This book documents how global surface temperature anomalies (GSTAs) and multidecadal trends are obtained. While ocean heat content change is a more robust metric with which to diagnose global warming, GSTAs have become a primary icon in the climate change debate. The book begins with a brief overview chapter of the Earth's radiative energy budget followed by two chapters on measurement approaches to monitoring temperature, including an interesting discussion of temperature scales. Chapters 4–6 concern measuring land and ocean temperatures. Chapters 7 and 8 discuss global networks and how point measurements are converted to obtain global averages. Chapter 9 focuses on changes in time of temperatures, including maximum and minimum values. This is followed by a short chapter on temperature profiles through the atmosphere and a final chapter of recommendations for future observations of this metric.