Tag Archives: climate reconstruction

Presto-Chango! The medieval warming period has disappeared, or not!

“An old sarcastic saying goes, “When the facts doesn’t fit the theory, change the facts.” Mann and Hayhoe provide perfect real-world examples of such perniciousness. Powerful scientific evidence supported near-universal agreement about the existence of the Medieval Warm Period. Then Mann and Hayhoe, supported by little or no compelling evidence, waved a magic wand and made the Medieval Warm Period conveniently disappear.” click here

The science is settled: the Medieval Warming Period was indeed global

“Indeed the claim that it was global is now backed up by a huge body of scientific studies meticulously compiled by Dr. Sebastian Lüning of Die kalte Sonne and presented at Google Maps here.” click here

The medieval warming period is settled science

“Claims that modern temperatures are globally warmer than they were during Medieval times (~800 to 1250 A.D.) have been contradicted by a flurry of new (2019) scientific papers.” click here

No correlation between CO2 and earth’s temperature

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.

Arbitrary climate data changes destroys credibility

“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

Early twentieth century warming is poorly understood

Gabriele C. Hegerl, Stefan Brönnimann, Andrew Schurer, Tim Cowan. The early 20th century warming: Anomalies, causes, and consequences. WIREs Clim Change. 2018;9:e522. wires.wiley.com/climatechange

The most pronounced warming in the historical global climate record prior to the recent warming occurred over the first half of the 20th century and is known as the Early Twentieth Century Warming (ETCW). Understanding this period and the subsequent slowdown of warming is key to disentangling the relationship between decadal variability and the response to human influences in the present and future climate. This review discusses the observed changes during the ETCW and hypotheses for the underlying causes and mechanisms. Attribution studies estimate that about a half (40–54%; p > .8) of the global warming from 1901 to 1950 was forced by a combination of increasing greenhouse gases and natural forcing, offset to some extent by aerosols. Natural variability also made a large contribution, particularly to regional anomalies like the Arctic warming in the 1920s and 1930s. The ETCW period also encompassed exceptional events, several of which are touched upon: Indian monsoon failures during the turn of the cen- tury, the “Dust Bowl” droughts and extreme heat waves in North America in the 1930s, the World War II period drought in Australia between 1937 and 1945; and the European droughts and heat waves of the late 1940s and early 1950s. Under- standing the mechanisms involved in these events, and their links to large scale forcing is an important test for our understanding of modern climate change and for predicting impacts of future change.

Little Ice Age Conditions as Benchmarks of Hydroclimatic Variability

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.