| 1. |
- Charpentier Ljungqvist, Fredrik, et al.
(författare)
-
Assessing non-linearity in European temperature-sensitive tree-ring data
- 2020
-
Ingår i: Dendrochronologia. - : Elsevier BV. - 1125-7865 .- 1612-0051. ; 59
-
Tidskriftsartikel (refereegranskat)abstract
- © 2019 The Authors We test the application of parametric, non-parametric, and semi-parametric calibration models for reconstructing summer (June–August) temperature from a set of tree-ring width and density data on the same dendro samples from 40 sites across Europe. By comparing the performance of the three calibration models on öpairs” of tree-ring width (TRW) and maximum density (MXD) or maximum blue intensity (MXBI), we test whether a non-linear temperature response is more prevalent in TRW or MXD (MXBI) data, and whether it is associated with the temperature sensitivity and/or autocorrelation structure of the dendro parameters. We note that MXD (MXBI) data have a significantly stronger temperature response than TRW data as well as a lower autocorrelation that is more similar to that of the instrumental temperature data, whereas TRW exhibits a öredder” variability continuum. This study shows that the use of non-parametric calibration models is more suitable for TRW data, while parametric calibration is sufficient for both MXD and MXBI data – that is, we show that TRW is by far the more non-linear proxy.
|
|
| 2. |
- Charpentier Ljungqvist, Fredrik, 1982-, et al.
(författare)
-
Climatic signatures in early modern European grain harvest yields
- 2023
-
Ingår i: Climate of the Past. - 1814-9324 .- 1814-9332. ; 19:12, s. 2463-2491
-
Tidskriftsartikel (refereegranskat)abstract
- The association between climate variability and grain harvest yields has been an important component of food security and economy in European history. Yet, inter-regional comparisons of climate–yield relationships have been hampered by locally varying data types and the use of different statistical methods. Using a coherent statistical framework, considering the effects of diverse serial correlations on statistical significance, we assess the temperature and hydroclimate (precipitation and drought) signatures in grain harvest yields across varying environmental settings of early modern (ca. 1500–1800) Europe. An unprecedentedly large network of yield records from northern (Sweden), central (Switzerland), and southern (Spain) Europe are compared with a diverse set of seasonally and annually resolved palaeoclimate reconstructions. Considering the effects of different crop types and time series frequencies, we find within regions consistent climate–harvest yield associations characterized by a significant summer soil moisture signal in Sweden, winter temperature and precipitation signals in Switzerland, and spring and annual mean temperature signals in Spain. The regional-scale climate–harvest associations are weaker than the recently revealed climate signals in early modern grain prices but similar in strength to modern climate–harvest relationships at comparable spatial scales. This is a noteworthy finding considering the uncertainties inherent in both historical harvest and palaeoclimate data.
|
|
| 3. |
- Charpentier Ljungqvist, Fredrik, et al.
(författare)
-
The significance of climate variability on early modern European grain prices
- 2022
-
Ingår i: Cliometrica. - : Springer Science and Business Media LLC. - 1863-2505 .- 1863-2513. ; 16, s. 29-77
-
Tidskriftsartikel (refereegranskat)abstract
- Grain was the most important food source in early modern Europe (c. 1500-1800), and its price influenced the entire economy. The extent to which climate variability determined grain price variations remains contested, and claims of solar cycle influences on prices are disputed. We thoroughly reassess these questions, within a framework of comprehensive statistical analysis, by employing an unprecedentedly large grain price data set together with state-of-the-art palaeoclimate reconstructions and long meteorological series. A highly significant negative grain price-temperature relationship (i.e. colder = high prices and vice versa) is found across Europe. This association increases at larger spatial and temporal scales and reaches a correlation of -0.41 considering the European grain price average and previous year June-August temperatures at annual resolution, and of -0.63 at decadal timescales. This strong relationship is of episodic rather than periodic (cyclic) nature. Only weak and spatially inconsistent signals of hydroclimate (precipitation and drought), and no meaningful association with solar variations, are detected in the grain prices. The significant and persistent temperature effects on grain prices imply that this now rapidly changing climate element has been a more important factor in European economic history, even in southern Europe, than commonly acknowledged.
|
|
| 4. |
- Darudi, Ahmad, et al.
(författare)
-
The Robotic Earthshine Telescope
- 2010
-
Ingår i: Proceedings of the SPIE. - : SPIE. - 1996-756X .- 0277-786X. ; 7733, s. 8-77332
-
Konferensbidrag (refereegranskat)abstract
- Lund Observatory is presently designing and constructing a robotic telescope dedicated to studies of the Earth's albedo by measuring the ratio between the intensity of the dark and bright sides of the Moon. The telescope will operate both in broadband and narrow-band modes over the entire visible wavelength range and will transmit observational results back to the operation team over the Internet. Design challenges, in particular related to choice of CCD and stray light suppression, are described, together with the design of the optics, control system, and enclosure. Finally we present results from laboratory tests. The telescope will go into operation in the first half of 2011.
|
|
| 5. |
- Kjellström, Erik, et al.
(författare)
-
Emerging regional climate change signals for Europe under varying large-scale circulation conditions
- 2013
-
Ingår i: Climate Research (CR). - : Inter-Research Science Center. - 0936-577X .- 1616-1572. ; 56:2, s. 103-119
-
Tidskriftsartikel (refereegranskat)abstract
- A large ensemble of regional climate model projections was investigated regarding if and when they show an emergence of significant climate change signals in seasonal temperature and precipitation within Europe. The influence of the North Atlantic Oscillation (NAO), as simulated in the projections, was investigated. In most parts of Europe, the projections indicate robust emergence of temperature change in the first 2 decades of the 21st century, typically earlier for summer than for winter. For precipitation changes, signals generally emerge much later than for temperature. For Europe as a whole, the precipitation signals tend to emerge some 40 to 60 yr later than the temperature signals. In some sub-regions, robust signals for precipitation are not found within the studied period, i.e. until 2100. Some sub-regions, notably the Mediterranean area and Scandinavia, show different behaviour in some aspects compared to the ensemble-based results as a whole. NAO has some influence on the temperature change signals, which emerge earlier in winter for some models and regions if NAO is accounted for. For summer temperatures, the influence of NAO is less evident. Similarly, for precipitation, accounting for NAO leads to an earlier emergence in some regions and models. Here, we find an impact for both summer and winter.
|
|
| 6. |
- Støve, Bård, et al.
(författare)
-
A Test for Nonlinearity in Temperature Proxy Records
- 2012
-
Ingår i: Journal of Climate. - 0894-8755 .- 1520-0442. ; 25:20, s. 7173-7186
-
Tidskriftsartikel (refereegranskat)abstract
- Are temperature proxy records linear recorders of past temperature conditions? A statistical test for linearity is applied to 15 millennial-long proxy records with an annual resolution that was shown to significantly respond to Northern Hemisphere annual mean temperature selected from a collection of 30 proxies. The test, based on generalized additive modeling, shows that most of the proxies can indeed be shown to be linear functions of annual mean temperature, but two proxy records do not appear to have a linear relationship with temperature—this supports the assumption of linearity in most climate reconstruction work. The method tests for nonlinearity in a proxy relative to the group of proxies with which it is being used together. The robustness of the results is tested, and it was found that the results are stable to the choice of proxies. The linearity-testing method is quite general and could in the future be used for larger and more extensive sets of proxies.
|
|
