Carbon-dioxide content of atmosphere has increased in the past 150 years from

Carbon-dioxide content of atmosphere has increased in the past 150 years from 270 ⟶ 340 ppm.
In Earth's atmosphere, carbon dioxide is a trace gas that plays an integral part in the greenhouse effect, carbon cycle, photosynthesis and oceanic carbon cycle.
Estimates in 2001 found that the current carbon dioxide concentration in the atmosphere may be the highest in the last 20 million years.
The concentrations of carbon dioxide in the atmosphere are expressed as parts per million by volume. CO₂ absorption and release is always happening as a result of natural processes, the recent rise in CO₂ levels in the atmosphere is known to be mainly due to human activity.