it in the air, normally, higher CO2 count applies pressure for trees to grow bigger snd strong and make more bigger stronger trees to balance the cycle, but humans are killing off the trees that are supposed to be taking in this carbon. Also the pollution of the ocean inhibits it's ability to dissolve CO2, further creating a net positive queue of CO2 in the atmosphere. The worst part is that it creates a positive feedback loop that raises temperatures, subsequently the temperature of the oceans, further inhibiting it's ability to dissolve CO2, which creates an event bigger breach of the cycle.
So my point is that, sure we may not have a direct impact of the CO2 outputs, but we have a dangerous indirect impact. Even if we created absolutely 0 emissions of our own, just by inhibiting the absorbsion and dissolution aspects of the Carbon cycle, we cause climate change.
Its pretty much impossible that Earth has enough convertable carbon to become like Venus, which is like 95% carbon atmosphere and the atmosphere is much thicker, but Earth certainly has enough to melt the entirety of its icecaps, which is a big issue in itself.
Finally, the point I would like to make is that regardless of whether its manmade or natural, humans have a political, economic, and social interest to prevent climate change. Now that we have an idea of how it is caused (the ebb of greenhouse gases) we can control it to prevent disasters like the melting of the ice caps. If that we to occur, see levels would rise and wipe out thousands of coastal cities, causing trillions of dollars of damage, and displacing over a billion people (source:http://worldoceanreview.com/en/wor-1/coasts/living-in-coastal-areas/)
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Scottish MP on trial for lying
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