Welcome to
Science a GoGo's
Discussion Forums
Please keep your postings on-topic or they will be moved to a galaxy far, far away.
Your use of this forum indicates your agreement to our terms of use.
So that we remain spam-free, please note that all posts by new users are moderated.


The Forums
General Science Talk        Not-Quite-Science        Climate Change Discussion        Physics Forum        Science Fiction

Who's Online
0 registered (), 410 Guests and 1 Spider online.
Key: Admin, Global Mod, Mod
Latest Posts
Top Posters (30 Days)
Page 1 of 2 1 2 >
Topic Options
#23760 - 10/07/07 04:21 AM Greenland Melt Record High
Mike Kremer Offline

Megastar

Registered: 10/16/04
Posts: 1696
Loc: London UK
Though some might be interested in this. Others might not.

NASA Finds Greenland Snow Melting Hit Record High in High Places

A new NASA-supported study reports that 2007 marked an overall rise in the melting trend over the entire Greenland ice sheet and, remarkably,
melting in high-altitude areas was greater than ever at 150 percent more than average.
In fact, the amount of snow that has melted this year over Greenland could cover the surface size of the U.S. more than twice.

http://www.nasa.gov/centers/goddard/news/topstory/2007/greenland_recordhigh.html

_________________________
.

.
"You will never find a real Human being - Even in a mirror." ....Mike Kremer.



Top
.
#23771 - 10/08/07 12:40 AM Re: Greenland Melt Record High [Re: Mike Kremer]
Ellis Offline
Megastar

Registered: 01/08/07
Posts: 1490
Loc: Australia
I was hoping someone else would take this up, but this weekend I heard a radio discussion of the theory popular a few years ago, that this melting of the ice in Greenland could, by reducing the salinity of the water in the ocean currents, cause temperatures to fall in Europe. Certainly I was taught at school that the reason that the UK, on the same latitude as Northern Europe had a more mild temperature was that the warm currents swept past to the south. When it didn't, 12,000 years ago, due to a huge ice sheet dropping off Northern America, it triggered last of the Ice Ages.

And Greenland has a Diamond Rush!! Like a Gold Rush but Diamonds have been found in areas that were inaccessible a few years ago.

Top
#23791 - 10/09/07 06:59 PM Re: Greenland Melt Record High [Re: Ellis]
Chris Offline
Junior Member

Registered: 10/05/07
Posts: 22
Because the "ocean conveyor" which transports heat from the equatorial regions to the poles shutdown. Looks like the shutdowns were real, important, fast, had widespread consequences, but hard to get one now because the Laurentide ice sheet is no longer sitting on Canada and diverting winds to the south, so it is hard to keep sea ice off England in the winter even if you freshen the ocean. The more up-to-date literature suggests that this a very low probability event and the thermohaline decline is very small, if there is a signal at all. Looks like the more we burn, the more warming we get: about 3-5 C per doubling of CO2.
One paper I recommend is "Wally Was Right: Predictive Ability of the North Atlantic “Conveyor Belt” Hypothesis for Abrupt Climate Change" from Richard B. Alley (Annu. Rev. Earth Planet. Sci. 2007. 35:241–272) which I can e-mail if you can't get it.

Top
#23802 - 10/11/07 06:04 AM Re: Greenland Melt Record High [Re: Chris]
ImranCan Offline
Member

Registered: 09/04/07
Posts: 94
Loc: Brunei
Interesting reading. What I would like to know is why there is such localised warming in the Arctic when the overall global mean surface temperature has been static for nealy 10 years ??

My feeling is that this can only occur due to ocean current shifts such as a more northerly route for the Gulf Stream. Any views on this ?


Top
#23810 - 10/12/07 05:17 AM Re: Greenland Melt Record High [Re: ImranCan]
Chris Offline
Junior Member

Registered: 10/05/07
Posts: 22
The temperature hasn't been static, it has risen- 1998 got a weird year because of El Nino, but I think 2005 is the hottest on record. There are other influences like a decline in the solar cycle, but we might get 0.2 C on top of CO2 warming over the next 5 years when we head toward maxima (Camp and Tung 2007) You get polar amplification up in the Arctic (much faster than the southern hemisphere) because of feedbacks like ice-albedo, and the nature of ocean heat uptake.
http://data.giss.nasa.gov/gistemp/

You get more precipitation at both poles (which can lead to accumulation of ice at the interiors of either ice sheet) while sea-ice is lost at a higher rate in Greenland. If you go over the IPCC AR4 (pp 902-908 @ http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Print_Ch11.pdf) they go into detail about what is going on in the polar regions.

The arctic warming much faster is well understood and expected, but if you keep adding CO2 you keep getting more warming globally. The rapid rise of carbon dioxide is more than the slow response time of the oceans can keep up with and you get more solar radiation coming in than infrared going out, and you heat up. A couple of papers:

http://www.acia.uaf.edu/ (this is a big report, but recommended for anything relating to the arctic from geological to climatic to biological patterns)
http://www.atmos.washington.edu/~bitz/HollandBitz.pdf
http://www.springerlink.com/content/6lt5m95y36vd08yd/

Going back to the gulf stream transport, if there is a change in the system, it is very weak. Kanzow et al (2007) and Cunningham et al (2007), both in Science, show there isn't much weakening of the system which is in line with what models show- we aren't going to shut down the gulf stream for at least centuries, and if there is a cycle over the Holocene we are still uncertain in what direction the change is in. When water in the "conveyor belt" reaches northern latitudes it sinks before it freezes, if it shuts down it freezes before it sinks. It would cool the NH if this happened and we'd have widespread consequences but you don't get anything like the "day after tomorrow" movie- the Alley paper goes over this. There are other regional influences in the Arctic in addition to feedbacks and the human influence, which the AR4 goes over.

Chris

Top
#23811 - 10/12/07 05:35 AM Re: Greenland Melt Record High [Re: Chris]
ImranCan Offline
Member

Registered: 09/04/07
Posts: 94
Loc: Brunei
Thanks for the references - I will certainly read them. On the quote about global temps over the last 10 years, I was looking at the UK metoffice data on global temperatures - see below. I agree 1998 was a high year (for whatever reason) but the trend since then is flat - even maybe declining a little. Why is this ? Or is the data wrong ?

http://www.scienceagogo.com/forum/ubbthreads.php?ubb=showflat&Number=23476#Post23476


Top
#23812 - 10/12/07 05:37 AM Re: Greenland Melt Record High [Re: ImranCan]
ImranCan Offline
Member

Registered: 09/04/07
Posts: 94
Loc: Brunei

Top
#23819 - 10/13/07 01:23 AM Re: Greenland Melt Record High [Re: ImranCan]
Chris Offline
Junior Member

Registered: 10/05/07
Posts: 22
We're aren't really in a cooling trend (http://www.nasa.gov/vision/earth/environment/2005_warmest.html), but there are still natural factors- I've not read in detail about the last few years but we are in a solar cycle decline, there is still natural variability- if you're looking for a one or two year deviation, then you will succeed in finding "something wrong" but that really isn't indicative of much- we have certainly warmed since 1998 though after that one year jump- this page (and references therein) have a more high resolution graph to this time period and explanations of impacts of natural variability (such as the '91 Pinatubo eruption or El Nino)
http://www.globalwarmingart.com/wiki/Image:Short_Instrumental_Temperature_Record_png

Some studies even suggest we might not warm much until 2009 ie (Smith et al. 2007)because shifts in ocean currents and other natural changes may partially offset the warming signal for a couple of years, but we know what we get with a given amount of CO2 addition and we fully expect to be warming as time goes on- about 3 C per doubling of CO2 and feedbacks.

Chris


Edited by Chris (10/13/07 01:29 AM)
Edit Reason: fix

Top
#23828 - 10/14/07 04:15 AM Re: Greenland Melt Record High [Re: Chris]
ImranCan Offline
Member

Registered: 09/04/07
Posts: 94
Loc: Brunei
I'm not looking for "something wrong" ... its more like I'm looking for something definitively right. If it's possible that "natural variability" is used to explain why there hasn't been any significant warming since 1998 (notwithstanding 5 year rolling average graphs), isn't it also possible that the warming trend since the late seventies is also due to "natural variablility" ?? We might be still warming since the mini ice-age.

I agree that CO2 has the properties you describe, but there again water vapour does the same and it exists in orders of maginitude higher concentrations than CO2. Wouldn't any minor variation in this have a larger impact than CO2 ? And don't all the CO2 models also show the troposphere warming - which hasn't been observed yet ?


Top
#23830 - 10/14/07 08:02 PM Re: Greenland Melt Record High [Re: ImranCan]
Chris Offline
Junior Member

Registered: 10/05/07
Posts: 22
Originally Posted By: ImranCan
I'm not looking for "something wrong" ... its more like I'm looking for something definitively right. If it's possible that "natural variability" is used to explain why there hasn't been any significant warming since 1998 (notwithstanding 5 year rolling average graphs), isn't it also possible that the warming trend since the late seventies is also due to "natural variablility" ?? We might be still warming since the mini ice-age.

I agree that CO2 has the properties you describe, but there again water vapour does the same and it exists in orders of maginitude higher concentrations than CO2. Wouldn't any minor variation in this have a larger impact than CO2 ? And don't all the CO2 models also show the troposphere warming - which hasn't been observed yet ?



I specifically noted that the trends are completely in line with what we expect to see, 1998 just got one big jump because of mechanisms I've explained and linked you to. Natural variations have been extremely well studied and documented in the primary literature, and there is certainly no explanatory trend since about 1950- you cannot just say "well something else could have done it" you have to demonstrate what it is, if the magnitude matches current warming (or the direction for that matter), andwhy CO2 is not behaving as we expect it to (The CO2 effect is largely basic physics), or what the "zero point" is which the Earth is supposed to naturally return to after the LIA. If you want to give data to the scientific community on how we can get the warming of today, especially the rate and magnitude of increase since 1950, you'd win a nobel but we simply cannot explain it without adding the anthropogenic CO2



As for water vapor, you're making the same mistake physicists in the early century were making- treating the atmosphere like a single sheet even though we know it gets drier as you go up and just consider the total water vapor in the column, or ignoring any differences in absorption lines. ( history of radiation calculations- http://www.aip.org/history/climate/Radmath.htm ). a molecule of H2O or CO2 will absorb only in specific wavelengths and there are gaps between the H2O lines where radiation can get through unless blocked by CO2, such as at the 15 micron region. If H2O already absorbed there, it would in fact create a much less forcing influence from CO2. Rather than overwhelming CO2, it complements CO2, since CO2 absorbs much more strongly near the peak of the Planck function for Earth's temperature. In addition, there is little water vapor in the high, cold regions of the atmosphere (where CO2 is dominant and where the planets heat balance is determined), and at low pressures where H2O would let a lot of radiation through if not for CO2. Radiation at layers which escape determine the heat balance, and the place from which most of the heat energy escapes shifts to higher layers and when the radiation coming from below enters these high, cold regions, adding more CO2 will further delay that radiation and the high regions will get hotter until the higher radiative equlibrium is reached. If EITHER greenhouse gas we're missing, this planet would be too cold to support our life.

Another explanation which you'll probably find in basic "answers to contrarian arguments sites" like http://environment.newscientist.com/channel/earth/dn11462 or http://gristmill.grist.org/skeptics (these also go over your other arguments like post-1998 or the atmospheric trends, so I suggest you look at them) is that water vapor is not a climate forcing, it is a climate feedback. Kump (2002) quote: "The increase in water-vapour content of the atmosphere in response to the initial warming from elevated atmospheric CO2 partial pressure (pCO2) is a positive feedback that amplifies the warming." This is largely due to the short residence time in the atmosphere, but H2O is not a climate driver but rather equilibriates to climate forcing (so it stablilizes temperature). The cooling after Mt. Pinatubo is an example of how this worked, and as we now know the specific humidity (but not relative humidity) has increased due to humans as climate models and theory predict. A few more papers to give you
- http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2FJCLI3799.1&ct=1
- http://pubs.giss.nasa.gov/abstracts/2006/Bony_etal.html
- http://pubs.giss.nasa.gov/abstracts/2002/DelGenio.html

The troposphere is most certainly warming- old data from the nineties (ie Christy) may suggest otherwise (this is the only reference I've seen to support the claim) but this was corrected and accepted by Christy and Spencer from Mears and Wentz (2005) and Sherwood et al (2005).
ex. http://www.sciencemag.org/cgi/content/full/309/5740/1548
We know the troposphere and surface are warming, and stratosphere and above are cooling, in line with AGW theory (but not other natural forcings like the sun)- see http://www.climatescience.gov/Library/sap/sap1-1/finalreport/default.htm and http://www.sciencemag.org/cgi/content/full/314/5803/1253


I've given you quite enough to read recently :-) I'd go to the newscientist and gritsmill site for basic answers to other objections you may have heard; if you have further questions let me know.

Chris

Top
#23834 - 10/14/07 09:27 PM Re: Greenland Melt Record High [Re: Chris]
Canuck Offline
Senior Member

Registered: 03/16/07
Posts: 203
Loc: Ontario, Canada
Chris,
I think Imran stated that it looked like the recent trend (even excluding 98) had definitely changed, and instead of increasing, had flattened out.
And that NASA press release you linked to - was that before or after they noticed thier mistake which resulted in all US temperatures being shifted upwards by 0.15 degrees?

At any rate - I'm interested to hear you say "the CO2 effect is largely basic physics". I've done a fair amount of research into looking at exactly how a doubling of CO2 can give you a 3 degree rise, and simply can't find anything that describes from first principles the thermodynamic processes that can lead to the temperature increase.
I hear musings about how the absorption band of CO2 will increase at higher concentrations of CO2. This is obviously necessary for AGW to be correct, since extinction is already reached for the CO2 absorption band under pre-existing CO2 levels. But I don't have the appropriate background in physics to understand how the spectral properties of an molecule can change with it's concentration.
If you have any unbiased reference that explains from a first principles thermodynamics view, how a doubling of CO2 can lead to a 3 degree rise (I realize there are positive feedbacks included in that 3 degree rise), it would be appreciated.

One last point on your quote
"We know the troposphere and surface are warming"
I agree with you, but isn't a primary facet of AGW theory that the upper troposphere will warm faster than the lower troposphere? Recent (and accurate )satellite measurements have found the upper troposphere to be warming at a smaller rate than the lower troposphere (http://www.remss.com/msu/msu_data_description.html#msu_amsu_time_series). This suggests there is some other process in play which is warming the lower troposphere.
Let's not even bring up the differences between the lower troposphere temperature trends determined by satellites and the temperature record from surface stations.

Welcome to the forum though - it is appreciated to have somebody to discuss things with (not yell, scream or hurl obscenities at, but discuss), who seems to be well versed in the subject.

Top
#23840 - 10/15/07 12:13 AM Re: Greenland Melt Record High [Re: Canuck]
Chris Offline
Junior Member

Registered: 10/05/07
Posts: 22
Radiative forcing for CO2 is dF = 5.35 ln (C/ci) and with the increase in radiative forcing you have to get a higher temperature to get a balance- you have ~3.8 W/m^2 from the 2x CO2 and dT/ dF = (0.5 K)(6.1) from the temperature adjustment from one state to another: the 1.2 C increase is pretty much undisputed but you get additional feedbacks from water vapor, and you get a bit more broad climate sensitivities here, but an enormous amount of studies and paleoclimatic consistency suggests ~ 3 C as an average value, low-end now around 2 C.
See ex. http://www.gfdl.noaa.gov/reference/bibliography/2006/bjs0601.pdf
and go over some of the material here-



Most uncertainty is still in cloud parameterization and of course socio-economic projections (ie will we play business-as-usual or reduce emissions?), but for an overview of "all feedbacks"

Temperature (Planck) feedback: The major negative feedback on climate change (as Earth warms it radiates more according to Planck's law), and completely understood.

Water vapor feedback: Strongly positive, but still some uncertainty in its magnitude due primarily to the upper troposphere contribution

Lapse rate feedback: A major negative feedback that offsets part of the water vapor feedback; well understood conceptually (lapse rate change follows the moist adiabatic lapse rate approximately, so for a given warming at the emission to space altitude there's less warming at the surface) but magnitude depends on other feedbacks

Sea ice feedback: Positive, but magnitude is uncertain

Cloud feedback(s): There are many cloud feedbacks, on amount, height, optical thickness, etc., and different for different cloud types and at different latitudes. Overall, today's models produce cloud feedbacks ranging from approximately neutral to strongly positive. There could be an overall negative cloud feedback but it couldn't be very strong, because we have data that show that overall low clouds, which control the albedo more than any other kind, get thinner when it gets warmer.

I've not gone over the U.S Climate Change Report (2006) in a few months, but that and the IPCC (2007) report clearly show the temperature trends in the atmosphere are in line with the greenhouse forcing and not explainable by natural variability. It most certainly is not a "key component" for AGW to work, but since the troposphere is warmed from below and not from above I don't think it is a problem- and I've not seen any data to suggest otherwise.

If you want more technical analyses of the radiative physics, this is a good book http://geosci.uchicago.edu/~rtp1/ClimateBook/ClimateVol1.pdf (ch. 3 and 4 should answer some questions)and for specifically on the absorption bands of CO2 as a function of concentration, a guest post at RC from Dr. Pierrehumbert (the author) and Spencer Weart http://www.realclimate.org/index.php/archives/2007/06/a-saturated-gassy-argument-part-ii


Top
#23842 - 10/15/07 01:39 AM Re: Greenland Melt Record High [Re: Chris]
ImranCan Offline
Member

Registered: 09/04/07
Posts: 94
Loc: Brunei
Chris
Thanks for all this quality information. I am a climate change sceptic, but if I am to change my mind it would be based on this kind of dialogue. And I certainly agree there is enough reading material to keep busy for a while.

One quick question though - the graph above on 'Comparison of modelled and observed temperature". Do you have a version which continues beyond 2000 ? ie. shows the comparison up to the present and alo gives the modeled view into the future, ie. 2020 or 2030 ?

Thanks
Imran

Top
#23847 - 10/15/07 03:26 AM Re: Greenland Melt Record High [Re: ImranCan]
Chris Offline
Junior Member

Registered: 10/05/07
Posts: 22
I don't know of any other ones offhand, but documentation projects most warming by anthropogenic forcing. Let me know if you find anything-- Chris

Also, this myspace blog from Steven who is a geologist (we do this over in their Sci forums, you can get good info from more people there) is informative as a quick and broad post
http://blog.myspace.com/index.cfm?fuseaction=blog.view&friendID=91873788&blogID=253643452

Top
#23849 - 10/15/07 03:47 AM Re: Greenland Melt Record High [Re: Chris]
Canuck Offline
Senior Member

Registered: 03/16/07
Posts: 203
Loc: Ontario, Canada
Thanks for your reply Chris,
I haven't been able to go over it all thoroughly enough, but here's my initial take.

It seems the first portion of your post is focused on summarizing GCM parameterization, not really describing from first principles how that 3.8 Wm2 is calculated, or how the feedbacks have been quantified. Frankly, I don't trust computer models (or rather computer modellers). I model large non-linear systems as well, and I know I can crank certain parameters ever so subtly, and get the exact answer I'm looking for. Computer models are far too easily manipulated for me to buy into results from them.

Thanks for the link that explains the broadening of the CO2 IR absorption band as pressure decreases (pressure broadening). I'll do some more digging into that - but it is the first somewhat reasonable explanation I've heard.

You say that the upper troposphere warming faster than the lower troposphere isn't a requirement of AGW - but if the only additional absorbed IR can be in these "wings" caused by pressure broadening (which requires a lower pressure), shouldn't we see the majority of warming in the upper reaches of the troposphere (where the pressure is much lower than the surface)? We already know that at surface pressures, IR in the CO2 absorption band is removed to extinction, therefore additional absorption can only happen much higher up, at lower pressures.

And this may be nitpicking, but the warming isn't coming from below the troposphere, it's warmed from within, when it absorbs the IR. The IR of course is emitted from below, but the temperature increase is 'realized' within the troposphere.

Top
#23853 - 10/15/07 03:15 PM Re: Greenland Melt Record High [Re: Canuck]
Chris Offline
Junior Member

Registered: 10/05/07
Posts: 22
Have to be quick because I'm en route...

First of all, if you go to the right place on the wings, quite a lot of the additional absorption is happening low down. The IR heating change is pretty uniformly distributed, in fact. Moreover, the whole troposphere is well mixed in heat, and is more or less constrained by convection to stay near the moist adiabat. In that sense, the vertical structure is largely fixed by convection, and the heating only sets the intercept (e.g.
the lower trop temperature.). Hope that helps to clarify things.

I've given you the forumula for a CO2 doubling without feedbacks (the logarithmic equation and 5.35 to fit to line-by-line radiation model results for different CO2 concentrations- ie http://www.agu.org/pubs/crossref/1998/98GL01908.shtml) for a certain 1.2 C rise, and you add feedbacks; we use models, other forcings (ie what we get with a water vapor feedback), and paleoclimatic templates- the 1.5 to 4.5 C range has been established in the seventies and enormous emount of literature has not changed it much- we've narrowed it down in the AR4 a bit, but most uncertainty is pretty much in clouds, some aerosol effects, and socio-economic emission projections. Go over http://www.realclimate.org/index.php/archives/2004/12/index/#ClimateSensitivity and the Pierrehumbert book which discusses these issues in depth-- Chris

Top
#23856 - 10/15/07 07:57 PM Re: Greenland Melt Record High [Re: Chris]
John M Reynolds Offline
Senior Member

Registered: 08/14/06
Posts: 174
Loc: Canada
Mike, the line you highlighted in the original post is ridiculous. To suggest that "the amount of snow that has melted this year over Greenland could cover the surface size of the U.S. more than twice" would require at least an estimate to say how deep the water, ice, or snow would be.

Using Chris' first link, I went to the global graph:
http://data.giss.nasa.gov/gistemp/graphs/USHCN.2005vs1999.lrg.gif
Since 2001, the temperature has been quite level. Anthropogenic greenhouse gasses is supposed to be making us warmer, but now the southern hemisphere is experiencing record lows. Antarctica has record ice extent records and we have only had a weak La Nina so far. I did enjoy how Chris explained away 1998 as a wierd year without bothering to question why El Nino would raise the global temperature. Put that El Nino effect in with the reduction in ocean temperature (negative thermal expansion) and you see that the oceans are regulating the temperature not OCO.

Top
#23857 - 10/15/07 09:47 PM Re: Greenland Melt Record High [Re: John M Reynolds]
Chris Offline
Junior Member

Registered: 10/05/07
Posts: 22
The Antarctic cooling (in some areas and warmer in others) and accumulation is easily explainable and currently predicted by climate models. The oceans are heating, and CO2 content therein has increased indicative of an external signal, we know all of the extra CO2 is anthropogenic through isotopic signatures and the rate of increase. If you would take time to read the relevant literature, or at least ask in an intelligent tone as previous posters have done you would know this-- Chris

Top
#23862 - 10/16/07 01:21 AM Re: Greenland Melt Record High [Re: Chris]
Amaranth Rose II Offline

Superstar

Registered: 12/16/06
Posts: 962
Loc: Southeast Nebraska, USA
Chris, I got a 404 not found error on your first link.
John Reynolds, I got nothing on your link.

Do you have another that links the material cited?
_________________________
If you don't care for reality, just wait a while; another will be along shortly. --A Rose


Top
#23865 - 10/16/07 04:21 AM Re: Greenland Melt Record High [Re: Amaranth Rose II]
Chris Offline
Junior Member

Registered: 10/05/07
Posts: 22
backspace the parenthesis that got in the way at the end-- Chris

Top
Page 1 of 2 1 2 >



Newest Members
debbieevans, bkhj, jackk, Johnmattison, RacerGT
865 Registered Users
Sponsor
Facebook

We're on Facebook
Join Our Group

Science a GoGo's Home Page | Terms of Use | Privacy Policy | Contact Us
Features | News | Books | Physics | Space | Climate Change | Health | Technology | Natural World

Copyright © 1998 - 2016 Science a GoGo and its licensors. All rights reserved.