New insights into the reconstructed temperature in Portugal over the last 400 years

Abstract

Abstract. The consistency of an existing reconstructed annual (December-November) temperature series for the Lisbon region (Portugal) from 1600 onwards, based on a European-wide reconstruction, with (1) five local borehole temperature-depth profiles; (2) synthetic temperaturedepth profiles, generated from both reconstructed temperatures and two regional paleoclimate simulations in Portugal; (3) instrumental data sources over the twentieth century; and (4) temperature indices from documentary sources during the late Maunder Minimum (1675-1715) is assessed. The low-frequency variability in the reconstructed temperature in Portugal is not entirely consistent with local borehole temperature-depth profiles and with the simulated response of temperature in two regional paleoclimate simulations driven by reconstructions of various climate forcings. Therefore, the existing reconstructed series is calibrated by adjusting its low-frequency variability to the simulations (first-stage adjustment). The annual reconstructed series is then calibrated in its location and scale parameters, using the instrumental series and a linear regression between them (second-stage adjustment). This calibrated series shows clear footprints of the Maunder and Dalton minima, commonly related to changes in solar activity and explosive volcanic eruptions, and a strong recent-past warming, commonly related to human-driven forcing. Lastly, it is also in overall agreement with annual temperature indices over the late Maunder Minimum in Portugal. The series resulting from this post-reconstruction adjustment can be of foremost relevance to improve the current understanding of the driving mechanisms of climate variability in Portugal.

Atas do X Simpósio Nacional de Investigação em Psicologia, Universidade da Madeira, 2019

“…Em Portugal, pela primeira vez, desenvolve-se investigação histórica em relação ao clima, sendo que um dos resultados deste trabalho é a elevação da temperatura nos últimos 400 anos (Santos, 2015). Por sua vez, a identificação de fenómenos climatéricos extremos e das vulnerabilidades da costa portuguesa, o esforço de relacionar o comportamento da mortalidade com as mudanças climatéricas (Guimarães & Amorim, 2016).…”

On reconstruction of time series in climatology

“…If the cross-correlation coefficient between the time series of the proxy variable and the variable that is being reconstructed on the basis of the available simultaneous observations is high, a regression equation is built and the missing past values of temperature are reconstructed on the basis of that equation. This is how it is done both in the simplest bivariate case (a proxy and the variable to be restored) and in the multivariate case when the variable of interest is reconstructed on the basis of a multivariate linear regression equation (e.g., Bradley, 2015;Santos et al, 2015). The variables can be transformed in some way before the reconstruction (for example, time series of principal components of expansions into empirical orthogonal functions are used instead of the original data, see Tingley et al, 2012) but the general principle remains the same:…”