How much were the CO2 levels before the Industrial Revolution?

Carbon dioxide levels in the atmosphere have reached a symbolic high. For the first time in human history, daily measures of CO₂, which is an important factor in global warming, have topped 400 parts per million.(10)Before the Industrial Revolution, CO₂ levels were 280 parts per million. The Hawaii measuring station in the Pacific far from pollution sources is reckoned to be the most authoritative monitor of daily CO₂ levels and it’s now showed they have topped 400 parts per million. The last time CO₂ was regularly above that level was about three to five million years ago before modern humans existed. Scientists are alarmed that CO₂ levels keep rising because the climate was much warmer then. There’s no sign though that world governments have the political will to make real their promises to reduce emissions of greenhouse gases.