Science Daily: Solar radiation increasing


Richard Moore

Original source URL:

NASA Study Finds Increasing Solar Trend That Can Change Climate

Science Daily ‹ Since the late 1970s, the amount of solar radiation the sun 
emits, during times of quiet sunspot activity, has increased by nearly .05 
percent per decade, according to a NASA funded study.

"This trend is important because, if sustained over many decades, it could cause
significant climate change," said Richard Willson, a researcher affiliated with 
NASA's Goddard Institute for Space Studies and Columbia University's Earth 
Institute, New York. He is the lead author of the study recently published in 
Geophysical Research Letters.

"Historical records of solar activity indicate that solar radiation has been 
increasing since the late 19th century. If a trend, comparable to the one found 
in this study, persisted throughout the 20th century, it would have provided a 
significant component of the global warming the Intergovernmental Panel on 
Climate Change reports to have occurred over the past 100 years," he said.

NASA's Earth Science Enterprise funded this research as part of its mission to 
understand and protect our home planet by studying the primary causes of climate
variability, including trends in solar radiation that may be a factor in global 
climate change.

The solar cycle occurs approximately every 11 years when the sun undergoes a 
period of increased magnetic and sunspot activity called the "solar maximum," 
followed by a quiet period called the "solar minimum."

Although the inferred increase of solar irradiance in 24 years, about 0.1 
percent, is not enough to cause notable climate change, the trend would be 
important if maintained for a century or more. Satellite observations of total 
solar irradiance have obtained a long enough record (over 24 years) to begin 
looking for this effect.

Total Solar Irradiance (TSI) is the radiant energy received by the Earth from 
the sun, over all wavelengths, outside the atmosphere. TSI interaction with the 
Earth's atmosphere, oceans and landmasses is the biggest factor determining our 
climate. To put it into perspective, decreases in TSI of 0.2 percent occur 
during the weeklong passage of large sunspot groups across our side of the sun. 
These changes are relatively insignificant compared to the sun's total output of
energy, yet equivalent to all the energy that mankind uses in a year. According 
to Willson, small variations, like the one found in this study, if sustained 
over many decades, could have significant climate effects.

In order to investigate the possibility of a solar trend, Willson needed to put 
together a long-term dataset of the sun's total output. Six overlapping 
satellite experiments have monitored TSI since late 1978. The first record came 
from the National Oceanic and Atmospheric Administration's (NOAA) Nimbus7 Earth 
Radiation Budget (ERB) experiment (1978 - 1993). Other records came from NASA's 
Active Cavity Radiometer Irradiance Monitors: ACRIM1 on the Solar Maximum 
Mission (1980 - 1989), ACRIM2 on the Upper Atmosphere Research Satellite (1991 -
2001) and ACRIM3 on the ACRIMSAT satellite (2000 to present). Also, NASA 
launched its own Earth Radiation Budget Experiment on its Earth Radiation Budget
Satellite (ERBS) in 1984. The European Space Agency's (ESA) SOHO/VIRGO 
experiment also provided an independent data set (1996 to 1998).

In this study, Willson, who is also Principal Investigator of NASA's ACRIM 
experiments, compiled a TSI record of over 24 years by carefully piecing 
together the overlapping records. In order to construct a long-term dataset, he 
needed to bridge a two-year gap (1989 to 1991) between ACRIM1 and ACRIM2. Both 
the Nimbus7/ERB and ERBS measurements overlapped the ACRIM 'gap.' Using 
Nimbus7/ERB results produced a 0.05 percent per decade upward trend between 
solar minima, while ERBS results produced no trend. Until this study, the cause 
of this difference, and hence the validity of the TSI trend, was uncertain. 
Willson has identified specific errors in the ERBS data responsible for the 
difference. The accurate long-term dataset, therefore, shows a significant 
positive trend (.05 percent per decade) in TSI between the solar minima of solar
cycles 21 to 23 (1978 to present). This major finding may help climatologists to
distinguish between solar and man-made influences on climate.

NASA's ACRIMSAT/ACRIM3 experiment began in 2000 and will extend the long-term 
solar observations into the future for at least a five-year minimum mission.

Note: This story has been adapted from a news release issued by NASA/Goddard 
Space Flight Center.

Copyright © 1995-2007 ScienceDaily LLC
Contact: •••@••.•••

Escaping the Matrix website:  
cyberjournal website:             
Community Democracy Framework:
Subscribe cyberjournal list:            •••@••.•••  (send 
blank message)
Posting archives:                      
Moderator:                                         •••@••.•••  (comments