Abstracts Prepared by Workshop Speakers - The Effects of Solar Variability on Earth's Climate - page 36

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Abstracts Prepared by Workshop Speakers
Overview and Advances in Solar Radiometry for Climate Studies
Greg Kopp, Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder
The Sun provides nearly all the energy driving Earth's climate system. Even typical short-term
variations of 0.1 percent in this incident irradiance exceed all other energy sources combined. The
33 ‐ year space-borne total solar irradiance (TSI) measurement record, shown in Figure C.1, enables
estimates of the portion of climate change due to solar variability on global and regional scales.
Extensions of this modern record via proxies provide historical estimates of long-term solar variability
and the corresponding climate effects. Daily spectral solar irradiance (SSI) measurements over the
majority of the solar spectrum commenced a few years ago and show promise for helping researchers
understand heating, circulation, and chemistry effects in Earth's atmosphere.
To discern natural and anthropogenic effects, climate studies require long-term records of
incident solar irradiances. For TSI, the net radiative energy driving Earth's climate system, these are
based on the space-borne measurements shown in Figure C.1. The offsets between these measurements,
which are as large as 0.34 percent currently, are due to instrument calibration differences. Recent
laboratory tests by the international teams involved in these measurements have identified the primary
cause of these measurement offsets, helping improve the existing record retroactively. Such offsets,
along with differing instrument drifts, must be corrected to create a composite TSI record having the
accuracy and stability needed for reliable climate studies and estimates of Earth's radiative energy
balance.
I will give an overview of solar irradiance measurements and recent progress to improve this
record's accuracy. Using estimates of solar variability over long-term timescales relevant for climate
studies, I will derive the record's accuracy and stability requirements and assess the current status for
achieving these requirements, comparing to recent solar minima as examples. By extending the record
via proxies to paleo timescales, I will discuss estimates of climate sensitivity to solar forcing over recent
and historical times. I will also present the current state of the instruments acquiring these measurements
and the planned future means of continuing the TSI record as well as the newer SSI measurements.
Assessing Solar and Solar-Terrestrial Influences as a Component
of Earth's Climate Change Picture
Daniel N. Baker, Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder
Researchers have long been intrigued by questions about how solar variability and related solar-
terrestrial influences can affect Earth's middle and lower atmosphere. A goal of basic research programs
has been to establish a comprehensive intellectual foundation for the investigation of the effect of solar
variability on climate. It is clear that conclusive observations of cause-effect relationships (at the
requisite level of confidence) are a very large challenge. Satisfactory work in this arena requires close
collaboration between solar, magnetospheric, and atmospheric scientists. It is important to note that new
generations of atmospheric models now are able to couple together all the layers of Earth's extended
atmosphere. Through such models, and with increasingly complete observations, we are in a steadily