This item got fair coveragelately. We have been able to bettercalibrate solar energy and it has meant an adjustment downward in absoluteterms. Nice to know but not particularlyuseful except that we will feel better about the number plugged into our models.
In time we will have all the datawe want, and then we will have to wait decades to begin to plausibly understandthe range and meaning of variation. It would be really nice if someone justgave it to us already.
I actually see no mechanism availablethat will actually provide much variation over and above what we now have. That is significant in certain spectra. The net for us should be stable effectivelyforever. After all, the sun is a fusiongravity pile burning flat out. The fuelis diminishing extremely slowly and nothing is been added that makes anydifference. It cannot burn any fasterthan it already is.
Sun provides Earth with less energy than we thought
Jan 21, 2011
Researchers in the
claim to have the most reliable estimates yet of the amount of energy that theSun provides to Earth – and it is less than previously thought. The findingswill give scientists more robust solar data to feed into climate models, thoughmuch more work needs to be done to fully understand the relationship betweenthe Sun and the Earth. US
Historical and geological records reveal that the Sun has remainedrelatively stable for the past 250 years, with the total solar irradiance (TSI)fluctuating by less than 1% over the roughly 11-year solar cycle. And since thefirst space-based radiometers were launched in the late 1970s, scientists havebeen able to measure this irradiation directly. But to date, these spacemeasurements have remained uncalibrated – researchers had to assume that theirinstruments function in the same way in space as they do on Earth.
Greg Kopp of the Laboratory for Atmospheric and Space Physics (LASP) inBoulder, Colorado, and Judith Lean of the Naval Research Laboratory in
say they have acquired a more reliable estimate of solar activity. Theyanalysed data collected by NASA's Solar Radiation and Climate Experiment(SORCE), a satellite launched in 2003 to investigate why solar variabilityoccurs and how it affects Earth's atmosphere and climate. Washington DC
Simulating space on Earth
Crucially, Kopp and Lean were able to calibrate data collected by theTotal Irradiance Monitor (TIM) instrument aboard this craft at a newcalibration centre at LASP. This facility in
enables researchers to verify theirfindings by recreating the conditions of interplanetary space with vacuumoperations and high solar power levels. Kopp and Lean find that the TSI duringthe last solar minimum in 2008 was 1360.8 ± 0.5 W m–2,which is roughly 5 W m–2 less than the accepted value used inclimate models. Boulder
"Although it seems small, this level of difference is very largefor the instruments acquiring these measurements," Kopp tellsphysicsworld.com.He says that while the latest finding is purely an improvement in instrumentaccuracy, it can help to inform climate studies about the influence of the Sun.
"The major climate models agree that the majority of climatechange over the last century is caused by changes in greenhouse gases, whilethe Sun's influence is responsible for about 15% of the observed warming overthis time," he says. "Prior to the 1900s, the Sun was responsible formuch more of the changes in Earth's climate."
Little Ice Age
Indeed, geologists agree that over the course of Earth's history,variations in the Sun's energy output are likely to have influenced the climateon Earth. The "Little Ice Age", for instance, which extended from the16th to the 19th century, is often linked with a roughly 70-year stretchbeginning in 1645 known as the Maunder Minimum when the Sun was particularly weak.
Friedhelm Steinhilber, a geologist at the Swiss Federal Institute ofAquatic Science and Technology, near Zurich, agrees that Kopp and Lean'smeasurements of TSI are the most accurate to date. But he warns that thesignificance of the lower value is far from fully understood.
"The Sun's influence on Earth's climate is not so much theabsolute value. It is the relative variation". Steinhilber believes thatthe significance of solar fluctuations is only really felt over longer timeperiods, like that observed during the Maunder Minimum.
These findings are presented in a paper in GeophysicalResearch Letters.