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. – Click to enlarge
Posted on 07/10/2012 12:53:24 PM PDT by Ernest_at_the_Beach
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Since Princeton’s Dr. Michael Oppenheimer conflated weather with climate last week, proclaiming a short lived heat wave as “This is what global warming really looks like” in a media interview, it seems only fair to show what real science rather than what he and Dr. Trenberth’s government funded advocacy looks like. I can’t wait to see how Dr. Michael Mann tries to poo-poo this one. – Anthony
From Johannes Gutenberg-Universität Mainz: Climate in northern Europe reconstructed for the past 2,000 years: Cooling trend calculated precisely for the first time
Calculations prepared by Mainz scientists will also influence the way current climate change is perceived / Publication of results in Nature Climate Change
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. – Click to enlarge
An international team including scientists from Johannes Gutenberg University Mainz (JGU) has published a reconstruction of the climate in northern Europe over the last 2,000 years based on the information provided by tree-rings. Professor Dr. Jan Esper’s group at the Institute of Geography at JGU used tree-ring density measurements from sub-fossil pine trees originating from Finnish Lapland to produce a reconstruction reaching back to 138 BC. In so doing, the researchers have been able for the first time to precisely demonstrate that the long-term trend over the past two millennia has been towards climatic cooling.
“We found that previous estimates of historical temperatures during the Roman era and the Middle Ages were too low,” says Esper. “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.”
The new study has been published in the journal Nature Climate Change.Was the climate during Roman and Medieval times warmer than today? And why are these earlier warm periods important when assessing the global climate changes we are experiencing today? The discipline of paleoclimatology attempts to answer such questions. Scientists analyze indirect evidence of climate variability, such as ice cores and ocean sediments, and so reconstruct the climate of the past. The annual growth rings in trees are the most important witnesses over the past 1,000 to 2,000 years as they indicate how warm and cool past climate conditions were.
Researchers from Germany, Finland, Scotland, and Switzerland examined tree-ring density profiles in trees from Finnish Lapland. In this cold environment, trees often collapse into one of the numerous lakes, where they remain well preserved for thousands of years.The international research team used these density measurements from sub-fossil pine trees in northern Scandinavia to create a sequence reaching back to 138 BC. The density measurements correlate closely with the summer temperatures in this area on the edge of the Nordic taiga.
The researchers were thus able to create a temperature reconstruction of unprecedented quality. 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.In addition to the cold and warm phases, the new climate curve also exhibits a phenomenon that was not expected in this form.
For the first time, researchers have now been able to use the data derived from tree-rings to precisely calculate a much longer-term cooling trend that has been playing out over the past 2,000 years.
Their findings demonstrate 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.”This figure we calculated may not seem particularly significant,” says Esper. “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.”
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Solar insolation changes, resulting from long-term oscillations of orbital configurations1, are an important driver of Holocene climate2, 3. The forcing is substantial over the past 2,000 years, up to four times as large as the 1.6 W m−2 net anthropogenic forcing since 1750 (ref. 4), but the trend varies considerably over time, space and with season5. Using numerous high-latitude proxy records, slow orbital changes have recently been shown6 to gradually force boreal summer temperature cooling over the common era. Here, we present new evidence based on maximum latewood density data from northern Scandinavia, indicating that this cooling trend was stronger (−0.31 °C per 1,000 years, ±0.03 °C) than previously reported, and demonstrate that this signature is missing in published tree-ring proxy records. The long-term trend now revealed in maximum latewood density data is in line with coupled general circulation models7, 8 indicating albedo-driven feedback mechanisms and substantial summer cooling over the past two millennia in northern boreal and Arctic latitudes. These findings, together with the missing orbital signature in published dendrochronological records, suggest that large-scale near-surface air-temperature reconstructions9, 10, 11, 12, 13 relying on tree-ring data may underestimate pre-instrumental temperatures including warmth during Medieval and Roman times.
a, The reconstruction extends back to 138 BC highlighting extreme cool and warm summers (blue curve), cool and warm periods on decadal to centennial scales (black curve, 100-year spline filter) and a long-term cooling trend (dashed red curve; linear regression fit to the reconstruction over the 138 BC–AD 1900 period). Estimation of uncertainty of the reconstruction (grey area) integrates the validation standard error (±2 × root mean square error) and bootstrap confidence estimates. b, Regression of the MXD chronology (blue curve) against JJA temperatures (red curve) over the 1876–2006 common period. Correlations between MXD and instrumental data are 0.77 (full period), 0.78 (1876–1941 period), and 0.75 (1942–2006 period).
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I’m sure Steve McIntyre will give this paper a thorough examination for the same sorts of issues we’ve seen before in MBH98. Hopefully he won’t have to beg for years to get the data for replication like he did with Mann.
h/t to WUWT readers “Typhoon” and Dr. Leif Svalgaard
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kadaka (KD Knoebel) says:
Their findings demonstrate 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.
The Earth keeps gaining a relatively small amount of mass, online I see estimates from 10^7 to 10^9 kg per day, with the mass of the Earth about 6*10^24 kg. The Earth’s orbital speed over time should be slightly slowing due to drag from whatever particles are out there. I would think both of those would lead to the Earth getting closer to the Sun.
So why is the Earth moving away from the Sun? Is the Sun shedding so much mass (and energy that was mass) that its gravitational force is weakening?
MORE:
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ferdberple says:
Billy Liar says:
July 9, 2012 at 3:29 pm
Why not just accept that they are unreliable indicators of past climate?
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It isn’t the trees that are unreliable, it is the “calibration” methodology used by some climate scientists. A Lucia showed on her web-site, the divergence problem is a result of calibration.
It is interesting to note that this study does not demonstrate the divergence problem, which suggests that it does not have the calibration flaw found in the papers such and Mann and more recently Gergis.
I agree completely with that statement. As a student (a long time ago) I studied tree rings in the southwest US. There is a direct relation between tree-ring thickness and moisture and a more indirect relation between tree rings and temperature. First, most tree ring growth occurs in the spring and is a function of winter moisture. An El Niño winter generally is moist and cool which contributes to thicker tree rings as soil moisture is more likely to be retained for vegetation use. A La Niña winter is more likely to be drier and warmer leading to thinner tree ring growth. So indirectly, we can conclude that winter temperatures are likely warmer with a La Niña event.
However, summer precipitation and temperature, at least in the southwest US, are not driven by either seasonal climate event. In the summer, precipitation comes from tropical moisture from either or both the Gulf of Mexico and the far eastern Pacific Ocean. The occurrence and duration is dependent on the position of the continental high pressure dome which circulates moisture from these two areas clockwise over the southwest. If the location is over NM or west Texas, moisture will not flow northward. Further east over the central US, moisture will stream into the area in the pattern commonly known as the summer monsoon. A connection between La Niña/El Niño events and the high pressure area location has not been defined to my knowledge. In any event, summer temperatures and precipitation are not a markedly important factor in tree ring growth so conclusions as to historic summer temperature and climate based on tree rings are tenuous at best.
Hide the decline!
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