| 16 Sep 2025
Newly discovered series of meteorological measurements in SW Greenland (Nuuk) in the period 1806–13
Abstract. The article presents a description of a newly discovered, unique series of meteorological measurements in SW Greenland (Godthåb [now Nuuk]) from the beginning of the 19th century (1 November 1806 to 16 August 1813). The series is the longest available from before 1840, not only for Greenland but also for the entire Arctic. The handwritten meteorological register was discovered in the archives of the Royal Society in London (MA/154). The meteorological observations were carried out by the German mineralogist Dr Charles Lewis Giesecke. The observations include measurements, taken two to three times per day, of air temperature, atmospheric pressure and wind direction. In addition, the meteorological register briefly describes the weather conditions for each day. In the article, we present a detailed analysis of thermal conditions for the period covered by a complete series of measurements (Aug 1807–Jul 1813). The analysis of air temperature clearly shows that the study period was one of the coldest periods (possibly the coldest) in the past two millennia. A cooling of this severity has previously been found for the study region, the whole of Greenland and the whole Arctic. Among the available reconstructions that use different proxy data or that use climate models for this purpose, most of the reconstructions of air temperature are almost fully consistent with the available results of meteorological observations for this period. Intense volcanic activity and, to a lesser degree, the low solar activity connected with the Dalton minimum are most often given as reasons for the cooling of the early 19th century.
Summary: The manuscript presents an analysis of a newly discovered series of historical meteorological data comprising subdaily air temperature, wind and pressure taken by Charles Lewis Giesecke in Nuuk, Eastern Greenland, covering the period 1809-1813. The authors compare these observations with recent observations from the same location, analyse long-term changes in temperature and its connection to wind direction.
The main findings are that air temperature was almost always colder than in recent times, and that advection from the North-East played a more significant role than it does today. The colder temperatures agree with other indirect information derived from ice-core records.
Recommendation:
The study is interesting, as meteorological observations this old are very rare. The manuscript is, in my opinion, well and clearly written, although a few figures could be more clearly designed. There are some aspects that the study does not cover, and that could also be interesting for the reader, as I explained in more detail below. My recommendation is that the manuscript can gain from some moderate revisions, which are certainly feasible
Main points:
1) Clarity of some figures. Figure 5, perhaps one of the most relevant in the study, is not optimally designed, making it difficult for the reader to skim the relevant information. My suggestion is to display the 1D and 2D spreads of the modern temperatures as coloured surfaces in the background, against which the mean of the modern and of the historical temperatures is plotted as dark lines
Similarly, Figure 9 could include the temperature levels as circles, instead of a linear scale on the y-axis as it is now.
2) Perhaps more importantly, the study is strongly focused on the mean annual cycle, and essentially all figures display in some way or another the mean annual cycle derived from the 5 years of observations. No figures actually show a time series over the period of observations, such as monthly or annual means. The period is admittedly short, but this type of information would be useful when discussing the purported impact of volcanic eruptions. For instance, this period includes the 1809 Tambora (?) eruption, less known than its 1815 counterpart, but nevertheless intense. The time series of annual means or monthly anomalies might provide insights into the impact of this eruption on temperature in Nuuk and its recovery in the following years. Also, the lack of any clear signal would be relevant. A time series of wind direction frequency could also be interesting, as eruptions have been suggested to impact the state of the NAO towards a more zonal state. Would this impact be visible in the wind direction data? Again, a positive or negative answer would be, in my view, interesting
3) Following this time-series approach, another suggestion is to compare the monthly anomalies or annual means with those from the neighbouring cell in the 20CR reanalysis. The agreement probably cannot be expected to be good, but it would also be an interesting test for the 20CR reanalysis using independent historical observations.
Particular points:
4) 'A cooling of this severity has previously been found for the study region, the whole of Greenland and the whole Arctic.'
The meaning of this sentence in the abstract is not clear to me, unless it refers to previous studies (?). If yes, please state it so.
5) 'Intense volcanic activity and, to a lesser degree, the low solar activity connected with the Dalton minimum are most often given as reasons for the cooling of the early 19th century.'
I would be reluctant to include this sentence in the abstract, as it is actually not a conclusion of the present study. It can mislead the reader into thinking that this study also attributed the cooling to those climate forcings.
6) 'about the existence of long-term continuous meteorological observations'
What does 'continuous' mean here ? I guess daily temporal scales, but it is unclear.
7) 'We calculated MDATs according to eight different formulas:'
I would have a suggestion that the authors may want to follow, although it is not critical. Instead of testing different links between subdaily measurements and daily means, a linear regression would yield the proper weights for the three subdaily data to reconstruct the daily mean
8) 'temperature between 5 and 25 February never rose above ˗20 °C, and between 19 and 25
February it was even above ˗30 °C'
I guess the authors mean that the temperature remains above -30 °C. The formulation is ambiguous
9) 'The question arises: What could be the reason for such great heating from one day to
the next? '
The authors suggest that föhn was responsible for this sudden warming. It seems plausible, but perhaps
One analogous situation can be found in 20th-century observations to support this hypothesis, possibly dating back to before the retreat of the ice sheet.
10) line 410 , consider opening subsections for wind, daily temperature variability, etc. It would later help the reader skimming the article.
11) 'In historical times, the irregularity of thermal roses is..'
Perhaps not irregularity, but the deviation from circular symmetry