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Comments 26701 to 26750:

26701. Tom Curtis at 06:02 AM on 3 December 2015
       There's no empirical evidence
       

       blue65 @304:

       1)  The incoming radiation is for the most part, Short Wave radiation to which CO2 is transparent.  Hence there is not significant redirection of "... energy by the increased CO2 before it reaches the lower atmosphere".  It is the contrast between transparency to incoming radiation, and relative opaqueness to outgoing radiation that it is the key feature of greenhouse gases, and which makes them greenhouse gases.

       2)  Changes in the landscape are a factor, and are itemized by the IPCC as Land Use Changes (LUC).  Overwhelmingly the effect of LUC is to reflect more solar radiation back out to space (increase albedo), thereby cooling the planet.  However, the effect is small relative to the effect of changing concentrations of greenhouse gases and aerosols.  The effect is itemized on the chart below as "Albedo change due to land use":

       

       3)  The temperature effects of cities relative to countrysides are a combination of changes in albedo but that is variable (concrete has reduced albedo but ashpalt has increased albedo); changes in thermal inertia, with most modern construction materials having low thermal inertias relative to plant matter (probably due to limited water content); and a large number of sources of industrial waste heat in cities (the "urban heat island effect").  Changes in albedo from cities also result from increased aerosol production which also effects countryside downwind from cities (an effect that has been detected).  The net effect can be to warm or to cool cities relative to the local countryside.  The total globally averaged effect is small relative to the forcing from greenhouse gases.

26702. John JMesserly at 05:53 AM on 3 December 2015
       How much does animal agriculture and eating meat contribute to global warming?
       

       TomR was spot on about the weight mistake the EWG chart makes.  Consider the FAO report "Tackling Climate Change through Livestock" (2013), page 16, figure 3 where you will find a chart graphing against protein content.  What may surprise some vegetarians is that Milk is hardly one of the lowest as indicated in the EWG graph, but actually is higher in CO2e per kg of protein than some meats like pork or chicken.  This is due to the previously discussed massive amount of methane produced by ruminants- a byproduct of cellulose breakdown by methanogen microbes in their guts.  

26703. Reason_4 at 05:44 AM on 3 December 2015
       How much does animal agriculture and eating meat contribute to global warming?
       

       Dana @29

       I appreciate that, although as a permaculturalist I also understand the reverse is also possible (you can take already degraded land and dramatically improve carbon sequestration in a system that may well integrate raising animals to further enhance this aspect).

       But I'm still curious about the first point - why some animal emissions are tallied (eg methane from ruminant animals) and others not (CO2 respiration from any animal) and then listed as equivalent to the same emissions from fossil fuels (either burnt or fugitive) when one is effectively carbon neutral in the short term carbon cycle ... and the other definitely isn't. 

       We (of course) dismiss deniers who suggest humans need to stop breathing/belching/farting ... why are some livestock emissions treated differently?

26704. KR at 05:34 AM on 3 December 2015
       Models are unreliable
       

       reuns - You open your comment with an incorrect statement: "the best model is a will stay for a long time the linear interpolation of past observations". This is completely wrong when looking at non-linear forcings applied to (in this case) climate. If the behavior is non-linear, a linear projection will be wrong. 

       'Signal processing', or more appropriately statistics, is fine for analyzing past behaviors of a system. But projecting ahead in a SP approach requires (gasp) actual physics, and looking at the input/output relationships involved. 

       The rest of your comment is essentially a claim that the climate is too complex to model and project, which I believe has been sufficiently addressed by the fact that observed temperatures and for that matter regional patterns are indeed reproduced within expected variation by GCMs.

       It's physics all the way down - if modeling does a reasonable job of reproducing the physics, we don't need to test an infinite variety of cases. That's just a call for delay, which turns into a continually moving goalpost fallacy where there will never be enough information (in the opinion of the delayers) to make any kind of decisions...

26705. blue65 at 05:33 AM on 3 December 2015
       There's no empirical evidence
       

       The problem I see with this theory is that it seems to discount the effect of redirected energy by the increased CO2 before it reaches the lower atmosphere. Insulation works both ways. Put a dark background behind a 2 way mirror and almost light is reflected: put a light source behind it and it becomes see through. Changes to landscape are as much a factor as any in my belief. My imperical evidence is easier to prove; just check out the daily high and low temperatures of any metropolitan area and the rural areas next to them and see the contrast.

26706. Tom Dayton at 05:14 AM on 3 December 2015
       Satellites show no warming in the troposphere
       

       Eli has a great post on UAH's flaws, by a satellite engineer who gives lots of details: UAH TLT Series Not Trustworthy.

26707. foolonthehill at 04:41 AM on 3 December 2015
       How much does animal agriculture and eating meat contribute to global warming?
       

       RedBaron @27 - Re: Savory - plausability is nice but reproducability is better.

       'Holistic management does not permit replication. Because of this fact we can only validate the ‘science’ used and monitor or document ‘results achieved’. Note: This point is critical to understanding the great difficulty reductionist scientists are experiencing trying to comprehend holistic planned grazing – because no two plans are ever the same even on the same property two years running, planned grazing cannot be replicated which reductionist scientists do to try to understand the ‘science.’

       from here

        

       If one replaces 'holistic management' with 'homeopathy' then maybe you can understand my scepticism.

26708. Rob Painting at 04:29 AM on 3 December 2015
       Satellites show no warming in the troposphere
       

       We will know if the current super El Nino is affecting the satellite record like the super El Nino of 1997/1998 when the December & January data come in - assuming the behaviour is similar to past El Nino.

       As for Kevin Cowtan's Skeptical Science calculator - note the error bars are orders of magnitude larger than the trend, so there is no statistical basis for any claim that it has cooled. The time period is too short and the interannual variation (standard deviation) too large. We would need a longer time period in order to establish statistical significance. Note that contrarians never attempt this, they simply make a claim without supporting evidence.

       It would be interesting to find out why the satellite data 'overreacts' to El Nino and La Nina though. Is this a real phenomenon occurring in the lower troposphere? Or is this an artefact which all the processing fails to remove from the microwave soundings? 

26709. dana1981 at 01:43 AM on 3 December 2015
       How much does animal agriculture and eating meat contribute to global warming?
       

       Reason_4 @ 23 - you have to consider what the land would be used for if it weren't being used for livestock pasture land.  For example, when forest land is replaced by pasture land, that's actually a decrease in natural carbon sequestration.

26710. One Planet Only Forever at 01:11 AM on 3 December 2015
       Uncertainty is Exxon's friend, but it's not ours
       

       ryland@4

       Thinking a little more about your question the following may be the answer you were asking about.

       The typical design basis for structures and water run-off is not the range or variation of weather conditions for a location, it is the statistical expected extreme of a design condition such as the maximum large-field wind speed expected to occur once in a 50 year period. My use of the term large-field is meant to differentiate the wind speed experienced concurrently by all of a large structure vs. the faster wind speed and resulting larger local forces a structure.

26711. knaugle at 01:09 AM on 3 December 2015
       Satellites show no warming in the troposphere
       

       I agree with the RSS showing long term warming.  However, the claim from the "skeptics" is no warming since 1998.  If you throw out 1998 and look at the past 15 years, 2000.9 to present (that "escallator thing", RSS and now UAH 6.0 show cooling).  So long as that is the case, politicians like Lamar Smith will simply claim NOAA is fudging the numbers.  I do find it curious that UAH has adjusted its data about as often as any other entity out there with a temperature data set while RSS seems rather mum on versioning.  Yet whenever NOAA adjusts its data set, it's called "fraud". 

       Note also that back in 2013, RSS was very unapologetic in declaring that most all the climate models are "wrong" and their graphs claim the breakout occurred around 2000, not 1998.

       http://www.remss.com/research/climate

       Finally from Dr. Cowtan's temperature plotter, the warming from the satellites is
       0.122 C/decade since 1979 as was shown,
       but 20 year and 15 year trends show
       0.037 C/decade since Dec. 1995 and
       -0.017 C/decade since Dec. 2000.
       So interestingly while deniers bank all on the 1998 El Nino, we do need to avoid the mistake of expecting much from the current one as a fix.

26712. One Planet Only Forever at 00:55 AM on 3 December 2015
       Uncertainty is Exxon's friend, but it's not ours
       

       ryland@4

       The climate affected design values for any region are based on the past history of gathered observations and the associated related understanding of the weather effects at a location.

       Rapid Climate Change and the uncertainty of how any specific location's weather extremes will be affected reduces the certainty of appropriate design values because the observation history is a less certain basis for determining appropriate design values.

       So my reference to Climate Change is to the current term being applied to the more rapid climate changes now better understood to be caused by human impacts. Climate has always changed ... rather slowly.

26713. reuns at 00:39 AM on 3 December 2015
       Models are unreliable
       

       the best model is a will stay for a long time the linear interpolation of past observations :
       physical sub-models with many parameters are useful to predict events which vary importantly and are testable,
       but by defintion the global warming is not : it is a very small increase of temperature (of energy) resulting from very small increase of many parameters (the 1st one being CO2 concentration),
       so forget the physics and study signal processing instead !

       signal processing says that :
       the more the model is complicated and not testable and the more the observations are random and not pure signal (signal to noise ratio), the the more the simpler model will be the best (linear interpolation)
       
       the only way to overcome that problem is to get enough datas to model many sub-paramters which vary a lot and ARE testable :
       such as a huge change in rainfall somewhere, a big and suddent change in somewhere in the ocean temperature or acidity, anything which vary a lot,
       then find some physical explanations of that, test it and predict some non-trival facts (so prove your non-trivial physical explanation that was unknown or unproven before) and find some ways to extrapolate it to the global observations. do that many times with many researchers and after many time you'll be able to explain and predict and substract what was before considered as NOISE : once you explained that noise you'll get  much cleaner observations and with a better signal/noise ratio and so on you'll be able to create better models.
       
       this will take at least 20 years.

26714. Tom Curtis at 23:43 PM on 2 December 2015
       How much does animal agriculture and eating meat contribute to global warming?
       

       saileshrao @26, in the 322 months from April 1987 to Jan 2014, using Mauna Loa data, 142 had 12 month average CH4 concentrations less than the maximum 12 month average concentration to that date (most recent: April 2013.  10 of the 27 annual averages over that period are less than the maximum to date (most recent: 2006).  In short, CH4 concentrations are not increasing monotonically.

       The Pierrehmbert quote again was:

       "A re-examination of the issues shows that the benefits of early SLCP mitigation have been greatly exaggerated, largely because of inadequacies in the methodologies used to compare the climate effects of short-lived substances with those of CO2, which causes nearly irreversible climate change persisting millennia after emissions cease. Eventual mitigation of SLCP can make a useful contribution to climate protection, but there is little to be gained by implementing SLCP mitigation before (my emphasis) stringent carbon dioxide controls are in place and have caused annual emissions to approach zero."

       Again, he is not saying that addressing Short Lived Climate Pollution is pointless, but only that it is a second order priority to reducing CO2 emissions.  The reason for that is that the effects of SLCP in general, and of CH4 in particular will be negligible after 100-200 years, whereas the effects of CO2 emissions will persist for thousands and even tens of thousands of years into the future.  Three hundred years from now, current CH4 emission rates will be a matter of historical interest only; whereas current CO2 emission reates will be having ongoing negative impacts.  Prioritizing effects which are beneficial only over the short term ahead of effects that will persist longer than our civilization shows somewhat distorted values.

26715. RedBaron at 23:03 PM on 2 December 2015
       How much does animal agriculture and eating meat contribute to global warming?
       

       @ lorainel #17

       The issue is that you have two complex factors involved, one is the fact that feedlot beef is fed from cropland, and it does take substantial amounts of fossil fuels to run the tractors, fertilizers and insecticides made from fossil fuels, harvest the grain, dry the grain, ship the grain, turn various mixtures of grain/silage/hay into feed suitable for cows, ship the feed again. Not to mention you have to load up the beef cows and transport them live to the feedlots in the first place. There is a big difference between that and a cow simply walking over to the next fresh pasture. Feedlot production is very inefficient in terms of fossil fuel use.

       Then there are unexpected emergent properties of the system as well, compared to pasture, cropland also has a much lower community of methanotrophs, and mycorrhizal fungi, both of which are responsible for sequestering large quantities of greenhouse gasses. You could look at them as carbon pumps into the soil via the grassland's symbiotic relationships. So as it turns out, cows raised on properly managed pasture end up being part of a larger net carbon sink, not a net carbon emissions source, while cows raised in feedlots are an even larger emissions source than commonly known when you include the cropland supplying the feedlot.

       Nevertheless, even as bad as feedlots can be, they are not as bad as the exaggerated claims by certain Vegan propaganda sites, which have exaggerated their impact on AGW, to take advantage of the new "sexy" environmental awareness campaigns on global warming mitigation. They basically do this by first cherry picking the harmful parts, ignoring anything that doesn't promote their dogma like the 1/2 life of methane in the atmosphere, and then double counting things like transportation, cropland emissions etc. Finally the fallaciously claim that eliminating meat consumption is the solution, rather than changing the management and production methods.

       You also proclaimed your skepticism of Savory, the leading scientist in the field of rangeland management. OK skepticism is fine, I am a skeptic myself. However, to be a really good skeptic requires study. This may help. 

       LINK

       I think the more you study it, the more plausible Savory's work becomes, athough in the beginning, most people find it counterintuitive. Real hard to argue with the results though. For your personal ranch, I wouldn't worry too much about the impact to AGW. You have a grassfed production model, so more likely than not you are mitigating AGW  rather than causing it, assuming you are properly managing it for that purpose. Keep in mind undergrazing can be just as bad as overgrazing in certain climatic conditions. But as long as your management plan includes proactive monitoring, you'll be able to figure that out soon enough.

       Moderator Response:

       [RH] Shortened link that was breaking page format.

26716. saileshrao at 21:11 PM on 2 December 2015
       How much does animal agriculture and eating meat contribute to global warming?
       

       Tom Curtis @20:
       
       Pierrehumbert's assumption clearly does not match reality where methane concentrations in the atmosphere have been monotonically increasing year after year.

26717. ryland at 20:04 PM on 2 December 2015
       Uncertainty is Exxon's friend, but it's not ours
       

       One Planet Only Forever @3

       Not sure why you head your list of uncertainties to be considered as "The climate change uncertainties include:".  Surely these uncertainties have always applied to the climate rather than to climate change.  Are you saying these uncertainties are only now being considered? 

26718. Rob Painting at 19:25 PM on 2 December 2015
       Past 150,000 Years of Sea Level History Suggests High Rates of Future Sea Level Rise
       

       "A large amount of effort goes into "proving" a causation using correlation, multiple regression, etc., but consider that when the rooster crows, the sun comes up, but that certainly does not mean that he rooster causes the sun to rise."
       
       Yes, I am certain that none of the authors have suggested that evaporation in either the Red or Mediterranean Sea caused global sea level to fall.
       
       Your comments don't make a great deal of sense. How could the ocean basins shallow and deepen in concert with Milankovitch forcing? And where did the water locked up as ice in the vast Laurentide and Fennoscandian ice sheets disappear to if not into the ocean?    
       
       

       Moderator Response:

       [PS] Dr T comments suggest that he/she hasnt actually read the Grant (2012) paper.

26719. OnceJolly at 16:36 PM on 2 December 2015
       How much does animal agriculture and eating meat contribute to global warming?
       

       lorainel @18 - Stephen Walsh provided a useful critique immediately after the Goodland and Anhang analysis was released. I've filled in some additional details here, though the criticism is essentailly the same as Walsh's.

26720. Maaark at 15:54 PM on 2 December 2015
       Heat from the Earth’s interior does not control climate
       

       Thanks

26721. Tom Curtis at 15:10 PM on 2 December 2015
       How much does animal agriculture and eating meat contribute to global warming?
       

       chriskoz @22, a very good point, and one I should have picked up @20.

26722. Reason_4 at 14:58 PM on 2 December 2015
       How much does animal agriculture and eating meat contribute to global warming?
       

       Thanks very much for this much needed rebuttal Dana, but (yes sorry, always a 'but'!) for the scientifically challenged can you;

       (a) explain why carbon in the short term carbon cycle is not treated differently or (apparently) offset against carbon sinks in the pasture, soils and feed crops within the animal raising agricultural systems? Wouldn't the distinction between fossil fuel sourced emissions be much greater if it was?

       and 

       (b) one would expect that the American emissions would be close to worst case (being heavily dependant of industrial feedlot production. When defending oneself against rabid vegans of the 'you can't eat meat if you want to save the world' school - are there examples in the literature about best case, grass fed meat production?

       Maybe it is just wishful thinking, but isn't this at least feasibly a carbon negative pursuit especially when carbon sequestration in healthier soils is taken into account?

       TIA

26723. One Planet Only Forever at 14:22 PM on 2 December 2015
       Uncertainty is Exxon's friend, but it's not ours
       

       As a Civil Engineer, who also happens to have an MBA, I have always been very concerned about the 'uncertainty' related to the ability of built things to survive severe events (it has been my life's work).

       The most severe expected events are the design basis for so many things. Uncertainty of global climate change affects every existing and planned to be built structure (and rain run-off affected system) that Exxon (and every other pursuer of profit) relies on to hope to 'make money'.

       The climate change uncertainties include:

       • how fast the winds will blow?
       • how intense can a localized gust be?
       • how rapidly can a localized rain event accumulate?
       • how much total rain can fall in an event (in a day or a multi-day event)?
       • how much snow might accumulate including wind blown drifts?
       • how wet and heavy will accumulated snow be?
       • how much ice may form due to freezing rain?
       • how much ice will form on a waterway - enough for a winter bridge?
       • how rapidly will ice breakup on a waterway and potentially dam it, damning anyone upstream and threatening everyone downstream when the unplanned dam breaks?
       • what is the highest temperature condition a structure will be exposed to?
       • Will permafrost be able to be kept as permafrost?
       • What is the highest water wave likely to hit a sea-side feature?
       • And so much more ...

       Increased uncertaintiy of the design requirements results in increased risk of failure of existing items to perform their required function. And it results in increased risk of failure of newly designed items unless extra expense is made upfront in the hopes that some degree of 'hoped to be over-design' will be enough over-design.

       The truth has always been that gambling risk-takers pursuing maximum personal gain willingly gamble on getting away with cheaper, riskier and more damaging pursuits betting that they will 'not personally suffer the consequences (even if they know that other people would be likely to suffer immediate consequences but be unlikely to be able to penalize the trouble-making gambler). And those gamblers love it when the consequences are likely to be in the future rather than be immediate consequences because future people are even less likely to be able to penalize such a deliberate gambling trouble-maker. An engineer's responsibility is to protect the public from such pursuers, not to maximize profit for them.

       The truth is there will always be some people who are determined to demand more freedom to do things they actually understand are less acceptable. And those people will always try and try again to get away with less acceptable pursuits of personal benefit by claiming their freedoms cannot be restricted except by absolutely certain proof, not just proof beyond a reasonable doubt, of the unacceptability of what they want to get away with.

       National design and construction standards are also under arttack as international competition leads pursuers of profit to challenge why a national standard 'has to be met when they can find a lower standard somewhere else'. That pursuit combined with the denial of climate change is a double-down bet made by many wealthy gamblers who illigitimately won through their competetive advantage that was obtained by deliberately caring about others and the future as little as they can get away with.

26724. DrivingBy at 14:14 PM on 2 December 2015
       Uncertainty is Exxon's friend, but it's not ours
       

       I find it hard to get too wound up about what a bunch of suits who are not scientists did or did not express on a scientific topic.  Morally, they made a bad choice, but since they are legally obligated to persue the interests of company shareholders rather than their own, or even a moral cause, it's a bit of a mess.       We (in the USA) no longer acknowledge that there exists any higher law than immediate convenience, and so a CEO of a public company who declares they are going to take a hit for the next 20 quarters because of X moral reason is likely to be fired, and could be personally sued for any lost company income. 

       Considering that they're required to express the interests of the shareholders, I don't understad why anyone would even ask them about climate change, much less give their answers any weight.   Exxon did not have climate science locked away from the public, the science of interest was and is available to the public for anyone who cared to read it.  

       In short, the execs made a bad choice, but it is absurd to blame them for the failure of others to use their own minds.  

       -----------------

       What is popularly believed to be true changes from time to time, usually due to fashion, sometimes due to passion, and within natural science and on rare occasions due to an advance of knowledge.  If we get in the habit of putting people in the dock for expressing incorrect thoughts, the people in the concrete cells will be the creative ones, the scientists and those insist on pointing out that the emperor has a hairy ugly beer gut.  

26725. Ken in Oz at 13:01 PM on 2 December 2015
       Uncertainty is Exxon's friend, but it's not ours
       

       I find it dismaying that Exxon executives, like tobacco execs, will only be in formal trouble for misleading Congress or giving other kinds of false sworn testimony; the climate consequences of their decisions will probably not even be in the running as something they will be held responsible for.

       More broadly I wonder if there is a clear incentive for executives to avoid being well informed because if they remain ignorant they can argue they didn't know and avoid liability arising from their decisions.

26726. chriskoz at 12:40 PM on 2 December 2015
       How much does animal agriculture and eating meat contribute to global warming?
       

       IMO, lifestock methane should be treated differently to other sources of methane (e.g. fugitive emissions from mining) because their carbon is part of C exchange within OA reservoir. But statements like this:

       ruminant animals like cattle produce methane, which is a greenhouse gas about 20 times more potent than carbon dioxide

       if taken out of context, create confusing scare campaign.

       Apart from short CH4 lifetime, (subject to oxidation to CO2 by hydroxyl radicals within a dacadal timescale) I would like to add that the resulting CO2 does not contribute atmospheric CO2 rise. The carbon that ruminants expell, comes from vegetation that grew by assimilation of CO2 by photosynthesis in the first place.

       It would be a different story if said CH4 came from the "old carbon" (e.g. milion y old fossil fuels). And this is the case of fertiliser input that comes from fussils. This is what really counts in the long term. So, livestock input to global warming (also manure and rice cultivation) is really exaggereted in the figure IMO. Oil/gas extraction and coal mining (fugitive emissions) are of much more dire consequences.

       With the above in mind, in response to foolonthehill@17: if your "fertiliser input is almost zero" (I guess zero fossil fertiliser), then you are fine, nothing to feel sorry with respect to C emissions. Of course, you need to follow other sustainable practices to make sure your land is not dagraded but that is outside of the scope of this forum.

26727. Tom Curtis at 12:34 PM on 2 December 2015
       The Road to Two Degrees, Part Two: Are the experts being candid about our chances?
       

       Digby Scorgie @35, in principle that is correct.  In practise it is not so clear.  In particular, the time line over which we must drop to zero net emissions is approximately equal to the design lifetime of most power plants and significantly larger than the design lifetime of most other infrastructure.  Consequently a carbon tax introduced now which will predictably be maintained or increased into the future will not have to deal with sunk costs on current infrastructure which will be replaced over the relevant timescale in any event.  Further, so long as its long term imposition is predictable, it will be factored into any new construction thereby limiting any new construction of fossil fuel infrastructure, and ensuring such sunk costs are factored into the investment decision on any such infrastructure.  That is, any future fossil fuel power plants will be built and costed with a reduced lifetime expectancy if reasonable certitude of a carbon price can be generated.

       In addition to that, the effect of sunk costs will be limited by the ability to retrofit carbon sequestration technology and/or the ability to gain "carbon credits" for paying to more rapidly decrease emissions, or sequester emissions elsewhere at lower cost.

       Having said that, as we delay taking adequate action to reduce emissions (as we appear to be doing even with optimistic estimates of the outcome from Paris), the time scale required for decarbonization sinks and sunk costs become a much larger factor.  Put another way, the more we delay implimenting a carbon price, the larger the carbon price will need to be to move us to zero net emissions in a timely manner.

26728. RedBaron at 12:10 PM on 2 December 2015
       How much does animal agriculture and eating meat contribute to global warming?
       

       While I certainly agree with the gist of the article, the Vegan sites have grossly exagerated the effect of animal husbandry, even this article is probably exagerating the impact somewhat due to flaws inherent in a methodology that primarily focuses on emissons rather than complex biological cycles. Emissions focussed methodology works great when we talk about fossil fuels and concrete, because those sources of carbon are from stable pools. The active pools act in a fundamentally different manner. For example, counter intuitively, land use change from forest to pasture can actually can actually have an overall cooling effect rather than a warming effect. http://blogs.uoregon.edu/gregr/files/2013/07/grasslandscooling-nhslkh.pdf

       http://www.airseadalian.com.cn/Column/UploadFiles_7536/200703/20070302104207896.pdf

       What matters is the net flux from stable to active carbon cycles. Basically we are talking the stable soil carbon fraction and fossil fuels as the stable pools, and the rest of the carbon that cycles actively is just part of life. There are frozen methane clathrates in the ocean and permafrost that can be a concern should they melt rapidly, but that's more of a feedback concern, if we fail to get the other pools stabilized. More of a symptom that magnifies, not an initial cause. This is one of the things, that if it happens, will dramatically amplify the seriousness of AGW.

       Any agriculture of any type that increases the stable carbon pool in the soil is not creating AGW, but rather is helping mitigate AGW.

       So when you discuss the issue with Vegan advocates intent on humanity giving up animal foods, point out that rather the solution is using agricultural methods that increase soil carbon at a higher rate than they use fossil fuels, for a net reduction in atmospheric greenhouse gasses back into the stable pools.

       If anyone wants to help mitigate AGW by giving up certain foods, give up foods produced from land decreasing in soil carbon, and replace it with food produced from land increasing in soil carbon.

        

26729. Digby Scorgie at 11:09 AM on 2 December 2015
       The Road to Two Degrees, Part Two: Are the experts being candid about our chances?
       

       Tom Curtis

       I've thought some more about carbon taxes.  They not only have to make fossil fuels more expensive than alternative fuels, they also have to make it more economical to decommission the fossil-fuel infrastructure while introducing and developing the infrastructure for the alternatives.  The net effect is therefore likely to be a carbon tax much greater than anticipated.

26730. Tom Curtis at 10:29 AM on 2 December 2015
       How much does animal agriculture and eating meat contribute to global warming?
       

       saileshrao @19:

       "The 1.8ppm of methane that existed in the atmosphere 12 years ago has added 1.8ppm of CO2 to the atmosphere this year, which is a significant fraction of the 2.34ppm of CO2 added to atmosphere from Oct 2014 to Oct 2015."

       That is not correct.  The 12.4 years "lifetime" of CH4 in the atmosphere is the "e-folding time", designated by the unit τ (greek lower case tau).  That means of the 1.8 ppmv of CH4 in the atmosphere 12 years ago, approx 1.1 ppmv will have decayed to CO2 over  the intervening 12 years.  A further 0.4 ppmv will decay over the next 12 years, and another 0.2 ppmv in the twelve years after that.  As CH4 emissions are sufficient to maintain and even increase CH4 concentration against this rate, a better way of looking at it is that CH4 emissions contribute 1.8 ppmv every 12.4 years (assuming equilibrium has been reached), or 0.15 ppmv per annum.  More accurately, at equilibrium the contribution to CO2 from CH4 decay equals the CH4 emission rate.

       Further, you have assumed that 100% of CO2 from CH4 decay is retained in the atmosphere whereas in fact, just like direct CO2 emissions, the airbourne fraction will be about 50%.

       If atmospheric CH4 was allowed to rise to equilibrium concentration with current emission rates, the CO2 concentration per annum (0.017 PgC) would represent 0.425% of current direct CO2 emissions.  That is small enough to be inconsequential except in the very long term (and possibly even then).

       Turning to Pierrehumbert's claim - his point is that in the long term, and assuming CH4 emissions are stabilized, the anthropogenic effect on Earth's temperature is entirely governed by CO2 emissions - which to a first approximation is correct.  CH4 emissions strongly influence how we approach that long term temperature increase.  With initially high CH4 emissions we will approach it rapidly and then possibly settle back down to it.  With low CH4 emissions we will approach it slower.  Therefore, in Pierrehumbert's opinion tackling direct CO2 emissions is the first priority.  He is mounting a counter argument to the claim that industrial emissions of CH4 and black carbon represent "low hanging fruit" that can be tackled cheaply and quickly while largely ignoring the CO2 problem.  Pierrehumbert is correct in rejecting that approach - but I (and no doubt he) believe that we can tackle both at once.

26731. scaddenp at 10:07 AM on 2 December 2015
       Heat from the Earth’s interior does not control climate
       

       Even doubling crustal heat flow is utterly insignificant compared to other climate forcings. Changes in heat flow leave their mark and are a critical input to petroleum models used to determine when and where sediments heat to the point that oil and gas are expelled. (I maintain one of these models). At least over the last 180million years, there is no evidence for any cycle or significant change in these heat flows, let alone something that could have climatic effect. Because of the importance of heat flow to petroleum, measurement and analysis is ongoing throughout the world.

       I also do not see any period in earth climate history over last 500my where change cannot be explained by the existing well-understood physics.

26732. DrT at 09:38 AM on 2 December 2015
       Past 150,000 Years of Sea Level History Suggests High Rates of Future Sea Level Rise
       

       One of the problems with "correlations" especially serial (time related) correlations is that they do not prove cause and effect. A large amount of effort goes into "proving" a causation using correlation, multiple regression, etc., but consider that when the rooster crows, the sun comes up, but that certainly does not mean that he rooster causes the sun to rise.
       
       Also, other factors are raising sea levels, including Plate Tectonics, the continental shift that is impacting the depth of the ocean floor where one plate moves under another. It causes earthquakes, it releases heat into the ocean that cause frozen methane to become gaseous and rise to the surface (a far more potent greenhouse gas than CO2), but most important, it raises the ocean floor.
       
       Imagine the same amount of water in the oceans, and the sea floor rising, it clearly would raise the level of the surface of the water.
       
       There is also Solar output, the orbital radius from the sun, the "tilt" of the axis that changes over thousands of years, all impact climate (the weather).
       
       Be very careful about assuming that scientists have "proven" anything if they rely on correlations of any kind, and ignore some clear and obvious geological issues that have a large impact on ocean levels, and the release of methane into the atmosphere.
       
       Dr. T — A scientist interested in factual analysis, not correlations that are not proof of cause and effect.

       Moderator Response:

       [PS] You appear to be engaging in a straw man. Nowhere is correlation being used to imply a cause and effect. However, if your model predicts a correlation (and the physical models most certainly do make these predictions), then an important test of your model is see that such correlations do in fact exist. If they dont, this is evidence against a model. If they do exist, then it strengthens the model. In science, nothing is ever "proven" (you can only do that in maths) and noone has suggested it has. The other factors you mention are already part of standard climate theory, and taken into account in models. Eustatic changes in sealevel have been known and accounted for since the 1980s eg (http://www.earth.ox.ac.uk/~tony/watts/downloads/WattsThorne84.pdf)

26733. michael sweet at 09:31 AM on 2 December 2015
       Heat from the Earth’s interior does not control climate
       

       Maaark,

       This web site has all the information that you ask about.  It is not the responsibility of posters here to spoonfeed you the answer to your questions.  It is your responsibility to look for it and inform yourself.  

       I typed "climate in the past has changed before"  into the search box above and got this post which addresses your first question.  Please read that post and then follow up with questions there where they will be on topic.

       The OP here addresses your other question.  It states:

       "The net increase in the amount of planetary energy flow arising from human activities (mainly the greenhouse effects from emissions of carbon dioxide) since the industrial revolution is more than twenty times the steady-state heat flow from the Earth’s interior. Any small changes in the Earth’s heat flow over that time period—and there is no evidence for any change at all—would plainly be inconsequential."

       If you have a question that is not addressed by this quote about mantle heat you need to be more specific about the changes you suggest which would increase heat flow by a factor of 20 without anyone noticing.  The method of measuring the heat flow is described in the OP, it is not necessary for NOAA to install additional thermometers.

       If heat from the mantle was warming the ocean, the ocean would warm from the bottom up.  Extensive data shows clearly that the ocean is warming from the top down which contradicts your hypothesis.

       Please make use of the search box, your questions will be better after you read more.

26734. saileshrao at 09:25 AM on 2 December 2015
       How much does animal agriculture and eating meat contribute to global warming?
       

       This "rebuttal" misses several key aspects of the contribution of animal agriculture to anthropogenic greenhouse gas emissions:

       1. As Tom Curtis (#4) points out, methane is a significant player in the short term. Over a short term horizon, say 20 years, methane has a CO2 equivalence factor of 86. Even if each molecule of methane becomes a molecule of CO2 with a half-life of 12.4 years, the fact that atmospheric concentrations of methane have been monotonically rising over the past century shows that the arguments of Pierrehumbert etc., are shooting false straw men. The 1.8ppm of methane that existed in the atmosphere 12 years ago has added 1.8ppm of CO2 to the atmosphere this year, which is a significant fraction of the 2.34ppm of CO2 added to atmosphere from Oct 2014 to Oct 2015. This is significant.
       
       

       2. As Andy Skuce (#3) points out with the XKCD graphic, the biomass of livestock grossly exceeds the biomass of humans and wild mammals. Livestock are an invasive species in most ecosystems and as Anthony Barnosky shows, our use of fossil fuels has allowed us to increase the biomass of megafauna from 200Mt to 1500Mt, most of which is livestock. Therefore, the breathing contribution of livestock should be considered an anthropogenic addition to the carbon cycle. Livestock is estimated to cause 8.7Gt of CO2 emissions through breathing alone. This is significant.
       
       3. Finally, animal agriculture uses 35% of the ice-free land area of the planet for grazing alone. The foregone carbon sequestration from the potential reforestation of this land is calculated to be at least 265 GtC (please note, this is C not CO2) as we show in our upcoming paper to be presented at the AGU Fall Meeting in a couple of weeks. This is significant.
       
       

26735. Maaark at 08:39 AM on 2 December 2015
       Heat from the Earth’s interior does not control climate
       

       Glen and Tom thank you both. I think that my hypothesis may be over simplified. I am not addressing the possibilty of the tidal energy. That discussion may be valid for some but that is far removed from my points so I will state very slowly.

       Premise #1: if earth has a history of heating/cooling cycles then we should be seeking a pattern that explains those and also is somehow connected with today's situation. Example: I have had 7 migrane headaches in the last month. Today I ate icecream so that must be the source of my headaches = poor science. Good science would seek to find a common factor in all 7 headaches. Therefore we should find common patterns in the previous cycles. Does anyone agree? Are there theories on past cycles?

       If greehouse gases were the causes before fine, but we should see some science on this. There are some books that speculate that one cycle may have been triggered by an asteroid in the Yucatan area of Mexico.

       I do not propose that earth's core is increasing in heat. So I accept what Tom says but it does not adress my question.

       Hypothesis: I propose that due to continual movements of tectonic plates areas of the upper mantle engage the crust as the lithospheric plates move allowing variations in the way that heat reaches the surface. In a very primitive example it would be like sliding a pan over the stove burner so different parts of the pan are exposed and heated even though the burner itself is constant. The plates are constantly moving some diverging down to be reheated while others move nearer to the surface.
       Maybe a constant temperature is maintaned because while some submerge others emerge in equilibrium. However, what if there are cycles where large portions of hot mantle emerge under large portions of the sea? This hypothesis would at least be reconciable with cycles prior to human contributions.

       It seems prudent that NASA and NOA should place thermometers a couple meters deep incrementally across our seas to monitor changes in crust temperatures.

       Thanks for your patience gentlemen. I should learn to explain myself in my best scientific language in this type of setting. Please address both issues: premise of cycles and plate tectonics as related to heat movement.

26736. lorainel at 08:35 AM on 2 December 2015
       How much does animal agriculture and eating meat contribute to global warming?
       

       Can someone specifically discuss the points made in this report by the Worldwatch Institute?

       http://www.worldwatch.org/files/pdf/Livestock%20and%20Climate%20Change.pdf

26737. foolonthehill at 07:04 AM on 2 December 2015
       How much does animal agriculture and eating meat contribute to global warming?
       

       Thank you so much for this post Dana. I have been waiting for a post on agricultural emissions for some time and was at the point of requesting that you address this gap in the SKS resource library. 

       I am particularly interested in this topic as I own a grass fed beef farm. I have been struggling to find a sensible discussion forum that concentrates on the problem that I am contributing towards (searches on this topic primarily direct to the work of Allan Savory, about which I am rather sceptical). 

       On a personal note, I have begun the process of reducing my stock numbers by 40% on 1990 levels by 2030. I have set up a nursery to grow native trees for revegetation of land that is not grazed (my land is not suitable for arable production). Fertiliser input is almost zero. I am fortunate to have a secondary income that allows me to make these changes - other farmers around me do not have that luxury. 

       I am happy to discuss these choices.

26738. Tom Curtis at 06:48 AM on 2 December 2015
       Murry Salby finds CO2 rise is natural
       

       InnocentSmithReturns @17, I have a very low opinion of Murray Salby's honesty, for reasons partly explained here and here.  He immediately shows, in this new video, why that low opinion is justified.  He begins by referring to is sacking by Macquarie University (0:30).  He says:

       "If I am in retirement, let there by no doubt, it is forced retirement.  After being prohibitted from teaching climate, and then having my research files confiscated."

       He must have had a sense of deliberate mischief in making that claim, which makes it appear as though he was prohibitted from teaching prior to his dismissal.  In point of fact, he was dismissed, in part, because he refused to teach:

       "Professor Salby’s employment was terminated firstly, because he did not fulfil his academic obligations, including the obligation to teach. After repeated directions to teach, this matter culminated in his refusal to undertake his teaching duties and he failed to arrive at a class he had been scheduled to take."

       Salby demonstrates incredible chutzpah in accusing the University of preventing him from teaching, whereas in fact he was dismissed because he refused to teach.

       Of coure, that was only part of the reason.  A further reason was his undertaking a trip to Europe when his class schedule required him to be in Australia, and paying for that unauthorized trip through the unauthorized use of university funds.  Nor was that misappropriation the first by Salby, who ceased employment in the US because he had been found to undertake conduct that "...reflects a consistent willingness to violate rules and regulations, whether federal or local, for his personal benefit."

       Fast forwarding to 1:06:06 on the video, Salby shows a graph the obsolute HadCRUT3 data set.  Leaving aside why he uses the obsolete data set rather than the current HadCRUT4 data set, he shows two apparent trend lines on the graph at that point.  Careful examination shows that they are not in fact trend lines, but pseudo-trendlines.  They are intended to look like trend lines, but are not.  The periods are from 1877-1910 (actual trend: - 0.0089 C per annum), 1910-1945 (actual trend: 0.0159 C per annum).  This gives a mean change in temperature between start point and end point of the intervals of  -0.3 C and 0.4 C respectively.  Salby shows them as -0.7 and 1 C instead, inflating the values by 133% and 150% respectively.

       Earlier, in discussing the HadCRUT3 data he asserted that the warming post 1910 was "just as long and even faster" (1:05:00) than the warming post 1976.  His highlighted area for post 1976 actualy ends in 1998, but I have taken it to 2001 to cover the same period ("just as long").  That reduces the trend for the period.  Nevertheless the trend from 1976 to 2001 is 0.0172 C per annum, 8% faster than the earlier period.  That difference may not be statistically significant, but that does not justify claiming the period with the lower nominal trend had the higher nominal trend which is a direct falsehood.  Even that leaves aside the fact that Salby cherry picked the earlier period to give the maximum trend, but excluded years ('74 and '75) that would have resulted in an increased trend for the later period.

       (Analysis made using the Wood for Trees resource.  All trends calculated from January of the initial year through to December of the final year.)

       Clearly Salby has not abandoned the dishonest presentation of data on which so much of his argumenation depends in earlier videos.

       This may seem like shooting the messenger.  It is not.  The paradox of internet "experts" is that they seek tirelessly to convince the generally uniformed and inexpert public that what they say is true, while scrupulously avoiding putting their arguments before genuine experts who are long familiar with the relevant arguments, and the relevant data.  Specifically, while rusing to convince the uninformed public, they avoid peer review.  Somebody truly convinced of their theories would take the opposite approach.  There confidence in the soundness of their arguments should result in equal confidence that they will be able to persuade the majority of domain experts as to the truth of what they say.  Conversely, when a supposed expert insists in presenting their "revolutionary" theories time again to an uncritical public, while avoiding opportunties to present them before the well informed - you should take that as in indication of their confidence, or rather their lack of confidence, in the soundness of their arguments.

       That is particularly the case when they repeatedly (as Salby does) choose obsolete data over current data, cherry pick, use misleading presentations of the data, apply statistical tests to theories they oppose while avoiding similar tests for their own theories, and repeatedly misrepresent the nature and substance of the theories they criticize.  (The later is very evident in this video in Salby's complete failure to acknowledge the many other forcings other than CO2 that the IPCC recognizes and discusses, in addition to more pointed examples I may discuss later.)

       The scope of Salby's video is so broad that your request for a point by point rebutal amounts to a request to be given a free Climate Science 101 course; with the added onus on your respondents that they have to correct Salby's misleading presentations of data and theory at the same time.  It is a big ask.  It is not something I am inclined to do unless I see clear evidence of good faith in the form of an ability to recognize Salby's shoddy practise for what it is. 

26739. scaddenp at 06:08 AM on 2 December 2015
       Murry Salby finds CO2 rise is natural
       

       Leaving aside Salby's nonsense, it is worth noting that the over very long time scales (100s of million years), the trend in CO2 has been downward. Just as well because the sun is gradually getting hotter over similar time scales. At about end of Pliocene, CO2 got low enough for Milankovitch cycles to induce ice ages. With our massive release of millions of years worth of stored hydrocarbons, we have kind of reset that cycle.

26740. Jim Eager at 03:42 AM on 2 December 2015
       How much does animal agriculture and eating meat contribute to global warming?
       

       Re the "documentary" Cowspiracy, it includes every possible factor related to animal agriculture to arrive at their cited percentage of emissions, from land use changes and deforestation, to production of fertilizers for feed crops, to transport of those chemicals and feeds, etc, etc, factors that are already accounted for in other categories. They then compare their resulting aggregate figure to just the direct emissions of transport, which is a rather dishonest slight of hand.

       A proper and honest comparison would be to include a portion of the many factors related to transport, including the overwhelming bulk of petroleum extraction and refining emissions, perhaps the bulk of cement production (roadways, runways, canal locks, etc), a portion of deforestation and land use changes (construction of roadways, airports, docklands), a large portion of steel and aluminum mining and refining and chemical and  machinery manufacturing (cars, trucks, busses, trains, planes, ships).

       Doing so would obviously make for a much more apples to apples comparison, but it would hardly serve the purpose of the film, which is promoting veganism.

       For more see:
       https://www.quora.com/Cowspiracy/How-accurate-is-the-movie-Cowspiracy
       and
       http://www.fao.org/news/story/en/item/197623/icode/

       Moderator Response:

       [RH] Hotlinked URL's.

26741. KR at 01:42 AM on 2 December 2015
       Murry Salby finds CO2 rise is natural
       

       InnocentSmithReturns - The current science on CO₂ indicates that the recent warming of 0.8C over pre-industrial levels has released an additional ~10-12 ppm of CO₂ from the oceans. Salby claims that _all_ CO₂ increase from pre-industrial levels comes from ocean warming, a rate of perhaps 120 ppm per degree. And not from our (well known) emissions.

       If that relationship held true, given that the ice ages perhaps 6-7C cooler globally, CO₂ levels during the ice ages would have gone to zero (-300ppm or so by that relationship, in fact!), killing all life on Earth. That's absolutely not the case, and the failed relationship of Salbys presents a reductio ab adsurdum failure of his arguments.  

       Salby's arguments are nothing but nonsense. 

26742. KR at 01:33 AM on 2 December 2015
       Murry Salby's Correlation Conundrum
       

       InnocentSmithReturns - The earth system is a net sink now, as it accomodates the extra fossil CO2 we've put into the carbon cycle. If we were to stop emitting CO2 right now, that sink would draw atmospheric CO2 down to perhaps 20-35% over pre-industrial levels over several centuries, to the point where the oceans, biosphere, and atmosphere exchange rates balance. Longer term processes such as weathering and CaCO3 formation would draw down the remainder over perhaps 3-7 thousand years. This is the "long tail" commitment we're making with our current emissions. 

       See Archer et al 2009 for a discussion of this topic. 

26743. Rob Honeycutt at 23:44 PM on 1 December 2015
       How much does animal agriculture and eating meat contribute to global warming?
       

       I don't know if this comes from that Cowspiracy movie, but on another website I saw someone make the comment that we're projected to use up all of the 565GT of remaining budgeted carbon emissions through livestock by 2030. It's a completely absurd statement, but there it was. I asked where they got the information but the person didn't respond.

26744. Alexandre at 23:32 PM on 1 December 2015
       How much does animal agriculture and eating meat contribute to global warming?
       

       Those flow charts are a great visual resource. Very informative. It's a great way to communicate that any single solution would only tackle a small part of this huge problem. We need lots of these solutions.

       Any idea if there's an updated version of it? Would the SkS team consider doing it?

26745. IG at 23:29 PM on 1 December 2015
       How much does animal agriculture and eating meat contribute to global warming?
       

       Nice post.

       Can you please just clarify how are trucks, tractors and other machinery included in this analysis? Are they part of the transportation or animal and plant production.

26746. johncl at 23:25 PM on 1 December 2015
       How much does animal agriculture and eating meat contribute to global warming?
       

       Ok, I saw the "documentary" called Cowspiracy a while back, and although it paints the silly black and white picture that "meat is a big problem hence one should ignore all other emissions" I wondered a bit about their numbers. I see they have a number of cited sources on their web page. 18% of all greenhouse gases. I would assume they then also mean the production of food for the meat industry itself as well. How about transportation, does the chart above separate transportation within the agriculture or does it add that to the agriculture number? I do however think the film has a valid point about water usage which adds up a lot for every kg of beef compared to just eating the vegetables ourselves.

26747. MA Rodger at 22:28 PM on 1 December 2015
       Murry Salby finds CO2 rise is natural
       

       InnocentSmithReturns @17.

       You ask about "a mistake" but appear to ask for a detailed blow-by-blow rebuttal. Don't hold your breath on the latter. You may consider the following a response to the former and a taste of what the latter would contain.

       The first of Salby's graphics plots global CO2 emissions from fossil fuel & cement and onto this trace Salby draws two period trends and annotates the annual rate of change for these periods. He says this rate of change grew massively between the 1990s and the 2000s. The rate of change has changed! This is fine. The rate of change of fossil fuel (&cement) emissions increased during the 1960s, fell back through the 1970s, bulged up and down through the 1980s, stayed low through the 1990s (averaging 80Mt(c)/y/y) then rising again through the 2000s and staying high to 2013 (averaging 240Mt(C)/y/y 2002-2013). These therefore are probably what Salby means by "the growth of fossil fuel emissions increased by a factor of 300%."  It is however messy data, something Salby rather ignores.

       Where Salby is also silent here is the change in CO2 emissions between these two periods1990-2001 & 2002-2013. Between the two periods, the annual emissions rose from 6.4Gt(C)/y average to 8.6Gt(C)/y average due to FF+cement, a rise of 33%, but more correctly, including net land use emissions these figures are 7.9Gt(C)/y to 9.5Gt(C)/y a rise of 20%.

       Salby's second graphic is MLO CO2 data. When he claims the rate of change in atmospheric CO2 is "exactly" the same for the period 1990-2001 as it is to 2002-2013 (he may be using slightly different periods but the outcome would be the same) he is simply lying. For the two periods, the average annual increases were 1.6ppm/y and 2.1ppm/y respectively, a 40% increase. A least squares through the MLO data yields a 1.57ppm/y(+/-0.1) for the first period and 2.01ppm/y(+/-0.1) for the second, a 28% increase.

       So that's the first 3 minutes of the 70 minute presentation. Selby compares 300% with 0% and says science is wrong and ignores this mismatch. But the 300% is not what he should be comparing and the 0% is a lie. You can even spot the lie on the next graph he presents. While the remaining 67 minutes of Sably's analysis does get more complex, it fails to get more truthful.

26748. InnocentSmithReturns at 22:24 PM on 1 December 2015
       Murry Salby's Correlation Conundrum
       

       Thanks for patience with a very basic question:

       If the earth system is a net sink for CO2, and if human contribution prior to the industrial revolution was insignifigant, then shouldnt the long term trend of atmospheric CO2 prior to that point in time be headed towards zero ?  But that is not what our historical data shows is it ?  Or would it head towards a steady state where whatever is produced is constantly being completely absorbed (averaged over the long run)?  But again is that what the historical record shows ?  Thanks.

26749. Jonas at 21:18 PM on 1 December 2015
       How much does animal agriculture and eating meat contribute to global warming?
       

       Very interesting graphics, but please SkS, turn off the enhancing glass: it hinders me from taking the link of the graphics .. (anybody who wants to see bigger graphics use the browsers Ctrl/Cmd-"+" key: it's a nice looking gimmick, but for me it's disfunctional).

26750. meher engineer at 19:14 PM on 1 December 2015
       How much does animal agriculture and eating meat contribute to global warming?
       

        

       @2 C B Dunkerson, Regarding the futility of mitigating short lived Greenhouse Gases like CH4:

       "A re-examination of the issues shows that the benefits of early SLCP mitigation have been greatly exaggerated, largely because of inadequacies in the methodologies used to compare the climate effects of short-lived substances with those of CO2, which causes nearly irreversible climate change persisting millennia after emissions cease. Eventual mitigation of SLCP can make a useful contribution to climate protection, but there is little to be gained by implementing SLCP mitigation before (my emphasis) stringent carbon dioxide controls are in place and have caused annual emissions to approach zero." the quote is from Short-Lived Climate Pollution, by R.T. Pierrehumbert http://www.annualreviews.org/doi/abs/10.1146/annurev-earth-060313-054843. the paper is wprth reading. 

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