Question

question 8
1 pts
the levels of carbon dioxide in the atmosphere
began decreasing when the burning of fossil fuels increased.
are high but not higher than the highest estimated levels in the last 420,000 years.
are estimated to be higher than at any time in the past 420,000 years.
peaked around 1950 and have begun slowly decreasing since then.

Explanation:

The burning of fossil fuels releases carbon dioxide. Over the past 420,000 years, due to human activities like increased fossil - fuel burning, the carbon - dioxide levels have risen. It's not decreasing with more fossil - fuel burning (so the first option is wrong). Also, current levels are higher than past levels (so the second option is wrong). And carbon - dioxide levels have been increasing, not decreasing since 1950 (so the fourth option is wrong).

Answer:

are estimated to be higher than at any time in the past 420,000 years.