Sebastian Lüning, Mariusz Gałka, Fritz Vahrenholt, The Medieval Climate Anomaly in Antarctica, Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 532, 15 October 2019, 109251
The Medieval Climate Anomaly (MCA) is a well-recognized climate perturbation in many parts of the world, with a core period of 1000–1200 CE. Here we are mapping the MCA across the Antarctic region based on the analysis of published palaeotemperature proxy data from 60 sites. In addition to the conventionally used ice core data, we are integrating temperature proxy records from marine and terrestrial sediment cores as well as radiocarbon ages of glacier moraines and elephant seal colonies. A generally warm MCA compared to the subsequent Little Ice Age (LIA) was found for the Subantarctic Islands south of the Antarctic Convergence, the Antarctic Peninsula, Victoria Land and central West Antarctica. A somewhat less clear MCA warm signal was detected for the majority of East Antarctica. MCA cooling occurred in the Ross Ice Shelf region, and probably in the Weddell Sea and on Filchner-Ronne Ice Shelf. Spatial distribution of MCA cooling and warming follows modern dipole patterns, as reflected by areas of opposing temperature trends. Main drivers of the multi-centennial scale climate variability appear to be the Southern Annular Mode (SAM) and El Niño-Southern Oscillation (ENSO) which are linked to solar activity changes by nonlinear dynamics.
Click here for further discussion of this paper.
“In 1998, NASA showed 1934 as the hottest year on record in the US, and declining temperatures for the rest of the century. They have since rewritten the data to eliminate the post 1930s cooling.” click here
I find reconstructions of past global temperatures and carbon dioxide levels such as here to be very interesting from an academic perspective. But attempts to reconstruct temperatures of the geologic past are fraught with assumptions and interpretations of the geologic record driven by presuppositions. The weight of scientific evidence across scientific disciplines does not support dating the age-of-the-earth at billions of years.
However, I do agree with the major point being made here regarding CO2 and temperature. If you believe the past geological timescale temperature reconstruction posted here, and believe that CO2 is somehow mechanistically driving global temperatures, then you clearly have a problem because this particular geologic timescale reconstruction does not support such a position. In any case, since no one was preset in the past to measure actual temperatures and CO2 levels their past levels and correlation (or lack of correlation) is speculative.
“Tree-ring evidence reveals recent cooling and glacier thickening in Central Asia as well as flat temperatures throughout the last 432 years.” click here
“The files released cover emails from Michael Mann to Malcolm Hughes, Eugene Wahl, Caspar Amman, Ray Bradley, and Jonathan Overpeck. Plus there were additional requests for anything out of UEA (Phil Jones at CRU).
The FOIA request goes all the way back to December of 2011, it’s taken this long to get released. Mann fought the release all the way.
Here is a sample, where Keith Briffa of CRU says that Mann’s data (and others) do in fact show a Medieval Warm Period.” click here
“The hubris of the Australian Bureau of Meteorology is on full display with its most recent remodelling of the historic temperature record for Darwin. The Bureau has further dramatically increased the rate of global warming at Darwin by further artificially lowering historic temperatures.” click here
Tree ring studies such as this required several underlying assumptions which make the resulting projections and forecasts unreliable. Nevertheless, the study represents a lot of work by many very talented scientists and will be useful in furthering discussions of this topic.
Loisel J, MacDonald GM, Thomson MJ (2017). Little Ice Age climatic erraticism as an analogue for future enhanced hydroclimatic variability across the American Southwest. PLoS ONE 12(10): e0186282. https://doi.org/10.1371/journal.pone.018628
The American Southwest has experienced a series of severe droughts interspersed with strong wet episodes over the past decades, prompting questions about future climate patterns and potential intensification of weather disruptions under warming conditions. Here we show that interannual hydroclimatic variability in this region has displayed a significant level of non-stationarity over the past millennium. Our tree ring-based analysis of past drought indicates that the Little Ice Age (LIA) experienced high interannual hydroclimatic variability, similar to projections for the 21st century. This is contrary to the Medieval Climate Anomaly (MCA), which had reduced variability and therefore may be misleading as an analog for 21st century warming, notwithstanding its warm (and arid) conditions. Given past non-stationarity, and particularly erratic LIA, a ‘warm LIA’ climate scenario for the coming century that combines high precipitation variability (similar to LIA conditions) with warm and dry conditions (similar to MCA conditions) represents a plausible situation that is supported by recent climate simulations. Our comparison of tree ring-based drought analysis and records from the tropical Pacific Ocean suggests that changing variability in El Niño Southern Oscillation (ENSO) explains much of the contrasting variances between the MCA and LIA conditions across the American Southwest. Greater ENSO variability for the 21st century could be induced by a decrease in meridional sea surface temperature gradient caused by increased greenhouse gas concentration, as shown by several recent climate modeling experiments. Overall, these results coupled with the paleo-record suggests that using the erratic LIA conditions as benchmarks for past hydroclimatic variability can be useful for developing future water-resource management and drought and flood hazard mitigation strategies in the Southwest.