What is a baseline in climate data and why is it used?

• A. The latest year's value
• B. A reference period's average used to measure deviations or anomalies
• C. The maximum value observed
• D. The initial data point

Answer: (B)

A baseline in climate data is a reference period's average used to measure deviations or anomalies from typical conditions. By using this fixed reference, we express current values as how much they differ from what was normal during that period, making trends easier to spot and comparable across regions. For example, if the reference period is 1961–1990, the global temperature anomaly for a year is the actual temperature minus the 1961–1990 average. This approach highlights change rather than absolute numbers and helps combine data from different climates. It isn't just the most recent value, the maximum observed, or the first data point.