The new 1871-1900 normal from Norway

Understanding the pre-industrial climate is essential for making meaningful comparisons with present-day climate conditions and for setting accurate benchmarks in climate policy, such as those defined in the Paris Agreement. In meteorology, "normals" refer to average annual and monthly temperatures calculated over a standardized 30-year period, commonly referred to as a normal period. These normals serve as a critical reference for detecting and interpreting long-term climate trends, provided that they are based on high-quality data and consistent calculation methodologies.

Normals are a well-established and widely used tool in climate analysis; however, in Norway, climate normals have only been officially available from 1900 onward. Consequently, the current standard normal used in Norway is the 1991–2020 period. The first official climate normal for Norway, covering 1901–1930, recorded a national average temperature just below 1 °C. Subsequent periods showed notable variability: temperatures rose during 1931–1960, declined again during 1961–1990—reverting to levels similar to 1901–1930—and then increased markedly in the 1991–2020 period. The most recent normal reflects an approximately 1 °C increase in the national average temperature compared to the early 20th century.

To gain a deeper understanding of Norway's historical climate trajectory and to assess how modern warming compares to pre-industrial conditions, it is now timely and necessary to extend the normal period further back—to 1870. This study aims to reconstruct a climate normal for the 1871–1900 period using observational data from 45 meteorological stations across Norway, selected to ensure broad spatial coverage and robust regional representation. The reconstruction applies the same methodology previously used by the Norwegian Meteorological Institute to maintain consistency and comparability with existing normals.

In addition to this traditional approach, we implement the GRID method and compare its effectiveness to a downscaling technique, allowing for an evaluation of methodological accuracy in capturing regional climate variations. Preliminary findings indicate that the national average temperature has increased by slightly more than 1.3 °C between the 1871–1900 baseline and the 1991–2020 normal. However, ongoing analyses are required to confirm these trends with greater precision, particularly given the complexities involved in reconstructing earlier climate conditions. Ultimately, this study contributes to a more complete historical climate record for Norway and strengthens the foundation for future climate assessments and adaptation strategies.