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Forecast: Permanently Hotter Summers in 20-60 years

Posted on 13 June 2011 by oslo

Guest post by Donna Hesterman

The tropics and much of the Northern Hemisphere are likely to experience an irreversible rise in summer temperatures within the next 20 to 60 years if atmospheric greenhouse gas concentrations continue to increase, according to a new climate study by Stanford University scientists. The results will be published later this month in the journal Climatic Change Letters.

Noah Diffenbaugh, center fellow at the Woods Institute for the Environment

Credit: L.A. Cicero, Stanford News Service

In the study, the Stanford team concluded that many tropical regions in Africa, Asia and South America could see "the permanent emergence of unprecedented summer heat" in the next two decades. Middle latitudes of Europe, China and North America - including the United States - are likely to undergo extreme summer temperature shifts within 60 years, the researchers found.

"According to our projections, large areas of the globe are likely to warm up so quickly that, by the middle of this century, even the coolest summers will be hotter than the hottest summers of the past 50 years," said the study's lead author, Noah Diffenbaugh, an assistant professor of environmental Earth system science and fellow at the Woods Institute for the Environment at Stanford. The study is co-authored by Stanford research assistant Martin Scherer.

"When scientists talk about global warming causing more heat waves, people often ask if that means that the hottest temperatures will become 'the new normal,'" Diffenbaugh said. "That got us thinking - at what point can we expect the coolest seasonal temperatures to always be hotter than the historically highest temperatures for that season?"

Climate models, past and future

To determine the seasonal impact of global warming in coming decades, Diffenbaugh and Scherer analyzed more than 50 climate model experiments -including computer simulations of the 21st century when global greenhouse gas concentrations are expected to increase, and simulations of the 20th century that accurately "predicted" the Earth's climate during the last 50 years. The analysis revealed that many parts of the planet could experience a permanent spike in seasonal temperatures within 60 years.

"We also analyzed historical data from weather stations around the world to see if the projected emergence of unprecedented heat had already begun," Diffenbaugh said. "It turns out that when we look back in time using temperature records, we find that this extreme heat emergence is occurring now, and that climate models represent the historical patterns remarkably well."

According to both the climate model analysis and the historical weather data, the tropics are heating up the fastest. "We find that the most immediate increase in extreme seasonal heat occurs in the tropics, with up to 70 percent of seasons in the early 21st century (2010-2039) exceeding the late-20th century maximum," the authors wrote.
Tropical regions may see the most dramatic changes first, but wide swaths of North America, China and Mediterranean Europe are also likely to enter into a new heat regime by 2070, according to the study.

Large areas of the globe are likely to warm up so quickly that by mid-century the coolest summers will be hotter than the hottest summers of the past 50 years, according to a study co-authored by Center Fellow Noah Diffenbaugh.
Credit: Mark Shwartz

Environmental impact

This dramatic shift in seasonal temperatures could have severe consequences for human health, agricultural production and ecosystem productivity, Diffenbaugh said. As an example, he pointed to record heat waves in Europe in 2003 that killed 40,000 people. He also cited studies showing that projected increases in summer temperatures in the Midwestern United States could reduce the harvest of staples, such as corn and soybeans, by more than 30 percent.

Diffenbaugh was surprised to see how quickly the new, potentially destructive heat regimes are likely to emerge, given that the study was based on a relatively moderate forecast of greenhouse gas emissions in the 21st century.

"The fact that we're already seeing these changes in historical weather observations, and that they match climate model simulations so closely, increases our confidence that our projections of permanent escalations in seasonal temperatures within the next few decades are well founded," Diffenbaugh said.

The research was supported by the National Science Foundation, the Department of Energy, the National Institutes of Health and the World Bank.

Donna Hesterman is a science-writer intern at the Woods Institute for the Environment.

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Comments 1 to 50 out of 51:

  1. According to both the climate model analysis and the historical weather data, the tropics are heating up the fastest.

    This is for summer temperatures, right? I'd thought that overall the poles were going to be warming faster. So we should see the poles warming faster on the whole, but summer temperatures climbing faster in the tropics, correct?
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  2. If it has not already done so, I recommend that SkS inform both Diffenbaugh and Scherer that this article has been posted and invite them to participate in this discussion.
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  3. I have notified Stanford that the article is now online, and I have invited them to participate with comments. I can't promise anything as I have not been in direct contact with Diffenbaugh or Scherer.
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  4. I would like to understand which models they are using that show such good correlation with empirical data - this is always a point of contention amongst skeptics, that models are not accurate.

    Which models did this team rely on and how good was the fit?
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  5. I have been informed by Stanford (to be precise, Woods Institute for the Environment) that the full report is available online at

    Comments made so far can perhaps be revised after reading the full online article.
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  6. Oslo @5, that link only takes me to a reproduction of the first page of the article, ie, the abstract plus one paragraph. Registering with Springer-link seems to make no difference. However, from publicly accessible material:

    actually thoughtful @4, Diffenbaugh and Scherer used the CMIP3 climate model, and reproduce information from that model in their figures. They may also have used other models. In the graphs linked below they show the modelled (black) and observed (black dashed) probability density function for differences between mean and maximum temperatures in the 1980-1999 period, which should give some idea of empirical fit.

    WheelsOC @1, from the graphs of the probability density function of regional areas, it is evident that there is far more variability in temperature in mid latitude regions (China, North America, Mediterranian, Southern Africa) than there is in tropical regions (India, S E Asia, Northern South America, Central Africa). This is true in both JJA and DJF. The greater range in temperatures means a greater warming is required before the minimum temperatures consistently exceed the maximum temperatures. Consequently this study is probably consistent with previous studies showing greater mean warming outside the tropics.  
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  7. I was able to download the pdf file, thanks for the link. Having suffered and survived (just) record extreme heat during 2009 IMO more attention to extremes is very useful. It's the extremes that get you more than the mean.

    Home air conditioners often don't work in extreme heat. People don't work either, especially when it's humid as well and your internal body temperature rises too high and you've no way of sweating it out. That's leaving aside the effect on crops, rainfall or lack of, power supplies that give up the ghost along with public transport etc - all of which has happened already in my home state during the heat waves of a couple of years ago.

    (Under Fig 1 there seems to be a typo - 20th Century when I think they mean 21st Century - if it's not too late to correct.)
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  8. They compare heat to a 1981-1999 baseline. If they compared to say 1900-1920 it might have already shifted into a new regime. In their conclusions they say:

    "actual GHG emissions over the early 21st century have exceeded those projected in the SRES scenario used here (Raupach et al. 2007), suggesting that our results could provide a conservative projection of the timing of permanent emergence of an unprecedented heat regime"
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  9. As an example, he pointed to record heat waves in Europe in 2003 that killed 40,000 people.

    Please take a look - what really happened in 2003 and 2006 - when - especially in Europe - have been heat waves. Global and regional temperatures, SOI, were significantly lower than in the years, "neighbors " - especially in the SH was cold. We had a La Nina with rapid beginning. In Europe, hot summers 2003 and 2006 were preceded by a very cold winter ...
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  10. What are the latest findings about how the enhanced greenhouse effect is impacting the frequency and duration of the La Nina and El Nino events?
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  11. Arkadiusz - I'm not sure what you're pointing to.

    You're not contesting that those heatwaves were exceptional or that a lot of people died I presume.

    So, are you saying that cooler temperatures elsewhere somehow 'offset' exceptional heat in particular places ... or ... what?
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  12. Adelady @11,

    Good points. The person in question is trying to argue a strawman, and move the argument from where we are heading. Their argument is also incoherent. They do not demonstrate using the scientific literature that ENSO/SOI teleconnects with summer temperatures over Europe. But their argument is moot, because contrary to their claim, ENSO conditions were in fact neutral during and in the months leading up to the European heat wave; there was a moderate El Nino in late 2002 (peaked just before Christmas), but it terminated in early 2003.

    Also, we should be urging the poster @9 to please read the paper by Stott et al. (2004). What we do know about that 2003 heat wave is this, an attribution study by Stott et al. (2004) found that:

    "Here we use this conceptual framework to estimate the contribution of human-induced increases in atmospheric concentrations of greenhouse gases and other pollutants to the risk of the occurrence of unusually high mean summer temperatures throughout a large region of continental Europe. Using a threshold for mean summer temperature that was exceeded in 2003, but in no other year since the start of the instrumental record in 1851, we estimate it is very likely (confidence level >90%) that human influence has at least doubled the risk of a heatwave exceeding this threshold magnitude".

    The contrarians continue to try and derail and muddy the discussion, float red herrings and make strawman arguments......don't be fooled folks.
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  13. While not disputing the thesis that summers toward the end of century could be warmer in the coldest years than the warmest summers in recent times, I cringe when I see phrases like "Permanently Hotter Summers" or "an irreversible rise in summer temperatures". Nothing in climate is permanent. Such language is sloppy and opens climate scientists up to unnecessary attacks by deniers. How about "persistent" instead? "Persistently hotter summers for centuries or longer", for instance. Just my two cents.
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  14. Tamino has an excellent comment on the paper:
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  15. Robert,
    It is currently accepted in the climate literature that any concequences that last more than 200 years can be considered permanent. They are permanent for people currently living, and our children and grandchildren. Everyone knows that in 500,000 years the Earth will be able to heal itself- except for those things that go extinct. Constantly bringing that up is catering to the deniers. They play on "not permanent" to make people think it will change in a few years. Changes that cannot be unwound in the lifetimes of those currently living are permanent.
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  16. Of course it will be hotter in 20 years- the multidecadal oscillation will kick in. Its going to get colder for 20 years just like in 1930-70 period (then they thought we heading for an ice age).
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    [DB] Both of these claims have been thoroughly researched and debunked.  Any interested parties should go to:

    It's a natural cycle

    Did scientists predict an impending ice age in the 1970s?

  17. cloa513 wrote : "Its going to get colder for 20 years just like in 1930-70 period (then they thought we heading for an ice age)."

    Four questions :

    1) When do you believe it is going to start getting colder ? Please discuss this further here.

    2) What scientific evidence do you base that on ? Please discuss further as above.

    3) Which 20 years in the (40 year) 1930-70 period are you referring to ? Please discuss further as above.

    4) Who do you think "thought we heading for an ice age" ? Please discuss his point further here.
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  18. I will help out here. Much of the focus related to "cooling" in the next 20 years comes from presentations like Latif and Easterbrook with regards to the multidecadal oscillation.

    While the long term trend will remain positive, the oscillation (as some claim) has resulted in two periods of overshooting the trend (1930s and 1990s). The "cooling" or "lack of warming," as other have referred to it, would bring us back down to the long term trend (probably undershoot like 40 years ago).

    Anothers similar forecast:

    A comparison between decadal oscillation (Orssengo) and exponential rise (Broberg) shows that either model has a correlation of 0.89 depending on the coefficients:

    We have a million years of data showing that we will eventually enter another ice age. Unless something drastic occurs that alters that cycle.
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    [DB] We can also choose to believe the physics of greenhouse gases, which tell us (all other forcings remaining unchanged) that if we keep CO2 concentrations above 350 PPM we will never have another ice age again.

    "At the end of the last snowball Earth, the sun's brightness was within 6% of its present value.  There will never be another snowball Earth, because the sun continues to get hotter.  In fact, with humans on the planet, there will never be another ice age."

    ~James Hansen, Storms Of My Grandchildren, p. 229.

  19. Eric the Red "We have a million years of data showing that we will eventually enter another ice age. Unless something drastic occurs that alters that cycle.

    If we look at everybody's favourite animation, the Time History of CO2, we notice something. The only time ice ages have done their thing effectively is when CO2 concentrations have been below 200ppm. Unless we do some compensatory drastic thing, CO2 concentration won't be anywhere nearly low enough by the time the Milankovitch cycle should be kicking in for an ice age.

    And have a look at this item.
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  20. adelady,
    CO2 concentrations do not fall before 200 ppm until the height of the ice age, when temperatures are lowest. According to the ice core data, the temperature (and CO2 concentrations) fall slowly until reaching their minimum, then rise rapidly into the interglacial.
    It is entirely possible that increasing CO2 levels will prevent the Milankovitch cycle from kicking in a new ice age. That would depend upon which is the greater forcing.
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  21. adelady @19, studies of CO2 levels over the last 500 million years show a CO2 threshold of 1000 ppm, above which ice ages do not occur. Because the sun has been warming in the long term, that threshold has probably declined (and is inexact), but is certainly not below 300 ppm. There is some argument that it is now around 400-500 ppm, but that is not a consensus opinion.

    Following your link, 300 G tonne release represents anthropogenic emissions to date. 1000 G tonnes release represents the budget for a 450 ppm stabilisation (from memory).
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  22. Tom Curtis at 02:15 AM on 15 June, 2011

    You may know of this paper which supports the interpretation that under conditions with a solar constant not that different to the present, that the thresholds for Antarctic glaciation is around 750 ppm and for Greenland is of the order of 280 ppm.

    Since these values correspond to thresholds for the onset of the respective polar icesheets, there is presumably signficant hysteresis for the loss of polar ice under warming conditions (due to offsetting albedo effects). However I think the evidence supports the conclusion that we are already near the CO2 threshold where the Greenland ice sheet is committed to disappear. Haven't looked at data that bears further on this from last couple of years.

    (I might point out that adelady and I think Eric were referring to the [CO2] threshold which, coupled with appropriate period in the Milankovitch cycles, would be required for descent from the current interglacial to glacial period).
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  23. Eric the Red at 23:50 PM on 14 June, 2011

    "Much of the focus related to "cooling" in the next 20 years comes from presentations like Latif and Easterbrook with regards to the multidecadal oscillation."
    Eric, Latif certainly doesn't think the Earth is going to "cool" in the next 20 years. His simulations, taking account of ocean circulation changs that (he thinks) will put a slight break on warming for a decade or so (2005-2015ish), indicates a rather rapid subsequent warming such that by 2030 he consiers we'll be a further 0.4-0.5 oC (globally averaged) warmer.

    see e.g. Figure 4 of Latif's recent paper on global warming forecast here.
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  24. Chris @23,

    To add to you post. Last November RealClimate had a look at how Keenlyside et al's forecast panned out...the short story is that is has not.


    I really would like to put the whole Mojib Latif debacle that has been doing the rounds for a couple of years now to rest (thanks to the efforts of some misguided journalists and the denialist spin machine, including Lindzen), and it is annoying to see that to this day 'skeptics' are still touting it, even in the face of reality.

    Anyhow, I am not sure why we are focussing on this when the post is about future warming and preponderance of extreme heat.
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  25. Albatross at 03:15 AM on 15 June, 2011

    Yes fair enough Albatross. There are two relevant points though:

    1) Eric was citing Latif as an indication of "cooling" in the next 20 years. So it's worth pointing out that Latif doesn't predict that at all. He predicts a large warming by the decade centered around 1930.

    2) There is uncertainty about the extent to which "natural variability" is suppressing current warming a little. The evidence (including Latif's) suggests that ocean circulation variabilty might be suppressing surface temperatures a tad. We know that the extended solar minimum will also be countering greenhouse warming a little (we expect the drop of solar output from the max to min of the solar cycle to pretty much counter greenhouse-induced warming, although natural variability masks this somewhat).

    The point is that despite any current short term slowdown in warming, Latif (and pretty much all physics-based projections) indicate that the Earth will be quite a bit warmer by 1930. That's relevant to the subject of this thread.
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  26. Hi Chris,

    Re your #25. Sorry if I was not clear-- my dig was at Eric, not you-- I very much appreciate you clarifying the Keenlyside et al. issue :)

    I concur with you that the Earth will be quite a bit warmer by 2030.
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  27. Chris,
    That is why I quoted both "cooling" and "lack of warming."
    Figure 4 to which you referenced was an older graph. His most recent presentation in Geneva, 2009 shows three decades of cooling or a lack of warming until 2030, then continued warming. It looks more like Latif predicts the warming to start around 1930, rather than centered around it, leaving about two more decades of a "lack of warming."

    ( -Link to disinformation site snipped- )

    If the decadal oscillation results in insignificant warming, then the Earth will be a lot warmer by 2030. If the predictions hold true, as predicted by Latf, et. al., then temperatures will be similar (or cooler) in 2030 to 2010.

    I have no problem with you taking a dig at me, but at least get the data correct.
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    [DB] Link to disinformation site snipped.  Advice: In the spirit of getting things correct, stick to reputable sources.

  28. 27, Eric the Red,

    Your disinformation is, once again, clear evidence of denial. The entire Latif-says-the-globe-will-cool meme has been done to death. It's ancient history... and you are representing a serious falsehood in all of your statements about his position.

    His words:
    “I don’t know what to do. They just make these things up.”
    Read more here.

    And stop spreading lies.

    [The easiest way to start is to stop getting your misinformation from WUWT.]
    ...but at least get the data correct.
    Hmmmph. Yeah, the data, and the interpretation, and who says what, and all the rest. Physician, deny thyself!
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  29. 27, Eric the Red,

    For emphasis, let me repeat 3 main points about Latif and Keenlyside:
    • The work of Dr. Latif and Dr. Keenlyside in Nature “does not allow one to make any inferences about anthropogenic global warming.” (Latif's own words).
    • Their work has no forecasting skill after 2015. “We don’t trust our forecast beyond 2015.” (Latif's own words).
    • Dr. Latif is not making any predictions about what will happen after 2015 other than that the long-term temperature warming trend driven by anthropogenic GHGs will continue and that the near-term temperature trend must catch up with the long-term trend, likely during a period of rapid warming.

    Please note that last point. Dr. Latif's logic is that any oscillation is not warming or cooling the planet. It is merely moderating the observed result. A period of "non-warming" is a period of "delayed-warming." The end result is still the same. There is just internal variability that masks the actual year-by-year results.

    Terming this as either "cooling" or "lack of warming" are both inaccurate. At best, you might describe it as "delayed warming" or "hidden warming."

    In any event, it is a complete non-issue, and not worth the time that has already been spent on it (except with respect to the fact that any such periods of delayed warming are a very useful weapon in the arsenal of those who wish to nearly deny anthropogenic climate change).
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  30. Sphaerica @28,

    Sigh-- I agree with your coments about the post @27. Eric @27 directs us to slide 3 of Latif's 2009 WCC3 talk and neglects to mention that the figure in question is not in fact an official prediction, it is essentially fictitious, a cartoon. Dr. Latif presented that slide, which depicted a hypothetical temperature trace in which random internal climate variability was superimposed on a monotonic increasing
    temperature curve. When speaking to this slide/cartoon Dr. Latif said:

    "It may well happen that we enter a decade, or maybe even two-you know- when the temperature cools, alright- relevant to the present level, alright, and then, I know what is going to happen I will get millions of phone calls you know saying "what is going on, so is global warming disappearing". You know. Have you lied on us". You know, so, and therefore this is to me why we need to tackle this decadal variability prediction issue".

    Had the 'skeptics' here actually taken the time to listen to Latif's talk he would have known that. And again, so far the Keenlyside forecast has been a bust.

    I request that the moderators please consider snipping that piece of blatant misinformation (the link to wcc3 and associated text) @27-- I'm sure that SkS does not wish to assist in the distribution of confusion and misinformation. And while we fiddle Rome prepares to burn.
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  31. Let me get this straight Sphaerica. It may well be that the temperature is lower in 2030 than 2010, but it is not appropriate to call it cooling, or lack of warming, but delayed warming or hidden warming is okay? Talk about nitpicking.
    It certainly appears that any presentation that does not exemplify your own beliefs, you label as "misinformation." Oscillation only "masks" the warming when it is in the cooling phase. During the warming phase, it is enhancing the warming. One cannot accept the premise of decadal oscillation resulting in cooling without also accepting its role in warming.
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  32. 31, Eric The Red,

    You grossly misrepresented Latif and Keenlyside's work, you were wrong, and it represents a huge mistake on your part.

    Admit it, and move on.

    Trying to argue your position is evidence of nothing but total and complete denial on your part, and nothing more.
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  33. chris @22, I think the question of whether the Greenland ice sheet can survive at current CO2 levels and insolation and whether at current CO2 levels changes in insolation due to the Milankovitch cycles could trigger an ice age are distinct. Although NH insolation is approaching its minimum for the current cycle, it can be reduced to much lower levels (and will in the next cycle), so that even with current CO2 levels a glaciation may still be triggered.

    With regard to the Greenland Ice sheet, significant parts of the ice sheet survived the Eemian interglacial. Given that, it is certainly possible that significant parts of the ice sheet would survive if CO2 levels were maintained at 400 ppm, at least for the next few thousand years. That is still consistent with a very substantive melt of the GIS and the West Antarctic Ice Sheet leading to sea level rises of the order of 8 meters over the coming centuries.
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  34. Sphaerica,

    Prof. Latif stands by his statements and predictions, and that we should not open the champaign until we see whose projections better match the climate observations.

    I will not admit a mistake, as I have not misrepresented his predictions. However, I will move on.

    Interesting is the timing of this discussion about Latif's work concerning the potential for unpredictable external influences and the recent press release concerning the potential for a another solar minimum.
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  35. 34, Eric the Red,
    Prof. Latif stands by his statements and predictions, and that we should not open the champaign until...
    Citation, please. Evidence. I have seen nothing except frustration from Dr. Latif at how deniers misrepresent his statements and work, so you have to come through on supporting this, or else this is a particularly egregious and unforgivable inaccuracy on your part.
    ...the potential for unpredictable external influences and the recent press release concerning the potential for a another solar minimum.
    Citations please. Evidence. And I don't care about press releases, I care about scientific studies. A vague insinuation based on an anonymous press release is meaningless (and desperate).

    [And what do you think happens if we do have a solar minimum, temps rise but not as much, so we foolishly burn even more CO2 because people like you think everything looks just wonderful... and then the solar minimum ends? And when we finally cut back, the negative aerosol feedback ends? What exactly are you arguing for? Hesitate and be fooled into allowing an ultimate 6˚C temperature rise?]
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  36. Eric @34,

    As I demonstrated @30, you misrepresented his talk at WCC3.

    Anyways, can we please (pretty please) get back on topic.
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  37. Sphaerica,

    I have not been able to link to the audio directly, but you can access both the powerpoint presentation and accompanying audio here:

    Do you really believe that temps will rise in a true solar minimum? IF that is the case, then we can once and for all eliminate solar activity from the climate forcings. The same can be said for decadal oscillations.
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  38. 37, Eric the Red,

    My goodness, did you even read the link you sent? It completely destroys your position.

    Apparently I have to be more specific with you. Please provide an exact quote, by Dr. Latif, which supports your claims about his position on the matter.

    If you can't, just drop it. It's OT. Actually, even if you can, just drop it, it's OT.

    And this isn't the place to discuss the fact that solar activity as long since been eliminated as a factor in recent warming, or the silly and unscientific approach of clinging to magical decadal oscillations as some sort of reason to ignore CO2 levels.

    As Albatross said, time to get back on topic.

    If you want to keep posting about Latif, you can do so here, but don't expect me to join you. Your position is absurd to the nth degree and rebutting such complete nonsense holds no interest to me.
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  39. If you are unwilling to listen to his presentation, then fine. That is your loss.

    Also, if you are so willing to dismiss every other climate forcing and cling to the "its only CO2" argument that influences the climate, then why do you even bother posting?

    Since his presentation is a direct challenge to the above statement that "simulations have accurately predicted the Earth climate during the past 50 years," which is so blatantly false, I would consider it quite relevant. Not to mention the questionable statement that, "the tropical regions may see the most dramatic changes first."

    In the U.S., summers may be hotter than the most recent 50, but will they be hotter than the hottest summers of 75 years ago?
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    [DB] Please see  Also, please try to keep the tone more civil.  As others have pointed out, Latif himself is on record as saying he was misrepresented.  But that entire episode is off-topic here.  If you wish to pursue it, then do so at the link Sphaerica provided.

  40. To get back on topic, Tamino has a very interesting discussion on the Diffenbaugh research, and explains why the departures from hitherto natural variability is expected to occur in the tropics first. Recommended reading for all interested in this post.

    Note: And Eric, IIRC no-one here, and certainly not the science cited in the IPCC reports is dismissing "every other climate forcing". You are tearing down a strawman that you have created...well done, and please reply to this on an appropriate thread.
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  41. Deep solar minimuam and continued temperature rise = solar activity is less important in climate issues. Nobody in their right mind would eliminate it entirely from the list of climate forcings. That would be foolish and naive, and is not what climate science is all about.

    Dreams of oscillations in the climate of the past 100 years, created using an eyecrometer on the wiggles in the rising temperature curve inevitably have a bad ending - they are, as Tamino observes, mathturbation. Each wiggle has it's own cause - aerosols in the 1960s, deep solar minima now and early in the 20th century for example, and the sume effect on the temperature curve is to make some think of an oscillation that isn't really there. Seeing as the background continues to rise steadily, summers and winters will be much hotter soon enough, and no fantasy oscillation will help the cause.
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  42. Exactly Sky,
    If we experience a deep solar minimum, then the influence of solar activity can be put to rest. Since solar activity increased for much of the last century, its influences has not been satisfactorily dismissed.
    I am not sure why you are so quick to dispute decadal oscillations though. Especially since paragraph one indicates that solar influences are minimal, but paragraph two says that a deep solar minimum is significant.
    Yes, the background continues to rise. But the rise is very bumpy, and if we can identify the bumps (at least the larger ones), then we can more accurate make forecasts.
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  43. "According to both the climate model analysis and the historical weather data, the tropics are heating up the fastest. "We find that the most immediate increase in extreme seasonal heat occurs in the tropics..."

    The finding that the tropics are warming up the fastest seems to run counter to the fact that the polar regions are warming up faster than any region on the planet. It doesn't make much sense why the tropics would heat up faster than the mid-lattitudes. Does anyone have an explanation for this?
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  44. For those discussing the expected impact of a solar min on global temperature, please continue the discussion here ("What would happen if the sun fell to Maunder Minimum levels?").
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  45. Karaminski @43, see my final paragraph in 6 above.
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  46. Karamanski - Lower temperature ranges in the tropics (warm all year around) mean that any increase in average temperature will exceed the ranges faster than will happen at the poles.

    Arctic summer temperatures are somewhere around −10 to +10°C (20°C range). Fiji, on the other hand, has a temperature range of about 27 to 31°C (4°C range). So a 2°C rise in temperature in Fiji will make averages exceed current maxes, while it would take at least ~5°C for that to happen in the Arctic.

    The tropics don't heat as fast as the poles, but they don't have to for average temperatures to exceed all extremes. And tropical biota are much less adapted to temperature changes - this is going to be a serious stress on the tropical biosphere.
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  47. For consideration of what would happen if sun went into deep minimum, see Feulner and Rahmstorf 2010. Quick answer - by 2100, only a small temperature decrease compared to standard SRES scenarios.
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  48. 42, Eric the Red,

    You are taking an alchemists approach to climate science. You are treating all of the components as great mysteries of the aether and phlogiston, with the idea that if you can just tease out all of the variables -- not by understanding the mechanics through constructing simple, logical laws and then clearly predicting the impacts, but rather merely through observation, correlation and inference -- then you'll eventually have enough information to prove to yourself that the one variable that is derived from and defined by mechanistic understanding, and which has all along predicted observed events, is in fact the major and almost only cause of the trend.

    But in the meantime, do you counsel that we should wait and see (what, 30 years?), to be sure the PDO isn't some magical perpetual motion machine that is somehow adding energy to the system with no source to propel it?
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  49. No, I do not propose that. However, much research has shown (not proven) that the PDO has significant climate implications. If much of the recent warmer is attributable to decadal oscillations rather than climate feedbacks, then that needs to be incorporated into climate models.
    It is not the physics of climate science that is resulting in the greatest uncertainty, but rather the mathematically-modelled responses to the physics.
    I think you are deluded yourself if you think that testing mathematical models is alchemy. When did observation, correlation, and inference become extinct? The modern day term for model testing is called engineering.
    I know a new thread has started since I first brought up a potential grand minimum, but what if a combination of a negative PDO and solar minimum reduced global temperatures significantly more than modelled?
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  50. 49, Eric the Red,

    My understanding is that the PDO is an observed pattern within the climate system, not a forcing. Like ENSO, it does not and cannot possibly change climate, it merely affects observed global mean temperatures. PDO is not a forcing, but merely another factor (although with a vaguely repeating pattern) in observed global mean temperatures.

    Studying the PDO allows one to better predict weather, not climate.

    The net effect of the PDO over long time frames is zero.

    The PDO cannot, in and of itself, alter the climate of the planet in the way we are seeing. It may add noise to the observations, but nothing more.

    To hope that that noise is in fact the source of most or all of current warming, or even that it is exaggerating the warming that we do see, and that warming will now reverse itself is, I think, overly optimistic (and pretty much in simple denial of all of the other facts that are available).

    Beyond this, it doesn't matter all that much what one is seeing at any point in time, or how it is masked by the PDO or anything similar. The fact is that climate sensitivity studies point to a 3˚C increase per doubling, and the existence, non-existence, impact or non-impact of the PDO on observed temperatures is irrelevant. It won't change the end result.

    To your other point, observation, correlation, and inference have not become extinct, but could never exist with any value in a vacuum, by themselves. To put it another way, observation, correlation and inference without understanding and mechanics amount to nothing more than superstition. They are the incomplete precursor to science (begin speech by Theodoric, Medieval Barber of York here).

    The PDO is nothing more than a "good blood-letting."
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