Thanks to one of our commenters (thanks Henry), this unique project called “Earthshine” being done at the Big Bear Solar Observatory has been brought to my attention. The project is simple in concept:
The Earth’s climate depends on the net sunlight deposited on the globe, which is critically sensitive to the Earth’s albedo. A global and absolutely calibrated albedo can be determined by measuring the amount of sunlight reflected from the Earth and, in turn, back to the Earth from the dark portion of the face of the Moon (the `earthshine’ or `ashen light’).
What earthshine looks like on the moon, using photo enhancement on the lower left. BBSO uses a blocking filter to dim the moonshine crescent, typically about 10,000 times brighter than the earthshine.
In simple terms, the lower the albedo of the Earth, the greater amount of solar radiation it will absorb. The greater the albedo, the more solar radiation is reflected. This of course affects earthly temperatures.
The Earthsine project is producing some very interesting results. Notably, that the Earth’s Albedo has risen in the past few years, and by doing reconstructions of the past albedo, it appears that there was a significant reduction in Earth’s albedo leading up to a lull in 1997. 1998 has been touted as one of the warmest years on record, and the time lag may have had to do with the thermal inertia of the oceans. Then the albedo increased, making the earth more reflective. Clouds have the greatest potential for changing albedo on a short time scale.
Reconstructed annual reflectance anomalies, Δp* (black) with respect to the mean anomaly for the regression calibration period, 1999-2001 (gray band). The large error bars result from the seasonal variability of the Earth’s albedo, which can be 15-20%. Also plotted (blue) are the ES-observed annual anomalies for 1999-2003 and 1994-1995. The right-hand vertical scale shows the deficit in global SW forcing relative to 1999-2001. The red solid bar represents the accumulated forcing (in W / m2) attributed to the greenhouse gases concentration increase over the last 100 years, from the International Panel for Climate Change (2001).
Image credit: Earthshine Project, BBSO.
The most interesting thing here is that the albedo forcings, in watts/sq meter seem to be fairly large. Larger than that of all manmade greenhouse gases combined:
This rapidly changing albedo lends some credence to Svensmark’s theory of Earth’s cloud cover being modulated by Galactic Cosmic Rays, but it could also be caused by other factors such as aerosols.
Whatever the cause for the rapid change in albedo, it seems to have quite an effect of earth’s radiation budget. The California Instttute of Technology made a press release in 2004 that summed up the project fairly well:
By using a combination of earthshine observations and satellite data on cloud cover, the earthshine team has determined the following:
= Earth’s average albedo is not constant from one year to the next; it also changes over decadal timescales. The computer models currently used to study the climate system do not show such large decadal-scale variability of the albedo.
= The annual average albedo declined very gradually from 1985 to 1995, and then declined sharply in 1995 and 1996. These observed declines are broadly consistent with previously known satellite measures of cloud amount.
= The low albedo during 1997-2001 increased solar heating of the globe at a rate more than twice that expected from a doubling of atmospheric carbon dioxide. This “dimming” of Earth, as it would be seen from space, is perhaps connected with the recent accelerated increase in mean global surface temperatures.
= 2001-2003 saw a reversal of the albedo to pre-1995 values; this “brightening” of the Earth is most likely attributable to the effect of increased cloud cover and thickness.
These large variations, which are comparable to those in the earth’s infrared (heat) radiation observed in the tropics by satellites, comprise a large influence on Earth’s radiation budget.
Discover more from Watts Up With That?
Subscribe to get the latest posts sent to your email.
Chris – I don’t know the answer as to why satellite measurements show a different result. The only advice I can offer is that we’ve got two completely different measuring systems, using different optical paths, run under different methodology.
The earth based telescope albedo method has been in use for almost 100 years, and hasn’t been shown problematic. Satellite albedo measurements are much newer, and we don’t know if they are problematic or not.
I would point out that with a satellite measurement, the environment and instrumentation platform sometimes has unknowns or things not thought of. A perfect case in point was John Christy’s satellite measurements of atmospheric temperature which initially showed a cooling trend, until someone pointed out that he hadn’t factored in an orbital decay issue [ I think that’s what it was] on the measuring platform, and the cooling trend turned into a slight warming trend.
NASA has been known to make huge blunders over simple things, like launching the flawed Hubble mirror into space without first testing it, or losing a mars probe because one group worked in metric and the other in English units, resulting in a navigation error which crashed the probe into the surface. Then there’s the shuttle incidents, both products of an inflexible hierarchy that refused to see problems. Then we have the .15 degree temperature error in NASA GISS surface temperature data found on August 8th.
For all we know, the satellite albedo sensor system may have a sign error or there could be some other factor, or it may be absolutely right. My hunch is that they are using sensors on the spacecraft not specifically designed to sense albedo, but are putting other sensors into service for the purpose. Correct me if I’m wrong.
The point is, space based measurement is not easy and has many complexities over ground based measurement.
My money is on the earth based telescope method because it is a simpler and established technique, and more importantly, there’s less to go wrong when you have a small group of dedicated scientists working on a single ground based measurement than when you have a whole far flung government bureaucracy working on a space platform.
Simplicity is not a strong attractor of entropy.
I’m sure that with all the mention they’re getting here, it won’t be long before they revisit their article. In the meantime, post THEIR version of the chart (with proper credit, of course) below the one taken from the BSSO website.
From “RTFR” that rabett recommends, we find that it was Pallé et al. [2004] that modified the chart. Which makes it even more strange, because the “et al” includes the folks at BSSO.
Note to Anthony: When the researcher replies, ask if he knows if the old (1920 – 1960) data by Danjon and Dubois is available. Pallé et al didn’t say anything about the old data.
Thanks for the insight. When Googling, I came across a presentation which attempts to explain the difference. It seems a bit one-sided in criticizing the Earthshine methodology without considering the flaws of satellite measurements.
http://asd-www.larc.nasa.gov/ceres/STM/2005_05/loeb_earthshine.pdf
I guess that’s our tax dollars at work. By the way, NASA has also made outlandish predictions for solar cycle 24.
Some of the problems between surface readings and satellite readings were mentioned in some of the stuff I’ve browsed.
1. Surface readings limited by view (cloud cover, moon phase, etc) and satellites not effected.
2. Satellites get a “spot” or swath of an area, while the surface readings get more of a “global” reading.
3. It could be a carry-over “error” like the one that affected the satellite temp readings: they forgot to take into account orbital decay (apogee/perogee). Earth-to-moon distance stays relatively stable, doesn’t it?
This albedo question is all the more reason to get the Triana satellite out of storage and launched to it’s L1 point.
It’s one of the few things, perhaps the only thing, that Gore came up with that I agree with.
See: http://en.wikipedia.org/wiki/Triana_%28satellite%29
and its official NASA page: http://science.hq.nasa.gov/missions/satellite_53.htm
You mean besides the internet?
Oh wait, let me amend “It’s one of the few things, perhaps the only thing, that Gore came up with that I agree with.”
After looking at the DSCOVR mission page
http://science.hq.nasa.gov/missions/satellite_53.htm
I see a design life listed of only TWO YEARS! Jeez, comm satellites have longer lives than that and do a lot more.
A two year albedo plot does not a trend make, no matter how accurate. I’m really surprised at such a short life span. It seems almost pointless to launch it then.
Chris I read the short paper from CERES, and it seems that they have a point. It appears that seasonal and angular variations aren’t well considered in the BBSO data.
I’ll check a couple of other sources to see how the CERES critique holds up.
RE: 20071018 – (10:00:34)
I would add that inevitably, the Earth based telescope – earthshine measurement integrates everything reaching that part of the moon from that side of the earth, and would also tend to filter out higher frequency noise. Sounds pretty good to me!
It’s too bad we can’t come with a way to use the most stable satellite base we have: the moon.
If we could launch a probe, set it to face the earth, and take continuous pictures, unhampered by cloud, atmosphere, and pollution problems.
It would see the entire face, all 360 degrees, and radio that data back to earth.
For those of you who are interested;
A reasonably good site for Cosmic Ray trends is available here. http://cr0.izmiran.rssi.ru/mosc/main.htm
The Oceans are the local “flywheel” for Earth bound climate variations and current graphics of the respective temperature conditions is represented here,
http://weather.unisys.com/surface/sst_anom.html
And here,
http://weather.unisys.com/surface/sst.html
@henry,
No, the Earth-Moon distance doesn’t stay relatively stable. The distance is increasing, and this has been measured by laser (Apollo missions left mirrors on the moon just for this purpose). See this article or search for “Tidal Recession Earth Moon”.
Yes the laser reflector data does show Earth’s Moon increasing in overall distance, about 3 inches per century.
[…] The Big Bear Solar Observatory’s Earthshine is an attempt to study changes in Earth’s albedo (reflectivity)…http://wattsupwiththat.wordpress.com/2007/10/17/earths-albedo-tells-a-interesting-story/ […]
[…] unusually cool year? According to Anthony Watts, the Earth`s albedo reached a nadir in 1997, and has risen sharply since. Is this related to the weakening of solar activity? We`ve seen few sunspots in Solar Cycle […]
What is the current data on grey snow from soot deposition on the polar cap? Isn’t there a measurable reduction in albedo that would increase absorption and accelerate snowmelt? I see China’s official ‘Polar Climatologist’ Dr. Rebecca Lee (actually a PLA graphic artist) stating that Global Cooling is a direct consequence of Global Warming! They’re using their clever ‘Jedi mind tricks’ to deflect the blame on their infamous ‘Brown Cloud’ as a contributor to climate change. Perhaps their ‘alleged’ $300 mil investment in Al Gore’s $5 bill global green fund is albedo increasing whitewash reflecting back the shaming gaze of a watching world.
[…] cool year? According to Anthony Watts, the Earth`s albedo reached a nadir in 1997, and has risen sharply since. Is this related to the weakening of solar activity? We`ve seen few sunspots in Solar Cycle […]