The Effects of Solar Variability on Earths Climate

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The Effects of Solar Variability on Earths Climate
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Preface

Experts on solar physics, solar variability, climate science, climate models, paleoclimatology,
atmospheric science, and experts on other stars came together on September 8-9, 2011, at the National
Center for Atmospheric Research (NCAR) in Boulder, Colorado, to discuss how the Sun’s variability
over time has affected Earth’s climate. The National Research Council was asked by program managers
at the National Science Foundation (NSF) and the National Aeronautics and Space Administration
(NASA) to organize an interdisciplinary public workshop to examine the state of knowledge of Earth’s
climate response to solar variability and to explore some of the outstanding science questions that might
guide future research endeavors. As noted above, this particular topic touches upon a number of diverse
research areas; a workshop such as this brings together scientists that do not always have an opportunity
to interact as a group.
A committee was formed and met on April 25, 2011, at the National Academies Keck Center in
Washington, D.C., to develop an agenda for the workshop. Speakers were invited to submit abstracts, and
these talks were organized into sessions by the committee. The workshop was advertised to the public
through various media. During the workshop, the audience was encouraged to interact with the speakers
and discuss the issues from different viewpoints. A final panel discussion was lead by chairs of the
sessions, and the entire group was encouraged to share their thoughts on open research questions in these
fields.
A complete statement of task and workplan for the project can be found in Appendix A. The
workshop featured presentations on a variety of topics related to solar variability and climate change,
organized as follows:
• The Sun and Solar Variability: Past and Present
—Overview of solar and heliospheric variability
—Observations of the Sun’s variable outputs
—Techniques for revealing past solar changes
• Sun-Climate Connections on Different Timescales
—Evidence of solar influences in the troposphere and stratosphere
—How the climate system works and how it might respond to solar influences
—Indications of influence based on paleoclimate records
• Mechanisms for Sun-Climate Connections
—Mechanisms connecting variations in total solar irradiance directly to the troposphere
—Mechanisms that influence upper parts of the atmosphere, such as variations in solar
ultraviolet radiation and possibly solar energetic particles
—Mechanisms that link variations in galactic cosmic rays to climate change.
This workshop report contains no recommendations, findings, or statements of consensus.
Instead, this workshop report summarizes the views expressed by individual workshop participants
(invited speakers and guests). Also included is background information intended to provide context to the
reader on both the solar and climate science topics presented at the workshop; however, this is not
intended to be an exhaustive review of the current state of the science. Although the committee is
responsible for the overall quality and accuracy of the report as a record of what transpired at the
workshop, the views contained in the report are not necessarily those of all workshop participants, the
committee, or the National Research Council.
The committee thanks the NCAR Mesa Laboratory, in particular, Gerald Meehl, Stephanie
Shearer, and Eron Brennan, for providing meeting space and excellent technical support.

Contents

OVERVIEW 1
1 BACKGROUND 3
The Potential Sun-Climate Connection, 3
The Measurement Record from Space, 4
Potential Perturbations of Climate Due to Solar Variability, 6
This Workshop Report, 8
2 WORKSHOP PRESENTATIONS 9
The Sun and Solar Variability—Past and Present, 9
Evidence of Sun-Climate Connections on Different Timescales, 18
Mechanisms for Sun-Climate Connections, 21
3 PANEL DISCUSSION 28
APPENDIXES
A Statement of Task and Preliminary Workplan 33
B Workshop Agenda and Participants 34
C Abstracts Prepared by Workshop Speakers 38
D Biographies of Committee Members and Staff 51
E Acronyms and Terms 57