Final answer:
The current atmospheric level of CO₂ is 408 ppm, and it has been increasing since pre-industrial times. Human activities, mainly the combustion of fossil fuels, are the major contributors of CO₂ emissions. These emissions have significant impacts on the environment, including climate change and its associated effects.
Step-by-step explanation:
The current atmospheric level of CO₂ is approximately 408 parts per million (ppm). This is higher than it has been in at least 800,000 years. Human activities, particularly the combustion of fossil fuels, are the major contributors of CO₂ emissions to the atmosphere. These emissions have a significant impact on the environment, leading to climate change and its associated effects, such as rising temperatures, sea level rise, and disruption of ecosystems.