cold climate in Finland, lakes

Tree rings indicate: World has been cooling for 2000 years

In 2012, an international team of scientists published a study, where they reconstructed climate in northern Europe for the past 2 000 years. For the first time, the cooling trend was calculated precisely. Read more about this interesting discovery! 

A research team, under the leadership of Professor Dr. Jan Esper from Johannes Gutenberg University in Mainz, used a tree-ring density to produce a climate reconstruction reaching back to 138 BC. Researchers used measurements from sub-fossil pine trees originating from Finnish Lapland region. It was first time, when long-term climate cooling trend, over the past two millennia, has been demonstrated.

Jan Esper said about their results published in Nature Climate Change journal:

“We found that previous estimates of historical temperatures during the Roman era and the Middle Ages were too low. Such findings are also significant with regard to climate policy, as they will influence the way today’s climate changes are seen in context of historical warm periods.”

How did the Romans grow grapes in England?

Researchers examined tree-ring density profiles from sub-fossil pine trees in northern Scandinavia. As we know, the climate in Scandinavia is very cold. The landscape was formed many times by glacier, and in consequence many lakes were created. Interestingly, in such a place trees were often collapsing into one of the thousands lakes, where they remain very well preserved up to now.

Global warming is due to sun’s radiation – NOT carbon emissions!

Scientists from Germany, Finland, Scotland, and Switzerland were able to create a sequence reaching back to 139 BC (see graph below).

The reconstruction provides a high-resolution representation of temperature patterns in the Roman and Medieval warm periods, but also shows the cold phases that occurred during the Migration Period and the later Little Ice Age. Source: Johannes Gutenberg University Mainz (JGU), with own modifications.

A graph shows that the Britain of 2 000 years ago and Medieval period of 1000 years ago experienced a lengthy period of hotter summers than today. The Medieval Warm Period was already known, while the toga-wearing Roman times when temperatures were apparently 1 deg C warmer was quite a new discovery.

What can tree rings tell us about Earth’s past?

In addition, the graph presents very clear cooling trend that occured for last 2000 years. Scientists demonstrated that this trend involves a cooling of -0.3°C per millennium due to gradual changes to the position of the sun and an increase in the distance between the Earth and the sun.

Professor commented this result in the following way:

“This figure we calculated may not seem particularly significant. However, it is also not negligible when compared to global warming, which up to now has been less than 1°C. Our results suggest that the large-scale climate reconstruction shown by the Intergovernmental Panel on Climate Change (IPCC) likely underestimate this long-term cooling trend over the past few millennia.”

Source: Esper J., DC. Frank, M. Timonen, E.Zorita, RJ. S. Wilson, J. Luterbacher, S. Holzkämper, N. Fischer, S. Wagner, D. Nievergelt, Anne Verstege and Ulf Büntgen. 2012. Orbital forcing of tree-ring data. NATURE CLIMATE CHANGE, VOL 2. 

Main photo: Lake in Finland. Photo credit: Rafal Chudy

6 thoughts on “Tree rings indicate: World has been cooling for 2000 years

  1. Interesting information for sure, not a particulary interesting article though as it entirely fails to elaborate the findings in the context of the current scientific climate debate.

    The professor: “…..Our results suggest….. (IPCC) likely underestimate this long-term cooling trend over the past few millennia….” – and?

  2. The real concern should be the last few bars to the right of the chart, look at the spikes, and the trend line. If that was a share graph we would all be jumping in. And why does the trend line end in AD1900 while the data just keeps rolling on and up?

  3. What is the standard deviation on that trend? Is it s statistically significant trend?

    The trend since 1900 has been strongly warming, and this trend is statistically significant, of course. It’s also a global trend and not based on proxies.

    Given that this is a land trend (since the trees are on land!) one should compare it with the global land trend.

    The global land trend (NOAA) since 1900 is +1.16 degrees per century +/- 0.12 degrees

    So the global land trend since 1900 is 30 times greater than the ‘trend’ established here.

  4. It is true that natural climate variability can cause alterations on a continental to global scale. Research has shown some apparently natural variability increased global warming by about 0.3 degrees between 1890-1920. That is irrelevant compared to the rapid onset and growth in global warming and climate forcing which has been apparent since the 1960s.

    In 50 years, warming rates have been at 0.4 degrees compared to a claimed 0.3 degree cooling over 1000 years. Any natural resource scientist knows the rate of change is as important as the total/maximum change in any natural system – whether climate cycles, rivers or ecosystems.

    The correlation of trends in emissions and warming gas densities to warming rates has been examined using relevant tests such as Hill’s criteria (devised to test links between smoking and cancer). All these clearly demonstrate the linkages between rising emissions from fossil fuel use, land clearing etc and global warming and climate forcing are real and a growing threat to health, security, food production and ecosystem resilience.

    1. Fergus,
      I guess that in the past there were also increases in global temperatures by let’s say 0.3, and thereafter these periods were followed by cooling ones (as on the reconstruction graph).

      There is also an issue, that we are able to measure temperature more precisely since XVIII century, and other long-term data provided by scientists is a reconstruction.

      Nevertheless, scientists showed long-term trend that takes into account local maxima and minima points (current global warming may be considered as local or even global maximum, but this is only one bump on the historical timeline, that may push linear trend up, but may not be the most influential).

      Personally, I think that we will never be able to get the answer to the question if the world is cooling or warming, because it depends on many factors, such as for instance place on the planet. In some parts of the words it will be warmer, in some colder – one general conclusion may generalize too much the complexity of our planet.
      In my opinion, global cooling is more dangerous to humans than warming. In the ice age it is much harder to produce food. What do you think?

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