What are CO₂ levels currently and how does that compare to levels in the past?

Since the industrial age, when we began burning fossil fuels, the atmospheric concentration of CO₂ has gone up by 40%, from a level of 280 parts per million to 400 parts per million, mainly as a result of mankind’s burning of fossil fuels. This may not sound like a lot but is actually huge – imagine if your body temperature went up 40%, or the level of alcohol in your blood went up by 40%. Not only has the overall level of CO2 increased massively, the rate of increase has been much faster due to human impact than under natural processes, actually around 60 times faster.