Final answer:
The amount of carbon dioxide in the atmosphere has increased by almost 45% since pre-industrial times, mainly due to human activities such as burning fossil fuels and deforestation.
Step-by-step explanation:
The amount of carbon dioxide in our atmosphere has increased by almost 45% since pre-industrial times, from approximately 280 parts per million (ppm) in the 18th century to 408 ppm in 2018. This increase is mainly due to human activities such as burning fossil fuels and deforestation.
The current level of atmospheric CO₂ is higher than it has been in at least 800,000 years, and it is predicted that the concentration will reach double the pre-industrial level by 2050. Measurements of the isotopic signatures of the added CO₂ demonstrate that it is mostly coming from burning fossil fuels.
Based on the given options, the correct answer would be 40%, as it falls within the range of the actual increase in carbon dioxide levels since 1750.