Peer-reviewed scientific articles by Gudrun Brattström
We analyse the spatio-temporal patterns of temperature variability over Northern Hemisphere land ... more We analyse the spatio-temporal patterns of temperature variability over Northern Hemisphere land areas, on centennial time-scales, for the last 12 centuries using an unprecedentedly large network of temperature-sensitive proxy records. Geographically widespread positive temperature anomalies are observed from the 9th to 11th centuries, similar in extent and magnitude to the 20th century mean. A dominance of widespread negative anomalies is observed from the 16th to 18th centuries. Though we find the amplitude and spatial extent of the 20th century warming is within the range of natural variability over the last 12 centuries, we also find that the rate of warming from the 19th to the 20th century is unprecedented in the context of the last 1200 yr. The positive Northern Hemisphere temperature change from the 19th to the 20th century is clearly the largest between any two consecutive centuries in the past 12 centuries. These results remain robust even after removing a significant number of proxies in various tests of robustness showing that the choice of proxies has no particular influence on the overall conclusions of this study.
Papers by Gudrun Brattström
Climate of The Past, Sep 17, 2010
We undertake a study in two parts, where the overall aim is to quantitatively compare results fro... more We undertake a study in two parts, where the overall aim is to quantitatively compare results from climate proxy data with results from several climate model simulations from the Paleoclimate Modelling Intercomparison Project for the mid-Holocene period and the pre-industrial, conditions for the pan-arctic region, north of 60 • N. In this first paper, we survey the available published local temperature and precipitation proxy records. We also discuss and quantifiy some uncertainties in the estimated difference in climate between the two periods as recorded in the available data. The spatial distribution of available published local proxies has a marked geographical bias towards land areas surrounding the North Atlantic sector, especially Fennoscandia. The majority of the reconstructions are terrestrial, and there is a large over-representation towards summer temperature records. The available reconstructions indicate that the northern high latitudes were warmer in both summer, winter and the in annual mean temperature at the mid-Holocene (6000 BP ± 500 yrs) compared to the pre-industrial period (1500 AD ± 500 yrs). For usage in the model-data comparisons (in Part 1), we estimate the calibration uncertainty and also the internal variability in the proxy records, to derive a combined minimum uncertainty in the reconstructed temperature change between the two periods. Often, the calibration uncertainty alone, at a certain site, exceeds the actual reconstructed climate change at the site level. In high-density regions, however, neighbouring records can be merged into a
Melanoma Research, Jun 1, 2003
ABSTRACT Individuals with an increased risk of developing cutaneous malignant melanoma (CMM) incl... more ABSTRACT Individuals with an increased risk of developing cutaneous malignant melanoma (CMM) include members of kindreds with hereditary cutaneous malignant melanoma (HCMM) and patients who have already been treated for a CMM. Some of these patients develop multiple primary cutaneous malignant melanomas (MCMMs). Ultraviolet radiation is the main instigator of CMM. There are indications that patients in these high-risk groups react differently to sunlight than patients who develop a single sporadic CMM. The objectives of this study were to analyse tumour site in patients with HCMM and sporadic MCMM. Data on 2517 patients with 2608 CMMs from a population-based regional cancer registry were used. The new computer program EssDoll was used for the analyses of primary tumour sites. This software is able to analyse any chosen body area(s) with reference to the number of tumours arising there. When the site of the first and second tumours in patients with sporadic MCMM were analysed in a skin 'field division', there was a significant concordance with respect to site (P < 0.0001). In patients with MCMM, the second primary tumour was significantly thinner than the first (P = 0.001). Primary tumour sites in patients with HCMM were compared with those in patients with a single sporadic CMM. In HCMM we found significantly fewer tumours in the head and neck area and more on the trunk. These differences remained significant in two different body area models, even when stratified for age (P < 0.05). In conclusion, a site-concordance was noted for sporadic MCMM. This may be the result of a 'field effect'. Our results indicate that intermittent ultraviolet exposure may be of relatively greater importance than chronic exposure in HCMM.
Compositio Mathematica, 1984
L'accès aux archives de la revue « Compositio Mathematica » (http: //http://www.compositio.nl/) i... more L'accès aux archives de la revue « Compositio Mathematica » (http: //http://www.compositio.nl/) implique l'accord avec les conditions générales d'utilisation (http://www.numdam.org/conditions). Toute utilisation commerciale ou impression systématique est constitutive d'une infraction pénale. Toute copie ou impression de ce fichier doit contenir la présente mention de copyright. Article numérisé dans le cadre du programme Numérisation de documents anciens mathématiques http://www.numdam.org/
Att anvanda barns informella kunskaper i matematikundervisningen : Slutrapport fran ett uppfoljni... more Att anvanda barns informella kunskaper i matematikundervisningen : Slutrapport fran ett uppfoljningsprojekt
Palaeogeography, Palaeoclimatology, Palaeoecology, Aug 1, 2011
The estimation of past climate variations is a statistical prediction problem, where climate prox... more The estimation of past climate variations is a statistical prediction problem, where climate proxy data are calibrated against instrumental observations. Although noise is always present in both instrumental and proxy data, motivating the use of so-called errors-in-variables or measurement error methods, such methods have not yet been widely accepted by palaeoclimatologists. We define a univariate measurement error model that allows for white noise in instrumental and red noise in proxy data, and derive new formulae to construct prediction intervals for past climate values. The new method can be applied to either unsmoothed data or to data smoothed after calibration. Using synthetic simulated data, we demonstrate that the new formulae perform well for noise levels and calibration period lengths typical of many palaeoclimate series, in particular tree-rings and other annually resolved data. With an example, using a recently published 500-year long temperature reconstruction, we demonstrate that conclusions about the statistical significance of the difference between the present and past climates may be incorrect if the noise is not adequately modeled.
Mathematica Scandinavica, Dec 1, 1989
University Microfilms International eBooks, 1981
Understanding mathematical induction in a cooperative setting : merits and limitations of classro... more Understanding mathematical induction in a cooperative setting : merits and limitations of classroom communication amongst peers
EGU General Assembly Conference Abstracts, Apr 1, 2012
ABSTRACT A set of global climate model (GCM) simulations for the last thousand years developed by... more ABSTRACT A set of global climate model (GCM) simulations for the last thousand years developed by the Max Planck Institute is compared with palaeoclimate proxy data and instrumental data. This GCM/reality intercomparison utilizes a newly developed statistical framework using optimized quadratic distance and correlation based statistical measures of goodness-of-fit. An advantage of this statistical framework is that a range of regions with different data quality, seasonal representativeness and time periods covered can be used to evaluate the performance of GCM simulations. Moreover, it includes a significance test of whether a forced simulation performs better than unforced (control) simulations. A selection of high quality proxy series and instrumental records are used to compare with corresponding model simulation output. Given the present uncertainty in solar forcing history over the last millennium, it is helpful to attempt to constrain these estimates by comparing simulations over this period driven with varying solar forcing histories. The climate model simulations used here are driven by a "low" and "high" solar forcing series in both single-forcing and full-forcing (i.e. also with volcanic, land-use and greenhouse gas forcing) settings; they are therefore suitable for this task. High and low solar simulations have been compared with a range of recently published hemispheric/global mean reconstructions, as well as various configurations of regional proxy and instrumental series, using both the correlation and distance goodness-of-fit measures. At present, neither low or high solar forcing histories can be ruled out, but further analysis incorporating additional high quality proxy series from around the world is expected to yield greater understanding as this research progresses.
Dialog om studenters larande i ett gransland mellan vetenskaperna didaktik och matematik. Artikel... more Dialog om studenters larande i ett gransland mellan vetenskaperna didaktik och matematik. Artikeln diskuterar fruktbarheten i en sadan dialogisk ansats dar underlaget utgors av 11-aringars forstael ...
Scientific Reports, Jul 27, 2016
In climate change science the term 'Arctic amplification' has become synonymous with an estimatio... more In climate change science the term 'Arctic amplification' has become synonymous with an estimation of the ratio of a change in Arctic temperatures compared with a broader reference change under the same period, usually in global temperatures. Here, it is shown that this definition of Arctic amplification comes with a suite of difficulties related to the statistical properties of the ratio estimator itself. Most problematic is the complexity of categorizing uncertainty in Arctic amplification when the global, or reference, change in temperature is close to 0 over a period of interest, in which case it may be impossible to set bounds on this uncertainty. An important conceptual distinction is made between the 'Ratio of Means' and 'Mean Ratio' approaches to defining a ratio estimate of Arctic amplification, as they do not only possess different uncertainty properties regarding the amplification factor, but are also demonstrated to ask different scientific questions. Uncertainty in the estimated range of the Arctic amplification factor using the latest global climate models and climate forcing scenarios is expanded upon and shown to be greater than previously demonstrated for future climate projections, particularly using forcing scenarios with lower concentrations of greenhouse gases.
Utredning av problem med rekrytering och avhopp : fran grundlaggande studier i fysik och matemati... more Utredning av problem med rekrytering och avhopp : fran grundlaggande studier i fysik och matematik vid Stockholms universitet
Att finna fel i ett bevis : Studenter pa Chalmers D-linje loser en bevisuppgift i matematik
Vagar till matematisk forstaelse : I universitetsutbildning som syftar till att utjamna konsskill... more Vagar till matematisk forstaelse : I universitetsutbildning som syftar till att utjamna konsskillnader
Advances in statistical climatology, meteorology and oceanography, Dec 14, 2022
Evaluation of climate model simulations is a crucial task in climate research. Here, a new statis... more Evaluation of climate model simulations is a crucial task in climate research. Here, a new statistical framework is proposed for evaluation of simulated temperature responses to climate forcings against temperature reconstructions derived from climate proxy data for the last millennium. The framework includes two types of statistical models, each of which is based on the concept of latent (unobservable) variables: confirmatory factor analysis (CFA) models and structural equation modelling (SEM) models. Each statistical model presented is developed for use with data from a single region, which can be of any size. The ideas behind the framework arose partly from a statistical model used in many detection and attribution (D&A) studies. Focusing on climatological characteristics of five specific forcings of natural and anthropogenic origin, the present work theoretically motivates an extension of the statistical model used in D&A studies to CFA and SEM models, which allow, for example, for non-climatic noise in observational data without assuming the additivity of the forcing effects. The application of the ideas of CFA is exemplified in a small numerical study, whose aim was to check the assumptions typically placed on ensembles of climate model simulations when constructing mean sequences. The result of this study indicated that some ensembles for some regions may not satisfy the assumptions in question.
Acta Radiologica, 1997
Purpose: the ultrasound characteristics of 5 common tumours of the hand and forearm were used to ... more Purpose: the ultrasound characteristics of 5 common tumours of the hand and forearm were used to build a statistical model that could assess the weight of each trait or combination of traits in the correct diagnosing of the tumours. the model was used for calculating the first and second diagnostic alternatives. Material and Methods: the basic data of the model were the ultrasound findings in previously presented material on the 5 common benign soft-tissue tumours. the material consisted of 96 tumours: 18 villonodular synovites, 26 haemangiomas, 14 lipomas, 27 nerve tumours, and 11 glomus tumours. to build the statistical model, the ultrasound characteristics that were significant at 5% level were calculated. with stepwise logistic regression, 3 of these were selected as explaining variables. the degree of influence of the explaining variable on the response variable was calculated by way of odds quotients. the material was then analysed by means of the Statistical model. the correct diagnosis was calculated as first and second alternatives for each tumour and for the whole material. Results: the diagnostic accuracy for the whole material was 51% in the first choice and 77% in first plus second choices. Conclusion: Ultrasound should be the first imaging modality for soft-tissue tumours of the hand. However, MR should also be performed when diagnosis continues to be obscure and when malignancy is suspected.
Lyrikvännen, 2008
Den danska poeten Inger Christensen byggde sin diktsamling Alfabet pa Fibonaccis talserie. Artike... more Den danska poeten Inger Christensen byggde sin diktsamling Alfabet pa Fibonaccis talserie. Artikeln ar en kort historisk essa over Fibonacci, och beskriver aven hur talserien ar konstruerad.
Advances in statistical climatology, meteorology and oceanography, Dec 14, 2022
The performance of a new statistical framework, developed for the evaluation of simulated tempera... more The performance of a new statistical framework, developed for the evaluation of simulated temperature responses to climate forcings against temperature reconstructions derived from climate proxy data for the last millennium, is evaluated in a so-called pseudo-proxy experiment, where the true unobservable temperature is replaced with output data from a selected simulation with a climate model. Being an extension of the statistical model used in many detection and attribution (D&A) studies, the framework under study involves two main types of statistical models, each of which is based on the concept of latent (unobservable) variables: confirmatory factor analysis (CFA) models and structural equation modelling (SEM) models. Within the present pseudo-proxy experiment, each statistical model was fitted to seven continental-scale regional data sets. In addition, their performance for each defined region was compared to the performance of the corresponding statistical model used in D&A studies. The results of this experiment indicated that the SEM specification is the most appropriate one for describing the underlying latent structure of the simulated temperature data in question. The conclusions of the experiment have been confirmed in a cross-validation study, presuming the availability of several simulation data sets within each studied region. Since the experiment is performed only for zero noise level in the pseudo-proxy data, all statistical models, chosen as final regional models, await further investigation to thoroughly test their performance for realistic levels of added noise, similar to what is found in real proxy data for past temperature variations.
Advances in statistical climatology, meteorology and oceanography, Dec 14, 2022
Evaluation of climate model simulations is a crucial task in climate research. Here, a new statis... more Evaluation of climate model simulations is a crucial task in climate research. Here, a new statistical framework is proposed for evaluation of simulated temperature responses to climate forcings against temperature reconstructions derived from climate proxy data for the last millennium. The framework includes two types of statistical models, each of which is based on the concept of latent (unobservable) variables: confirmatory factor analysis (CFA) models and structural equation modelling (SEM) models. Each statistical model presented is developed for use with data from a single region, which can be of any size. The ideas behind the framework arose partly from a statistical model used in many detection and attribution (D&A) studies. Focusing on climatological characteristics of five specific forcings of natural and anthropogenic origin, the present work theoretically motivates an extension of the statistical model used in D&A studies to CFA and SEM models, which allow, for example, for non-climatic noise in observational data without assuming the additivity of the forcing effects. The application of the ideas of CFA is exemplified in a small numerical study, whose aim was to check the assumptions typically placed on ensembles of climate model simulations when constructing mean sequences. The result of this study indicated that some ensembles for some regions may not satisfy the assumptions in question.
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Peer-reviewed scientific articles by Gudrun Brattström
Papers by Gudrun Brattström