Temperature Trends

New Study: During Past 2,000 Years Temperatures Trended Downward Until 1900


Nature Geoscience has published a remarkably interesting new article, "Continental-scale temperature variability during the past two millennia," by an international team of researchers using proxy temperature data from each continent. As LiveScience notes

.. the researchers drew up temperature curves for large regions at seven continents, using 511 local temperature records. These were based on the analysis of tree rings, pollen, corals, lake and marine sediments, ice cores and stalagmites as well as historical documents. In most cases the data used were highly resolved, attesting to short-term variations over decades or less, rather than smoothing over centuries. In Africa, there were too few records to accurately determine long-term temperature changes for that continent.

The researchers found that, while some areas and eras had been warmer than the 20th century, there has been an overall 2,000-year global cooling trend that was reversed around 1900. As the abstract reports:

Past global climate changes had strong regional expression. To elucidate their spatio-temporal pattern, we reconstructed past temperatures for seven continental-scale regions during the past one to two millennia. The most coherent feature in nearly all of the regional temperature reconstructions is a long-term cooling trend, which ended late in the nineteenth century. At multi-decadal to centennial scales, temperature variability shows distinctly different regional patterns, with more similarity within each hemisphere than between them. There were no globally synchronous multi-decadal warm or cold intervals that define a worldwide Medieval Warm Period or Little Ice Age, but all reconstructions show generally cold conditions between ad 1580 and 1880, punctuated in some regions by warm decades during the eighteenth century. The transition to these colder conditions occurred earlier in the Arctic, Europe and Asia than in North America or the Southern Hemisphere regions. Recent warming reversed the long-term cooling; during the period ad 1971–2000, the area-weighted average reconstructed temperature was higher than any other time in nearly 1,400 years.

The chart below from the study compares their data with temperature trend data from other researchers.

Temperature Trend data 1-2000 AD

LiveScience adds:

The most consistent feature across the regions over the last 2,000 years was a long-term cooling trend, which was likely caused by a combination of factors such as an overall increase in volcanic activity, a decrease in solar irradiance, changes in land cover, and slow changes in earth's orbit. This cooling only came to an end toward the end of the 19th century.

The warming during the last century has reversed this long-term cooling, the study found. It remained cold only in Antarctica. An analysis of the average temperatures over 30-year periods indicates that interval from 1971-2000 was probably warmer than any other 30-year period in the last 1,400 years.

Cooler 30-year periods between the years 830 and 1910 AD were particularly pronounced during weak solar activity and strong tropical volcanic eruptions. Both phenomena often occurred simultaneously and led to a drop in the average temperature during five distinct 30- to 90-year intervals between 1251 and 1820.

Warming in the 20th century was on average twice as large in the northern continents as it was in the Southern Hemisphere. During the past 2,000 years, some regions experienced warmer 30-year intervals than during the late 20th century. For example, in Europe the years between 21 and 80 AD were possibly warmer than the period 1971-2000.

While the study does not attempt to attribute temperature changes to natural or man-made factors, one of the lead authors, Northern Arizona University earth scientist Darrell Kaufman added:

"The pre-industrial trend was likely caused by natural factors that continued to operate through the 20th century, making 20th century warming more difficult to explain if not for the likely impact of increased greenhouse gasses."

Back in March, another team put together a contested global temperture trend analysis encompassing the past 14,000 years based proxy temperature data. That report also found a long-term cooling trend until 1900. However, the proxy data in that study turned out to be not sufficiently robust to resolve 20th century temperature trends.

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  1. So what this shows is that the peak of the roman warming period was warmer then it was today.

    Those damn Gauls and their iron age SUVs

    1. There was Hero's steam engine. Maybe it was more widely used than we once thought?

      1. Steam doesn't put out CO2... duh.

        Just like batteries don't.

        1. What did they burn--oh, you're putting me on.

          1. Nice late-sentence redemption.

            Funny though, how few people understand these simple concepts. My car is ZERO emissions! Because it runs off Nickel Metal Hydride batteries!

    2. hockey stick! hockey stick! /the AGW mantra

      1. I don't think the Romans played hockey, dude.

        1. Well lack of hockey was probably the first sign of a declining empire

          1. No hockey?! They deserved to fall.

            1. Tough to play hockey without global cooling.

              1. Field hockey, then? With Christian heads?

            2. Roma was the original too-big-to-fail, after Greece.

        2. feeding Christians to the lions is sorta like hockey.

          1. Come on, no pucks, no ice. Though they did have goalie masks and maybe sticks.

            1. Maybe it derived from the old Children's Matinee?

  2. Once Greek fire was lost, the cooling came.

  3. Ron,

    Could you link to a bigger copy of that chart? Pretty hard to read.

    1. It's also hard to read because of its incredibly poor design.

      It's like you give an asshole Tableau and he decides it's his job to use charts to make information as incomprehensible as possible.

  4. Well looky here, Mr. Forbes.

    "Spatio-temporal" isn't hyphenated according to Wikipedia or Merriam-Webster. There goes your entire thesis. Next.


  5. Oh my god!

    They just can't stop putting lipstick on the pig that is proxy reconstructions.

    This is yet another risible attempt to get around the fact that the cult's mechanism of how CO2 is supposed to bake the Earth has been falsified by atmospheric observations by claiming something mysterious is happening now and that only man could be the cause.

    And, as usual they are using bad stats, pal review (vice peer review) and bullshit to make their case.

    It's not interesting, Ron. It's really, really, pathetic.

    1. But the chart is so fancy and colorful. I like colors.


    2. Ron was also uncritical when he wrote about the Marcott study.

      Liars cheats and frauds keep putting this stuff out and Ron keeps eating it up.

      Do other areas of science outside of climatology have such a terrible record? At what point do reasonable (this is not a dig on reason magazine) people like Ron stop falling for it?

      1. At what point do reasonable (this is not a dig on reason magazine) people like Ron stop falling for it?

        I think Ive found the flaw in your question.

        1. Here's what's going to happen; all the action is in the empirically calculated sensitivity value: how much hotter the surface temperatures will be if CO2 were doubled.

          What's happening now is serious scientists are walking the number down from the 3.0 degree nonsense that was the orthodox line among the cultists.

          Nobody wants to be labeled a heretic (aka a denier) so they look for excuses to shift their figures to be just a little lower than the orthodox figure. And then once that shift is accepted, they'll go lower still, until eventually they number they promote will be the one based on observations. The same thing happened when Miliken got the charge of the electron wrong.

          1. The same thing happened when Miliken got the charge of the electron wrong.

            which side of that debate said the world was going to end unless we astronomically grow the size of government because electron charges were so very very high/low?

            I am sorry I do not think this is some scientific debate. This is people lying for the goal of taking away freedoms and growing their own power and wealth.

          2. We've learned those tricks nowadays, and now we don't have that kind of disease -- Feynman 1974


      1. In brief:

        "Similar", only in Climate Science! I plotted Hanhij?rvi's recons (based on the same data as the "official" recons plotted by Steve above). Results:
        Australian (Gergis) Hockey Stick ? poof ? gone
        European Hockey Stick ? poof ? gone
        South American Hockey Stick ? poof ? gone
        Asia (no hockey stick even in P2k version) ? poof ? much elevated MWP
        Only Arctic hockey stick remaining. Pretty funny as Hanhij?rvi did not find any hockey stick in his own recent Arctic Atlantic area reconstruction:

        1. Shocking, I say! SHOCKING!

  6. That report also found a long-term cooling trend until 1900. However, the proxy data in that study turned out to be not sufficiently robust to resolve 20th century temperature trends.


    The Marcott study was full on fraud masquerading as science and this is all you can say about it after writing uncritically about it nearly a month ago with no update?

    1. This isn't the Marcott study. This another one that got hastily banged through Nature after another paper using many of the same proxies couldn't make it past the gate-keepers in Science.

      Most paleoclimatologists' approaches to statistics make Alex Jones approach towards terrorist attacks in the U.S. look positively reality based.

      1. Wups! I now see you knew that. Sorry!

  7. Serious question for those who pay more attention to the AGW donnybrook than I. How do they know what the temperature was at any given point in history? Is there some sort of Domesday Book where the king and his alchemists and astrologers were keeping precise records?

    1. Mainly it's icecore/soil/treering data that has been extrapolated from analysis of the atmospheric content locked in the medium for centuries.

      AGW proponents claim that it's reliable, but when modern climatologists using modern data collected from modern scientific equipment can't even agree what the current world temperature is... Well, let's say I'm skeptical that they can accurately depict how warm the earth was from some cherrypicked, small samples.

    2. We don't.

      Essentially, each decade back you go, the worse the temperature record gets. Prior to the 1880's or so, they are essentially useless.

      We can make guesses based on records covering crop yields and what was growing at different locales (the stuff the Romans grew in Britain implies it was warmer then than now). But that's pretty piss poor.

      Most of the attempts to tie at some temperature proxy like oxygen isotope levels to temperature, are full of massive uncertainties that makes them all but worthless.

  8. Does the reconstruction require that the data has some kind of a priori known distribution? Because it seems that they assume there is reversion to the mean...

    1. Kinda sorta. They take the data that I talked about (icecore, etc) and compare it to the type of data tarran was talking about (crops, etc) and then smooth it out.

      unfortunately, the data samples from the icecores and such isn't like carbon dating. It's not an exact science. and the crop yields and such are not very reliable. There is A LOT of cherry picking that goes into what data to include and how to interpret it. This is why the past temperatures vary so much. Just look at the top set of lines, there are portions of history that one method says was cool and another says was extremely hot.

  9. Chris Hayes grasping at straws to tie West explosion to "deregulation"

    Concerns were raised in 2002 that chemical plants in populated areas ? like the one that recently exploded in West, Texas ? were vulnerable to terrorist attacks.

    The heads of Department of Homeland Security and Environmental Protection Agency had planned to regulate the security of chemical sites, but Dick Cheney's son-in-law Philip Perry stepped in and informed them they lacked the authority to do so without congressional legislation.

    So there was no "deregulation", there just wasn't more. And it wasn't safety regs, it was anti-terrorism security bullshit. I can not stand how highly regarded this guy is on the left. They fucking love them some dishonesty, don't they?

    1. damn, wrong thread

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