European summer temperatures since Roman times
By Paul Homewood
I touched on the latest attempt to remove the Roman and Medieval Warming Periods. This is the Abstract:
The spatial context is critical when assessing present-day climate anomalies, attributing them to potential forcings and making statements regarding their frequency and severity in a long-term perspective. Recent international initiatives have expanded the number of high-quality proxy-records and developed new statistical reconstruction methods. These advances allow more rigorous regional past temperature reconstructions and, in turn, the possibility of evaluating climate models on policy-relevant, spatio-temporal scales. Here we provide a new proxy-based, annually-resolved, spatial reconstruction of the European summer (June–August) temperature fields back to 755 CE based on Bayesian hierarchical modelling (BHM), together with estimates of the European mean temperature variation since 138 BCE based on BHM and composite-plus-scaling (CPS). Our reconstructions compare well with independent instrumental and proxy-based temperature estimates, but suggest a larger amplitude in summer temperature variability than previously reported. Both CPS and BHM reconstructions indicate that the mean 20th century European summer temperature was not significantly different from some earlier centuries, including the 1st, 2nd, 8th and 10th centuries CE. The 1st century (in BHM also the 10th century) may even have been slightly warmer than the 20th century, but the difference is not statistically significant. Comparing each 50 yr period with the 1951–2000 period reveals a similar pattern. Recent summers, however, have been unusually warm in the context of the last two millennia and there are no 30 yr periods in either reconstruction that exceed the mean average European summer temperature of the last 3 decades (1986–2015 CE). A comparison with an ensemble of climate model simulations suggests that the reconstructed European summer temperature variability over the period 850–2000 CE reflects changes in both internal variability and external forcing on multi-decadal time-scales. For pan-European temperatures we find slightly better agreement between the reconstruction and the model simulations with high-end estimates for total solar irradiance. Temperature differences between the medieval period, the recent period and the Little Ice Age are larger in the reconstructions than the simulations. This may indicate inflated variability of the reconstructions, a lack of sensitivity and processes to changes in external forcing on the simulated European climate and/or an underestimation of internal variability on centennial and longer time scales.
As stated, the research only looks at European summer temperatures, and even then can’t find anything unprecedented about 20thC temperatures, only the last 30 years.
They claim that, based on instrumental data from HADCRUT, Europe has experienced a pronounced summer (June–August) warming of approximately 1.3 °C over the 1986–2015 period, but ignore a similar rate of rise in the first half of the 20thC, which was then followed by a sharp drop. Certainly from the peak around the 1940’s, current temperatures are not alarmingly high.
And on what do they base they base their claim that the latest 30 year period is the warmest in the last 2000 years?
Eight sets of tree ring studies, of which only two go back 2000 years, along with some documentary historical records. Many would think it remarkable that such wide ranging claims could be made from such a small amount of dodgy data!
How does all this compare with HH Lamb had to say? In Climate, History & The Modern World, Lamb reproduced this graph of central England temperatures, based on both documentary and proxy data, together with instrumental data at the end:
Although the chart does not include the last thirty years, this makes little difference – the CET 50 year average has only risen from 15.5C to 15.7C since 1980. Whichever way you look at it, it is clear that summer temperatures were at least as high, and probably higher, in the Middle Ages, as far as England was concerned.
This is also evident from plentiful evidence that in many parts of Britain, tillage was extended to greater heights than for some previously or at all since. Lamb quotes the example of medieval tilled fields 1300 ft up on Dartmoor, and similar examples in Northumberland, land that could not even be used when food was scarce in the Second World War.
Of course, Britain does not represent the whole of Europe, but Lamb also comes up with similar findings in Norway, and uses analysis of vine cultivation to find that:
Average summer temperatures were probably between 0.7 and 1.0C warmer than the 20thC average in England, and 1.0 to 1.4C warmer in central Europe.
There is also the evidence from the study of upper tree lines in the Alps, which again clearly show a peak of warmth in the Middle Ages, far exceeding recent warmth.
Finally, let’s take a closer look at 30-year trends in the CET:
The 30-year average currently stands at 15.8C,having stalled for the last decade. This is only 0.4C higher than 30 years ago, and only 0.2C higher than it stood in 1960.
Going further back, the 30-year average was also 15.6C in 1800, so it is plainly nonsense to pretend that there has been anything alarming or unprecedented about summer temperatures in the last 30 years.
Paleoclimatology has become a veritable industry in recent years, as can be seen from the array of authors of this paper. Funding is provided with the clear intention of removing those pesky earlier warming periods, thus leading to the sort of fraud regularly uncovered by Steve McIntyre, as we have seen again today.