Final answer:
The current concentration of atmospheric carbon dioxide (CO₂) by volume is beyond 410 ppm, far exceeding pre-industrial levels and the highest in over 800,000 years due to human activities.
Step-by-step explanation:
The approximate concentration of carbon dioxide (CO₂) in the atmosphere, by volume, is currently beyond 410 parts per million (ppm). This represents an increase from pre-industrial levels of about 280 ppm in the 18th century to today's levels, which is higher than any concentration seen in the last 800,000 years. The rise in CO₂ levels is attributed to human activities such as the burning of fossil fuels and deforestation, with current human CO₂ emissions outpacing the natural absorption rate and leading to a continuous accumulation in the atmosphere.