Warm periods in the 20th century are not unprecedented during the last 2,000 years

Public Release: 8-Aug-2017

From Eurekalert

Institute of Atmospheric Physics, Chinese Academy of Sciences

 

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IMAGE: 2,000-year temperature reconstruction in China. view more

Credit: Yang Liu & Jingyun Zheng

A great deal of evidence relating to ancient climate variation is preserved in proxy data such as tree rings, lake sediments, ice cores, stalagmites, corals and historical documents, and these sources carry great significance in evaluating the 20th century warming in the context of the last two millennia.

Prof. Quansheng Ge and his group from the Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, collected a large number of proxies and reconstructed a 2000-year temperature series in China with a 10-year resolution, enabling them to quantitatively reveal the characteristics of temperature change in China over a common era.

“We found four warm epochs,” says Prof. Ge, “which were AD 1 to AD 200, AD 550 to AD 760, AD 950 to AD 1300, and the 20th century. Cold periods occurred between AD 210 and AD 350, AD 420 and AD 530, AD 780 and AD 940, and AD 1320 and AD 1900. The temperature amplitude between the warmest and coldest decades was 1.3°C”.

Prof. Ge’s team found that the most rapid warming in China occurred over AD 1870-2000, at a rate of 0.56 ± 0.42°C (100 yr)?1; however, temperatures recorded in the 20th century may not be unprecedented in the last 2000 years, as reconstruction showed records for the period from 981 to 1100, and again from 1201 to 1270, were comparable to those of the present warm period, but with an uncertainty of ±0.28°C to ±0.42°C at the 95% confidence interval. Since 1000 CE–the period covering the Medieval Climate Anomaly, Little Ice Age, and the present warm period–temperature variations over China have typically been in phase with those of the Northern Hemisphere as a whole.

Prof. Ge’s team also detected some interactions between temperature variation and precipitation change. The ensemble means of dryness/wetness spatial patterns in eastern China across all centennial warm periods illustrate a tripole pattern: dry south of 25°N; wet from 25°-30°N; and dry to the north of 30°N. For all cold periods, the ensemble mean drought/flood spatial patterns showed an east to west distribution, with flooding east of 115°E and drought dominant west of 115°E, with the exception of flooding between approximately110°E and 105°E.

The general characteristics of the impacts of climatic change historically were negative in the cold periods and positive in the warm periods. For example, 25 of the 31 most prosperous periods in imperial China during the past 2000 years occurred during periods of warmth or warming. A cooling trend at the centennial scale and social economic decline run hand-in-hand. The rapid development supported by better resources and a better environment in warm periods could lead to an increase in social vulnerability when the climate turns once more to being relatively colder.

The study is published in Advances in Atmospheric Sciences.

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47 thoughts on “Warm periods in the 20th century are not unprecedented during the last 2,000 years

  1. The chart looks pretty consistent with European historical proxies for temperature. Of course, this will have no effect on the devotees of Mann.

    • Imagine that. local temperature varies more than regional. regional varies more than hemispherical
      and hemispherical varies more than global.

      • “local temperature varies more than regional”. That’s the simple mathematical effect of averaging. The average is always between the highs and the lows. Not specific to climate.

      • And daily temperature change at my location exceeds the average for the past 2000 years, by a factor of 10. Imagine that. In a single day. And the plants and animals survive without the slightest notice.

        But somehow, a change of 2C over 100 years will be catastrophic. Unless of course we send money to someone somewhere to save us from our sins. Why is prayer never enough?

        Why does the religion of the day always need us to send money? And why does that money almost always go to the people that already have plenty? Why does it almost never go to those that have none?

      • It’s important because the growing season depends on local conditions. In Canada, the growing season has increased about fifteen days since 1950. link The temperature change of the agricultural part of Canada didn’t increase much during the same period. It doesn’t take much temperature difference to make a big difference in agricultural output.

      • Steve Mosher

        Unless climate is fractal, the signature of a chaotic system. Then variation is the same on all spatial scales. Imagine that?

      • Imagine that: temperature is an intensive property, averaging spatially inconsistent discrete temperatures in the absence of thermal equilibrium is therefore a meaningless nonsense.

    • Yeah I remember it well, the warmest part of the 20th Century was the last 2,000 years. Of curse the whole 21st century has been flaming hot compared to that warm 2,000 years in the 20th century.

      g

  2. Warmth is associated with prosperity and cold is associated with misery! Where else have we seen similar results. Back in my college days, we were taught about medieval climate optimum and the dark (little ice age) ages. Now, our Anthropocene advocates want us to go back to the dark ages.

  3. Did the researches slap on modern temperature records to older proxies (paywalled)? Mann’s Hockey Stick went back 1000 years. On this graph, going back the lesser of 600 years, there is another Hockey Stick (oh noes). The sharp Red Vertical arrow drawn in only for the modern temperature record, why not the other peaks and troughs, do they want to distract the viewer’s eye’s?

    While this graph is flattering, suggesting there is nothing unprecedented about modern warmth, it still makes me uneasy.

  4. Now plot the error bars of +1 to -1, then expand the Y-scale with range of +10 to -10 to show the extent of the error bars.

  5. I suspect that the 1800-1850 mean being selected to represent 0° on the temperature scale is to reflect the disparities since the industrial revolution. I seems to me that the overall mean is too low considering there seems to be more gold that blue on the graph. This might indicate that the current increase in global temperatures is not that far from the true mean.
    But then again I am highly suspect of “proxy data” from such unproven sources.

  6. This report, however interesting it may seem, covers only 2000 years. Not long enough to be significant in terms of Earth history, nor to speak to “trends”.

  7. In the past cold periods were of course less prosperous than warm periods. I am not sure that will hold for the future though. Consider that prior to 1900 the majority (80% ?) of labor was dedicated to food, basic shelter, and heating. In a cold period the labor required for all three of those goes up. However, in many economies the portion dedicated to food, basic shelter, and heating is now relatively small. I suspect we will see less correlation between temperature and economies. Unless of course Chicago gets buried under a mile of ice. I suspect at that point they will produce fewer goods and services than they do now.

    • No. Economic activity slows down in most northern countries in the winter. Go look at seasonally unadjusted quarterly GDP growth data for the U.S.

    • Since we have many more people dependent on far fewer farmers now, I suspect the effect of a cold snap will be even worse.

  8. The Sui-Tang countertrend warming cycle during the Dark Ages Cold Period shows up in other Asian proxy studies as well, maybe some included in this survey. I’m not sure if it were global or not.

  9. Why were there no 3 foot to 12 foot rises in the ocean during the warm spells 1000 , 2000 and 6,000 years ago? If there were then how much did the ocean rise. Especially during the Holocene Maximum?

    • There were such rises, as shown dramatically clear around the world. In southern Britain, despite rebound from loss of ice off northern Britain, sea level was higher there during the Medieval and Roman Warm Periods, as shown by high and dry former seaside forts and castles.

      Holocene Optimum MSL is hard to measure, given so much land uplift and downward motion since then. During the Minoan WP (~3500 BP), it was probably about two meters higher than now, if not more, based upon Hawaii:

      http://www.soest.hawaii.edu/ericg/kap_paper.pdf

      MSL in Australia during the HCO has been estimated three meters higher than now:

      http://people.rses.anu.edu.au/lambeck_k/pdf/139.pdf

  10. Dear Professor Steven Mosher, I would like to know who funded the China Study and who funds you? Full disclosure is necessary for the rest of the environmental community to understand the inherent bias of the each study and its point of view.

    • Mosh is a salesman, not a prof. He’s an English and Philosophy major, but lists himself on the BEST site as a “scientist”. Which is a hoot, since he not only doesn’t practice the scientific method, but has a warped view of what it even is.

      Funding:

      http://berkeleyearth.org/funders/

      He claims that CACA is “just physics”, but real physicists, including the best in the world, disagree with him.

  11. Don’t expect the IPCC to loudly proclaim this graph, unlike other graphs. It would ‘dilute the message’, ‘give fodder for skeptics’.

  12. The warmist argument “but it’s only local” that Mosh chipped in with above, is a double edged sword.
    It can be used to negate warmist alarmism.
    Arctic warming? Local curiosity, no relevance to us.
    Greenland warming? Local curiosity, no relevance to us.
    Small peninsula on western Antarctic warming? Local curiosity, no relevance to us.
    The rest of Antarctica cooling? Local curiosity, no relevance to us.
    China cooling? Local curiosity, no relevance to us.
    South America cooling? Local curiosity, no relevance to us.

    In the UK, by this line of reasoning, the only data that is important is the CET (Central England Temperature record). This shows nearly 400 years of no warming, flat-line temperatures with only decade scale wiggles. The decadal scale warming in the 1700’s in the CET was greater than 20th century warming. So in the UK there is no warming and the AGW scare is an empty falsehood. (Hint – it is everywhere else also.)

      • Chris, global temps are going up since 1750.

        As for temperature, the only reliable data we have is the sat data and it only goes back to the 70s.

        The surface data sets 1880 to 2017 are for the most part completely made up for most of the planet for most of the record. That made up “data” has then been adjusted hundreds of times since 2000

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