Guest commentary from Spencer Weart, science historian
Despite the recent announcement that the discharge from some Antarctic glaciers is accelerating, we often hear people remarking that parts of Antarctica are getting colder, and indeed the ice pack in the Southern Ocean around Antarctica has actually been getting bigger. Doesn’t this contradict the calculations that greenhouse gases are warming the globe? Not at all, because a cold Antarctica is just what calculations predict… and have predicted for the past quarter century.
It’s not just that Antarctica is covered with a gazillion tons of ice, although that certainly helps keep it cold. The ocean also plays a role, which is doubly important because of the way it has delayed the world’s recognition of global warming.
When the first rudimentary models of climate change were developed in the early 1970s, some modelers pointed out that as the increase of greenhouse gases added heat to the atmosphere, much of the energy would be absorbed into the upper layer of the oceans. While the water was warming up, the world’s perception of climate change would be delayed. Up to this point most calculations had started with a doubled CO2 level and figured out how the world’s temperature would look in equilibrium. But in the real world, when the rising level of gas reached that point the system would still be a long way from equilibrium. “We may not be given a warning until the CO2 loading is such that an appreciable climate change is inevitable,” a National Academy of Sciences panel warned in 1979.(1)
Modelers took a closer look and noticed some complications. As greenhouse gases increase, the heat seeps gradually deeper and deeper into the oceans. But when larger volumes of water are brought into play, they bring a larger heat capacity. Thus as the years passed, the atmospheric warming would increasingly lag behind what would happen if there were no oceans. In 1980 a New York University group reported that “the influence of deep sea thermal storage could delay the full value of temperature increment predicted by equilibrium models by 10 to 20 years” just between 1980 and 2000 A.D. (2)
The delay would not be the same everywhere. After all, the Southern Hemisphere is mostly ocean, whereas land occupies a good part of the Northern Hemisphere. A model constructed by Stephen Schneider and Thompson, highly simplified in modern terms but sophisticated for its time, suggested that the Southern Hemisphere would experience delays decades longer than the Northern. Schneider and Thompson warned that if people compared observations with what would be expected from a simple equilibrium model, “we may still be misled… in the decade A.D. 2000-2010.” (3)
The pioneer climate modelers Kirk Bryan and Syukuro Manabe took up the question with a more detailed model that revealed an additional effect. In the Southern Ocean around Antarctica the mixing of water went deeper than in Northern waters, so more volumes of water were brought into play earlier. In their model, around Antarctica “there is no warming at the sea surface, and even a slight cooling over the 50-year duration of the experiment.” (4) In the twenty years since, computer models have improved by orders of magnitude, but they continue to show that Antarctica cannot be expected to warm up very significantly until long after the rest of the world’s climate is radically changed.
Bottom line: A cold Antarctica and Southern Ocean do not contradict our models of global warming. For a long time the models have predicted just that.
(1) National Academy of Sciences, Climate Research Board (1979). Carbon Dioxide and Climate: A Scientific Assessment (Jule Charney, Chair). Washington, DC: National Academy of Sciences.
(2) Martin I. Hoffert, et al. (1980) J. Geophysical Research 85: 6667-6679.
(3) Stephen H. Schneider and S.L. Thompson (1981) J. Geophysical Research 86: 3135-3147.
(4) Kirk Bryan et al. (1988). J. Physical Oceanography 18: 851-67. For the story overall see Syukuro Manabe and Ronald J. Stouffer (2007) Journal of the Meteorological Society of Japan 85B: 385-403.
Re Tom @ 183: “Please cite proof of the statement. List the species that you believe will not be able to adapt fast enough and the proof that backs this assertion. Also, please quantify the ‘many’ in your statement.”
“Many” was sloppy writing on my part. Would you be more comfortable with “some species will be able to adapt, some won’t. Some will be able to migrate to find habitats similar to those they are already adapted to, some will simply not be able to migrate fast enough or at all?”
Or, is it the very premise that climate change will result in the extinction of some species that you object to? If so, that horse is already out of the barn. Let me introduce you to Bufo periglenes:
http://animaldiversity.ummz.umich.edu/site/accounts/information/Bufo_periglenes.html
This toad was highly adapted to the very narrow range of climate conditions of the cloud rain forest. When those conditions changed during the 1986-87 El Nino the entire known population of the toad was extirpated. Since no other populations are known to exist, it is now listed as extinct.
Environmental change and habitat loss are both well established causes of extinction, and climate change will result in both on a global scale. The golden toad is but one example of a species that is so highly specialized to a very narrow range of habitat and climate variation that it will be unable to either adapt or migrate when those conditions change.
Your request for a list the species that will not be able to adapt fast enough is a nice try, but no one can predict the future to that specific degree, and you know it, or should. That said, many species are risk, and as Hank Roberts demonstrated, it’s not very hard to research the subject if you’re interested in more than trying to score a point.
> 183, 187
No, Tom, you’re seeing what you “suspected” because you’re replying to blog postings instead of reading the science. This is not an argument or a debate. This is an attempt by all of us amateurs to learn what’s known.
If you don’t read the science and can’t cite your sources, you’re just opinionating. Recreational typing or homework help, either way, it wastes everyone’s time.
Seriously — read at least the link on how to ask questions the smart way and consider trying it. As, you know, an experiment.
Experiment. It’s good for you, if you want to learn something new. If not, don’t.
Re #197. Excel is a nifty little tool. Using the monthly ocean temperatures from the NCDC and plotting the trendline slope backward in time from the most recent month (close enough to today for me) provides a graph of the current trend in ever increasing ranges. The trend is currently negative going back 7 years before crossing over to positive for the long term.
La Nina is the obvious explaination for average temperature anomoly drops recently. My simplified question is, what was driving the slight ocean surface temp drops prior to 2007?
#176 Justin
Re: Harries et al and observed OLR.
In IPCC AR4 Chapter 2 of the scientific basis report “Changes in Atmospheric Constituents and in Radiative Forcing” you’ll find reference on page 153 which states:
“The reduced brightness temperature observed [by Harries et al] in the spectral regions of many of the greenhouse gases is experimental evidence for an increase in the Earth’s greenhouse effect. In particular, the spectral signatures were large for CO2 and CH4. The halocarbons, with their large change between 1970 and 1997, also had an impact on the brightness temperature.”
So it is “experimental evidence for” the enhanced greenhouse effect. Not though global warming due to human activity, that’s a further line of reasoning.
Sorry but I too can’t find a copy of Harries et al outside of Nature’s Golden Ramparts.
Re: 204.
I’m taking the enhanced greenhouse effect to be caused by humans as a well-founded given (re: isotopic analysis; oxygen usage; etc.)
> currently negative
Statistical significance?
It has been published that 12,500 years ago the earth went through a warming of approx 20 degrees F in 50-80 years. (James White et al)
If species survived this warming why would a vastly more gradual warming now be harder on them? Has the evidence of this warming been debunked that I’m not aware of?
[Response: No way. Global warming out of the ice age as about 5 – 6 deg C (~10 deg F) and it took 10,000 years, not 50. You are most likely talking about local warmings in Greenland coming out of the Younger Dryas – but the global change associated with this was much smaller. – gavin]
Re #204 Cobblyworlds, what you probably want is the article:
Griggs, JA, Harries, JE, Comparison of spectrally resolved outgoing longwave radiation over the tropical Pacific between 1970 and 2003 using IRIS, IMG, and AIRS, J CLIMATE, 2007, Vol: 20, Pages: 3982 – 4001, ISSN: 0894-8755
not so much the letter to Nature.
Look at: http://www.ggy.bris.ac.uk/staff/staff_griggs.html under “recent presentations” for two accessible PDF presentations on the subject.
Interesting information, a review of the icecore data shows the antarctic went through a fair amount of warming at the same period, a couple degrees C in 500 years or so. This debate has kept me quite interested for a few years now. I actually look forward to the release of monthly temperature anomaly data and the like. (although clearly for the purposes of climate change a single months data is fairly irrelevant)
To say that humans are changing the climate is a given, to say the earth is so fragile it’ll likely hit some crazy tipping point and kill everyone and everything is a little absurd in my opinion.
Re: #208: here’s a real article to read:
http://hdl.handle.net/1983/999
#209, Ryan Patterson says “To say that humans are changing the climate is a given, to say the earth is so fragile it’ll likely hit some crazy tipping point and kill everyone and everything is a little absurd in my opinion.”
And you base your opinion on what exactly? Doesn’t it bother you just a little bit that the survival of the human species should be trusted to opinion? In any case, killing everyone and everything is not the threat most people are concerned about. Rather the concern is how we maintain a complicated global civilization with 9-12 billion people when the climate upon which our agriculture, transport, health and culture depend becomes unpredictable or hostile to maintenance of that civilization. The concern is that we will reach some tipping point where feedbacks make all of our efforts meaningless and strip away what little control we have over future climate. And that concern is anything but absurd.
Hank 206. The significance at the zero cross of the slope graph is expectedly low. Checking a few months forward the significance is much higher. At 6.75 years the current negative trend’s significance has a value less than 1%.
Ryan (209), I have seen it estimated that between 99 – 99.9% of all species that have ever existed are now extinct. Still the earth teems with life. You are right the “earth” is very resistant. Humans and cockroaches (among others) have proven themselves to be very adaptable (cockroaches actually have much more impressive track record). The issue at stake here is not really “life” or “the earth”. I agree with you that “they” will both survive whatever we throw at them. The issue is “life as we know it” and the earth’s continued ability to support a (growing) population of humans who are at least partly dependent upon the level of species diversity that now exists.
I haven’t done much reading on the various global warming controversies yet, but it’s great to see a site where people actually discuss the evidence.
Antarctic ice record warns of greater warming than today’s climate …
Climate Model Predicts Greater Melting, Submerged Cities …
BBC NEWS | Science/Nature | Unexpected warming in Antarctica
Antarctic temperatures disagree with climate model predictions
Doesn’t this contradict the calculations that greenhouse gases are warming the globe? Not at all, because a cold Antarctica is just what calculations predict… and have predicted for the past quarter century.
Huh? What they call a posteriori reasoning, which does not mean talking out of your backside but means being wise after the event. The theory is not wrong. The model is. So if this model is wrong?????
I understand this post to be saying that oceans absorb heat so the atmosphere over oceans heats more slowly than the atmosphere over land. So Antarctica heats up more slowly.
I have also read somewhere that the poles are heating more quickly than the equator. Is this incorrect, then; is it just the Arctic that is heating up faster?
Wotan,
The models that predict cooling in Antarctica were not “fit” to the observations. Rather, the parameters are fit independently and then the results are the results, so there is nothing a posteriori about it.
Thanks Martin(#208).
Holly Stick (216) — Yes, just the Arctic. The difference is that most the land is in the northern hemisphere and most of the ocean in the southern.
Latest French & CSIRO research reports some evidence that the Southern Ocean to be warming on the surface and at depth.
The joint Australian-French-US program has produced a 15-year dataset based on readings taken by the volunteers and crew of the 65-metre French ship, L’Astrolabe, on regular voyages between Hobart, Tasmania and the French Antarctic base at Dumont D’Urville.
Podcast here http://www.csiro.au/files/files/pisg.mp3
http://www.abc.net.au/news/stories/2008/02/18/2165601.htm
Doesn’t this show a cooling trend for Antarctica?
http://vortex.nsstc.uah.edu/data/msu/t2lt/uahncdc.lt
Gavin, do you know of Prof. Ross Garnaut? He’s just presented his interim report to our Prime minister Kevin Rudd and the contents of that report are chilling – so say those who read it. He says that climate change and AGW is happening much faster than anyone before had predicted. He said the Stern report missed the mark by a long shot and he has urged the australian government to now take ‘immediate’ action on all fronts to try to do our bit to mitigate climate change. He also said that a 60% reduction by 2050 was far too little and that we need an almost complete ban on CO2 emissions by that time if not sooner, but he also said that the economic cost will be enormous but it’s something we will have to face. Why Kevin Rudd was so non-comittal in Bali is because he was waiting for that report to formulate action. BTW the presidential candidates for the white house seem to give AGW very little mention, Obama seemsto be the most switched on but they all seem very uninspiring to me.
[Response: We are not going to discuss presidential politics here – but I am not aware of Garnaut or his report. It sounds a little too strong, but I’d have to see it to judge. Post a link if you find one. – gavin]
Re: 222 Here is the link to that report http://www.garnautreview.org.au/CA25734E0016A131/WebObj/GarnautClimateChangeReviewInterimReport-Feb08/$File/Garnaut%20Climate%20Change%20Review%20Interim%20Report%20-%20Feb%2008.pdf
Re #207 Ryan Patterson Says:
20 February 2008 at 12:31 AM
“It has been published that 12,500 years ago the earth went through a warming of approx 20 degrees F in 50-80 years. (James White et al.)”
A rather fuller reference would help. That is not a paper I, or even Gavin, appears to be familiar with. Even with Google Scholar I cannot find the paper you are referring to.
Ryan asks: “If species survived this warming why would a vastly more gradual warming now be harder on them?”
Why would it be gradual? The main danger is from an abrupt climate change like the one White describes or that which ended the Younger Dryas to which Gavin referred.
Ryan then asks: “Has the evidence of this warming been debunked that I’m not aware of?”
No! There was a rapid warming in the Northern Hemisphere at the end of the last glacial maximum, but everyone concentrates on the rapid cooling at the start of the Younger Dryas. We are in a period of global WARMING, and the main danger to those people living in the Northern Hemisphere today is not a cooling aka Hollywood’s “The Day After Tomorrow” but a rapid warming as recorded in the ice cores for 12,500 BP and 10,500 BP.
Re #209 where Ryan says: “To say that humans are changing the climate is a given, to say the earth is so fragile it’ll likely hit some crazy tipping point and kill everyone and everything is a little absurd in my opinion.”
It does seem a little absurd to most people that the climate is fragile, but the events that happened in 12,500 BP, 11,500 BP and 10,500 BP show that it is true. The climate can be either stable or unstable. When it is stable it sits there, until external factors change it into instability. When it is unstable it changes rapidly until it becomes stable in a new way. Stable periods are long. Unstable periods are short. The unstable end of the Younger Dryas lasted perhaps only 3 years. The subsequent stable Holocene has lasted ten thousand years.
During this stable Holocene the human population has grown from around 600,000 to 600,000,000. A rapid change to a warmer climate will mean droughts, floods, hurricanes, and rising sea levels. On a crowded planet, it is not unconceivable to imagine more people dying from famine than the total population of the world 12,500 years ago!
Cheers, Alastair.
Popular account of Greenland melting detection:
http://www.sciencedaily.com/releases/2008/02/080220175223.htm
This is important because much of the southern coastal area of the ice sheet is already near the melting point (0 degrees Celsius) during the summer.
This is one that should interest the modelers — good find, David. Gavin, does this sort of correlation attract attention?
—-excerpt follows——-
The paired surface temperature and gravity data confirm a strong connection between melting on ice sheet surfaces in areas below 6,500 feet in elevation, and ice loss throughout the ice sheet’s giant mass. The result led Hall’s team to conclude that the start of surface melting triggers mass loss of ice over large areas of the ice sheet.
The beginning of mass loss is highly sensitive to even minor amounts of surface melt. Hall and her colleagues showed that when less than two percent of the lower reaches of the ice sheet begins to melt at the surface, mass loss of ice can result. For example, in 2004 and 2005, the GRACE satellites recorded the onset of rapid subsurface ice loss less than 15 days after surface melting was captured by the Terra satellite.
“We’re seeing a close correspondence between the date that surface melting begins, and the date that mass loss of ice begins beneath the surface,” Hall said. “This indicates that the meltwater from the surface must be traveling down to the base of the ice sheet — through over a mile of ice — very rapidly, where its presence allows the ice at the base to slide forward, speeding the flow of outlet glaciers that discharge icebergs and water into the surrounding ocean.”
—–
Alastair McDonald #224, I think you missed a zero there; the human population increased from 600,000 to 6,000,000,000.
And of course, the stable climate over the past 10,000 years or so allowed the invention of agriculture, which allowed that enormous population growth to take place. Now that the climate is going unstable, agriculture is going to be adversely affected. We need to figure out how to avoid crop failures in an unstable climate.
re 211.
This statement “Rather the concern is how we maintain a complicated global civilization with 9-12 billion people when the climate upon which our agriculture, transport, health and culture depend becomes unpredictable or hostile to maintenance of that civilization” presumes an optimal climate.
Do we know what the optimal climate is for 9-12 million people on this planet?
One of the faulty premises of AGW is that the optimal climate is NOW, and any change would be negative. ALmost every analysis I see about temperature increase is how BAD it would be, as if NO good would come of warmer temps. that , to me, is absurd.
I’ve made what may be an original observation but I would like to have my logic checked by someone more knowledgeable in the field. The observation is that the conventional idea that greenhouse gases have more effect at the poles than the tropics is wrong. In fact, the opposite is true. That is, there is not only no polar amplification, there is actually tropical amplification.
Here’s why: The tropopause is higher and colder in the tropics than at high latitudes. This means that emission from CO2 is lower in the saturated region around 15 micrometers (667 cm-1) in the tropics. Hence, an increase in CO2 will cause a higher forcing in the tropics than at the poles so the delta T required to balance that forcing is lower at the poles than the tropics.
I’ve checked this with the Archer MODTRAN calculator for doubling CO2 and methane. I have also looked at observed spectra from the tropics and high latitudes published in Grant W. Petty, A First Course in Atmospheric Radiation and the calculated and observed spectra show similar features.
Comments would be appreciated.
Tom, #228: Our infrastructure–especially our agricultural infrastructure evolved in the current climate. It will not produce as efficiently in a significantly warmer or significantly colder climate. Moreover, the past 10000 years has been a time of exceptional climatic stability–adding energy to that system will certainly make it less predictable. Predictability is a good thing when you have 12 billion mouths to feed.
tom — The optimal climate is that which enabled the human population to grow from less than one million persons to 6,600 million persons (so far). This was the climate of the Holocene, a climate we no longer enjoy, having created the Anthropocene, primarily by burning fossil carbon.
Climate is not just temperature, but also precipitation patterns. Changing those lowers agricultural yields, via droughts and floods.
Re: 225 andd 226
The Greenland info is interesting, particularly that we now have remote sensing capabilities to better monitor what is going on up there. And indeed, the GISS data suggest fairly rapid warming since at least the mid-90s with some ups and downs from the lows in the early 80s. However, before we abandon all hope, it should be noted that the few long-term Greenland GISS stations, particularly Godthab Nuuk and Angmagsallik, suggest that this area was consistently at least as warm if not warmer than 2000-2007 from ca. 1930-1950 (as do data from Iceland). Doesn’t say anything one way or another about what to expect but it does indicate we are not exactly in uncharted territory.
Regards,
Bob North
That’s an untrue statement. The worry is about the RATE OF CHANGE, and the ability of ecosystems, agricultural systems, and infrastructure to adapt to such rapid change in a way that’s not exceedingly painful for the human species. There’s no claim that today’s climate is “optimum”, only that it’s the climate current ecosystems and human infrastructure are adapted to.
Scientists aren’t as stupid as you apparently think they are.
RRe # 228 Tom: “ALmost every analysis I see about temperature increase is how BAD it would be, as if NO good would come of warmer temps. that , to me, is absurd.”
One of the peculiar features of science is that conclusions must be based on the evidence. As you have acknowledged, not ALL the predicted impacts are negative. But, if the data consistently point in one direction, then the conclusions have to reflect that trend. That is not absurd, it is science. Like it, or not.
OK, these models predicted less warming at the South Pole. Were there models that predicted the opposite (surely, there were some) and, if so, what was the ratio of numbers that did to those that didn’t? Were the early conjectures broad enough that one can essentially pull up those which happened to, at least temporarily, fit the later observations and claim it was known all along?
My question is related to the “Random Walk down Wall Street” exercise, in which 1,000 persons are gathered in a room and told to flip a coin. Those that get heads are segregated and asked to flip again. The process repeats until there is one person who has consistently flipped heads, at which point he is proclaimed an expert coin flipper. But, there is no predictive knowledge gained as to whether the individual will flip heads again on the next try. The odds are still 50/50.
In the same way, if this is simply choosing those early studies which have played out more or less correctly so far, does this confer upon them any particular predictive power with which to gauge the future?
Re tom @ 228: “Do we know what the optimal climate is for 9-12 million people on this planet?”
Perhaps the climate that allowed the population to grow to that size?
Seriously, look back through time and you will see numerous examples of the kind of impacts that both warmer and cooler climates–and don’t forget, warmer vs cooler also means dryer vs wetter–had on human populations and their civilizations.
Tom: “One of the faulty premises of AGW is that the optimal climate is NOW, and any change would be negative. ALmost every analysis I see about temperature increase is how BAD it would be, as if NO good would come of warmer temps. that , to me, is absurd.”
So, tell us, then, what the good impact would be…
… of a longer growing season if there is not enough rainfall at just the right time to water your crops?
… of increased CO2 fertilization for plants if your food species can’t use it as well as weed species can, and that same CO2 increase also acidifies the oceans and leads to a collapse of the marine food chain?
… of warmer average temperatures for rice, which is already at its upper limit of heat tolerance in much of the regions where it is grown?
… of decreased river flows in the Indus, Ganges, Mekong, Yangtse and other south and southeast Asian rivers as the glaciers that feed them shrink?
… of a northward shift of the climate zone suitable for growing wheat if the new zone lies in what is now shield, boreal forest and muskeg, and all of our infrastructure is built to transport and process wheat grown in the midwest?
… of a Northwest Passage open to shipping if the world’s port facilities and cities have been built for present sea level?
Please, do tell us what good impacts of global warming will offset these negative impacts should they come to pass?
Reid, Here:
https://www.realclimate.org/index.php/archives/2004/12/antarctic-cooling-global-warming/
https://www.realclimate.org/index.php/archives/2006/03/catastrophic-sea-level-rise-more-evidence-from-the-ice-sheets/
https://www.realclimate.org/index.php/archives/2006/08/antarctica-snowfall/langswitch_lang/in
Educate yourself.
I recommend Brian Fagan’s “Floods, Famines, and Emperors – El Nino and the Fate of Civilizations”.
Tom: you aren’t a farmer, are you? Farm kids learn Liebig’s Law of the Minimum (although not necessarily by the formal name) by the time they’re 10.
In any case, developed-world ag is going to be stressed anyway, even without AGW to make it worse:
– oil gets more expensive [tractors, combines, transport]
– nitrogen fertilizer [natural gas] gets more expensive
– water is under stress, just from aquifier draw-down
I stongly believe that it is just because of the current stable global climate before AGW that made our human proliferation possible..population growth in artic climes is nowhere near as great as in the warmer climates..as it get hotter stress on the reproductive process rises as well. And it is within the relatively narrow framwork of our current climate that the great breadbaskets of the world were developed, not too cold, not too hot, reasonably predicable rainfall etc. If that was to change as is happening now, the breadbaskets will be under enormous pressure to adapt..and largely they ‘will not’..as the precipitation patterns move elsewhere and the earth bakes underfoot not even genetic engineering of crops will be sufficient..and all this time the world pop keeps rising and rising, Ok not at quite the same stupendous rate as decades ago but fast enough. We are and will be entering a prolonged period of unprecedented climatic change and thart means all bets are off. The world breadbaskets are going to have to move to cooler and/or wetter areas of the world..only trouble is the land has not been allocated to that type of intensive agriculture, so massive expenditure is required to build canals, dams, drainage, infrastructure etc in different areas of the world. I believe in our medium term future the global economic and monetory systems will have to radically change as countries will have to help neibouring countries to meet the challenge of a changing agricultural paradigm.
Re #227 Where Holly Stick says:
“Alastair McDonald #224, I think you missed a zero there; the human population increased from 600,000 to 6,000,000,000.”
Yes, in fact David Benson #231 has it at 6,600,000,000!
He continued “And of course, the stable climate over the past 10,000 years also allowed the invention of agriculture, which allowed that enormous population growth to take place. Now that the climate is going unstable, agriculture is going to be adversely affected. We need to figure out how to avoid crop failures in an unstable climate.”
This morning problems with food were discussed on the BBC’s Radio 4 “Farming Today” programme. It can be heard again here.
Although it is put from a British perspective, global warming affects the whole world including the United States.
Cheers, Alastair.
tom writes:
[[One of the faulty premises of AGW is that the optimal climate is NOW, and any change would be negative.]]
You miss the point. It may be that some other climate would be better. But our agriculture and economy are adjusted to the climate we have NOW. A transition, even to a better climate, is much more likely to be damaging than not. Especially since we know we are looking forward to increased drought in continental interiors, increased violent weather along coastlines, and rising sea levels.
Dewitt Payne writes:
[[the conventional idea that greenhouse gases have more effect at the poles than the tropics is wrong. In fact, the opposite is true. That is, there is not only no polar amplification, there is actually tropical amplification.]]
Temperature records of the last fifty years falsify your hypothesis.
Re #229 DeWitt Payne:
Did you consider that interlatitudinal advection of latent heat increases in a warmer atmosphere? In other words, a more uneven forcing (if true; haven’t checked) may still produce a more even temperature as a function of latitude. As appears to be observed.
Re #229 Barton’s claims that the temperature record falsifies DeWitt’s hypothesis that polar amplification does not occur. But the temperature record shows that there is no sign of a temperature rise at the South Pole, far less polar amplification in Antarctica. I think that this has been pointed out in this thread already.
It is actually the paleo-temperature record for the Eemian inter-glacial and the Eocene Period that show polar amplification. However it is mainly confined to the Northern Hemisphere, because the North Pole is covered by an ocean whereas the South Pole is at the centre of a continent.
The greenhouse effect is not a simple value which depends on the carbon dioxide level. It also depends on the water vapour concentration. At the frozen poles there is very little water vapour so the greenhouse effect is dominated by the CO2 concentration. In the tropics there is lots of water vapour and that is what controls the temperature there.
When the CO2 level reaches a high enough level the sea ice in the Arctic melts, and water vapour then becomes available. This warms the sea surface causing more water vapour in a positive feedback loop. It is this positive feedback loop which causes the polar amplification. But it is only effective in the NH where the sea ice is melting. Except for a part of Antarctica that is surrounded by sea(which I cannot name because the spam filter thinks I have another part in mind :-) polar amplification does not have much effect on the South Pole region.
Thus I would say to the skeptics, if you think global warming does not matter because Antarctica is not warming, then try living there!
Re # 228 Tom’s concern about a bias towards negative consequences of AGW:
Here are a couple of examples of how global warming can have both positive and negative effects, with the net result being unclear:
1. Insect development and population growth tend to be positively correlated with temperature:
Frazier, M., R.B. Huey, and D. Berrigan. 2005. Thermodynamics constrains the evolution of insect population growth rates: “warmer is better.” American Naturalist 168:512-520.
If that means more bees and other insects pollinating crops, that should be good for the insects and for humans. Unfortunately, many insects are human pests: they eat valuable crops and transmit various diseases – good for the insects, bad for humans.
2. Tropical grasses that carry out C4 photosynthesis (sugar cane, maize, sorghum, switchgrass plus many non-commercial species) thrive in warm climates,and should do well with global warming. However, the leaves of C4 plants tend to be low in nitrogen, hence, they are a poor quality food for grazers: Good for the plants, not so good for cattle.
Ehrlinger,J.R., T.E. Cerling, and M.D. Dearnign (2002)Atmospheric CO2 as a global change driver influencing animal-plant interactions. Integrative and Comparative Biology 42: 424-430. (see also http://en.wikipedia.org/wiki/C4_carbon_fixation)
On the other hand, C3 plants (99% of all plant species) tend to have more nutritional value for grazers, but they don’t do so well with warmer temperatures. To complicate this matter, the C3 plants tend to grow better with elevated levels of CO2, so they may be able to better complete against the C4 plants. One problem, though: Those C4 plants that will likely face new competition for space and nutrients presently comprise only 5% of plant biomass, yet they carry out an estimated 30% of terrestrial carbon fixation, i.e., they are important providers of atmospheric oxygen and consumers of CO2. So, who wins with global warming? Hard to tell, but this uncertainty doesn’t bode well for our agricultural systems. And then there is the not-so-minor problem of where those C4 and/or C3 plants will get the additional nitrogen and phosphorus need to sustain their elevated growth in a warmer, CO2-rich climate, or (as John Mashee pointed out) how they will deal with a very different soil conditions as their range migrates north into the exposed pre-Cambrian granite shield and tundra of the Boreal regions.
3. It seems fairly clear that coral reefs don’t do well with rising temperatures, or the resulting rising sea levels, and will be further impacted by the elevated atmospheric CO2 levels:http://www.ucar.edu/communications/Final_acidification.pdf
However, one possible saving grace for coral reefs is highlighted in a recent study suggesting that hurricanes might alleviate thermal stress to corals by mixing the water column,thereby bringing cooler water to the surface:
Manzello, D.P, M. Brandt, T. B. Smith, D. Lirman, J. C. Hendee, and R. S. Nemeth (2007) Hurricanes benefit bleached corals. Proc. of the National Academies of Sciences, 104: 12035-12039
So, more hurricanes, or stronger hurricanes, despite their destructive power, could possibly help coral reefs in the face of global warming. But, as the skeptics love to point out (and as Urs Neu has explained to us in his two RC threads), there is no clear evidence that global warming is increasing hurricane frequency or strength. Too bad for the coral reefs – guess they’ll have to go it alone.
4. Finally, there is the shrinking Arctic ice that could open up new shipping lanes: AGW skeptics are fond of proclaiming this to be good for companies shipping products around the world. Unfortunately, the ice-free pathways through the Arctic are difficult to navigate because of shoals and rapidly shifting ice flows. Plus, there is currently no shipping infrastructure (ports, repair facilities, rescue services) in the Arctic, and the risk of significant environmental damage if a ship runs aground, or hits an ice flow, is great. So, the shipping companies are not exactly champing at the bit to send their ships through the famed Northwest Passage. At least not yet.
Bottom line: Many of the predicted consequences of global warming would seem to depend on one’s perspective: Some ecosystmes, organisms, and people will likely thrive, others could well perish. I know next to nothing about risk assessment, but it seems prudent to give careful consideration to the negative impacts, which, at this point, do seem considerable from the human perspective.
Re: my post about global warming effects
Correction: It was Jim Eager (#236) who pointed out the problems faced by agricultural crops moving north to areas of exposed bedrock and tundra. Sorry for the misattribution. John Mashee did raise some very important concerns, as well.
Re: #242
I didn’t say there could be no polar amplification at all, I said there was no polar amplification of radiative forcing. There is a difference.
Re: #243
It is very likely that any increased heat in the tropics will increase the rate of advective heat transfer. There is already excess OLR at high latitudes and a deficit in OLR at low latitudes because of advective heat transfer. But that wasn’t my point. Here’s a quote from Judith Curry of Georgia Tech on February 21, 2008:
But when you actually do the calculations the effect of the higher and colder tropopause in the tropics appears to overwhelm the effects quoted by Professor Curry.
The radiation transfer codes in the computer climate models almost certainly get this right. It’s possible that this effect may have been neglected when calculating the total forcing from doubling CO2. I don’t know because the details of this calculation are not readily available. It should be important to everybody, however, to explain (and teach) theoretical predictions correctly.
Alastair McDonald (240) — For the record, I did not write “And of course, the stable climate over the past 10,000 years also allowed the invention of agriculture, which allowed that enormous population growth to take place. Now that the climate is going unstable, agriculture is going to be adversely affected. We need to figure out how to avoid crop failures in an unstable climate.”
Although I agree with that quotation.
Martin Vermeer (#243) wrote:
The models will take into account the lower tropopause in the tropics, higher tropopause in the higher latitudes, the warmer troposphere in the tropics, the cooler troposphere in the higher latitudes, interlatitudinal advection (both oceanic and atmospheric), the rising water vapor content of the atmosphere, the rising tropopause, the expansion of the Hadley cells, etc..
The numbers won’t be exact. Some things will be overestimated, others underestimated due to parameterizations and numerical approximations. The relative strengths of competing effects will differ from model to model. But when they tell us that the temperature distribution will be more even, its not because they have somehow neglected to take into account something as basic as the variation in height and temperature of the troposphere according to latitude. And I believe all of the current models predict a more even distribution of temperature as the result of an enhanced greenhouse effect.
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As for the actual warming trends according to latitude to present and interlatitudinal comparisons, I would strongly recommend checking out:
Hit You Where You Live
January 11, 2008
http://tamino.wordpress.com/2008/01/11/hit-you-where-you-live/
Down Under
January 17, 2008
http://tamino.wordpress.com/2008/01/17/down-under/
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Not much warming in the southern hemisphere as of yet — except near the coasts of Antarctica, particularly the West Antarctic Peninsula. This is what has been predicted, given that there is more ocean and less land in the southern hemisphere, and given both ocean circulation and thermal inertia, ocean warms more slowly than land. But long-term, models are predicting roughly the same degree of polar amplification at both poles.
Re: #249
I want to re-emphasize a point. I never said the full models are wrong, particularly on radiative heat transfer. I used a simple radiative transfer model to prove my point. My problem is with the hand waving explanations with no quantitative back up like that of Professor Curry quoted above. If they are incorrect, as appears to be the case, they damage the AGW case by giving talking points to skeptics.
Saying that the models predict that high northern latitudes warm faster than high southern latitudes without much in the way of details on why is insufficient. If a model doesn’t include details on heat flow in its output, it should. Correcting the public record on radiative polar amplification actually makes this easier, IMO, because you can then concentrate on what is most likely the true reason, the MOC. That’s a one way (in the short term) heat pump from south to north.