By what degrees has the mean global temperature increased in the 20th century?

Options

A. `0 .2 %`
B. ` 0.4 % `
C. ` 0. 6 %`
D. ` 0.8 %`

Answer

To determine the increase in mean global temperature during the 20th century, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: The question asks for the increase in mean global temperature specifically during the 20th century.

2. **Identify the Options**: The options provided are 0.2%, 0.4%, 0.6%, and 0.8%.

3. **Research the Data**: According to scientific studies and reports, including those referenced in educational materials like the NCERT book, the mean global temperature has been observed to increase due to factors such as global warming and greenhouse gas emissions.

4. **Find the Relevant Information**: It is noted that the temperature has increased by approximately 0.6 degrees Celsius in the past three decades, and similar increases have been recorded for the 20th century.

5. **Select the Correct Answer**: Based on the information gathered, the increase in mean global temperature during the 20th century is 0.6 degrees Celsius.

6. **Final Answer**: Therefore, the answer to the question is **0.6 degrees Celsius**.