From a new paper by Dr. Greg Kopp and Dr. Judith Lean, new finding on the solar minimum TSI in 2008:
The most probable value of total solar irradiance representative of solar minimum is 1360.8 ± 0.5 W m−2, lower than the canonical value of 1365.4 ± 1.3 W m−2 recommended a decade ago. This new value, measured by SORCE/TIM, is validated by irradiance comparisons to a NIST‐calibrated cryogenic radiometer in the new TSI Radiometer Facility. Uncorrected scattering and diffraction are shown to cause erroneously high readings in non‐TIM instruments.
That’s lower by 4.6 watts per square meter. This may mean that many climate models will have to be reinitialized if it is decided that this value they derive from SORCE is more accurate than the value established previously.
By way of a forcing comparison to this suggested revision, according to NOAA ESRL:
The total effective climate forcing for all GHGs including CO2 and ozone (O3) from the beginning of the industrial revolution in 1750 to the year 2000 is 2.63 watts per square meter.
So a change of 4.6 watts per square meter to the old baseline TSI is more than double the total GHG forcings. (Averaged over the earth’s curvature, it works out to about 0.85 watts per meter*) That’s still not chump change. It will be interesting to see how this shakes out in models. It is important to note this caveat from their abstract:
TIM’s lower solar irradiance value is not a change in the Sun’s output, whose variations it detects with stability comparable or superior to prior measurements; instead, its significance is in advancing the capability of monitoring solar irradiance variations.
Improved measurements of sun to advance understanding of climate change
From Eurekalert: WASHINGTON—Scientists have taken a major step toward accurately determining the amount of energy that the sun provides to Earth, and how variations in that energy may contribute to climate change.
In a new study of laboratory and satellite data, researchers report a lower value of that energy, known as total solar irradiance, than previously measured and demonstrate that the satellite instrument that made the measurement—which has a new optical design and was calibrated in a new way—has significantly improved the accuracy and consistency of such measurements.
The new findings give confidence, the researchers say, that other, newer satellites expected to launch starting early this year will measure total solar irradiance with adequate repeatability – and with little enough uncertainty – to help resolve the long-standing question of how significant a contributor solar fluctuations are to the rising average global temperature of the planet.
“Improved accuracies and stabilities in the long-term total solar irradiance record mean improved estimates of the sun’s influence on Earth’s climate,” said Greg Kopp of the Laboratory for Atmospheric and Space Physics (LASP) of the University of Colorado Boulder.
Kopp, who led the study, and Judith Lean of the Naval Research Laboratory, in Washington, D.C., published their findings today in Geophysical Research Letters, a journal of the American Geophysical Union.
The new work will help advance scientists’ ability to understand the contribution of natural versus anthropogenic causes of climate change, the scientists said. That’s because the research improves the accuracy of the continuous, 32-year record of total solar irradiance, or TSI. Energy from the sun is the primary energy input driving Earth’s climate, which scientific consensus indicates has been warming since the Industrial Revolution.
Lean specializes in the effects of the sun on climate and space weather. She said, “Scientists estimating Earth’s climate sensitivities need accurate and stable solar irradiance records to know exactly how much warming to attribute to changes in the sun’s output, versus anthropogenic or other natural forcings.”
The new, lower TSI value was measured by the LASP-built Total Irradiance Monitor (TIM) instrument on the NASA Solar Radiation and Climate Experiment (SORCE) spacecraft. Tests at a new calibration facility at LASP verify the lower TSI value. The ground-based calibration facility enables scientists to validate their instruments under on-orbit conditions against a reference standard calibrated by the National Institute of Standards and Technology (NIST). Before the development of the calibration facility, solar irradiance instruments would frequently return different measurements from each other, depending on their calibration. To maintain a long-term record of the sun’s output through time, scientists had to rely on overlapping measurements that allowed them to intercalibrate among instruments.
Kopp said, “The calibration facility indicates that the TIM is producing the most accurate total solar irradiance results to date, providing a baseline value that allows us to make the entire 32-year record more accurate. This baseline value will also help ensure that we can maintain this important climate data record for years into the future, reducing the risks from a potential gap in spacecraft measurements.”
Lean said, “We are eager to see how this lower irradiance value affects global climate models, which use various parameters to reproduce current climate: incoming solar radiation is a decisive factor. An improved and extended solar data record will make it easier for us to understand how fluctuations in the sun’s energy output over time affect temperatures, and how Earth’s climate responds to radiative forcing.”
Lean’s model, which is now adjusted to the new lower absolute TSI values, reproduces with high fidelity the TSI variations that TIM observes and indicates that solar irradiance levels during the recent prolonged solar minimum period were likely comparable to levels in past solar minima. Using this model, Lean estimates that solar variability produces about 0.1o Celsius (0.18o Fahrenheit) global warming during the 11-year solar cycle, but is likely not the main cause of global warming in the past three decades.
GEOPHYSICAL RESEARCH LETTERS, VOL. 38, L01706, 7 PP., 2011
A new, lower value of total solar irradiance: Evidence and climate significance
Laboratory for Atmospheric and Space Physics, Boulder, Colorado, USA
Judith L. Lean
Space Science Division, Naval Research Laboratory, Washington, D. C., USA
The most accurate value of total solar irradiance during the 2008 solar minimum period is 1360.8 ± 0.5 W m-2 according to measurements from the Total Irradiance Monitor (TIM) on NASA’s Solar Radiation and Climate Experiment (SORCE) and a series of new radiometric laboratory tests. This value is significantly lower than the canonical value of
1365.4 ± 1.3 W m-2 established in the 1990s, which energy balance calculations and climate models currently use. Scattered light is a primary cause of the higher irradiance values measured by the earlier generation of solar radiometers in which the precision aperture defining the measured solar beam is located behind a larger, view-limiting aperture. In the TIM, the opposite order of these apertures precludes this spurious signal by limiting the light entering the instrument. We assess the accuracy and stability of irradiance measurements made since 1978 and the implications of instrument uncertainties and instabilities for climate research in comparison with the new TIM data. TIM’s lower solar irradiance value is not a change in the Sun’s output, whose variations it detects with stability comparable or superior to prior measurements; instead, its
significance is in advancing the capability of monitoring solar irradiance variations on climate-relevant time scales and in improving estimates of Earth energy balance, which the Sun initiates.
Received 7 October 2010; accepted 30 November 2010; published 14 January 2011.
Citation: Kopp, G., and J. L. Lean (2011), A new, lower value of total
solar irradiance: Evidence and climate significance, Geophys. Res.
Lett., 38, L01706, doi:10.1029/2010GL045777.
See the paper here (PDF)
big h/t to Dr. Leif Svalgaard
* UPDATE: from ClimateWatcher in comments:
The TSI averaged over the earth’s surface area and the amount not reflected to space:
1/4 ( 1 – a ) * S
1/4 – the ratio of circle through which radiation passes to the surface are of sphere.
a – albedo ( let’s use 0.3 even though nobody knows for sure)
So the comparison should be
0.25 * 0.7 * 4.6 W/m^2
or about 0.85 W/m^2
That’s still not negligible but not a doubler.
Interesting to note that 0.85 W/m^2 was the amount the earth was supposedly
out of balance by per Hansen and Trenberth.
Given the uncertainty in Solar constant, albedo and mostly thermal emission,
there’s no way anyone really knows if the earth is out of balance or not.