What percentage of the atmosphere is CO₂, and what percentage of it is man-made?

Carbon dioxide (CO₂) currently makes up only about 0.04% of the Earth’s atmosphere (around 420 parts per million) [usatoday.com]. That sounds like a tiny fraction, but even trace amounts of CO₂ have a big impact because CO₂ is a potent greenhouse gas that traps heat in our atmosphere [reuters.com]. What really matters is how much CO₂ has changed – and humans have changed it a lot. Since the Industrial Revolution (~1750), atmospheric CO₂ has risen from about 280 ppm to over 420 ppm today, a roughly 50% increase [en.wikipedia.org]. In other words, about one-third of the CO₂ in the air today comes from human activities (burning fossil fuels, deforestation, etc.) [usatoday.com]. So while CO₂ is only 0.04% of the air, the human-driven increase in that concentration is very significant for Earth’s climate [reuters.comreuters.com].