Comment on cp-2021-127

Stephen Burt

doi:10.5194/cp-2021-127-rc1

Stephen Burt

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https://doi.org/10.5194/cp-2021-127-rc1

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Publication Date: Nov 30, 2021
Citations: 1	License type: cc-by

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Abstract. There is considerable import in creating more complete, better understood holdings of early meteorological data. Such data permit an improved understanding of climate variability and long-term changes. Early records are particularly incomplete in the tropics, with implications for estimates of global and regional temperature. There is also a relatively low level of scientific understanding of how these early measurements were made and, as a result, of their homogeneity and comparability to more modern techniques and measurements. Herein we describe and analyse a newly rescued set of long-term, up to six-way parallel measurements undertaken over 1884â1903 in Mauritius, an island situated in the southern Indian Ocean. Data include (i)Â measurements from a well-ventilated room, (ii)Â a shaded thermograph, (iii)Â instruments housed in a manner broadly equivalent to a modern Stevenson screen, (iv)Â a set of measurements by a hygrometer mounted in a Stevenson screen, and for a much shorter period (v)Â two additional Stevenson screen configurations. All measurements were undertaken within an â¼â80âm radius of each other. To our knowledge this is the first such multidecadal multi-instrument assessment of meteorological instrument transition impacts ever undertaken, providing potentially unique insights. The intercomparison also considers the impact of different ways of deriving daily and monthly averages. The long-term comparison is sufficient to robustly characterize systematic offsets between all the instruments and seasonally varying impacts. Differences between all techniques range from tenths of a degree Celsius to more than 1ââC and are considerably larger for maximum and minimum temperatures than for means or averages. Systematic differences of several tenths of a degree Celsius also exist for the different ways of deriving average and mean temperatures. All differences, except two average temperature series pairs, are significant at the 0.01 level using a paired t test. Given that all thermometers were regularly calibrated against a primary Kew standard thermometer maintained by the observatory, this analysis highlights significant impacts of instrument exposure, housing, siting, and measurement practices in early meteorological records. These results reaffirm the importance of thoroughly assessing the homogeneity of early meteorological records.

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Data include: i) measurements from a well-ventilated room, ii) a shaded Thermograph; iii) instruments housed in a manner broadly equivalent to a modern Stevenson Screen; 10 iv) a set of measurements by a Hygrometer mounted in a Stevenson Screen; and for a very much shorter period v) two additional Stevenson Screen configurations
The adoption of the Paris Agreement, with its focus upon efforts to keep global surface temperature warming below 2 degrees Celsius (°C) above pre-industrial levels and strive to remain below 1.5 °C has led to a renewed focus upon early instrumental records given their importance in establishing estimates 5 of the pre-industrial baseline and how close we are to these levels of warming (e.g. Hawkins et al, 2017)
The principal measurements consisted of a well-ventilated room, a 5 Thermograph and a Stevenson Screen, supplemented by a Hygrometer and, for a short period, parallel Stevenson Screen measurements

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The adoption of the Paris Agreement, with its focus upon efforts to keep global surface temperature warming below 2 degrees Celsius (°C) above pre-industrial levels and strive to remain below 1.5 °C has led to a renewed focus upon early instrumental records given their importance in establishing estimates 5 of the pre-industrial baseline and how close we are to these levels of warming (e.g. Hawkins et al, 2017). In the early 20th Century the advent of the International Meteorological Organization (IMO, the precursor to the modern day World Meteorological 10 Organization (WMO)) strengthened the push to standardisation of surface meteorological station instrumentation and observing practices at national, regional and international levels and the expansion of networks to be more geographically complete. This served to greatly improve spatio-temporal comparability of these latter measurements. There are vast swathes of the tropics with no information in current archives and stations drop in and out, which may speak more to data rescue progress and data policy issues than to the lack of potential long-term records (Allan et al, 2011)

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