What do we know for sure?  We know for a fact that CO₂ levels are rising and that human activity is the cause.

How do we know this?  A simple calculation. Let’s start with the year 1750, generally accepted as the beginning of the Industrial Revolution, when the standard measure for CO₂ levels was 278ppm. We’ll begin then, add the known level of human-generated CO₂ for that year, then subtract 2.84% of the excess CO₂ – because that’s how fast nature tries to restore the balance. If we do this for 255 years, up to 2005, we get the pink line in the graph below. It fits the black line – the actual CO₂ level – like a glove.

How accurate is this fit? Considering the difficulties of gathering data from centuries past, amazingly close. We know, for example, that up until 1950, deforestation was putting about as much CO₂ into the atmosphere as were burning fossils, but it’s not easy to know how many trees were chopped down in, say, 1850, and how much CO₂ this put into the air. In spite of imperfect data, the fact that a simple calculation predicts the extraordinary shape of actual CO₂ so well is clear evidence this can not be a coincidental convergence. Human CO₂ emissions must have caused the upsurge is atmospheric CO₂.

So what?  The link between human activity and rising CO₂ levels is the first step. The next one is between CO₂ and global warming. That was predicted over 100 years ago, but the evidence has become convincing only very recently. ZFacts will be adding pages about this during February, 2006.

Fossil Fuel data are from the U.S. DOE, including an estimate that fossil fuel emissions will increase at 1.2% per year until 2030. We assume this rate to 2050. However, the average rate for the last 5 years was about 1.9%, so this may be optimistic. Cement manufacture also releases CO₂ from the rocks it processes, so that source is tracked separately.