2011-01-22 03:28:34New Flanner et al paper on NH albedo changes
MarkR
Mark Richardson
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My first take, needs editing down and some additions. I'll also include the feedback calculations in the end.

 

 

 

Flanner et al snow and ice feedback parameter estimated from observations

A new paper by Flanner et al in Nature Geosciences tries to estimate the so called ‘cryosphere albedo feedback’ to climate change. The basic idea is that as Earth warms ice and snow will melt in some areas, or deserts will possibly expand and this will change how reflective the Earth is.

If ice and snow melts, then the darker surfaces underneath will absorb more sunlight and lead to more global warming. If deserts expand then they tend to be slightly more reflective than greener areas and they give a cooling effect.

Climate models expect that the effect of melting snow and ice will be the biggest contributor to changes in reflectivity: with thinner ice or wet melting ice being less reflective than thick cold ice and no ice or snow at all being even worse.

The strength of a feedback can be calculated to be a number (see endnote for some of the maths), and climate models typically expect that over the Northern Hemisphere for snow and ice reflectivity changes since 1980 this should have been about 0.25. Globally, and in the long run it’s expected to be 0.2 because there’s less snow cover in the South and in the long run you might run out of summer snow to melt.

Flanner et al use satellites to measure the change in reflectivity across the Earth’s surface for each month from 1979 to 2008 and the changes they measured in heating from reflectivity are shown in the picture before:

 

 

They find that the entire hemisphere value is between 0.33-1.07  with a best estimate of 0.62. Climate models for the same period estimated 0.08-0.42  with a best estimate of 0.25.

i.e. climate models have underestimated the rate of the darkening of the Northern Hemisphere for the past 20 years. This could be caused by Arctic ice and summer snow melting more quickly than expected, or possibly other changes like black carbon pollution helping to make snow & ice more absorptive.

It is possible that in the long run the feedback will revert to model projections – perhaps we melted the first snow and ice a lot more quickly than expected and eventually we’ll run out of the ‘easy to melt’ bits. However, if the pattern observed here holds then this could add something like 0.8-1.3 °C to the expected global warming for a doubling of CO2 - i.e. all of the warming we saw in the 20th Century which was enough to melt half of summer Arctic ice on top of what climate models already expect!

Here’s hoping it’s just a blip.

 

2011-01-22 06:51:43comments
dana1981
Dana Nuccitelli
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"The basic idea is that as Earth warms [insert comma] ice and snow will melt in some areas, or deserts will possibly expand [comma] and this will change how reflective the Earth is."

"If deserts expand then they tend to be slightly more reflective than greener areas and they give a cooling effect."

I'd suggest changing to "Deserts tend to be slightly more reflective than greener areas, so if they expand, it will result in a cooling effect."

"with thinner ice or wet melting ice being less reflective than thick cold ice [comma] and no ice or snow at all being even worse.

"The strength of a feedback can be calculated to be a number"

This is kind of awkward phrasing.  I would just say "the strength of a feedback can be estimated", or something similar.

"over the Northern Hemisphere for snow and ice reflectivity changes since 1980 [comma] this should have been about 0.25 [units?]."  Is this Wm-2K-1 ?

"Globally, and in the long run it’s expected to be 0.2 because there’s less snow cover in the South and in the long run you might run out of summer snow to melt."

I'd expand on this for clarity.  Change South to Southern Hemisphere, and clarify that once the summer snow is gone, the albedo won't increase anymore.

When referencing Flanner, link to the study.

"Flanner et al use satellites to measure the change in reflectivity across the Earth’s surface for each month from 1979 to 2008 and the changes..."  I'd break this into two sentences: "...from 1979 to 2008.  The changes they measured in heating from reflectivity are shown in the picture before: [before what?]"

"They find that the entire hemisphere value is between..."  Can we give "the value" a name?  What's the parameter called?  And again, units.

"Climate models for the same period estimated [that "the value" should have been]..."

"i.e. climate models..." => "This suggests that climate models have underestimated..."

When you mention black carbon, it might be worth explaining in a bit more detail (black carbon is another byproduct of burning fossil fuels and other materials...)

"However, if the pattern observed here holds [comma] then..."

It would be nice if we could publish this post before Monckton Myth #7 (in the next couple days), so I can reference it in that post.

2011-01-23 06:30:59
MarkR
Mark Richardson
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I was at a gig last night and now I'm away from my computer that actually had access to the article. I want to put it in on Monday once I've added the pics.

 

Had time to re-read and highlight some key bits, plus double check I understood how their calculations work... they include some more interesting values too.

 

Overall radiative forcing from the cryosphere (with and without clouds) done by month, and month by month changes split between sea ice and snow. Some really interesting stuff in there... and shows how winter changes in snow make very little difference.

2011-01-23 07:05:47Monday
dana1981
Dana Nuccitelli
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Think you can get it done on Monday Mark?  I don't want to wait too long between Monckton Myths, but it makes sense to publish your post first.

Or I guess we can use mine as a lead-in to yours.  Just a brief introduction before you go into it in more detail, then I can go back later and add a link once yours is published.  That would work too.

2011-01-23 08:18:56Two things
John Cook

john@skepticalscience...
60.231.100.70
Firstly, I would suggest Mark's post should go first. Then Dana, you don't have to change your text at all - just link to Mark's post from your existing text. Seamless and reinforcing.

second, mark, good straightforward and short post. Main comment, echoing Dana, I would clarify the first time you use the 0.25 value. What is it? Watts per square metre? If so, perhaps include short bit of text explaining what that means.

2011-01-23 20:11:10
MarkR
Mark Richardson
m.t.richardson2@gmail...
134.225.187.80

I've got this so far. Comments? Needs a good title.

 

I need to add the footnote with the calculations in. Not sure how best to do equations in html though!? Maybe I'll just link to a picture.

2011-01-23 21:46:26
Rob Painting
Rob
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Mark - Reads very well. Only bits I thought a bit slow to grasp:

- the two graphs in figure 1. Any way to break them up, explaining each in turn?.

- W m-2 K-1 needs explanation the first time you refer to it.

Other than that, sweet.

Title? - A Flanner in the works for albedo feedback?.

2011-01-23 23:05:38
MarkR
Mark Richardson
m.t.richardson2@gmail...
134.225.187.80

Rob, your titling is excellent! I should just come straight to you in future :p

 

I've changed it a bit more. Calculations go to another post that that I link to. I could do with someone checking since I did it  from memory/working it out as I went along so it's probably got mistakes.

Edited the first graph but a bit differently from Rob's suggestion; I thought I'd try big words on the graph - does that make it clear? I could split it up if it isn't.

 

I changed the wording a fair bit so I could use another read through and correction of my English! Used dana's suggestions where still relevant.

2011-01-23 23:09:25
MarkR
Mark Richardson
m.t.richardson2@gmail...
134.225.187.80
And if it's good to go, I'll publish it this evening, giving it some time to be absorbed before dana does Monckton's next thing.
2011-01-24 05:37:28
Rob Painting
Rob
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118.93.198.250
A sterling job of making this subject comprehensible for the majority. Great work. I didn't look at your calculations due to the math warning!.
2011-01-24 06:17:16nice job
dana1981
Dana Nuccitelli
dana1981@yahoo...
71.140.0.210
Looks really good Mark.  The math looks good, except the very end:

"...then global feedback is increased to 0.39 from the current estimate of 0.2..."

I didn't follow where the 0.39 came from, and I thought it was closer to 0.7.  Did you maybe mean to say 0.69, or am I missing something?

I'd also suggest linking to the math page again at the end of the blog post.  Maybe link this part of the text - "by about 20%".

Other than that, I'd say it's good to go.  By the way, is it accurate to say that the feedback is larger than expected because sea ice and snow have been declining faster than expected?

2011-01-24 06:56:42
MarkR
Mark Richardson
m.t.richardson2@gmail...
134.225.187.80

I got the 0.39 in this way:

 

Mean value globally expected to be 0.4. Expected NH = 0.25, therefore SH should be 0.15. Assuming SH constant, then the new measured NH value of 0.62 means that the global is (0.62+0.15) /2 = 0.39 to 2 sf.

I'll add the maths link at the end as well.

 

 

 

It appears that the main reason is faster than expected decline, at least from spring/summer. They comment that it's a combination of melting, reduction in extent and more first year sea ice. They also comment that they have reasons for thinking they underestimated the effect: with overestimation of the albedo of lost ice and not accounting properly for changes in melt onset. They have some field data to support this, but don't include it because they don't have enough - generally the authors think they've simply put a minimum value on it and it could be higher.

2011-01-24 07:02:22underestimated?
dana1981
Dana Nuccitelli
dana1981@yahoo...
71.140.0.210
Already a significantly larger effect than projected and they think it's a minimum value?  That's not good.
2011-01-24 07:17:31error?
dana1981
Dana Nuccitelli
dana1981@yahoo...
71.140.0.210

Mark, I think I just caught an error:

"Even though there is much less ice in the winter..."

I presume this should say much more ice, yes?  I'm going to edit the article accordingly.