Temperatures over the last 5,000 years
Number of papers: 9
Mechanisms of the Early 20th Century Warming in the Arctic — Earth Science Reviews, 2021; Bokuchava & Semenov
“The Early 20th Century Warming (ECTW) reached its peak in 1940s, with maximal 30-year global warming trend of 0.47 °C/30 years in 1916–1945 comparable to the modern warming 30-year trend of 0.56 °C/30 years in 1976–2005.”
Prominent role of volcanism in Common Era climate variability and human history — Chronologia, 2020; Buntgen et al.
Super interesting paper showing the strong correlation between human flourishing (and empires) and warmer temperatures, whereas the long hard periods were usually colder. Something I didn’t know: “The lowest June–August temperature anomaly in 536 not only marks the beginning of the coldest decade, but also defines the onset of the Late Antique Little Ice Age (LALIA).”
Correction to: A 2000-Year Global Temperature Reconstruction Based on Non-Treering Proxies — Energy and Environment, 2008; Loehle & McCulloch
Tree rings are notoriously bad, variable, and cherrypickable as temperature proxies. In this update to their 2007 paper, the authors establish very credible baselines for the Medieval Warm Period as well as the Little Ice Age. Their data is proxy data, so they don’t include the 20th century. This is their best guess, which in my view is the best work so far:
The file also includes the original 2007 paper.
Highly variable Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy data — Nature, 2005; Moberg et al.
“According to our reconstruction, high temperatures — similar to those observed in the twentieth century before 1990 — occurred around AD 1000 to 1100, and minimum temperatures that are about 0.7 K below the average of 1961–90 occurred around AD 1600. This large natural variability in the past suggests an important role of natural multicentennial variability that is likely to continue.”
Corrections to the Mann et al. (1998) Proxy Data Base and Northern Hemispheric Average Temperature Series — Energy & Environment, 2003; McIntyre & McKittrick
“The data set of proxies of past climate used in Mann, Bradley and Hughes (1998, ‘MBH98’ hereafter) for the estimation of temperatures from 1400 to 1980 contains collation errors, unjustifiable truncation or extrapolation of source data, obsolete data, geographical location errors, incorrect calculation of principal components and other quality control defects. We detail these errors and defects. … The particular ‘hockey stick’ shape derived in the MBH98 proxy construction — a temperature index that decreases slightly between the early 15th century and early 20th century and then increases dramatically up to 1980 — is primarily an artefact of poor data handling, obsolete data and incorrect calculation of principal components.”
Hockey sticks, principal components, and spurious significance — Geophysical Research Letters, 2005; McIntyre & McKittrick
“The ‘hockey stick’ shaped temperature reconstruction of Mann et al. (1998, 1999) has been widely applied. However it has not been previously noted in print that, prior to their principal components (PCs) analysis on tree ring networks, they carried out an unusual data transformation which strongly affects the resulting PCs. Their method, when tested on persistent red noise, nearly always produces a hockey stick shaped first principal component (PC1) and overstates the first eigenvalue. In the controversial 15th century period, the MBH98 method effectively selects only one species (bristlecone pine) into the critical North American PC1, making it implausible to describe it as the “dominant pattern of variance”. Through Monte Carlo analysis, we show that MBH98 benchmarks for significance of the Reduction of Error (RE) statistic are substantially under-stated and, using a range of cross-validation statistics, we show that the MBH98 15th century reconstruction lacks statistical significance.”
The M&M Critique of the MBH98 Northern Hemisphere Climate Index: Update and Implications — Energy and Environment, 2005; McIntyre & McKittrick
“The recent Corrigendum by Mann et al. denied that these differences between the stated methods and actual methods have any effect, a claim we show is false. We also refute the various arguments by Mann et al. purporting to salvage their reconstruction, including their claims of robustness and statistical skill. Finally, we comment on several policy issues arising from this controversy: the lack of consistent requirements for disclosure of data and methods in paleoclimate journals, and the need to recognize the limitations of journal peer review as a quality control standard when scientific studies are used for public policy.”
The Effect of a Short Observational Record on the Statistics of Temperature Extremes — Geophysical Research Letters, 2023; Zeder et al.
“In June 2021, the Pacific Northwest experienced a heatwave that broke all previous records. Estimated return levels based on observations up to the year before the event suggested that reaching such high temperatures is not possible in today’s climate. We here assess the suitability of the prevalent statistical approach by analyzing extreme temperature events in climate model large ensemble and synthetic extreme value data. We demonstrate that the method is subject to biases, as high return levels are generally underestimated and, correspondingly, the return period of low-likelihood heatwave events is overestimated, if the underlying extreme value distribution is derived from a short historical record. … Furthermore, if the analysis is triggered by an extreme event, the implicit selection bias affects the likelihood assessment depending on whether the event is included in the modeling.”
Medieval Warm Period
Reconstruction of Environmental Conditions in the Eastern Part of Primorsky Krai (Russian Far East) in the Late Holocene — Contemporary Problems of Ecology, 2021; Nazarova et al.
Shows that in Eastern Russia-during the Medieval warm period temperatures were on average 1.5 degrees C higher than today. Also shows that the Little Ice Age was 1.5–2 degrees C lower than today. This is one of four recent papers on historical temperatures that do not support the manmade CO2 theory.