Which of the following is the main cause of global warming?

Options

A. Decreasing levels of `CO_2`
B. Increasing levels of `CO_2`
C. Decreasing levels of `NO_2 `
D. Decreasing levels of `O_2`

Answer

To determine the main cause of global warming, we need to analyze the options provided and understand the role of greenhouse gases. Here’s a step-by-step solution:

### Step 1: Understand Global Warming
Global warming refers to the long-term rise in Earth's average surface temperature due to human activities, primarily the emission of greenhouse gases.

### Step 2: Identify Greenhouse Gases
Greenhouse gases trap heat in the atmosphere. The main greenhouse gases include:
- Carbon Dioxide (CO2)
- Nitrous Oxide (NO2)
- Methane (CH4)
- Water Vapor (H2O)

### Step 3: Analyze the Options
Now, let’s evaluate each option provided in the question:

1. **Decreasing level of CO2**: If CO2 levels decrease, it would lead to less heat being trapped, thus reducing global warming. This is not a cause of global warming.

2. **Increasing level of CO2**: An increase in CO2 levels leads to more heat being trapped in the atmosphere, which contributes to global warming. This is a correct cause of global warming.

3. **Decreasing level of NO2**: Similar to CO2, if NO2 levels decrease, it would lead to less warming. This is not a cause of global warming.

4. **Decreasing level of O2**: Oxygen (O2) does not have a significant role in the greenhouse effect and does not contribute to global warming. This is not a cause.

### Step 4: Conclusion
Based on the analysis, the main cause of global warming from the options given is:
**Increasing level of CO2.**

### Final Answer
The correct option is **2. Increasing level of CO2.**

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