Which two trends are commonly observed in modern monthly atmospheric CO\(_2\) concentration charts?

• A. Constant levels with no significant variation
• B. A long-term downward trend and random fluctuations
• C. A long-term upward trend and a regular seasonal oscillation
• D. A sharp decline every summer with no recovery

Answer: (C)

Verified step by step guidance

1. Step 1: Begin by understanding the context of the problem. Atmospheric CO\(_2\) concentration charts are graphical representations of CO\(_2\) levels in the atmosphere over time, typically measured monthly. These charts are used to study trends in greenhouse gas levels and their implications for climate change.
2. Step 2: Recognize the two key trends commonly observed in these charts. The first trend is a long-term upward trend in CO\(_2\) levels, which reflects the increasing emissions of CO\(_2\) due to human activities such as burning fossil fuels, deforestation, and industrial processes.
3. Step 3: Identify the second trend, which is a regular seasonal oscillation. This oscillation occurs because of natural processes like photosynthesis and respiration in plants. During spring and summer, plants absorb more CO\(_2\) for photosynthesis, causing a temporary decrease in atmospheric CO\(_2\). In fall and winter, plants release CO\(_2\) back into the atmosphere, leading to an increase.
4. Step 4: Eliminate incorrect options based on your understanding of the trends. For example, 'Constant levels with no significant variation' is incorrect because CO\(_2\) levels are not constant; they show both long-term increases and seasonal fluctuations. Similarly, 'A long-term downward trend and random fluctuations' is incorrect because the long-term trend is upward, not downward.
5. Step 5: Conclude that the correct answer is 'A long-term upward trend and a regular seasonal oscillation,' as this accurately describes the observed patterns in modern monthly atmospheric CO\(_2\) concentration charts.