The final workshop session was a discussion led by chairs of the sessions, and all participants
were encouraged to share their thoughts on the open research questions in these fields. The principal
topics for discussion were as follows:
Solar irradiance variability (total solar irradiance [TSI] and spectral). What do we know
about TSI variability now and in the past?
Sun-climate connections on different timescales. What do we know about the variability of
climate on global and regional spatial scales on timescales of years, decades, and longer?
Mechanisms for Sun-climate connections. Do we understand and have we correctly modeled
the top-down, bottom-up, galactic cosmic ray forcings and chemical couplings that determine the system
The discussion was led by Joanna Haigh; Daniel Baker was the facilitator. The panel members—
Joe Giacalone, Ka-Kit Tung, Isaac Held, and Peter Pilewskie—were the chairs of the four workshop
sessions (with the exception of Joe Giacalone, who stood in for Peter Foukal).
The basic question in understanding the Sun's role in climate change is a compelling one: How
well is past and present total solar irradiance known and understood? As Haigh pointed out, it is certainly
an issue of concern that the existing TSI database has been derived from measurements that could not be
intercalibrated to the degree of accuracy necessary for climate studies.
Giacalone led off the panel discussion by providing an overview of what he felt were the key
issues, stating that understanding the Sun's role in climate is an important and compelling issue. The
research community has to understand the Sun's variability and how it can be tied to proxy
measurements, and with what degree of accuracy. Greg Kopp pointed out that understanding the Sun, its
output, and the various proxies used to infer its output may inform the ability to specify the accuracy of
back-projections of paleo-TSI based on various proxies (including sunspot number). Mark Rast pointed
out the difficulty of the issue, given that simplifying assumptions are currently made about the
relationship between sunspots, faculae, and TSI when in fact modern observations have indicated that the
situation is really quite complex.
Baker questioned the audience for key steps that NASA and NSF can pursue to address these
questions. Rast responded that radiometric imaging of the Sun is important not only to extrapolate
irradiance, but also to understand the substructure of the magnetic field and its relationship to spectral
irradiance. Giacalone and others also pointed out as a research area that needs to be more fully
understood the relationship between the galactic cosmic-ray flux and details of the interaction with the
variable solar wind and magnetic field configuration. He and other audience members noted that now, as
the extended solar minimum ends, would be an excellent time to study this phenomenon. Philip Judge
suggested that, at the moment, the research is limited by time series length and that it will be necessary to
continue with accurate measurements in the future. Giacalone posed the question of whether other
potential proxy records exist, for example from Mars or a meteorite.
Tung led a discussion that reflected the talks and comments from the audience on the issues
surrounding the modeling of past climate events. He noted that, when viewed from the perspective of the
global response, there is a coherent structure of predictable patterns in latitude, longitude, height, and