Paper Reviewed
Payomrat, P., Liu, Y., Pumijumnong, N., Li, Q. and Song, H. 2018. Tree-ring stable carbon isotope-based June-September maximum temperature reconstruction since AD 1788, north-west Thailand. Tellus Series B: Chemical and Physical Meteorology 70: 1443655, https://doi.org/10.1080/16000889.2018.1443655.

One of the most oft repeated claims of climate alarmists is that temperatures of the past few decades are the warmest they have been over the past one or two millennia, which warmth they additionally claim is caused by rising atmospheric CO2 concentrations.

Although much can be said and done to debate and refute these two assertions, we never cease to be amazed at the constant flow of scientific studies unveiling newly published historical proxy temperature records that challenge such hypotheses.

The latest case-in-point is the work of Payomrat et al. (2018), who developed a Δ¹³C tree-ring proxy for June-September maximum temperatures for northwest Thailand. The new chronology was derived from Merkus pine (Pinus merkusii) trees cored in the Mae Hong Son province in the northwestern region of the country, spanning a period of 226 years (1788-2013 AD).

A graphical presentation of the proxy temperature record is presented in the figure below. Perhaps the most significant observation to note from this graph is the decline in temperatures since the mid-1980s, with current values approaching the lowest recorded in the 226-year record. What is more, temperatures are not rising in response to the supposedly large CO2 forcing that has occurred in the atmosphere since World War II. Indeed, Payomrat et al. report that a majority of the ten warmest years of the record occurred prior to second half of the 20th century, including the six warmest years of 1950, 1949, 1948, 1947, 1945 and 1946.

Clearly, there is nothing unusual, unnatural, or unprecedented about the northwest Thailand temperature record. And that fact adds to the growing mountain of evidence that regularly refutes climate alarmist claims of current temperatures being the warmest of the past millennium and driven by the modern rise in atmospheric CO2.

Figure 1. The June-September maximum temperature reconstruction (grey line) with a 0.1-Hz low-pass filter (red line). The standard deviation (σ) was ± 0.29. Source: Payomrat et al. (2018).