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New studies confirm weakening of the Gulf Stream circulation (AMOC)

Filed under: — stefan @ 17 September 2020

Many of the earlier predictions of climate research have now become reality. The world is getting warmer, sea levels are rising faster and faster, and more frequent heat waves, extreme rainfall, devastating wildfires and more severe tropical storms are affecting many millions of people. Now there is growing evidence that another climate forecast is already coming true: the Gulf Stream system in the Atlantic is apparently weakening, with consequences for Europe too.

The gigantic overturning circulation of the Atlantic water (dubbed AMOC) moves almost 20 million cubic meters of water per second – almost a hundred times the Amazon flow. Warm surface water flows to the north and returns to the south as a cold deep current. This means an enormous heat transport – more than a million gigawatts, almost one hundred times the energy consumption of mankind. This heat is released into the air in the northern Atlantic and has a lasting effect on our climate.

But since the 1980s, climate researchers have been warning of a weakening or even a cessation of this flow as a result of global warming. In 1987, the famous US oceanographer Wally Broecker titled an article in the scientific journal Nature “Unpleasant surprises in the greenhouse”. Even Hollywood took up the subject in 2004 in the film “The Day After Tomorrow” by the German director Roland Emmerich. However, there were no measurement data that could prove an ongoing slowdown.

Only since 2004 has there been continuous monitoring at 26°N in the Atlantic (RAPID project). Although the data show a weakening of the current system, the measurement series is still too short to distinguish a possible climate trend from decadal variability. For the longer-term development of the Gulf Stream system, we must therefore rely on indirect evidence.

A long-term AMOC weakening should lead to a cooling in the northern Atlantic. Such a regional cooling in the middle of global warming has been predicted by climate models for a long time. And indeed, the evaluation of data on sea surface temperatures shows that the northern Atlantic is the only region of the world that has escaped global warming and has even cooled down since the 19th century (see graph). In addition, one can see a particularly strong warming off the North American coast, which according to model simulations is part of the characteristic “fingerprint” of a weakening of the Gulf Stream circulation.

Diagram of the Gulf Stream system with the warm surface current and the cold deep current. The actual Gulf Stream off the US coast is a part of this more comprehensive circulation system. The color shading shows the measured temperature trend since the late 19th century. This diagram is based on Caesar et al., Nature 2018 and first appeared in the Washington Post.

This fingerprint is regarded as important evidence, and not least because of this, the Intergovernmental Panel on Climate Change (IPCC) stated for the first time a year ago in the Summary for Policy Makers of its Special Report on the Oceans:

 “Observations, both in situ (2004–2017) and based on sea surface temperature reconstructions, indicate that the Atlantic Meridional Overturning Circulation (AMOC) has weakened relative to 1850–1900.”

New studies support long-term weakening

Two new studies now provide further independent evidence of this weakening. In August a paper by Christopher Piecuch of the Woods Hole Oceanographic Institution on the Florida Current – the part of the Gulf Stream system along the Florida coast – was published. Although continuous measurements of the current have only been available since 1982, Piecuch was able to reconstruct the strength of the Florida Current over the last 110 years from measurements of the sea level difference between the two sides of the current. To do so, he used 46 tide gauge stations in Florida and the Caribbean as well as a simple physical principle: the Coriolis force deflects currents in the northern hemisphere to the right, so that the water on the right side of a current stands higher than on the left. The stronger the current, the greater the difference in sea level. Comparison with measurements since 1982 shows that the method works reliably.

The result: the Florida current has weakened significantly since 1909 and in the last twenty years has probably been as weak as never before. Piecuch’s calculations also show that the resulting reduction of heat transport is sufficient to explain the ‘cold blob’ in the northern Atlantic.

This Monday, in Nature Climate Change a further study appeared, of researchers of Peking University and Ohio State University (Chenyu Zhu and Zhengyu Liu). For the first time, their paper provides evidence for an AMOC slowdown based on data from outside the North Atlantic. Model simulations show that a weakening of the AMOC leads to an accumulation of salt in the subtropical South Atlantic. This is due to the fact that strong evaporation in this region constantly increases the salinity, while the upper branch of the ocean circulation drains the salty water northwards, continually bringing in less salty water from the south. When this current weakens, the water in this region becomes saltier. This is exactly what the measured data show, in accordance with computer simulations. The authors speak of a “salinity fingerprint” of the weakening Atlantic circulation.

Video animation of ocean currents in the CM2.6 climate model of the Geophysical Fluid Dynamics Lab in Princeton:

In addition to these oceanographic measurements, a number of studies with sediment data indicate that the Gulf Stream circulation is now weaker than it has been for at least a millennium.

These current changes also affect Europe, because the ‘cold blob’ out in the Atlantic also influences the weather. It sounds paradoxical when you think of the shock frost scenario of the Hollywood blockbuster The Day After Tomorrow: but British researchers found that in summer the jet stream in the atmosphere likes to take a route around the south side of the cold blob – this then brings warm winds from the southwest into Europe, leading to heat waves there, as in the summer of 2015. Another study found a decrease in summer precipitation in northern Europe and stronger winter storms. What exactly the further consequences will be is the subject of current research.

However, the latest generation (CMIP6) of climate models shows one thing: if we continue to heat up our planet, the AMOC will weaken further – by 34 to 45% by 2100. This could bring us dangerously close to the tipping point at which the flow becomes unstable.

This article appeared originally in German in Der Spiegel: Das Golfstromsystem macht schlapp

171 Responses to “New studies confirm weakening of the Gulf Stream circulation (AMOC)”

  1. 51
    zebra says:

    For KVJ And Those Discussing Psych/Social Stuff,

    https://www.washingtonpost.com/lifestyle/food/why-making-your-diet-part-of-your-identity-is-bad-for-your-health–and-society/2020/09/23/c5efeaac-fd1e-11ea-9ceb-061d646d9c67_story.html

    I’ve pointed out in the past that group identity (major part of Authoritarian Personality) is not genetic… people are born with the potential to ‘go either way’ or end up ‘somewhere on the spectrum’.

    But this is too simple, rational for people… if we accept a scientifically well-established concept, we can’t go on and on moralizing and nitpicking. This means you, KVJ.

    To say that Obama’s policies represented “lukewarmism” is beyond ridiculous. They represent pragmatism.

    For example, read what the article says about masks. What’s your plan to change that, KVJ…make indignant comments on RC, or maybe Twitter? That’ll do it for sure!

  2. 52
    Victor says:

    32 nigelj says:

    Victor @27 indulges in the “argument from incredulity fallacy”. This is the same Victor who claims to be a master of “critical thinking”. Sad!

    V: What’s sad is your inability to tell the difference between an “argument from incredulity” and simple incredulity. I presented no argument. I’m simply incredulous.

  3. 53
    Victor says:

    Ray Ladbury: It’s called physics. Maybe you should look it up.

    V: Nah. Too lazy. I’d rather have you explain it to me, Ray.

  4. 54
    Susan Anderson says:

    @nigelj: yes, I was aware that in writing to the subject that there are many good people who have made major efforts and live wisely and well. But I think we all prefer to ignore threats to the high standard of living we have come to take for granted. It’s unfair to put that on the hardworking people who take this seriously. I’ve seen many topnotch climate advocates confess that when it comes to doing without stuff, it’s not as easy as thinking we should, because it means giving up so much. Hope Jahren says as much, and I remember Hank Green of SciShow made the point as well. And that’s just a tiny sample of honest people of goodwill who recommend action.

    My argument was a little “play” with the idea that denial arises from a kind of “honesty” (scare quotes intentional) about consequences that those facing the starkness of reality might be tempted to set aside in the argument.

    I still find arguing against reality inexcusable, but it is complicated by the fact that action is deeply uncomfortable. All be a few of even the most honest and ethical are tempted to avoid the deep pit of awareness of how bad it is because of the nature of the action needed.

  5. 55
    mike says:

    at Nigel 46: I think your thought that politicians should “force” people to do more is a very bad idea. I live in a country that is beset by conspiracies and stupidity like QAnon and more. Any politician who attempted or proposed that we force people to do more about changing our footprint would guarantee electoral setbacks and advance parties and politicians who would promise to protect our freedoms.

    I think this is a carrot or stick problem. You are suggesting the stick. I think the carrot is the way to go. Establish more rebates and subsidies for folks who choose actions which reduce the carbon load for the planet. If carbon taxes are impossible to establish to fund the subsidies and rebates, simply have the fed government print the dollars as they have done to address the Covid problem. Modern monetary theory in action.

  6. 56

    #42, Mal–

    Of course. It’s what a troll does.

    But then, but that point I was doing some ‘messing’ of my own. Maybe I shouldn’t succumb to the temptation, but if it’s necessary not to leave this crap completely unrebutted–cf., “Swiftboating”–you might as well have some fun along the way.

  7. 57

    M 47: Reality doesn’t always agree with “the math”.

    BPL: The math is a way to describe the reality precisely. Also, from everything I’ve seen, you don’t actually understand the math.

  8. 58
    Ray Ladbury says:

    Weaktor: ” I presented no argument. I’m simply incredulous.”

    Actually, even when you think you are presenting an argument, you are simply basking in your own ignorance.

    Neither are you incredulous, but merely selectively incredulous. Why would you not expect ice to melt in a warming world. Why would you not expect more intense precipitation events when warmer air gets saturated with more moisture–and why would you not expect warmer air to become relatively drier when there is no moisture to add? Hell, it’s not just physics where you fail, but even basic logic.

  9. 59
    mike says:

    At Mal and Kev: I think it’s hard to know what to do with the folks who post in bad faith or are simply trolling. A “no response” response does leave the crap completely unrebutted. and it seems wrong to just let the misinformation go unchallenged. This is one of the traps of online discussion. I think it makes sense for the moderators to clean up the discussion and keep it on an even and sensible keel, but that’s a lot of whack a mole work. I think it makes sense to simply from time to time that folks like Victor and KIA and EP are just spewing nonsense and leave it at that. For me, life is too short to get more engaged than that with the bad faith posters.

    Some discussion with the site owners/moderators may make sense, but I am not sure of that.

    Cheers,

    don’t feed the trolls, but maybe occasionally make note that their submissions are primarily provocative nonsense.

    M

  10. 60
    Susan Anderson says:

    @Killian, sorry I didn’t see your comment before I wrote my second. Thanks for revisiting and emphasizing my comment.

    I don’t think you can have read Hope Jahren’s Lab Girl and The Story of More (with an appendix: The Story of Less, which makes your points quite well) with an open mind if all you have to say about her is that she is a nature capitalist (oversimplification, I know). I am not a PhD myself, in fact I have often described myself as someone who is the fool who steps in where angels fear to tread, but I found her one of the more informative and thoughtful voices recently. (I read that and The World Without Us (clearly I read too many books, another form of substitute action like commenting on blogs) in parallel.

    I adopted her simplification – use less and share more – as a plain language shortcut of value. It calls up another favorite, Annie Leonard and The Story of Stuff.

    I don’t know where your apparent rage comes from (“circular firing squad” to mind), but I think you underestimate our understanding of the fix we’re in. I am not your enemy, and I wish you would stop projecting. We need each other, and exclusion is not the answer. I appreciate voices of value where I find them, and lately many of them, like Chef Andre, are not high achieving academics. In general, putting people’s backs up strengthens their resistance, and self-righteousness can defeat the purpose of the complainant.

    To everyone else, I apologize for going off topic; I should perhaps have put my comment in the open thread to avoid this mishigass.

  11. 61
    Western Hiker says:

    @Mack and friends, #47

    You are pretending atmospheric pressure even though there is no atmosphere, right?

    The more literal interpretation is interesting too. The near-surface ocean would instantly boil, creating a new atmosphere made up entirely of water vapor. I imagine really hot and crazy weather.

  12. 62

    #52, Victor–

    I’m simply incredulous.

    Duly noted. And we should care because–?

  13. 63
    Mack says:

    @ 57 BPL
    I do understand the math and I do know the mistake in the math. You are obviously still ignorant of the mistake in the math. A mistake so bad we have supposedly intelligent people like yourself trying to tell me that the ATMOSPHERE is keeping the oceans in liquid state.
    When is is your boat going to fall off the edge of the Earth.?

  14. 64
    Mack says:

    @ 61 Western Hiker

    “You are pretending atmospheric pressure even though there is no atmosphere, right?”

    Not me WH, I’m not pretending anything. The rest of the mob here are pretending. They’re even pretending that ATMOSPHERE is keeping the oceans liquid.
    Some of them are still playing with their toys in the play-pen.

  15. 65

    SA 60,

    It’s “mashugas.” Yiddish for “craziness.”

  16. 66
    Jim Eager says:

    Note that KIA is equating not just himself and the rest of humanity, but the entire biota of earth with hypothesized microbial life inhabiting sulphur dioxide clouds 50-60 km above the Venusian surface.

    Tells you everything you need to know about KIA’s hypothesized intellect.

  17. 67
    Mal Adapted says:

    Mack:

    “Any denial of a round Earth was, and still is, from ignorant superstitious people. Much like climate denialism.”

    You mean the ignorant and superstitious people like the President of the Flat Earth Society who believes in “climate change”?

    OK, this guy has got to be a poe. It sure looks like he’s making a grade-school syllogistic error: “some ignorant superstitious people nonetheless acknowledge the truth of X” does not mean “all people who acknowledge the truth of X are ignorant and superstitious”.

  18. 68
    nigelj says:

    Mike @55, I was not literally saying force people as in “reduce your carbon footprint or we will cut off your legs”. I meant that a carbon tax kind of impels everyone to respond together, and change their buying decisions to cleaner greener alternatives, but I agree carbon taxes are probably not the best approach in a country like America because of its politics, and subsidies sound more viable.

  19. 69
    Mack says:

    @ 67 Mal Function,

    Ok, I looked up your “syllogistic” link…. and, plus, you’ve given me a 2 lined Syllogism. From your wikipedia link…. “Syllogistic arguements are usually represented in three-line form.”

    Something like climate science really. 5 lines OK for you, Mal Adjusted ?

    We have a “greenhouse gas”
    A “greenhouse gas” “warms”
    More “greenhouse gases” results in “more warming.”
    More “warming” results in “warming of the surface and oceans”
    Warming of the oceans results in “sea-level rise”

    Just ABCDE, one follows the other…. perhaps not a syllogistic but certainly science for imbeciles.

  20. 70
    Mack says:

    @ 67 Mal Function,

    Ok, I looked up your “syllogistic” link…. and, plus, you’ve given me a 2 lined Syllogism. From your wikipedia link…. “Syllogistic arguements are usually represented in three-line form.”

    Something like climate science really. 5 lines OK for you, Mal Adjusted ?

    We have a “greenhouse gas”
    A “greenhouse gas” “warms”
    More “greenhouse gases” results in “more warming.”
    More “warming” results in “warming of the surface and oceans”
    Warming of the oceans results in “sea-level rise”

    Just ABCDE, one follows the other…. perhaps not syllogistic but certainly science for imbeciles.

  21. 71
    Killian says:

    60 Susan Anderson:@Killian, sorry I didn’t see your comment before I wrote my second. Thanks for revisiting and emphasizing my comment. I don’t think you can have read Hope Jahren’s Lab Girl and The Story of More (with an appendix: The Story of Less, which makes your points quite well) with an open mind if all you have to say about her is that she is a nature capitalist (oversimplification, I know).

    She literally talks of ecosystem services as capital. Literally. It’s much like Doughnut Econ: Looks nice if you don’t understand economics and/or ecosystem functioning and/or actual sustainability, but if you *do* understand those three, you see the shortcomings immediately. Doughnut economics is #greenwashed Capitalism. People look at the tertiary aspects and forget to look at the first order and first principles issues, yet if one does look at them it’s very clear Doughnut Econ and Jahren don’t actually “get it.” The reason is simle: Their goal is to fit ecosystems into economics rather than fitting economics into the ecosystem, and the reason is clear: If you do the latter, there is no room for any kind of economics of ownership.

    So, you can tell yourself my critique has no merit, but all that shows is you, like them, do not understand the issues as clearly as you believe yourself to. No insult, just a fact.

    I adopted her simplification – use less and share more – as a plain language shortcut of value. It calls up another favorite, Annie Leonard and The Story of Stuff.

    I repeat my point: Why did you have to read a book to “adopt” that language when you’ve heard it here, from me, complete with a proposed full-system solution set, for years? The issue isn’t you don’t have a PhD, the issues is why you ignore what you hear unless it comes from a PhD/VIP.

    I don’t know where your apparent rage comes from

    Don’t play psychologist because you really suck at it. Since when does sarcasm = rage?

    (“circular firing squad” to mind)

    You would know, yes?, given you’ve been negative toward me on more than one occasion and should not be surprised I am not a fan. That, however, is immaterial. I respond to the issues. I could care less who says something; I care about what it is they said. More than one “ally” has made the mistake of thinking that because we agree on some things I won’t correct them or call them out when we do not.

    You’re not an enemy, you’re just wrong.

    but I think you underestimate our understanding of the fix we’re in.

    You ignore the same messaging supported above for YEARS here in this blog, but you suddenly see the light? Hmmm… And, the messaging you are supporting is an insufficient response to the emergency we are in, but I am to agree with you that you fully understand the emergency?

    I am not your enemy, and I wish you would stop projecting.

    No, you’re not, but neither are you a friend. You’re a stranger on a blog who is still not fully understanding things. I am not projecting. I don’t even know how to interpret that comment. Projecting what? There is nothing in anything I have said that would remotely qualify as projection (and I do have a background in psychology.)

    We need each other, and exclusion is not the answer.

    Yet, my history with you has been exactly you doing that.

    I appreciate voices of value where I find them

    Except here?

    and lately many of them, like Chef Andre, are not high achieving academics.

    Good. But he’s a chef. He works in a high-consumption industry, but talking about sustainability? See the problem? See where the lack of “getting it” comes in? Good intentions are one thing, actually understanding the issues and solutions is another.

    In general, putting people’s backs up strengthens their resistance, and self-righteousness can defeat the purpose of the complainant.

    It has never mattered how polite or impolite I am. I was, in fact, so polite in my youth my best friend once yelled at me for being too polite. True story! But nobody listened then, either.

    When I was in Detroit, there was a new long-term city plan process happening. It became evident very quickly the public aspect of it was an elaborate show. Pretty much all the “progressive” activists agreed about this. The plan was to roll out in January. It was late August or early September at the time. The rest of the activists – meaning the “leaders” – sketched out a plan to talk about stuff then do – something – in January.

    I told them during a meeting at the Boggs Center that would be too late. The city apparatus and the huge corporate and NGO money coming in would swamp our efforts if we waited that long to counter with a people-friendly process due to sheer momentum, let alone the active effort to minimize the voices of the people.

    By January, all resistance had evaporated, as predicted.

    You likely know nothing of the Boggs Center and Grace Boggs, nor me, but believe you me, I sure as hell did not talk in those meetings as I write on this blog response to years of bullying – just as I don’t teach this way nor do counseling this way. They are different arenas and I treat them so. So, completely polite, utterly correct, not listened to.

    If people understood the message, it would not matter except to those with little intellect. There is a very long list of important people who are/were considered extremely difficult to deal with. Again, not an insult, just a fact: If you are willing to ignore a person’s thinking because you don’t like how they speak, you’re just plain stupid, imo.

    That choice is yours alone to make.

    But know this: The only thing relating to climate I have been wrong about thus far is when the first Blue Ocean event would take place. I have been correct on everything else. Everything. Else. (Including this year’s new 2nd lowest ice extent.)

    So, whether you agree with me or not, listen or don’t. Your choice. But don’t try to dismiss me with your own head worms. Your issues are yours. Don’t like how I talk? OK, die, instead, with the rest of humanity and most other species. Brilliant choice… right?

  22. 72
    Killian says:

    “as I write on this blog *in* response to years of bullying…”

  23. 73
    Russell says:

    67
    Sorry Mal- the flat earth is as thingy and permanent a feature of the alt. crank landscape as Structuralism, Lit Crit. or the Vegetarian Liberation Front (Provisional)

    https://vvattsupwiththat.blogspot.com/2020/09/critical-climate-theory-makes-turn-from.html

  24. 74
    Victor says:

    Ray Ladbury: “Why would you not expect ice to melt in a warming world.

    V: Well, a whole lot of ice melted in the wake of the last ice age, when temperatures were a lot lower than they are today.

    Ray: Why would you not expect more intense precipitation events when warmer air gets saturated with more moisture–and why would you not expect warmer air to become relatively drier when there is no moisture to add?

    V: Sorry Ray, but that does not compute. If warmer air gets saturated with more moisture, then how does it “become relatively drier when there is no moisture to add”? What “moisture to add” are you talking about? If warm air is moist then warm air is moist — period. So yes, moister air produced by higher temperatures might induce increased precipitation, but how does that same moister air suddenly become dry enough to induce prolonged droughts and increase the likelihood of forest fires?

    Just asking. You’re the expert, not me. So please explain.

  25. 75
    Russell says:

    Mack:

    ‘You mean the ignorant and superstitious people like the President of the Flat Earth Society who believes in “climate change”?’

    Which one ? The geocentric Flat Earth Society guy, the heathen epicycle denier , or the head Theocentric heretic of Notre Dame?

    https://vvattsupwiththat.blogspot.com/2014/01/how-can-co2-trap-heat-of-sun-when-earth.html

  26. 76
    MA Rodger says:

    Mack @63,
    You assert “[you] do understand the math and [you] do know the mistake in the math. [We] are obviously still ignorant of the mistake in the math” and you say that it is a “bad” mistake.
    So that is good to know, although my side of the pond we call it ‘maths’.
    One of the wonderful things with mathematics is our ability to set out our mathematical method in a form understandable enough that folk can demonstrate when others depart from the straight and narrow. So if you are indeed knowledgeable of this “mistake in the math,” that is “so bad,” you should have no trouble whatever setting out “the math” to demonstrate the “the mistake.” Give you “understand the math,” I am actually surprised you haven’t done so already.
    So a gentle nudge, chum. Set out this alleged mathematical mistake you are bleating on about, or shut you cake hole!!

  27. 77
    Mack says:

    MA Roger @76.

    I was only saying “math” to appease BPL. Where I come from we say, maths.
    You are obviously some ignorant pedantic pom… so I won’t bother to answer your querulous blatherings until I’ve heard from BPL.

  28. 78
    nigelj says:

    Killian @71,

    “It has never mattered how polite or impolite I am”

    Perhaps have another look, or perhaps you had bad luck. Our prime minister is reasonably polite and is getting tremendous results and is very persuasive, and she gets plenty of attention without having to be snarky and too shouty. The leader of the opposition is the opposite she is snarky and nasty and is getting poor results! She is also expending a lot of horsepower for minimal results and is not really winning over the public. Its all human nature, psych 101. That doesn’t mean having to be “painfully” polite.

    “Their goal is to fit ecosystems into economics rather than fitting economics into the ecosystem, and the reason is clear: If you do the latter, there is no room for any kind of economics of ownership.”

    Maybe but many animals are very territorial or possessive, which is kind of like the economics of ownership. (Ownership is really about control). Its the way of nature. Some share, some don’t. So its not clear why only shared ownership (as opposed to private ownership) fits into the ecosystem of nature.

  29. 79
    Mack says:

    Russell @75

    “Which one? ”

    I would say the lot, Russell.

  30. 80
    Mack says:

    MA Rodger again @76

    Also another thing that pisses me off about you, MA Rodger, is this..

    “One of the wonderful things with mathematics is OUR ability to set out OUR mathematical method ..blah..blah .”

    YOUR mathematics ?? Maths doesn’t belong to you…. or an elite few. Obviously you’re an arrogant academic who thinks he’s a cut above everybody else.

  31. 81

    Ray Ladbury: “Why would you not expect ice to melt in a warming world.

    V 74: Well, a whole lot of ice melted in the wake of the last ice age, when temperatures were a lot lower than they are today.

    BPL: Victor, Ray didn’t say “warm.” He said “warming.” If you think that’s merely a semantic quibble, you’ve misunderstood the whole issue.

  32. 82
    nigelj says:

    MAR @106, on Mack, maths and cake holes. Well said. I think we will have a long wait seeing any actual maths from this guy. Or he will be scurrying around trying to find a link to some crank science article. While I’m a big believer in free speech I wonder if that really gives people like Mack a right to fill up websites with childish, snarky, completely idiotic and empty rantings.

  33. 83

    #74, Victor–

    If warmer air gets saturated with more moisture, then how does it “become relatively drier when there is no moisture to add”? What “moisture to add” are you talking about? If warm air is moist then warm air is moist — period.

    Uh, you have heard of the Law of Conservation of Matter*, right? It says, inter alia, that a packet of air that holds ‘x’ moles of water, if it is to grow moister, must acquire that water from *somewhere.* The water can’t just spontaneously appear from nowhere, and it can’t be teleported in from a distance.

    The source may be plants, which transpire water as a by-product of their metabolism. (So do animals, but there are a lot fewer of us.) The source may be an open body of water, or it may be moist soil, in which case the process that gets the water vapor into the air is evaporation.

    However, it is not guaranteed that there will always be a handy source of water, or that whatever processes are moving water into the air are operating as quickly as the temperature may be rising. If not, then the relative humidity will fall, because the the equilibrum vapor pressure is a function of temperature. That’s the process Ray is talking about.

    So, no–the proposition that “If warm air is moist then warm air is moist — period” is false.

    Now consider the case where there is a packet of air with a suitable moisture source. If the air warms, its EVP increases and so–speaking anthropomorphically–does its appetite for water vapor. In this situation, the warmer air will end up holding more water vapor than would cooler air.

    In schematic simplified math:

    relative humidity = temperature * water content

    (You can get the real math in the link above.)

    *Yeah, relativity, yadda yadda. Let’s ‘KISS.’

  34. 84
    nigelj says:

    Victor, I suggest google Boyles gas laws then you will learn something, and wont make a fool of yourself quite so often and KM wont have to waste his time explaining things :)

  35. 85
    Ray Ladbury says:

    Oh, Weaktor, Weaktor, Weaktor,
    Dude, wouldn’t it be simpler to just take a class in climatology so you wouldn’t embarrass yourself all the fricking time?

    If you look at prevailing climates around the world, some are dry and some tend to have humid air most of the time. Conditions fluctuate, but the relative conditions and relative humidity prevail. In a warming climate, humid air takes up more water vapor, because warm air can hold more water. The warm air may rise from a coastal area over a range of mountains where it cools, dumps the water, leaving a “rain shadow” of very dry air on the leeward side of the mountains. If the air starts with more water, it dumps more rain, and the air is still warmer on the leeward side. Since it could hold more water, it is relatively drier.

    So dry gets drier, wet gets wetter. It’s about relative humidity.

  36. 86
    Western Hiker says:

    Kevin McKinney, 83

    Good comment!…..
    “However, it is not guaranteed that there will always be a handy source of water, or that whatever processes are moving water into the air are operating as quickly as the temperature may be rising. If not, then the relative humidity will fall, because the equilibrum vapor pressure is a function of temperature.”

    I dug around and found this:

    “In recent decades, the land surface has warmed substantially more than the ocean surface, and relative humidity has fallen over land. Amplified warming and declining relative humidity over land are also dominant features of future climate projections, with implications for climate-change impacts.”

    https://tinyurl.com/y5dfg9xe

  37. 87
    Victor says:

    83
    Kevin McKinney says:

    #74, Victor–”If warmer air gets saturated with more moisture, then how does it “become relatively drier when there is no moisture to add”? What “moisture to add” are you talking about? If warm air is moist then warm air is moist — period.”

    KM: Uh, you have heard of the Law of Conservation of Matter*, right? It says, inter alia, that a packet of air that holds ‘x’ moles of water, if it is to grow moister, must acquire that water from *somewhere.* The water can’t just spontaneously appear from nowhere, and it can’t be teleported in from a distance.

    V: I was responding to the claim, not the science. The claim is that warm air holds more moisture, thus making more rainfall likely. However: The claim is ALSO that warm air causes the atmosphere to be drier, thus making droughts and forest fires more likely. I don’t understand how both claims can be valid. If warm air must acquire moisture from *somewhere* then the moisture is clearly NOT produced by the warm air, but from the “somewhere.” And if warm air promotes dryness that can only be due to the lack of moisture to be drawn from that same “somewhere.”

    Once again, I am not posing an argument. I am simply wondering how warm air in itself can promote both increased rainfall AND increased dryness.

  38. 88
    nigelj says:

    Victor @87,

    “The claim is that warm air holds more moisture, thus making more rainfall likely. However: The claim is ALSO that warm air causes the atmosphere to be drier, thus making droughts and forest fires more likely. (apparent contradiction)”

    I don’t think anyone is claiming warm air makes the atmosphere drier. In fact global warming increases absolute humidity because of evaporation, so essentially makes the atmosphere wetter.

    I think you might be confusing it all with the fact that a warming atmosphere makes vegetation drier and more prone to burning, and can change weather patterns that lead in turn to more droughts and higher temperatures can dry out the land.

    And global warming increases atmospheric moisture so causes more intense rainfall events as well. This is not inconsistent with more droughts because its at different times and places.

  39. 89
    MA Rodger says:

    It could be the Troll has discovered a new tactic – act like an imbecile asking questions. “Why’s that then?” which elicits a helpful answer resulting in “Why’s that then?” ad nauseam.
    Mind it shouldn’t be the easiest position to adopt with any sincerity if like the Troll you’ve been saying for years that you have been blessed with superior critical thinking, except we have always known he is deluded on that score.

    Victor the Troll,
    Roll this ‘moisture in warmer air’ back to where it started and before you started making ridiculous inferences about what was said. It kicked off up-thread @58 when Ray Ladbury asked you:-

    Why would you not expect more intense precipitation events when warmer air gets saturated with more moisture–and why would you not expect warmer air to become relatively drier when there is no moisture to add?

    Obviously this was too complicated for you in your new imbecile mode. So let us translate this for you into an easily understood analogy.

    Why would you not expect ‘bigger spillages’ when ‘ a bigger beer glass gets full of beer’–and why would you not expect ‘bigger and deeper beer glasses’ to become relatively ‘less spillable’ when there is no ‘beer left in the keg’ to ‘keep the glass topped up’?

  40. 90
    William B Jackson says:

    #87 If you read your own post with perhaps even a tiny bit of at least attempting to understand, rather than trying to come up with an argument. You would see the answer to your question. Do try to keep up!

  41. 91
    jb says:

    Victor at 87,
    I think the idea is that in dry regions (mostly inland), warmer air is more effective at pulling water out of the soil – and, because it has a higher carrying capacity for water, is less likely to rain that moisture back out.

  42. 92

    V 87: I am simply wondering how warm air in itself can promote both increased rainfall AND increased dryness.

    BPL: Global warming, under the present continental configuration, moves the rain. Continental interiors dry out, coastlines get soaked. The contrast between dry areas and wet areas increases as the temperature rises.

  43. 93
    Susan Anderson says:

    @Killian – Despite your insistence, none of my comments until this most recent were addressed to you or about you. Your hostility does nobody any favors; I recommend getting a life instead of picking endless fights with people you don’t know based on misrepresentations, in extended monologues. Hatred is a distorting destructive toxin.

    I read the Jahren books, and your eagerness to misrepresent her is only exceeded by your insistence that I’ve been bullying you. I promise I will not respond to any further comments from you, and you may assume that anything further I say is not about you.

    @bpl
    Sorry, I should have stuck to plain English instead of trying to be cute. I meant to apologize for dragging the conversation away from the subject of the RealClimate post and creating a distracting nonsense. I am a silly person.

  44. 94

    #87, Victor–

    Once again, I am not posing an argument. I am simply wondering how warm air in itself can promote both increased rainfall AND increased dryness.

    And I was simply trying to answer your question. It may seem radical, but you could try reading the answer for comprehension.

    However, and with my emphasis–

    The claim is that warm air holds more moisture, thus making more rainfall likely. However: The claim is ALSO that warm air causes the atmosphere to be drier, thus making droughts and forest fires more likely. I don’t understand how both claims can be valid. If warm air must acquire moisture from *somewhere* then the moisture is clearly NOT produced by the warm air, but from the “somewhere.”

    You’re confusing different things. Yes, warmer air *holds* more moisture. No, it doesn’t *produce* that moisture by itself ex nihilo. But now I’m repeating what I said in the first place.

    Another confusion is embedded in this sentence: “The claim is ALSO that warm air causes the atmosphere to be drier…”

    “Drier” is the confusing word, because it doesn’t differentiate between types of humidity. If you are considering “absolute humidity” then in principle the statement is false, because absolute humidity is not directly dependent on temperature (see link below for more). But if you are talking about *relative* humidity, then the statement is true, because as temperature rises RH will decline if AH remains constant. This is why clothes generally dry faster outside as the day goes on.

    And that’s the operative point here. As RH rises with warmer temperatures, the evaporation rate (from open water or soil) will tend to rise, too. Thus, soils will dry faster, or tend to, at least, in warmer conditions.

    An analogy: Imagine you have just come from swimming or showering, and you wish to dry yourself. You can dry yourself with a fluffy cotton towel (warm air), or a woven plastic tarp (cold air). Obviously, you pick the former because you know it will absorb and hold the water on your skin, whereas the latter basically won’t. Yet you *also* know that when you are done, the towel will be wetter than would the tarp. Its ‘thirst’ dries *you* even as it becomes moist itself.

    Everyday example: consider the action of a hot-air dryer, which operates precisely by artificially warming the air it passes over your hands.

    Link for ‘types of humidity’:

    https://en.wikipedia.org/wiki/Humidity#Types

  45. 95
    MartinJB says:

    Victor, you need to distinguish between absolute and relative humidity. Absolute humidity increases because warmer air holds more water. However, relative humidity declines. Combine lower relative humidity and warmer air and you get higher vapor pressure demand. Think of this as how much moisture the air wants to suck out of the ground and plants.

  46. 96
    Victor says:

    nigelj: I think you might be confusing it all with the fact that a warming atmosphere makes vegetation drier and more prone to burning, and can change weather patterns that lead in turn to more droughts and higher temperatures can dry out the land.

    V: No. A drier atmosphere makes vegetation drier. If a warming atmosphere made vegetation drier then all those tropical rainforests would be deserts.

    n: And global warming increases atmospheric moisture so causes more intense rainfall events as well. This is not inconsistent with more droughts because its at different times and places.

    V: I get the first sentence. But the second sentence eludes me, sorry. Droughts occur at times and places where moisture is scarce. Duh. Sorry but I fail to get the connection with higher temperatures, which, as you say “increase atmospheric moisture.” And sure, moisture levels are different at “different times and places,” but what does that have to do with temperature?

    MAR: Why would you not expect ‘bigger spillages’ when ‘ a bigger beer glass gets full of beer’–and why would you not expect ‘bigger and deeper beer glasses’ to become relatively ‘less spillable’ when there is no ‘beer left in the keg’ to ‘keep the glass topped up’?

    V: My oh my, Mr. Rodger, that’s one for the books. Possibly the silliest analogy I’ve ever seen. But oh yes, I do get it: an atmosphere full of moisture is more likely to spill over into rainfall. And one with all the moisture drained out of it is unable to spill over into rainfall — because there ain’t any moisture left, dummy.

    Only problem: this tells us NOTHING about temperature. So thanks for nothing, maestro. I’m still confused.

  47. 97

    @86:

    I dug around and found this:

    “In recent decades, the land surface has warmed substantially more than the ocean surface, and relative humidity has fallen over land. Amplified warming and declining relative humidity over land are also dominant features of future climate projections, with implications for climate-change impacts.”

    Good find.

    Note that the opposite is also probably true:  if we slashed GHG levels, the oceans would cool by evaporation and likely lead to more precipitation on the cooler land masses.

    Which brings me around to the topic of the effect of eliminating all of the atmosphere except water.  This would not lead to an increase in net greenhouse effect, because the humidity over bodies of water is roughly at saturation anyway (partial pressure equal to vapor pressure).  Quite the contrary; eliminating all the CO2, CH4, N2O etc. would open up many radiation windows to space, leading to the polar ice caps re-freezing in short order and the atmospheric pressure dropping further.  The ice caps (and new ice sheets where condensation fell on colder land masses) would then grow fairly rapidly until the entire Earth was an iceball with an albedo of roughly 0.9 and running well below freezing even at the equator.

  48. 98
    William B Jackson says:

    #96 Victor, Victor, Victor…… you are confused because you refuse to understand. SAD!

  49. 99
    Victor says:

    Thank you, JB, Kevin and Martin for (finally) providing what sounds like a sensible scientific explanation for the problem I posed. I’m not completely satisfied, however, because:

    1. it’s hard to see how such a small increase in global temperatures (1 degree celsius) could have such a dramatic effect on not only rainfall but also droughts and forest fires.

    2. given the reasoning you’ve provided wouldn’t we expect to see more extreme effects in regions that are normally warmer than others (such as the tropics) and less extreme effects elsewhere, regardless of the global average? Is that the case?

  50. 100

    I’ve sat back and listened to all this absolute rubbish. You think science is about guessing how things work.? Look at some raw data for a change, this isn’t philospophy! Tell me how this fits in with ANYTHING ANY OF YOU have said
    http://www.bom.gov.au/climate/change/#tabs=Tracker&tracker=trend-maps&tQ=map%3Drain%26area%3Daus%26season%3D0112%26period%3D1900

    The majority of Australia has had a slight to noticeable increase in rainfall over the last 120 years. But the key is that it is no more common in wet or dry areas. Conversely the areas of decreased rainfall are again not typically wetter or dryer areas.

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