Does anyone know what's missing here?

Question

Recently, a skeptic made this claim:

"And as far Earths energy balance the clouds reflect about 24% of incoming solar radiation, thats roughly 322 W/m^2. A 2% decrease in cloud cover allows an additional +6 W/m^2 to enter the lower atmosphere."

However, there are a couple of problems with this analysis in terms of determining the net radiative forcing due to clouds, and whether a +/- 2% change in cloud cover would really result in a change in the net forcing of -/+ 6 W/m^2. What is missing in this analysis?

More importantly, how does one reconcile the skeptic's claim that the top-of-the-atmosphere (TOA) shortwave forcing from clouds is 322 W/m^2 when published studies indicate it is on the order of 47 W/m^2?

http://www.agu.org/pubs/crossref/2008/2007JD008434.shtml

Answer 1

First, the nameless skeptic is missing an elementary geometric factor of 4 arising because the earth is spherical rather than flat.  The skeptic's number is reduced to 80 W/m^2 by this factor.  Secondly, the earth is not covered with clouds all the time.  At least where I live, I see blue sky quite frequently.  The effect needs to be scaled by the actual fractional cloud cover.  The error is confusing a local condition with a global average.  Third, clouds alter the effective surface albedo because light reflected from the surface can be reflected back to the ground by clouds.    Given these further effects, a value of 47 W/m^2 seems  reasonable.

Answer 2

dude my brain hurts

Answer 3

All I have is old news, 65% cloud coverage over a given spread. Has it changed, I don't really know? Mostly over oceans where it's more or less a constant factor, but not an absolute. I do know this is one area that has befuddle scientist, as well as me. As for terrestrial coverage it changes, in correlation with ocean patterns, derived from solar input. I hate answering a question with one, but I don't have a clue. As to what type of strata, predominance, area, or if it's seasonal. I know that they try to standardize forcing, but how accurate can a chaotic system be?

Your link was a forbidden site, But I'll take your word for it. You seem to have an innate sense for this type of info, and I would like to know if it has been upgraded to relevance.

Answer 4

The IPCC FAQ (it was easier to check than the full report) shows an "Incoming Solar Radiation" of 342 (not 322) Wm^2.  The incoming solar radiation reflected by "Clouds, Aerosol and Atmospheric Gases" is 77, which is about 22.5%.

A 2% decrease in cloud cover (along with the Aerosol and other atmospheric gases effect) would reflect 75.46 W/m^2, a change of just -1.54 W/m^2, not +/- 6 W/m^2. The skeptic multiplied the 2% by the wrong term.

The TOA forcing from clouds isn't 322 (or 342), but the TOA incoming solar radiation is that.

Edit:

I barely had time to skim this, but it may be of use to you:

"Trends in upper-level cloud cover and surface divergence over the tropical Indo-Pacific Ocean between 1952 and 1997"

Joel R. Norris, Scripps Institution of Oceanography

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 110, D21110, doi:10.1029/2005JD006183, 2005

http://meteora.ucsd.edu/~jnorris/reprint...

Answer 5

To take your second point--the skeptics don't know science--that should be obvious.

As to the first, two things are missing. First--no criticism, but you didn't include enough to be clear about what they are driving at. That's really minor.

What is relevant is this: the statment as you quoted it would imply that a decrease in cloud cover would result in warming.  I don't know if this birdbrain bothered to include any "evidence"--made up or otherwise--to establish this.  But that brings us to what's missing.

This idiot doesn't know basic physical chemistry--or is deliberately misrepresenting the facts (take your pick). Here it is: water vapor is also a greenhouse gas.  True , it reflects sunlight--but it also tends to trap and retain what isn't reflected. Consequently, a decrease in average water vapor in the atmosphere (inevitable if there is a decrease in cloud cover) would result in LESS, not more, heat energy in the atmosphere (particularly thelower atmosphere.

Answer 6

sorry i get pretty lost with that stuff.