During roughly the past one hundred years, by how much has the average global temperature at the surface of Earth increased?

Introduction / Context:
Global warming refers to the long term increase in average temperature of the Earth climate system, mainly due to human activities such as burning fossil fuels and deforestation. One simple indicator of this warming is how much the average surface temperature has risen over about the last century. Many environmental science and general knowledge questions ask for an approximate value that summarises this trend.

Given Data / Assumptions:

- The time span considered is roughly the past one hundred years.
- We are asked to estimate the rise in average global surface temperature.
- Options offer increases of 0.6, 1.6, 2.6 and 3.6 degrees Celsius.
- We assume an approximate value suitable for exam level understanding, not exact decimal precision.

Concept / Approach:
Climate studies summarise long term temperature trends by comparing present averages with those from pre industrial or early twentieth century baselines. Many introductory sources state that global average temperature has increased by around half to three quarters of a degree Celsius over the last century, often quoted near 0.6 degree Celsius in older textbooks. Higher values like 1.6 or more degrees Celsius are larger than typical school level estimates for that time frame and represent more extreme warming than generally reported for the last century in basic materials.

Step-by-Step Solution:
Step 1: Recall that global warming over the past century is typically described as an increase of less than one degree Celsius in many school references.Step 2: Among the options, 0.6 degree Celsius is the only value below one degree and matches the usual approximate figure.Step 3: Values of 1.6, 2.6 and 3.6 degrees Celsius are significantly larger and are not commonly used as century scale approximations in basic texts.Step 4: Therefore, based on standard exam oriented sources, the best approximate value is 0.6 degree Celsius.Step 5: Mark 0.6 deg C as the correct option.

Verification / Alternative check:
To cross check, remember typical phrases used in environmental science chapters stating that global temperature has increased by about half a degree or slightly more in the last hundred years. Current research may update the exact figure, but older data used in many exams still refer to around 0.6 degree Celsius. Since competitive exams often rely on these widely used textbook numbers, 0.6 degree Celsius is the safe and accepted choice.

Why Other Options Are Wrong:
1.6 deg C: This value is more than double the commonly quoted basic textbook estimate and would represent a much stronger warming than usually stated for the last century in school material.
2.6 deg C: Such a large increase is far beyond standard reported values and is not consistent with the usual approximate figures given for global warming over a century.
3.6 deg C: This extremely high increase would imply dramatic climate change far beyond typical exam content and is not supported by standard introductory sources.

Common Pitfalls:
Students sometimes overestimate the temperature rise because they confuse degrees Celsius with percentage values or misinterpret graphs. Another common error is to choose higher numbers under the impression that climate change must be represented by very large differences. In reality, even a change of less than one degree in global average temperature is significant. Memorising a moderate, textbook based figure such as 0.6 degree Celsius helps avoid these exaggerations in exam answers.

Final Answer:
The approximate increase in average global temperature over the past century is about 0.6 deg C.