By Andy May
In the last post (see here) we reexamined the Marcott, et al. (2013) proxies for the Southern Hemisphere mid-latitudes and the tropics. In this post, we will present two more reconstructions using their proxies, these are for the Northern Hemisphere mid-latitudes (30°N to 60°N) and for the Arctic region (60°N to 90°N). These two regions contain over half of the proxies used in this study. The next post will present a global area-weighted composite temperature reconstruction. As we did in the previous two posts, we will examine each proxy and reject any that have an average time step greater than 130 years or if it does not cover at least part of the Little Ice Age (LIA) and the Holocene Climatic Optimum (HCO). We are looking for coverage from 9000 BP to 500 BP or very close to these values. Only simple statistical techniques that are easy to explain will be used.
Northern hemisphere mid-latitudes
There are 10 proxies that meet our basic criteria for the Northern Hemisphere reconstruction, although two of them are combined into one record. The final reconstruction is shown in figure 1. Figure 1A includes all proxies that meet our basic criteria, figure 1B excludes two anomalous proxies and trims the early data from two more to avoid spikes caused by proxy drop out. The R code, input and output datasets can be downloaded here.
If all proxies are included, as in figure 1A, this reconstruction shows a very flat Holocene Climatic Optimum (HCO) from 10000 BP to 6800 BP and then a steady decline in temperatures to the Little Ice Age (LIA) around 240 years ago (180 BP or about 1770 AD). The range of Holocene temperatures in both reconstructions is 4°C, this is the largest range of any region, including the Arctic. We generally prefer the reconstruction in figure 1B and will discuss the features of this reconstruction here. Since the temperature change in this reconstruction exceeds that seen in the Antarctic and Arctic reconstructions, it calls into question the concept of “Polar Amplification.” We cannot say polar amplification does not exist, but we do not see evidence of it in these proxies. Excluding the two anomalous proxies the coldest portion of the LIA was around 1610 AD.
The 17th and 18th centuries were a time of intense cold weather in Europe, Asia and North America, these centuries were the worst part of the LIA. The early 18th century saw lakes freeze solid in Italy and ice skating took place in Venice. Ships were frozen into ice in New England in 1740. More stories of the severe cold in the Northern Hemisphere in the 18th century can be seen here. The 17th century, if anything, was worse. The 17th century revolutions, droughts, famines, wars and other calamities are detailed in Geoffrey Parker’s book Global Crisis.
In Parker’s book, we see historical records of unusually cold and devastating winters that occurred in Europe and the Middle East in 1620, the United States between 1640 and 1644, China in 1640, Hungary between 1638 and 1641. 1641 remains the coldest year ever in Scandinavia. In the Balkans, in 1654, wine and olive oil froze in jars. In Egypt, in the 1670’s, a country were furs were unknown, was so cold that the citizens started wearing fur coats. Crop yields plunged in Guangxi and Guangdong (Hong Kong area) in southern China due to very cold weather in 1633 and 1634. Icebergs floated down the Thames River in January of 1649 as Charles Stuart was beheaded. In 1698 it was reported, in London, by John Evelyn that the weather was colder than anyone could remember. Harvests failed in Scotland every year between 1688 and 1698 mainly due to cold. And the stories go on and on.
The highest Medieval Warm Period (MWP) peak is at 890 AD. The Medieval Warm Period is very tepid in this reconstruction. Some of the proxies show a bump near the historical MWP and some do not. Below are plots of each set, figure 2 is the set with a visible MWP and figure 3 is the set without.
The proxies with an apparent MWP in figure 2, reach their peaks at different times and they do not line up well, this spreads out the MWP in a reconstruction and dampens the amplitude. The only two that line up are Flarken Lake (Sweden) and D13822 (Portugal). The MWP peak in the MD01-2421 composite from Japan occurs a little later it does in the Newfoundland proxy OCE326-GGC26. MD95-2015 (southwest of Iceland) is a very anomalous proxy with peaks at 1110 AD and 760 AD. In short, in this reconstruction, while it appears the LIA is well defined, the MWP is not. The historical warming from around 760 AD to 1200 AD shows up in these proxies, but not as a single well-defined event.
The Northern Hemisphere proxies in figure 3 do not have a noticeable temperature anomaly in the MWP. KY07-04-01 is in the East China Sea, south of Japan. CH07-98-GGC19 is off the US east coast near Washington, DC; it shows a minor bump around 1060 AD to 900 AD. OCE326-GGC30 is near Nova Scotia, Canada; it shows no response at all. The IOW merged dataset is from the Baltic Sea near Sweden and it also shows no MWP response. These proxies run counter to historical records for this time period.
The Roman Warm Period peak is at 90 BC (figures 1A and 1B) and very noticeable in the reconstruction. So, we see the LIA and the Roman Warm Period here, but the MWP not so clearly. This could be because the proxies are erroneous or because the MWP occurred at different times in different areas and was dampened by averaging. The MWP exists, it is a matter of historical record, but it does not show up well in these proxies.
All nine proxy records are…