How much of a climate forcing is attributable to the Earth's albedo?

Question

According to the graph on this Anthony Watts page, the forcing attributed to the Earth's albedo has varied from -2 W/m^2 to 6 W/m^2 over a span of just 6 years from 1997-2003. It was as high as 9 W/m^2 in 1986.

http://wattsupwiththat.wordpress.com/2007/10/17/earths-albedo-tells-a-interesting-story/

Now these numbers strike me as completely bogus because CO2 accounts for only 1.5 W/m^2 forcing and all greenhouse gases for 2.4 W/m^2. If the albedo forcing were varying by over 1 W/m^2 per year, that would be causing absolutely massive global temperature changes.

Moreover, the IPCC sets the forcing from the Earth's albedo at -0.7 W/m^2, within a range of -1.8 to -0.3 W/m^2. See page 4 here:

http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Print_SPM.pdf

So where the heck is Watts getting these numbers from? How much climate variation is realistically due to variations in the Earth's albedo?

Interesting article on the subject here:

http://www.space.com/scienceastronomy/planetearth/earth_shine_010417.html

And a good RealClimate discussion here:

http://www.realclimate.org/index.php?p=261

Answer 1

The wide range of albedo values from earthshine measurements tells more about the error bars associated with the measurement than about the albedo. Some of the confounding factors are:

1. The magnitude of the diffuse reflectance is a function of the sun-earth-moon angle, which is constantly varying.
2. The measurement is skewed to low latitudes roughly as cos(latitude), so changes at the poles make no contribution.
3. The scattered light has a complex wavelength dependence at both earth and moon. The angular distribution of weakly absorbed wavelengths is more isotropic than strongly absorbed wavelengths. The BRDF is a better formulation than the albedo.

I would place more weight on direct satellite measurements than the earthshine measurements, but every bit of data helps. The IPCC error bars on albedo are large with good reason. More work needs to be done because the potential swings in the energy balance are large.

Answer 2

Earth's albedo isn't constant, but it doesn't change that much that fast. Existing measurements (from a variety of methods) put it at around 30% ± 1%. Doing a rough calculation, since incoming solar radiation totals 341 W m^-2, 30% reflectance would be 102 W m^2, which is a whopping amount by any standard. That's why long term ice-albedo changes trigger ice ages and inter-glacial periods.

Note that the IPCC's numbers represent anthropogenic *changes* to albedo, not the entire albedo.

Answer 3

i've got self assurance that guy does make contributions to climate replace interior the billions of a lot of as quickly as sequestered Carbon we shoot into the air. yet i do no longer think of there is something we ought to probably do approximately it. For one, arising economies like India and China have flat out refused to end burning coal and different fossil fuels as they enhance their infrastructure. 2d: we've created a international civilization atop a mountain of carbon - and it will take one hundred years to unwind and remodel the carbon civilization to a minimum of a few thing else. So what ever the effects of carbon prompted climate replace - that's going to ensue no remember what. i think of regardless of the undeniable fact that, apparently sufficient, the entire carbon climate situation is coming on the top of the petroleum age. i think of that petroleum supplies will start to dwindle long earlier disastrous climate prompted adjustments start to take bring about an excellent unmistakable way. The earth merely can no longer spit out carbon quickly sufficient for a becoming international financial gadget and inhabitants.

Answer 4

The more strident global warming alarmists have become, the more conspiracy theorists have had to don their tinfoil hats (shiny side out, of course). The reflectivity of all that exposed tinfoil has greatly increased the Earth's albedo, so much so that we now risk a global cooling catastrophe.

Seriously, the graph to which your refer has two y-axis scales, the left for the black and blue lines and the right (W/m^2) for the red line. Thus, the dramatic changes you infer from the graph are merely a few percent changes according to the left scale, not great changes in W/m^2 on the right scale.

Answer 5

It's actually on the HIGH end of the IPCC data-
Nasa Data:
http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=16905

The data shows that albedo is dropping--- about .9 watts/m in just the last few years---- which causes avg temps to increase.

Answer 6

I think that figure is from Palle et al. Measuring albedo from ground-based earthshine data is tricky, and leads to much higher variability than space-based top-of-atmosphere measurements. See here:

http://www.agu.org/journals/gl/gl0703/2006GL028196/

I suspect, that when the dust settles in a few years, Palle et al. will sheepishly admit there are a few systematic sources of error that lead to much higher variability in their ground-based numbers.

Answer 7

Interesting, because being a layman, only got the drift. Sir are you the enraged parrot?

Answer 8

Seems like we either find a new parameter or requantify an 'established' parameter on a daily basis.

Go ahead, hang your hat on these climate models.

It's just like grape Kool-Aid. It tastes good. Everyone else is drinking is. It must be OK.

Answer 9

your so smart