In 1850 the percentage of carbon dioxide in the atmosphere was 278 ppm (parts per million), which is 0.0278% according to some sources.
From 1850 onwards the Industrial Revolution began. Factories sprang up and we started burning wood and coal to drive industry. When we discovered oil, we burned it to power transport and generate electricity. We have been doing this ever since.
Carbon dioxide in the atmosphere is now (March 2011) 392 ppm, which is an increase of 41% increase, entirely caused by anthropogenic or human activity.
Carbon Dioxide has NEVER stayed "still" at anytime in the history of the planet. Percentages have varied in the past 2000 years from 0.019% to as high as 0.04% (Beck 2008 and Vostok record) The fact is that CO2 has been shown to be rising steadily for over 10,000 years. CO2 has ALWAYS followed the 100K year solar cycles and is still doing so today.
It is interesting to note that the science of 1850 does not agree with the idea that CO2 was at 278 ppm. Over 90,000 measurements of the day, done with methods that we still use, show that CO2 ran over 400 ppm in the 1800's and reached highs of 440 ppm. Some of the creators of these measurements even won Noble prizes for their work. Today, alarmists ignore 100% of their measurements, in favor of proxies which show lower historical numbers.
Man's contributions to the total CO2 output is small. In terms of percentages we produce about 5.25% of all annually generated CO2. We produce about 0.28% of all greenhouse gas annually. Oceans produce over 90 to 100 Btonnes of CO2 annually. The difference though, is that some of man's contributions are not from sources that would otherwise produce CO2. Whether the planet is able to absorb this portion man introduces is what the real question with global warming really is. If man's portion is able to be absorbed by the planet, no warm, no foul. If it is not able to be absorbed, we are making a big problem for future generations.
Forests, when left natural and allowed to decay can produce substantially more CO2 than man does. Burning of wood produces the same CO2 as a tree rotting, yet becomes part of man's 5.25% contribution. You will find that percentage values range from as little as 2% to as high as 5.25% because of the incomplete science we still have on the subject. The oceans possible output variance is larger than our total involvement. Despite the consensus of political groups, we still have a great deal to learn before science can become as certain as politicians. Yes, the planet has seen a change in our atmosphere that could be as high as 0.007%. The issue is the small amount of CO2 in our atmosphere.
It should be noted that the past 10,000 years showed almost a 100% increase in CO2 levels BEFORE man started to burn fossil fuels. NONE of that can be considered man induced. No respectable science group claims that the entire known increase in CO2 levels is possibly caused by man. They DO state that man is a contributor. It is the level of involvement that is the question.