Tree rings show whether the Hittites were doomed by a spell of dry weather

Climate Anomalies and the Hittite Roman Collapse: Evidence from a robust chronology over the millennium bc

All proxy climate reconstructions are limited, and the human dimensions of effects and responses to climate are complex, with internal diversity and different systems within societies. Climate anomalies do not cause human societies to rise or fall. They are part of the context within which individuals, groups, and larger social, economic, and political entities make decisions, act, and react5,6,7,16,22,26,28,34,45,51,57. The main text states that long term climate challenges such as unusual dryness in a semi-arid context are creating circumstances that challenge existing systems. The correlation between crisis equalling collapse and real collapse is not simple and there are many cases in history of marked change in an existing political system. The collapse of a society depends on a number of factors, from the severity of a climate driver to the history of the society. In particular, for circumstances in which a ‘rigidity trap’ applies, as a previously successful, long-term system becomes entrenched and homogenous across a large area, there may be a harsh transformation62.

This article focuses on the Hittite case, which deals with all these issues. There is a period of increasing Dryness during the 13th century bc and a period of dry conditions throughout the early 12th century bc. There were three consecutive years with very dry conditions that probably created extreme stress on subsistence agriculture and food storage strategies. 8a) (see ‘Tree-ring data’ and ‘Stable isotope data’ below), which seems coincident with and part of the circumstances in which the large political entity of the Hittite Empire (probably falling into a rigidity trap context by this time) suffered a harsh transformation. At the same time, this collapse was a dynamic transformation, and many other aspects of society, economy and politics continued in the region (see further below)20,22,26,27,28,29,40,57,59.

An alternative dating scheme would place the Gordion juniper chronology approximately three years later or more recent. 18 trees are represented in the 23 samples, including the year 1200 bc. These were selected for the current project. Using the quality control COFECHA software (version 6.06P)74, the samples crossdate to form a robust chronology (Extended Data Fig. 2). All samples crossdate well with long (>100 years) overlaps with at least several other samples within the series set. The minimum acceptable cross date for Baillie–Pilcher is 3.5. For long (>100 years) crossdates this (somewhat arbitrary) value stands up well as an approximate threshold76. It has been shown for a long time that higher tBC values are required to produce certain crossdates. When the four tree-ring series with instances of tBP 3.5 against the rest of the chronology are excluded, our Gordion series have a mean tBP value of 8.98. Only two overlaps are found in the whole series, one at 73 years with an unsatisfactory tBP of 3.3 and the other at 71 years with a tBOX of n. The series intercorrelation is a Pearson correlation coefficients. Ring-width data employed are listed in Supplementary Table 1. COFECHA did not identify any errors in which all or part of a ring-width segment had higher correlation against the rest of the site chronology other than at the dated position. The default COFE CHA settings are segment lengths of 50 years and 25 years. If the segment length is increased, the number of flagged outliers reduces considerably, as shown by the robust chronology found by COFECHA.

The data obtained from the Cornell University Stable Isotope Lab was obtained using an isotope ratio mass spectrometer and high temperature analyser. The methodology using quality control standards at the lab has a within-run isotopic precision of 0.2 for carbon. The data from sample GOR-3S, 3E, 77A, 82A, and 87B has been listed in Supplementary Table 2 as well as the two different samples from the same tree. All data acquired are shown except for (1) the GOR-87 series was ended to exclude some data well after the time period of interest and (2) the GOR-87 series is shown from RY1287 as data were corrupted during the times preceding these data. In cases where a measurement was made on multiple tree rings, this value was applied to all of these tree rings; where data were collected on every second tree ring, linear extrapolation was used to create annual data for the comparisons reported. Since each individual tree derives from a unique microclimate, we do not expect them to have the same carbon isotope ratio. The exceptions are the two series from different elements of GOR-3. They both show a rising level relative to the baseline level but only for a single year (1316). The important observation across the sets of values concern where there is a pattern of similar divergences in the trends recorded around the same times across several of the individuals, such as relative year ~1230–1320 (GOR-77A, 3E, 3S, 87B) (Extended Data Fig. 9). This strongly suggests each tree was experiencing drier conditions, even though they have different baselines. There appears to be evidence of a small trend to less negative 13C values with increasing tree age. The observations of small age- related trends as recently quantified for a set of Pinus sylvestris L trees are consistent with 9a, lower. The magnitude of this trend is smaller than what we’ve observed to indicate changes to the drier conditions of this study. There is a general trend to less negative values in the period from around GOR RY1230 to 1320.

The National Centers for Environmental Information (NCEI), a part of the US government, has data from The Old World Drought Atlas58, which can be seen in Figure 3 and 7. The Tree-Ring Drought Atlas portal92 is an open access site where we could use these data to represent them.

“They just weren’t politically or economically prepared for that particular drought,” says Greaves. The capital could have been moved away from Hattusa if the weather had been better. Archaeologists are still searching for the ruins of that new capital, he adds.

The Hittite empire of Anatolia, Syria, wiped out in 1650-1200 BC and the first large-scale drought

The Hittite empire ruled the peninsula of Anatolia and the parts of northern Syria between 1650 and 1200 bc. The Hittite rulers were wiped out in 1200 bc, with no history of their rule after King Suppiluliuma II came to rule in 1207 bc.

The primary home of the Hittite gods is Hattusa, in Turkey’s orum province. Manning says that it was a spiritual and political centre. Hattusa was emptied and burned down around 1200 BC.

To evaluate the frequency of droughts in the region and understand their spatial extent, the authors then looked at modern climate records between 1929 and 2009 from the meteorological station nearest to Gordian. They found that on average the annual rain was less than 250 millimetres, which is below the 300-mm minimum required to grow wheat or barley in the region.

But a drought that went on for more than two years would have stressed food resources, undermined the economic and political force of the empire and made it vulnerable to attack by other empires.

But for Harvey Weiss, an archaeologist at Yale University in New Haven, Connecticut, focusing on the evidence from those three years misses a bigger picture. He says that the paper mispresents the climate history of that period.

According to Weiss, the first large-scale mega-drought occurred in 1190 and lasted for 200 years. Two or three years of drought are not a lot, but an abrupt mega-drOUGHT makes the cascading effects worse. The mega-drought extended from Spain through the Mediterranean and Turkey, all the way to India, adds Weiss.