1. improve data sets in space and time;

2. improve estimates of physical quantities;

3. improve understanding of processes;

4. improve representation of processes;

5. improve assessment of uncertainty, predictability, or predictive capabilities;

6. improve synthesis and assessment to inform;

7. improve the assessment and management of risk; and

8. improve decision support for adaptive management and policy making.

Case study examples of themes 3 and 8 appear in Chapter 5.

Related CCSP Questions, Milestones, and Products. Question 4.1.5: “To what extent are climate changes as observed in instrumental and paleoclimate records related to volcanic and solar variability, and what mechanisms are involved in producing climate responses to these natural forcings?”¹

Rationale. Understanding how human activities are altering the Earth’s climate requires an understanding of the role of natural variability in climate forcing. Therefore, it is essential to know how the Sun’s energy output varies and how these variations affect the Earth’s climate.

Background. Nine independent satellite measurements of total solar irradiance (TSI) have been made since 1978. These data show that the TSI has changed during recent 11-year solar cycles with 0.1 percent amplitude (Figure B.1). However, the lack of overlapping instruments having in-flight sensitivity tracking precludes detection of any long-term variations of the Sun’s TSI on climate time scales, if any are present. The construction of a long-term irradiance composite depends crucially on assumptions made about the degradation of radiometers that lack in-flight tracking capability. Different assumptions yield two different time series. For example, note the two different trends in the energy input at solar minimum in Figure B.1.