Internal variability in summertime heat extremes under global warming

In this dissertation, I study how internal climate variability shapes the changing characteristics of summertime heat extremes both in Europe and globally as the world warms. A substantial sampling of internal variability is crucial to capture the most ex- treme events and determine how their magnitude and frequency change in a warming world, and is hence a vital requirement for this evaluation. To achieve this, I use the largest existing ensemble of a comprehensive climate model: The Max Planck Institute Grand Ensemble (MPI-GE). Due to the large ensemble size, MPI-GE is the best tool available to precisely sample the simulated internal variability in a changing climate. First, I quantify the contribution of different driving mechanisms to extreme sum- mertime heat over Europe, and how changes in these contributions cause an increase of variability of summertime heat in a warmer world. With a multiple regression approach, that simultaneously considers all relevant sources of variability, I identify the large-scale atmospheric dynamics as the main driver of heat extremes over Europe; while the local thermodynamic effect of soil moisture limitation plays a secondary role. Most heat extremes occur under extreme atmospheric conditions, both in current and future climates. However, in the regions where variability increases, heat extremes occur 10-40% less frequently under extreme atmospheric conditions in 21st century, and 40% more frequently under extreme moisture limitation. An increasing number of extremes are driven by moisture limitation under warming, and occur even under a neutral or unfavorable atmospheric state, confirming that the increase in European heat extremes and associated variability increase are dominated by the the thermody- namic effect of moisture limitation. Second, I evaluate to what extent the increase in extreme European summer heat can be controlled by maintaining global warming below the limits in the UNFCCC Paris Agreement. Due to internal climate variability, only 40% of the summer months over Europe in a 2◦C warmer world would exhibit mean temperatures distinguish- able from those in a 1.5◦C world. This distinguishability is largest over Southern Europe, and decreases to around 10% of the summer months over Eastern Europe. Furthermore, the irreducible uncertainty arising from internal variability narrows the controllability of extreme maximum temperatures to the point that, by limiting global warming to 1.5◦C, only the 10% most extreme summer maximum temperatures in a 2◦C world could be averted. Lastly, I investigate where the major risk hotspots emerge under global warming for the main factors defining our vulnerability to extreme heat: maximum temper- atures, return periods of extreme temperatures, maximum temperature variability, sustained tropical night temperatures, and extreme wet bulb temperatures. My find- ings indicate that maintaining global warming below 2◦C is vital to minimize the risk of extreme heat and limit the exposure of non-adapted regions to harmful heat levels. However, each metric produces different major risk hotspots — from the highest maximum temperatures over the Arabic Peninsula, to the largest variability increase over India or Central Europe — highlighting the different potential risks and related adaptation measures that need to be considered over different regions. IIn dieser Dissertation untersuche ich, wie die interne Klimavariabilität Einfluss auf die sich ändernden Merkmale extremer Hitzeereignisse in Europa und global bei steigenden Treibhausgaskonzentrationen nimmt. Eine umfangreiche Stichprobe der internen Klimavariabilität ist eine unerlässliche Bedingung für die Beschreibung der Extremereignisse und deren sich veränderter Frequenz und Intensität in einer erwär- menden Welt. Um dies zu erreichen, verwende ich das größte existierende Ensemble eines globalen Klimamodells: Das Max-Planck-Institut Grand Ensemble (MPI-GE). Hinsichtlich der Ensemblegröße ist das MPI-GE derzeit das am besten geeignete Werk- zeug, um eine repräsentative Stichprobe der simulierten internen Klimavariabilität zu erhalten. Zuerst quantifiziere ich die Beiträge unterschiedlicher Antriebsmechanismen für extreme Hitzeereignisse über Europa und untersuche wie Änderungen der jewei- ligen Beiträge, bedingt durch eine Klimaerwärmung, sich auf die Variabilität der Hitzeereignisse auswirken. Mittels einer multiplen Regression, die gleichzeitig alle relevanten Quellen der Variabilität der Hitzeereignisse berücksichtigt, identifiziere ich die großskalige, atmosphärische Dynamik als den Hauptantrieb für Hitzeereignisse über Europa, während die lokalen thermodynamischen Effekte der Bodenfeuchte von zweiter Ordnung sind. Die meisten Hitzeereignisse werden begünstigt durch extreme atmosphärische Grundzustände, im gegenwärtigen wie auch im zukünftigen Klima. In Regionen, in denen die Variabilität von Hitzeereignissen bedingt durch die Klimaerwärmung ansteigt, reduziert sich allerdings der Beitrag des atmosphärischen Grundzustandes auf extreme Hitzeereignisse um 10-40%, während der Beitrag des lokalen thermodynamischen Effektes durch extreme Bodenfeuchte um 40% ansteigt. Diese, durch Bodenfeuchte verursachten Hitzeereignisse, entstehen sogar dann, wenn die atmosphärischen Grundzustände neutral oder ungeeignet für Extremereignisse sind. Dadurch wird deutlich, dass der Anstieg der extremen Hitzeereignisse über Eu- ropa im zukünftigen Klima durch lokale thermodynamische Effekte der Bodenfeuchte dominiert wird. In einem zweiten Schritt untersuche ich, inwieweit der Anstieg extremer Hit- zeereignisse über Europa durch die Einhaltung der Klimaziele des UNFCCC Paris Abkommens kontrollierbar ist. Die interne Klimavariabilität führt dazu, dass sich nur für 40% der Sommermonate über Europa die mittleren Temperaturen bei einer 2◦C globalen Erwärmung von jenen einer 1.5◦C globalen Erwärmung unterscheiden. Diese Unterscheidbarkeit ist am größten über Südeuropa und reduziert sich auf 10% der Sommermonate für Osteuropa. Zudem beschränkt die nichtreduzierbare Unsicherheit, die durch interne Klimavariabilität entsteht, die Kontrollierbarkeit von Temperatur- extremen nur soweit, dass die Reduktion der globalen Klimaerwärmung auf 1.5◦C lediglich 10% der extremen Sommermaximaltemperaturen einer 2◦C Erwärmung ver- hindern würde. In einem letzten Schritt analysiere ich, wo die größten Hotspots bezogen auf die globale Erwärmung und den Hauptfaktoren unserer Anfälligkeit gegenüber extremen Hitzeereignissen zu finden sind. Hierfür untersuche ich folgende Faktoren: Maximaltemperaturen, Wiederkehrperioden extremer Temperaturen, maximale Tem- peraturvariabilität, tropische Nachttemperaturen und extreme Feuchtlufttemperaturen. Meine Resultate zeigen, dass die Begrenzung der globalen Erwärmung auf unter 2◦C entscheidend für eine Minimierung der Risiken durch extreme Hitzeereignisse ist und die Gefahr von schädlichen Hitzeereignissen in nicht-angepassten Regionen ein- schränkt. Allerdings produziert jeder Faktor unterschiedliche regionale Hotspots — zum Beispiel die höchste Maximaltemperatur über der arabischen Halbinsel oder die größte Temperaturvariabilität über Indien und Zentraleuropa. Dies unterstreicht die unterschiedlichen potentiellen Risiken und Anpassungsstrategien, die für verschiede- ne Regionen berücksichtigt werden müssen

Hotspots of extreme heat under global warming

We evaluate how hotspots of different types of extreme summertime heat change under global warming increase of up to 4∘C; and which level of global warming allows us to avert the risk of these hotspots considering the irreducible range of possibilities defined by well-sampled internal variability. We use large samples of low-probability extremes simulated by the 100-member Max Planck Institute Grand Ensemble (MPI-GE) for five metrics of extreme heat: maximum absolute temperatures, return periods of extreme temperatures, maximum temperature variability, sustained tropical nights, and wet bulb temperatures. At 2∘C of warming, MPI-GE projects maximum summer temperatures below 50∘C over most of the world. Beyond 2∘C, this threshold is overshot in all continents, with the maximum projected temperatures in hotspots over the Arabic Peninsula. Extreme 1-in-100-years pre-industrial temperatures occur every 10–25 years already at 1.5∘C of warming. At 4∘C, these 1-in-100-years extremes are projected to occur every 1 to 2 years over most of the world. The range of maximum temperature variability increases by 10–50% at 2∘C of warming, and by 50–100% at 4∘C. Beyond 2∘C, heat stress is aggravated substantially over non-adapted areas by hot and humid conditions that occur rarely in a pre-industrial climate; while extreme pre-industrial tropical night conditions become common-pace already at 1.5∘C. At 4∘C of warming, tropical night hotspots spread polewards globally, and are sustained during more than 99% of all summer months in the tropics; whilst extreme monthly mean wet bulb temperatures beyond 26∘C spread both over large tropical as well as mid-latitude regions

Increasing spatiotemporal proximity of heat and precipitation extremes in a warming world quantified by a large model ensemble

Increases in climate hazards and their impacts mark one of the major challenges of climate change. Situations in which hazards occur close enough to one another to result in amplified impacts, because systems are insufficiently resilient or because hazards themselves are made more severe, are of special concern. We consider projected changes in such compounding hazards using the MPI Grand Ensemble under the moderate (RCP4.5) emissions scenario, which produces warming of about 2.25°C between pre-industrial (1851-1880) and 2100. We find that extreme heat events occurring on 3 or more consecutive days increase in frequency by 100-300%, and consecutive extreme precipitation events increase in most regions, nearly doubling for some. The chance of concurrent heat and drought leading to simultaneous maize failures in 3 or more breadbasket regions increases by about 50%, while interannual wet-dry oscillations become at least 20% more likely across much of the subtropics. Our results highlight the importance of taking compounding climate extremes into account when looking at possible tipping points of socio-environmental systems

A system of three transiting super-Earths in a cool dwarf star

We present the detection of three super-Earths transiting the cool star LP415-17, monitored by K2 mission in its 13th campaign. High resolution spectra obtained with HARPS-N/TNG showed that the star is a mid-late K dwarf. Using spectral synthesis models we infer its effective temperature, surface gravity and metallicity and subse- quently determined from evolutionary models a stellar radius of 0.58 R Sun. The planets have radii of 1.8, 2.6 and 1.9 R Earth and orbital periods of 6.34, 13.85 and 40.72 days. High resolution images discard any significant contamination by an intervening star in the line of sight. The orbit of the furthest planet has radius of 0.18 AU, close to the inner edge of the habitable zone. The system is suitable to improve our understanding of formation and dynamical evolution of super-Earth systems in the rocky - gaseous threshold, their atmospheres, internal structure, composition and interactions with host stars.Comment: Accepted for publication in MNRAS Letter

Rapidly Declining Body Temperature in a Tropical Human Population

Normal human body temperature (BT) has long been considered to be 37.0°C. Yet, BTs have declined over the past two centuries in the United States, coinciding with reductions in infection and increasing life expectancy. The generality of and reasons behind this phenomenon have not yet been well studied. Here, we show that Bolivian forager-farmers (n = 17,958 observations of 5481 adults age 15+ years) inhabiting a pathogen-rich environment exhibited higher BT when first examined in the early 21st century (~37.0°C). BT subsequently declined by ~0.05°C/year over 16 years of socioeconomic and epidemiological change to ~36.5°C by 2018. As predicted, infections and other lifestyle factors explain variation in BT, but these factors do not account for the temporal declines. Changes in physical activity, body composition, antibiotic usage, and thermal environment are potential causes of the temporal decline

The experience of taking methotrexate for juvenile idiopathic arthritis: results of a cross-sectional survey with children and young people

Background: Children and young people (CYP) with juvenile idiopathic arthritis (JIA) are known to have impaired health-related quality of life (HRQoL), which is improved significantly for many by treatment with methotrexate (MTX). However, a significant proportion of CYP experience difficulties in taking MTX, which may reduce its potential benefits for HRQoL. The aim of this research was to examine how CYP with JIA perceive MTX treatment and how this relates to HRQoL. Methods: CYP aged 8-16 years taking MTX for JIA completed an adapted Parent Adherence Report Questionnaire, which contains 100mm visual analogue scales, to assess difficulty taking MTX, adherence, frequency of negative reactions and helpfulness of MTX. They also completed the Pediatric Quality of Life Inventory (PedsQL) Generic and Rheumatology scales. We collected data on age, gender, JIA course, disease duration, MTX duration of use, route and dose. Number of inflamed and limited joints were indicators of disease severity. Results: 116 CYP participated. Most considered MTX helpful (median 87; interquartile range (IQR) 50.75–98) and reported adherence was high (median 98; IQR 90–100). There was greater variability on scores for difficulty (median 22; IQR 2–69) and frequency of negative reactions (median 14.5; IQR 1.25–80). Mean (S.D.) scores on the PedsQL Physical and Psychosocial subscales were 71.63 (24.02) and 71.78 (19.59) respectively, indicating poorer HRQoL than that reported by healthy children. After controlling for demographic and disease variables, poorer physical HRQoL was significantly accounted for by greater difficulty in taking MTX. Poorer psychosocial HRQoL was significantly accounted for by subcutaneous MTX administration, a lower rating of MTX helpfulness and a greater reported difficulty in taking MTX. Conclusions: Taking MTX for JIA was viewed as helpful by most CYP but HRQoL was poorer in those who reported greater difficulty in taking MTX