Stoeren wind farms wind flow patterns

Climate policy worldwide: experience with climate policy measures

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1 Zurich Open Repository and Archive University of Zurich Main Library Strickhofstrasse 39 CH-8057 Zurich Year: 2016 Climate policy worldwide: Experience with climate policy measures Michaelowa, Axel Abstract: Climate protection requires international cooperation. Their balance has been mixed so far. On the one hand, international and national climate protection policies have not been able to significantly slow down the global increase in greenhouse gas emissions over the past 20 years. On the other hand, emission taxes and regulations, accompanied by technical progress, have led to a considerable decrease in emissions in a number of countries, especially in Scandinavia, without weakening economic competitiveness. Cooperation outside the UN Framework Convention on Climate Change has so far not shown any visible effects worldwide, while the market mechanisms of the Kyoto Protocol have mobilized thousands of emission reduction projects around the world. Posted at the Zurich Open Repository and Archive, University of Zurich ZORA URL: Published Version Originally published at: Michaelowa, Axel (2016). Climate policy worldwide: experience with climate policy measures. Bern: Swiss Academies of Arts and Sciences.

2 Vol. 11, N o 5, Focus on Climate Switzerland Basics, Consequences and Perspectives

3 Editors Swiss Academies of Arts and Sciences House of Academies Laupenstrasse 7, Postfach, 3001 Bern A project by the Swiss Academy of Sciences (SCNAT) ProClim Forum for Climate and Global Environmental Change, Scientific Advisory Board ProClim Board of Trustees with the support of the Advisory Body on Climate Change Issues (OcCC) and the Federal Office for the Environment (FOEN) ISSN (print) ISSN (online) Editorial staff Sanja Hosi, Martina Mittler Editorial assistance Hannah Ambühl, Sarah Arnold, Linus Cadotsch, Michael Herger, Martin Kohli , Christoph Kull, Gabriele Müller-Ferch, Urs Neu, Christoph Ritz, Karin Ammon Editing Lucie Stooss Translation Jean-Jacques Daetwyler, Sciencepress Zieltext AG Design Olivia Zwygart Cover picture / montages Ruth Schürmann (FOEN archive, Matthias Hust, private archive) Print Vögeli AG, Langnau i. E. 1st edition, 2016 (3500 copies in German / 600 copies in French) The report can be obtained free of charge from ProClim or from the Swiss Academies of Arts and Sciences, 2016 Suggested citation from the Swiss Academies of Arts and Sciences (2016 ) Focus on Climate Switzerland. Basics, consequences and perspectives. Swiss Academies Reports 11 (5) report in electronic form and additional material available on

4 3 Focus on Switzerland's climate. Basics, consequences and perspectives Swiss climate Consequences and risks Infrastructures Cities and settlements Forests and fields Water resources Is Switzerland prepared for severe weather events? In the future, hospitals and rescue or security services could be more challenged than before in the event of extreme weather conditions. (Section 2.12) A world that is dependent on fossil fuels requires different infrastructures (road expansion, airports, power grids) than a CO 2 -free world. Therefore, today's infrastructure investments can later turn out to be unprofitable and endanger jobs. (Section 2.12) Infrastructures such as ski lifts or avalanche barriers that are now on permafrost soils can lose their stable subsoil. (Chapter 2.3 / 2.11) Hot summers transform cities into heat islands. Heat stress in our cities is one of the major challenges of climate change. In the summer of 2003, there were around 1,000 premature deaths from the heat. (Chapters 2.12 / 2.13 / 2.15) Settlements and buildings will be increasingly endangered by floods. Most large cities are built close to water. (Chapters 2.4 / 2.12 / 2.13) The spruce threatens to disappear from the Central Plateau, and it is also endangered in the protective forests in the mountains: The most important tree in Swiss forestry is sensitive to drought and suffers from the accelerated reproduction of the bark beetle. (Section 2.9) The cultivation of crops such as winter wheat and potatoes is made more difficult under the warmer conditions. Corn and vines, on the other hand, thrive better than they do today if there is enough moisture. (Section 2.10) pests such as B. the codling moth, will have two to three generations per year in the future instead of one or two as is now the case. (Chapter 2.10) The summer water shortage affects everyone who uses water, especially agriculture, which is increasingly dependent on water for irrigation. As a result, conflicts of interest about water use are increasing. (Chapters 1.8 / 2.4 / 2.10 / 2.11) The decrease in glaciers and snow as natural water reservoirs increases the need for artificial reservoirs for multi-purpose use. (Chapter 2.4 / 2.11) Consequences and risks Mitigation Adaptation Illustration: Sarah Arnold

5 Fields of action Active action is required, because the main cause of climate change is the burning of crude oil, gas and coal. If global warming is to be limited to below two degrees Celsius, as agreed by the global community, we must rapidly reduce greenhouse gas emissions. In the medium term, emissions must be net zero. We have many options for mitigating climate-related risks, taking advantage of opportunities and ensuring a climate-friendly society and economy. Mitigation: We influence climate change by reducing or even better avoiding greenhouse gas emissions. With this we throttle the temperature rise. Reduced commuting and traveling Fewer commutes: Thanks to modern telecommunications, work at home and video conferences are possible. (Section 3.4) Riding more bicycles and walking makes you fit and reduces motorized traffic. (Section 2.15 / 3.8) Good spatial planning, compact cities: where living, shopping, working and relaxing are close together, the transport routes are short. (Section 3.8) Adaptation Adaptation: We can respond to the challenge of "climate change" by minimizing risks and taking advantage of opportunities. Less air travel, but longer stays or holidays in Switzerland reduce travel time and travel stress. (Section 3.5) When buying a car, choosing low-emission and economical models with only as much power as is actually required helps improve energy efficiency. (Section 3.5)

6 Living and heating Use energy Eating and drinking Be healthy parks, shady trees and open water areas reduce the heat island effect and thus contribute to the quality of life in cities. (Section 3.8) Well-insulated buildings reduce the heating requirement and at the same time prevent heat build-up in summer. Climate-compatible building means more than just isolation. So it should e.g. also contribute to improving natural ventilation in cities. (Chapters 3.4 / 3.8) Solar systems, heat pumps, combined heat and power and district heating networks can replace oil and gas heating systems. (Section 3.4) Political regulations on CO 2 emissions and energy consumption, price signals and the consideration of external costs can promote CO 2 -free energy procurement and use. (Section 3.4) Energy labels on products or buildings motivate private households to invest in energy-efficient devices and systems. (Section 3.3) Changes in behavior can reduce energy demand, for example by switching off electronic devices when they are not in use. (Section 3.3) The energy saved in one place is often used in the same or even greater amount elsewhere. Anyone who recognizes this effect can avoid it. (Section 3.3) Distribute and save water for the field intelligently: If the soil is cultivated carefully, it retains water better, and winter crops such as winter rape or barley use less water for cultivation. Low-loss irrigation systems are increasingly being planned in the central and western plateau. (Section 2.10) We can all throw away less food, switch to a low-meat diet or reduce overall consumption and thus easily contribute to CO 2 reduction. (Chapter 2.10) Learning to deal with heat: Drink enough in hot weather, avoid the sun and balance the water and salt balance after exercising. (Section 2.15) Find out about the spread of diseases, e. B. How to protect yourself when mosquitoes transmit new diseases in Switzerland, or where ticks colonize new areas. (Section 2.15)

7 6 Focus on Switzerland's climate. Basics, consequences and prospects Switzerland is very sensitive to climate change. Compared to the global mean, the warming in the Alpine region is around twice as strong. The natural and cultural area of ​​Switzerland is affected in many ways by the effects of climate change. Animals and plants Mountains, snow and ice Extreme weather Rivers and lakes Drier summers with less runoff are more common. This is due to the decreasing amounts of summer precipitation and the significantly smaller proportion of water from the snow and ice melt. (Chapters 1.7 / 2.4) The runoff volumes tend to increase in winter. Winter precipitation falls more frequently than rain and contributes directly to runoff. (Chapters 1.7 / 2.4) The higher temperatures make the flood season longer, and the intensification of heavy precipitation increases the peak runoff. (Chapters 1.8 / 2.4) Many animals and plants that feel too warm or too dry migrate to the heights, with the risk of encountering cramped habitats with more competition. (Section 2.7) Some species can only shift their habitat slowly or they colonize flat areas where there is no way out to more favorable habitats. (Section 2.8) The seasonal rhythm of the flora and fauna changes and can disrupt the interaction of the species: Insects miss the flowering time. (Section 2.8) The Swiss glaciers are disappearing. Most of it should melt away by the end of the century. (Chapters 1.9 / 2.3 / 2.14) In the high mountains, a new landscape of rocks, rubble, sparse vegetation and many mostly smaller lakes is emerging. The latter increase the potential for natural hazards, but also offer possible uses. (Chapters 2.3 / 2.5) In the future, the snow season will be shortened by several weeks and the snow line will rise by several hundred meters. (Section 2.3 / 2.11) Permafrost in the high mountains thaws down to deeper layers over the long term, which can lead to increased rockfalls and rock falls. (Chapters 2.3 / 2.5 / 2.6) It is getting hotter: In summer, more frequent and longer periods of heat and more intense heat days can be expected. This trend is already being observed today. (Section 1.8) Heavy precipitation: In the future, it is expected that heavy precipitation will become more frequent and violent, trigger more debris flows and landslides and increase the risk of flooding. (Chapters 1.8 / 2.4) The risk of drought increases: Overall, fewer rainy days and longer dry periods are predicted for the summer. (Section 1.8)

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9 Swiss Climate Focus Basics, Consequences and Perspectives

10 Swiss Academies Reports, Vol. 11, N o 5, table of contents Editorial 11 Synthesis 13 Part 1: Physical principles 21 Introductory explanations 22 Why are climate scenarios needed?

11 10 Focus on Switzerland's climate. Basics, consequences and perspectives Part 3: Mitigation 149 Decarbonisation Transformation towards climate compatibility Introduction Emission trends Past and future emissions Changes in behavior Energy Transport Technical aspects Agriculture, forestry and other land use Urban strategies for climate change 186 Part 4: Climate policy Introduction Swiss climate policy Creation and development of a climate policy Climate policy worldwide: experience with climate policy measures international cooperation 205 experts 210 IPCC referencing 211

12 Swiss Academies Reports, Vol. 11, N o 5, Editorial 2015 was by far the warmest year on a global level since measurements began. In 2015, the highest annual mean temperatures since measurements began in 1864 were also recorded in Switzerland. Likewise, each of the past five decades has been warmer than the previous one. The current climate change manifests itself not only in the data series, but also increasingly in the global ecosystems and has effects on societies. The international research community has compiled the results of the current research in the Fifth IPCC Assessment Report. These facts impressively show how our environment has already changed due to climate change worldwide and which emissions reductions should be aimed for in order to keep the expected long-term negative effects for most societies as low as possible. In the present report, on the initiative of OcCC and ProClim, numerous experts from the Swiss research community have compiled the results relevant for Switzerland from the latest IPCC assessment report and expanded them with further research results that are central to Switzerland or that relate to Switzerland . The facts speak for themselves: Climate change will not leave Switzerland indifferent either. With the successful conclusion of the international climate negotiations in Paris under the auspices of the UN in December 2015, a first important milestone was reached at the international level in order to meet the challenges that arise. With the aim of limiting the rise in global warming to less than two degrees Celsius and even intensifying these efforts by limiting the temperature rise to a maximum of 1.5 degrees Celsius, massive and continuous emission reductions and finally a complete departure from that combustion of fossil fuels . But what do these goals mean for society, economy and politics? Here, science continues to be required to communicate clearly and understandably and to provide answers in all areas. What is certain is that great efforts are required to achieve these goals in Switzerland as well. Switzerland's national goal of reducing greenhouse gas emissions by 50 percent by 2030 (30 percent in Switzerland, 20 percent abroad) compared to 1990 levels is a first step. In a next step, emissions should then approach zero in the second half of the 21st century. This requires a fundamental transformation of society and the economy. All the planned investments with long investment cycles and the planned large infrastructure projects must already be critically examined today with regard to their climate compatibility. In future, society, business and politics will have to take climate issues into account in almost all issues in order to be able to master this change successfully. To this end, the necessary measures must be able to gain a majority at all political levels. In addition, an awareness of the urgency of the problem must be created. ProClim and OcCC thank the Swiss Research Association for compiling the weighty facts and showing the urgency of the problem as well as possible solutions for drastically reducing emissions and for adapting to climate change. Science calls on the various actors at all political levels to take the necessary measures consistently and against the background of promoting the common good. NR Dr. Kathy Riklin (OcCC) Prof. Dr. Heinz Gutscher (ProClim)

13 12 Focus on Switzerland's climate. Basics, consequences and perspectives

14 synthesis

15 14 Focus on Switzerland's climate. Basics, consequences and perspectives Climate observations and the results of research show clearly and unequivocally how the climate has already changed, which consequences are already clearly visible and in which direction the change is continuing. The problem areas associated with climate change have largely been identified and solutions are available. Concrete recommendations for action can already be derived for Switzerland today (see OcCC's strategic recommendations on climate policy 2015). The effects will intensify in the coming decades and present society and the economy with major challenges: since the beginning of systematic measurements (1864) until today (2016), the average temperature in Switzerland has increased by around 1.8 degrees Celsius (see also Chap 1.6 Temperature, p. 40), seen globally it is around 0.85 degrees Celsius. The main causes of warming are the use of fossil fuels, cement production and land use changes by humans (e.g. deforestation) as well as the associated emissions of CO 2 and other greenhouse gases. Due to the currently increasing greenhouse gas emissions, man-made climate change will continue in the future. The changes caused as well as the changed climate will persist for centuries. With increasing warming, the risks for ecosystems and society increase. The resulting dangers can only be countered to a limited extent with adaptation measures. In addition, these are associated with increasingly high costs. The greatest direct challenges of climate change for Switzerland are on the one hand extremes such as heat waves, dry periods or heavy precipitation as well as other related natural hazards. On the other hand, there are creeping, sometimes irreversible, changes in landscapes and ecosystems such as glacier retreat or changes in biodiversity, water quality and the effects of pests and diseases. These changes have a direct impact on society (e.g. health) and the economy (e.g. tourism) and are already causing costs. The financial outlay for averting and minimizing damage as well as the risks will continue to increase due to the ongoing changes with increasing climate change. Switzerland has a strong international network in economic terms. It will therefore also be affected by indirect climate impacts on a global level, for example in foreign trade or the consequences of migration. The question is not whether climate change will affect Switzerland, but how the effects will manifest themselves locally and what risks and costs will arise for individual areas and sectors. Understanding the local effects is the key to cost-effective adaptation, which must be coordinated spatially as well as technically. In order to prioritize measures, a detailed, macroeconomic view of the expenses already incurred and expected in the future is necessary.

16 Swiss Academies Reports, Vol. 11, N o 5, At the 21st Climate Conference in Paris (2015), international politics passed a legally binding agreement for all countries; This aims to limit the global rise in temperatures to well below two degrees Celsius and to limit the effects of climate change. This requires a consistent and drastic reduction in greenhouse gas emissions in all activities and processes in our society. In order to limit the already existing and expected future effects, target-oriented solutions in the areas of mitigation and adaptation are therefore required immediately: At present, climate change is still developing along an emission path that, if nothing is changed, will overshoot the agreed warming limit.Any stabilization of the global temperature regardless of the desired maximum warming can only take place if the net CO 2 emissions are ultimately reduced to zero globally. As a result, a complete replacement of all fossil fuels is necessary in all sectors (electricity, transport, industry, infrastructure and buildings); a large part of the fossil energy reserves that are still available must therefore not be extracted for combustion purposes. In terms of global emissions, a trend reversal must set in soon in order to still be able to achieve the climate targets. Mitigation and adaptation with the participation of all states are central to solving the global climate problem. Although few nations with their high emissions have so far been primarily responsible for increasing greenhouse gas concentrations, ultimately every state can and must make its contribution to improving the situation, reducing its CO 2 emissions and ultimately preventing them. Since the countries hardest hit by the consequences do not have the resources for low-carbon development, they are dependent on the help of industrialized countries. Failure to act today reduces the room for maneuver and later causes higher costs, both in the area of ​​adaptation and mitigation: increasingly ambitious mitigation steps are necessary in order to still be able to meet the set goal. If the measures remain inadequate, the warming will go well beyond the set temperature target. While the national and international level is required above all for the development and implementation of mitigation strategies, the implementation of adaptation measures requires increased commitment and cooperation between the actors at the local level, including in Switzerland.

17 16 Focus on Switzerland's climate. Basics, consequences and perspectives An ambitious Swiss climate policy that respects the internationally agreed climate goals shows Swiss society and economy on a sustainable, future-oriented path: A change towards a sustainable approach to the environment will be inevitable, on an international as well as national level; Climate policy is a key factor in this context. Switzerland has excellent intellectual, economic and technical prerequisites and the corresponding state structures to successfully commit to and advance this change. It can also increase its commitment by advocating effective global measures in international negotiations such as the United Nations Climate Change Convention on Climate Change (UNFCCC) or the World Trade Organization (WTO) trade law. Swiss companies, products and technology cause greenhouse gas emissions abroad, but can also help to reduce them, for example through technology transfers or exports of low-emission technologies. Swiss companies are therefore required to include climate change in their long-term strategies. Reduction and adaptation measures at home and abroad can be of increasing economic interest for Switzerland, as new, future-oriented technology can also be developed and marketed for this purpose. In order to take advantage of these opportunities in good time, Switzerland must remain internationally networked and innovative. It can thus act with foresight in the interests of globally sustainable economic development and thus also its welfare.

18 Swiss Academies Reports, Vol. 11, No 5, The challenge of climate change must be seen in the context of other challenges for society, the economy and the environment. Careful action and the inclusion of different perspectives make it possible to master current and worsening problems. Today's societies thus maintain their solid livelihood and hand over an environment that is as intact as possible to the following generations, which gives them room for maneuver and creative freedom without having to take on the major legacies of the present: In 2015, around 7.3 billion people lived on earth. That number is likely to grow to around 9.3 billion by 2050 and potentially over 10 billion by 2100. Rapid growth is taking place in emerging and developing countries in particular. Around 70 percent of the world's population is likely to live in urbanized areas as early as 2050 and participate in economic development, which may significantly increase their consumption of resources. It is therefore clear that the areas of infrastructures and buildings, energy supply, mobility, transport and industry will play a key role in future emissions development. If these developments are planned with foresight and implemented using efficient technologies, they offer an opportunity for the lowest possible emissions and sustainable development. Land use changes worldwide (deforestation, food production, etc.) also contribute a significant share of emissions that need to be reduced. The current problems are exacerbated by the fact that a large part of the rapidly changing areas has to struggle with difficult political and economic framework conditions, is feeling the effects of climate change more and more and therefore has to implement adaptation measures. This globally emerging population and social development requires that climate and resource-saving technology be used and that a transformation towards a sustainable lifestyle takes place. The industrialized nations are therefore required not only to implement the transformation process within their own borders, but also to actively provide support, know-how and financial resources in order to advance this generational task on a global level. Specifically, among other things, it is important to trim the global building stock to minimal energy requirements within 30 to 50 years, which for many industrialized countries requires the early depreciation of very large sums of money. In addition, fossil fuels in the electricity and transport sectors must be reduced significantly at the same time, which is also costly and will take a long time with the existing expensive infrastructures. That is why the truth about costs along the entire energy conversion chain is a priority, i.e. the internalization of external costs and a steadily increasing CO 2 price. To protect the climate, it is necessary to abandon fossil fuels or, for countries that are not yet industrialized, to skip the fossil fuel age. In order to make this possible, state structures are needed that set appropriate, favorable political, economic and social framework conditions. Ultimately, in order to find a sustainable path for global, social and economic development, a transformation to a sustainable lifestyle at the level of the individual is required. Living more consciously and sustainably does not mean giving up everything; on the contrary, this can lead to a higher quality of life, as currently increasing impairments, such as those caused by traffic, can decrease again.

19 18 Focus on Switzerland's climate. Basics, consequences and perspectives If Switzerland wants to stick to a path that is compatible with the international climate targets, it must now take decisive and effective steps to move away from the consumption of fossil fuels and keep electricity demand CO 2 -free. In addition, it should continue to campaign credibly internationally for an ambitious, target-oriented climate policy. Regardless of this, adaptation measures must also be taken in Switzerland. This requires an understanding of the local situation and the specific effects that is comprehensively supported by the sciences. Cost transparency is also required, as are political mechanisms that bind the cantonal, regional and local levels to action. Only a solid and uniform database on the past and the expected climate change enables appropriate measures to be weighed up and prioritized. In addition, especially in a direct democracy, it is important to convince the citizens of the importance of the challenges that arise and to show positive images of the necessary change. In order to form majority alliances for the lengthy political process that is now required, it is now urgent to put the above issues on the agenda of all citizens, all politicians, all parties and every association. The Advisory Body on Climate Change (OcCC) provides specific recommendations for action in its strategic recommendations on climate policy 2015. The synthesis was developed jointly by Prof. Dr. Chris tof Appenzeller (MeteoSwiss and ETH Zurich), Prof. Dr. Konstantinos Boulouchos (ETH Zurich), Prof. Dr. David Bresch (ETH Zurich), Andrea Burkhardt (FOEN), Prof. Dr. Andreas Fischlin (ETH Zurich), Prof. Dr. Heinz Gutscher (University of Zurich, President of the ProClim Board of Trustees), Prof. Dr. Martin Hoelzle (University of Freiburg), Prof. Dr. Fortunat Joos (University of Bern), Prof. Dr. Peter Knoepfel (University of Lausanne), Prof. Dr. Reto Knutti (ETH Zurich), Dr. Pamela Köllner (FOEN), Prof. Dr. Christian Körner (University of Basel), Dr. Christoph Kull (OcCC), Prof. Dr. Peter Messerli (University of Bern), Prof. Dr. Martine Rebetez (University of Neuchâtel and WSL), Dr. Kathy Riklin (President OcCC), Prof. Dr. Renate Schubert (ETH Zurich), Prof. Dr. Thomas Stocker (University of Bern), Prof. Dr. Philippe Thalmann (ETH Lausanne), Prof. Dr. Rolf Weingartner (University of Bern).

20 Adjustment reduction

21 Photo: Matthias Huss 20 Focus on Switzerland's climate. Basics, consequences and perspectives

22 Part 1: Basic physical principles Authors Prof. Dr. Stefan Brönnimann Professor of Climatology, Institute of Geography, Oeschger Center for Climate Research, University of Bern Dr. Andreas M. Fischer Research Associate, Analysis and Forecasting Department, Federal Office for Meteorology and Climatology (MeteoSwiss), Zurich Airport Dr. Erich M. Fischer Senior Researcher, Institute for Atmosphere and Climate (IAC), ETH Zurich PD Dr. Christian Huggel Head Researcher, Climate Impacts, Risks and Adaptation, Glaciology and Geomorphodynamics, Geographical Institute, University of Zurich Prof. Dr. Reto Knutti Professor of Climate Physics, Institute for Atmosphere and Climate (IAC), ETH Zurich Dr. Joeri Rogelj Research Fellow, Energy Program, International Institute for Applied Systems Analysis (IIASA), Laxenburg Until June 2014: Postdoc, Institute for Atmosphere and Climate (IAC), ETH Zurich Prof. Dr. Christoph Schär Professor for Climate and Water Cycle, Institute for Atmosphere and Climate (IAC), ETH Zurich Prof. Dr. Sonia I. Seneviratne Professor for Land-Climate Dynamics, Institute for Atmosphere and Climate (IAC), ETH Zurich Prof. Dr. Thomas F. Stocker Professor of Climate and Environmental Physics, Institute of Physics, University of Bern Co-Chairman of Working Group I Fifth IPCC Assessment Report Peter Mani Specialist natural hazards and member of the management, geo7 AG, Geoscientific Office, Bern Dr. Christoph Marty Research Associate, Snow and Permafrost, WSL Institute for Snow and Avalanche Research (SLF), Davos Dorf Dr. Urs Neu Deputy Director, ProClim Forum for Climate and Global Change, Swiss Academy of Sciences (SCNAT), Bern Dr. Jeannette Nötzli Research Associate, Snow and Permafrost, WSL Institute for Snow and Avalanche Research (SLF), Davos Dorf Until July 2015: Senior Assistant, Glaciology and Geomorphodynamics Group, Institute of Geography, University of Zurich Dr. Frank Paul Head Researcher, Glaciology and Geomorphodynamics Group, Institute of Geography, University of Zurich Dr. Gian-Kasper Plattner Directorate, Federal Research Institute for Forests, Snow and Landscape (WSL), Birmensdorf Until December 2015: Researcher, Climate and Environmental Physics, Physics Institute, University of Bern Until December 2015: Scientific Director, Secretariat IPCC Working Group I, University of Bern

23 22 Focus on Switzerland's climate. Basics, consequences and perspectives Introductory explanations of probability information in this report In this report, the information on the probability of a finding used in the IPCC assessment report is used in part for individual results of the IPCC (this relates to probability information in italics in this report). The specification denotes the estimated probability that the actual value or situation is in the specified value range or corresponds to the specified situation. The expressions used in italics correspond to the following ranges: practically certain% probability very likely% likely% just as likely as not 33 66% unlikely 0 33% very unlikely 0 10% particularly unlikely 0 1% Fifth IPCC Assessment Report Some of the statements in This report refers to the Fifth Assessment Report of the IPCC, which was published in three volumes in 2013 (Volume I) and 2014 (Volume II and III). 1 Volume I (Scientific Foundations) presents clear and reliable conclusions in the context of a global assessment of climate science. The results confirm and expand our scientific understanding of the climate system and the role of greenhouse gas emissions. Volume II (Consequences, Adaptation and Vulnerability) focuses on why climate change is important and looks at this issue at both global (Part A) and regional levels (Part B). It deals with effects that have already occurred and the risks of future effects. Volume III (Climate Change Mitigation) provides a comprehensive assessment of all possible options (technical or behavioral) for climate change mitigation in the energy, transportation, buildings, industry and land use sectors and assesses policy options at different levels of government from local to international scale. The IPCC The IPCC (Intergovernmental Committee on Climate Change) was founded in 1988 as an intergovernmental body jointly by the World Meteorological Organization (WMO) and the United Nations Environment Program (UNEP). It provides policy makers with the most reliable objective, scientific and technical advice. Since 1990, this series of IPCC Assessment Reports, Special Reports, Technical Documents, Methodology Reports and other products has become a standard reference work. The Fifth Assessment Report of the IPCC provides an important source of information for political decision-makers around the world and supports them in dealing with the challenges of climate change. The preparation of these reports was made possible through the commitment and voluntary work of hundreds of experts worldwide who represent a wide range of disciplines. What is «climate protection»? According to Duden, the term “climate protection” refers to “the entirety of measures to avoid undesirable climate change”. This term is only used in the German-speaking area. The IPCC does not use an analogous term. 1

24 Swiss Academies Reports, Vol. 11, N o 5, Why do we need climate scenarios? “Unthinkable” flood events in practice and science The past shows that when it comes to extreme events, one must also think about the “unthinkable”. When it comes to such questions, practice and science are equally challenged, and cooperation is essential. New methods must be developed to assess extreme risks, for example caused by extremely rare combinations of events with massive effects. These must take into account both past events and climate change. Peter Mani (geo7 AG), Christoph Schär (ETH Zurich) Introduction The major flood events in recent years (1999, 2005, 2007) resulted in enormous damage (Hilker et al. 2009). Various studies show that even larger events are possible. In 1480, for example, intensive snowmelt after a snowy winter, followed by three days of heavy precipitation, caused a record flood (Pfister & Wetter 2011). The “year without a summer”, caused by the eruption of the Tambora volcano, led to three packets of snow melting in the spring of 1817, which led to the highest lake level ever recorded at Lake Constance, and this for 89 days (Kobelt 1926; Pfister 1999). The study by geo7 et al. (2007) on extreme floods in the Aare catchment area shows that such extreme events are also possible in the future and that they have potentially far-reaching consequences for society, the economy and the environment. Such events often affect large areas and threaten not only settlement areas but also vital infrastructures such as hospitals, water supplies, transport and communication links and critical structures such as nuclear power plants and dams. These results in major challenges, all the more since disasters were rare in Switzerland between the end of the 19th century and the 1970s (Pfister 2009), which led to a false sense of security and insufficient sensitivity to rarely occurring events. Extreme flood events can be triggered by brief extreme heavy rain, but also by long periods of precipitation. If the hydrological system gets out of balance as a result of such loads, this can lead to tipping effects or feedback. The deposition of debris in a channel reduces the drainage and thus transport capacity, which in turn allows more debris to be deposited. Such situations can occur more frequently or to a greater extent due to the changes that can be expected as a result of climate change. As a result, observed time series from the past lose their value as a yardstick for the future. They must therefore be combined with the findings from the climate scenarios and reweighted. The reactor disaster in Fukushima shows that extremely rare events can occur: on March 11, 2011, the worst earthquake since records began occurred off the east coast of the Japanese main island. The tsunami caused by this devastated large stretches of coast, claimed more than 1,000 deaths and damaged around one million buildings (GRS 2015). The tsunami also destroyed important safety systems at the Fukushima Daiichi nuclear power plant, which resulted in a meltdown in four reactor blocks. Around people have been evacuated and the consequences will still take decades to rectify. In Switzerland, too, extremely rare events, especially floods, can have serious consequences: Most of the larger cities are located directly on rivers, and all nuclear power plants are on the banks of the Aare or Rhine. The analysis of rare flood events has therefore also become more topical in Switzerland in the wake of Fukushima. EXAR project: Assessment of the consequences of very rare flood events One project in Switzerland that uses existing series of measurements, analyzes of historical flood events and the results of climate simulations to create a new basis for assessing the consequences of very rare flood events is EXAR (Danger Bases for Extreme Floods on the Aare and Rhine). This was carried out by the Federal Offices for the Environment (FOEN), for Energy (BFE), for Civil Protection (BAPS) and

25 24 Focus on Switzerland's climate. Basics, consequences and prospects Figure 1.1: The flood of August 2005 caused major damage in Oey / BE, among other places. Throughout Switzerland, the flood caused costs of three billion Swiss francs. (Source: Fritz Schürch) as initiated by the Federal Nuclear Safety Inspectorate (ENSI). In a first phase, practical engineering and consulting companies worked with a group of scientific experts to develop a method for analyzing extreme floods with regard to their discharge peaks, duration, discharge volume, effects on river morphology and the influence of floating debris (Fig. 1.2).Since these are very rare events that can only occur every year, statements on the uncertainties are of central importance in addition to the quantitative values ​​for the event sizes. The natural, system-related variability as well as the model uncertainty must be taken into account. In a second phase, the analyzes are carried out with the method developed. Influence of climate change The meteorological conditions that lead to heavy precipitation and flood events are ultimately determined by the global climate system. In the Alpine region, the large-scale distribution of temperature and humidity, the position and intensity of low pressure areas and their trajectories as well as temperature-related changes in snow hydrology are decisive. Their effects on the summer climate are particularly important because many Swiss bodies of water have flood peaks in the warm season. However, changes in the winter half-year must also be taken into account, as the warming in winter means that more precipitation will fall in the form of rain instead of snow. The classic approach to dealing with such questions uses a model chain of global and regional

26 Swiss Academies Reports, Vol. 11, N o 5, Thunderstorms Precipitation Long-term precipitation Runoff formation Snowmelt Debris delivery Debris retention Riverside erosion and slides Flood waves Sediment processes, channel morphology Dam overflow, erosion Discharge (peak, permanent, volume) Driftwood entry Ice drift Flood transport, other retention blockage Figure 1.2: Overview of the EXAR method. Influencing factors for the investigation of extreme floods. (Source: Adapted from Emch + Berger et al. 2015) len climate models that are driven by emission scenarios. In a final step, this chain can also drive hydrological models. The climate models have been in qualitative agreement for about 10 years and predict a reduction in mean precipitation in Central Europe for the summer (CH; Rajczak et al. 2013). At the same time, according to the models, the daily precipitation peaks increase slightly and the hourly precipitation peaks increase significantly (Ban et al. 2015; Giorgi et al. 2016). This increase affects convective events, i.e. thunderstorms and showers, and is also visible in the observations made over the last few decades (Scherrer et al. 2016). So far, however, studies of this type have only analyzed comparatively frequent events with a return period of no more than 50 to 100 years. Indications of the development of floods in the course of climate change can also be obtained from the past, provided that appropriate indices can be derived from natural climate archives over long periods of time. The frequency of large-scale summer floods for the past 2500 years was recently reconstructed based on sediments from 10 lakes in the Alpine region (Fig. 1.3) (Glur et al. 2013). The results show that large-scale floods occur more frequently in comparatively cool summers. This agrees with earlier studies that found an increased frequency of severe floods in the Little Ice Age and a reduced frequency in the Medieval Warm Age (Schmocker-Fackel et al. 2010). This result is qualitatively consistent with the decrease in summer precipitation projected by the climate models, especially if one takes into account that the projected increase in heavy precipitation is short-term and mostly small-scale events and not large-scale events such as the summer floods of August So that would mean that short-term, small-scale events become more frequent, while stronger, large-scale events could decrease. Future challenges Although a qualitative understanding of the sensitivity of the summer climate and its heavy precipitation (large-scale decrease in precipitation coupled with an increase in intensity) is beginning to emerge, there are still great uncertainties. In particular, it should be emphasized that reliable quantitative statements are only possible for relatively frequent events with return periods of less than 100 years, even if climate change occurs

27 26 Focus on Switzerland's climate. Basics, consequences and perspectives bc Frequency of flood events (%) d Temperature anomalies (C) -2-1.5-1 -0.5 0 0.5 cooler warmer e Recorded glacier advances / 1,500 years (AD / BC) Chr) Figure 1.3: Comparison of the temperature anomalies with the frequency of flood events. Large-scale flood events were more frequent in phases with cool summers than in phases with warm summers. (Source: Glur et al. 2013) is neglected. Open questions arise in the following areas: Hydrometeorological event chains: This is understood to be a combination of hydrologically relevant rare events. One example is the coincidence of the accumulation of snow over two winters and one summer in connection with the Tambora eruption, as described in the introduction, followed by intense snowmelt and heavy precipitation. Snow hydrology: The increase in rain at the expense of snowfall is primarily temperature-driven and can have a major influence on runoff formation (FOEN 2012). Due to its water storage capacity, snow often has a dampening effect on runoff formation. As the snow line rises, certain flood scenarios will become more likely. Internal variability in the climate system: Changes in natural fluctuations such as the frequency of certain weather conditions (on a time scale from days to years) could have a decisive influence on the frequency of extremely rare events. In addition to interannual (year-to-year) variability, short time scales are also important. If, for example, the persistence of weather conditions changes, this can lead to prolonged precipitation or dry periods. Conclusion In the past ten years, significant advances have been made in modeling the climate system, including in the area of ​​extreme events. A project like EXAR would therefore have been hardly conceivable ten years ago, since the uncertainties in the model results in particular had hardly been quantified. Hydrological modeling has also made great progress and now allows the simulation of complex chains of events. This means that important information can now also be sketched out on very rare events. However, there are still major challenges, for example in connection with changes in variability or when considering an unexpected sequence of several events. With all this, however, it must not be forgotten that there is no such thing as absolute security and that there will always be “unknown unknowns”, i.e. unknown factors or developments that one is not even aware of. However, this does not release anyone from using the existing estimates as a guide.

28 Swiss Academies Reports, Vol. 11, N o 5, References FOEN (2012) Effects of climate change on water resources and bodies of water. Synthesis report on the project “Climate change and hydrology in Switzerland” (CCHydro). Federal Office for the Environment, Bern. Umwelt-Wissen 1217: 76 pp. Ban N, Schmidli J, Schär C (2014) Evaluation of the convection-resolving regional climate modeling approach in decade-long simulations. Journal of Geophysical Research 119: CH2011 (2011) Swiss Climate Change Scenarios CH2011. Published by C2SM, MeteoSwiss, ETH, NCCR Climate, and OcCC, Zurich, Switzerland, 88 pp. ISBN: Emch + Berger, geo7, HydroCosmos (2015) Extreme flooding events Aare-Rhein (EXAR). Methodology report. Geo7, IUB engineering company, Hunziker, Zarn & Partner, Emch + Berger (2007) Extreme floods in the Aare catchment area. Construction, Transport and Energy Directorate of the Canton of Bern. Giorgi F, Torma C, Coppola E, Ban N, Schär C, Somot S (2016) Enhanced summer convective rainfall at Alpine high elevations in response to climate warming. Nature Geoscience 9: Glur L, Wirth SB, Büntgen U, Gilli A, Haug GH, Schär C, Beer J, Anselmetti FS (2013) Frequent floods in the European Alps coincide with cooler periods of the past 2500 years. Scientific Reports 3: GRS (2015) Fukushima Daiichi Course of the accident, radiological consequences. Society for Plant and Reactor Safety (GRS) (4th ed.). Hilker N, Badoux A, Hegg C (2009) The Swiss flood and landslide damage database Natural Hazards and Earth System Sciences 9: Kobelt K (1926) The regulation of Lake Constance. Flood protection, power plant use and shipping. Bern. Pfister C (1999) Weather forecast: 500 years of climate variations and natural disasters (). Haupt Verlag, Bern. Pfister C (2009) The “disaster gap” of the 20th century and the loss of traditional risk awareness. GAIA 3: Pfister C, Wetter O (2011) The millennium flood of 1480 on the Aare and Rhine. Berner Zeitschrift für Geschichte und Heimatkunde 73: Rajczak J, Pall P, Schär C (2013) Projections of extreme precipitation events in regional climate simulations for Europe and the Alpine region. Journal of Geophysical Research Atmospheres 118: Scherrer SC, Fischer EM, Posselt R, Liniger MA, Croci-Maspoli M, Knutti R (2016) Emerging trends in heavy precipitation and hot temperature extremes in Switzerland. Journal of Geophysical Research: Atmospheres 121: Schmocker-Fackel P, Naef F (2010) Changes in flood frequencies in Switzerland since Hydrology and Earth System Sciences 14:

29 28 Focus on Switzerland's climate. Basics, consequences and perspectives 1.1 Introduction "The warming of the climate system is clear" and "The human influence on the climate system is clear". These main statements in the Fifth IPCC Assessment Report not only summarize the core problem, but also show that decades of research and observation of the climate system have led to clear findings, even if there are still numerous unanswered questions. Urs Neu (ProClim / SCNAT) Temperatures are rising and we know why The earth's surface has warmed extraordinarily strongly for several decades on a global average (see also Chapter 1.6 Temperature, p. 40) and we know why. The increasing emissions of greenhouse gases into the atmosphere through the burning of fossil fuels and fuels, especially carbon dioxide (CO 2), as well as the deforestation of tropical rainforests and land use are changing the earth's radiation budget. Greenhouse gases such as carbon dioxide, water vapor, methane or nitrous oxide have an effect in the atmosphere that is comparable to that of the windows in a glass house - they prevent efficient radiation, even if the physical process is different and more complex. This process has been scientifically well researched so that its effect can be reliably estimated. We also know that this climate development is extraordinary: We recognize this, for example, from the fact that the CO 2 concentration in the earth's atmosphere has barely exceeded the value of 280 ppm (parts per million) in recent years, but within the scope of the current increase in April 2014 exceeded the mark of 400 ppm for the first time and is therefore over 40 percent higher (Fig. 1.4). in the air and because water vapor is the most important greenhouse gas, the warming is intensified. This effect is well known. A second example is the effects of clouds: stronger evaporation and more water in the air also change the cloud cover, but it is not clear how exactly. High clouds increase warming (they are thin and act like greenhouse gases), low-lying clouds have a cooling effect (they reflect solar radiation). The warming effects are likely to predominate, but the uncertainties are considerable. The basic principle is known, the more greenhouse gases get into the atmosphere, the stronger the warming. We do not know the exact amount, but an approximate range, that is, between two to four degrees Celsius warming with a doubling of the CO 2 concentration. Observations from the recent past (see also chapter 1.2 The past climate, p. 32) show the effect of man-made emissions, those from the distant past show us how changes in the climate system can affect and allow us to observe and anticipate To put changes in a historical context. Complex feedback loops The climate system consists not only of the atmosphere, but is also influenced by the ocean, ice and snow, the soil, the vegetation and the land areas cultivated by humans. These components are in constant contact with the atmosphere. If one of these parts changes, the others change too. As a result, a warming of the atmosphere causes changes in the whole system, which in turn affect the whole system. So there is a series of feedbacks that can weaken or intensify the original change. An example of such feedback is that warming leads to an increase in the water vapor content. Natural fluctuations and human influence Timescale from many million years (due to the shifting of the continents), from to years (change in the Earth's orbit parameters) or from around 10 to 1000 years (change in solar radiation or volcanic activity). Changes in the order of magnitude of the current warming took significantly longer than is the case today. For the last time on a global scale it was 1 to 1.5 degrees Celsius warmer than today in the last interglacial period around years ago. The sea level was then between five and ten

30 Swiss Academies Reports, Vol. 11, N o 5, Globally averaged CO2 concentrations 380 CO2 (ppm) year (GtCO2 / year) Global anthropogenic CO2 emissions Fossil fuels, cement and flaring Forestry and other land use Year Figure 1.4: The increase global CO 2 concentrations and CO 2 emissions in the atmosphere over the past 150 years or so. In terms of quantity, the increase in CO 2 concentration corresponds to around half of the amount emitted. The other half was taken up by the oceans and the land surface. (Source: Excerpt from IPCC 2014 / SYR / Fig.SPM.1) Meters higher than today. Three million years ago, the last time it was around three degrees Celsius warmer than today (roughly what we expect in a mean emissions scenario by the end of the century), the sea level then was around 20 meters higher than it is today. However, this condition very likely developed over a much longer period of time than we would expect given the current development. Both the global and the regional climate are subject to natural fluctuations on a time scale from year to year up to a few decades (see also Chapter 1.3 Climate variability: Short-term fluctuations in the climate, p. 34). These fluctuations are partly the result of external influencing factors such as fluctuations in solar activity or volcanic eruptions as well as internal fluctuations in the climate system, such as the El Niño / La Niña phenomenon in the tropical Pacific. A significant part of these fluctuations, however, is random in nature, so it is difficult to predict such fluctuations up to now. This natural variability can be regionally much more dominant from year to year or over a few decades than the effects of the warming of the climate system. That is why it often takes a few decades before the long-term trend of human-made climate change also clearly shows up regionally from natural fluctuations. Where is the problem? But why is a warming of the climate system a cause for concern? When we look at the history of the earth, we are actually not moving in a new situation at all. In principle, this is only true if the effects on people and today's ecosystems are ignored. As the temperature increases, all parameters that are influenced by the temperature will change. Climate change is therefore a resource problem when we realize that the water cycle will also be severely affected, that extreme events will affect food production and that land will be lost due to rising sea levels, to name just a few examples. In this sense, the term "climate protection", which is used for measures against climate change, is comprehensive as protection of our living conditions, resource security and ecosystem service.

31 30 Focus on Switzerland's climate. Understand the fundamentals, consequences and prospects of services that are all influenced by climate change. So it is not about protecting the climate, but rather about protecting human society from the undesirable effects of climate change. Nature will undoubtedly adapt to the new conditions. For our society, or at least large parts of it, this can be an immense challenge. With increasing climate change, we reach limits where adaptation to the effects of climate change will no longer be possible because the change has made resources scarce or no longer available. Just imagine a geographic map with a sea level 5 meters higher, not to speak of 20 meters. Climate change manifests itself not only in a change in temperature, but also in other variables such as precipitation, evaporation, wind or ocean currents. Not only the mean values, but also the temporal and spatial distribution of these variables are influenced, in particular the extreme values ​​or extreme events such as heat waves, heavy precipitation or drought. The change in all of these variables then affects many areas of our life and our environment, e.g. B. on the animal and plant world, snow cover, glaciers, permafrost and many more. These effects are described in Part 2: Consequences and Adaptation, p. 69. The future development The expected development of the climate is practically given for the next few decades. The delayed reaction of the climate system to the changes in the radiation budget contributes to this, since the adaptation of the temperature of the oceans to the new conditions takes decades to centuries. The main reason, however, is that short-term emissions are strongly determined by our infrastructure and society, and we can only change them significantly in the long term (Matthews & Solomon 2013). Since the long-term development of emissions is not known, climate research works with different scenarios that represent different developments in these emissions (see also Chapter 1.5 Scenarios for future greenhouse gas emissions, p. 38). It is clear that today's emissions, especially long-lived carbon dioxide, will have an impact for centuries to millennia. The options for reducing emissions and thus curbing climate change are the subject of Part 3: Mitigation. Much is known but unanswered questions The accuracy with which the developments of the mentioned climatic phenomena can be estimated varies widely. It is primarily dependent on the complexity of the physical processes involved and the number of factors involved. Comparatively easy to estimate or simulate in climate models are, for example, global mean values ​​(see also Chapter 1.4 Climate models, p. 36); These are primarily determined by the radiation balance and basic physical laws, such as the absorption capacity of water through the air as well as the temperature and thus associated extreme values ​​such as heat waves or hot days.The reason for this is that the temperature is distributed relatively evenly and measurements are therefore representative for relatively large areas. It is comparatively difficult to make statements about: Regional climate change: This is primarily influenced by the distribution of heat and the change in currents in the atmosphere and in the ocean, as well as land processes and ice cover, which are much more difficult to determine than global parameters; Phenomena that are associated with changes in wind flow patterns or natural fluctuations such as El Niño: These are in the majority not yet adequately covered by climate models; Phenomena that are connected to the water cycle, for example clouds: The water is distributed over a very small area; local measurements are not very representative; many phenomena are smaller than the spatial resolution of the climate models. Different predictability of changes In Switzerland, some variables are already clearly visible today. This mainly applies to those areas in which the temperature is relevant. These are the temperature itself (see also Chapter 1.6 Temperature, p. 40) and the melting processes in the mountains, especially in the glaciers and permafrost as well as in the snow cover (see also Chapter 2.3 Snow, Glaciers and Permafrost, p. 80). In the area of ​​the water cycle (see also Section 1.7 Water cycle, p. 46) and extreme events (see Section 1.8 Climate and Weather Extremes, p. 52), as already mentioned, the natural fluctuations are so large and the processes so small-scale that the statements on both the observed trends and future developments are inevitably much more uncertain. However, there are some physical processes and phenomena that cause certain changes in precipitation

32 Swiss Academies Reports, Vol. 11, No 5, including the associated extremes, appear to be very likely and also appear relatively clear in the results of the climate models. These are, for example: A tendency towards the expansion of the subtropics in the direction of the Pole: The Mediterranean climate zone, which is very dry in summer / autumn, expands to the north and increasingly includes Switzerland. A decrease in precipitation in summer and an increase in the intensity and duration of dry phases in summer / autumn are a consequence of this. The climate models differ considerably in the strength of this development. The increase in the water content in the atmosphere: This manifests itself in an increase in global precipitation. However, the changes take place in special geographic patterns with three subtropics and weather high latitudes. In terms of precipitation, Switzerland is on the borderline between an increase in the north and a decrease in the south. This means that the annual total precipitation changes little, but seasonal differences can arise. The climate models project a decrease in mean precipitation in summer for all of Switzerland and an increase in other seasons for parts of Switzerland. A relatively large unknown in the development of the regional climate are changes in the circulation in the middle latitudes and the effects of the rapid warming of the Arctic compared to the tropics and the associated changes in the north-south difference in temperature. Since the flow in the atmosphere is essentially driven by this difference, changing it could have a noticeable effect on the type and frequency of wind patterns. Various possible processes are currently being discussed in science, but so far no clear results have emerged. One possible effect would be that the same or similar weather conditions last longer and, through their duration alone, could cause extreme conditions such as dehydration or waterlogging and high or low levels of water levels (lakes, rivers, groundwater). Certain changes affect Switzerland above average, others hardly. Due to its topography, Switzerland is affected above average by phenomena related to glacier melt, the thawing of permafrost and the reduction in snowfall. The so-called albedo effect plays an important role in the Alpine region: Due to the shrinking snow cover, more heat is absorbed by the ground and the warming is increased. The reason for this is that light-colored snow reflects most of the radiation, while dark ground absorbs most of the radiation. In summer, feedback with the soil moisture content also plays an important role for heat extremes: In dry soils, the energy that is normally used for evaporation leads to an additional increase in air temperature. By contrast, Switzerland is less affected by average changes in precipitation than, for example, many developing countries in the tropics and subtropics. Summer is an exception when the decrease in precipitation could be substantial (up to around 30 percent). Changes in the ocean have no direct local consequences in this country (see also Section 1.9 Ocean and Cryosphere, p. 60), in particular the rise in sea level, which has enormous effects in the affected regions and will make entire islands disappear or become uninhabitable in the medium term and in the longer term Coastal megacities such as New York and Mumbai are threatened. However, these changes can have indirect effects on Switzerland, because they can trigger crises and problems in poor regions, for example, which increase the pressure on Switzerland to migrate (see also the chapter on global interrelationships and migration, p. 136). References IPCC (2014) Climate Change 2014: Synthesis Report (SYR). Summary for Policymakers (SPM). Matthews D, Solomon S (2013) Irreversible does not mean unavoidable. Science 340:

33 32 Focus on Switzerland's climate. Basics, consequences and perspectives 1.2 The past climate In order to be able to classify today's climate change, an analysis of the past climate is required. This is possible with the help of early instrumental measurements, historical documents, tree rings, lake sediments or ice cores. The climate reconstructions show, for example, that summer temperatures in Switzerland over the past 25 years have been significantly above the range of the past 330 years. Stefan Brönnimann (University of Bern) Analyzes of the past climate are essential in order to be able to classify the climatic changes taking place today. Measurements on ice cores show that the concentrations of the greenhouse gases CO 2, methane and nitrous oxide are higher today than they have ever been in recent years. The comparison of the temperatures measured today with climatic reconstructions shows that the annual mean temperature of the northern hemisphere of the period was very likely 1 higher than during any other thirty-year period of the last 800 years, probably also the last 1400 years. On the continental scale, however, phases that lasted for decades probably occurred in the Middle Ages that were as warm as certain phases in the second half of the 20th century (IPCC 2013 / WGI / Chap. 5). Since the middle of the 19th century the sea level has risen faster than the average over the last 2000 years (IPCC 2013 / WGI / SPM). In the case of droughts and floods, where non-climatic factors also play a role, the situation is less clear: In the last thousand years there have been droughts that were stronger and lasted longer than those observed since 1900. Today's flood magnitudes in Europe are not unusual in the context of the last 1000 years (IPCC 2013 / WGI / Chap. 5). By contrast, for the last 25 years, especially in the summers of 2003 and 2015, the temperature was well above the previous range. In a comparison of the last centuries, the complete absence of a cold summer is also striking. The summer precipitation shows considerable fluctuations from year to year, sometimes fluctuations over several years. But they do not show any long-term changes. Extreme events in Switzerland Extreme weather such as hot days have increased in Switzerland since measurements began (see also Section 1.8 Climate and Weather Extremes, p. 52). The frequency of events such as floods and storms, which can be reconstructed even further back on the basis of historical documents and early measurements (Fig. 1.6; Wetter et al. 2011; Stucki et al. 2014), however, also shows strong fluctuations over several decades. In the past, temperature and precipitation in Switzerland leave several annual temperature and precipitation reconstructions for Switzerland and the Alpine region (Fig. 1.6). They are based on early instrument measurements, historical documents, tree rings, lake sediments and other sources (Pfister 1999; Casty et al. 2005; Büntgen et al. 2006; Trachsel et al. 2012). According to this, the summer temperatures have risen by more than two degrees Celsius since the height of the "Little Ice Age" in the late 17th century, with most of the increase occurring after 1975. In the early 19th century, among other things as a result of two volcanic eruptions, the temperature was well below the fluctuation range of the last 330 years. In the last 1 p. A. Probability data from IPCC, p. 22 Figure 1.5: Flood in Basel in 1852: historical documents of this kind make it possible to examine the frequency of flood events in the past (Wetter et al. 2011). (Source: State Archives Basel-Stadt, FIGURE 13, 323)

34 Swiss Academies Reports, Vol. 11, N o 5, precipitation deviation (%) temperature deviation (C) Rhine flood in Basel from 1714 storms in Switzerland from 1859 severe / medium / light: Figure 1.6: Temperature and precipitation in summer (June to August) in Switzerland over the last 330 years (as deviations from the period). The rows H and M show the mean of the measurements at Swiss stations, the rows C and T are based on reconstructions and row P on historical sources. The lower part of the figure shows the occurrence of floods on the Rhine in Basel (Wetter et al. 2011) and storms in Switzerland (Stucki et al. 2014). (Source: Auer H et al. 2007; Begert M et al. 2005; Büntgen B et al. 2006; Casty C et al. 2005; Trachsel T et al. 2012; P: Pfister 1999) again and again phases with rarer and identify those with more frequent floods and storms, for example in the late 19th century and again since the 1980s. In contrast, there were few floods and storms between about 1935 and 1985. This phenomenon is known as the “disaster gap” (Pfister 2009) and influenced the way natural disasters were dealt with in Switzerland. References Auer I, Böhm R, Jurkovic A, Lipa W, Orlik A, Potzmann R, Schöner W, Ungersböck M, Matulla C, Briffa K, Jones P, Efthymiadis D, Brunetti M, Nanni T, Maugeri M, Mercalli L, Mestre O, Moisselin JM, Begert M, Müller-Westermeier G, Kveton V, Bochnicek O, Stastny P, Lapin M, Szalai S, Szentimrey T, Cegnar T, Dolinar M, Gajic-Capka M, Zaninovic K, Majstorovic Z, Nieplova E. . (2007) HISTALP historical instrumental climatological surface time series of the Greater Alpine Region, International Journal of Climatology 27: Begert M, Schlegel T, Kirchhofer W (2005) Homogeneous Temperature and Precipitation Series of Switzerland from 1864 to International Journal of Climatology 25: Büntgen U, Frank DC, Nievergel D, Esper J (2006) Alpine summer temperature variations in the European Alps, AD Journal of Climate 19: Casty C, Handorf D, Sempf M (2005) Combined winter climate regimes over the North Atlantic / European sector Geophysical Research Letters 32: L IPCC (2013) Climate Change 2013: The Physical Science Basis (WGI). Summary for Policymakers (SPM). IPCC (2013) Climate Change 2013: The Physical Science Basis (WGI). Chapter 5 "Information from Paleoclimate Archives". Pfister C (1999) Weather forecast. 500 years of climate variations and natural disasters. Haupt Verlag, Bern. Pfister C (2009) The "Disaster Gap" of the 20th Century and the Loss of Traditional Disaster Memory. GAIA 18: Stucki P, Brönnimann S, Martius O, Welker C, Imhof M, Wattenwyl N von, Philipp N (2014) A catalog of high-impact windstorms in Switzerland since Natural Hazards and Earth System Sciences 14: Trachsel M, Kamenik C , Grosjean M, McCarroll D, Moberg A, Brázdil R, Büntgen U, Dobrovolný P, Esper J, Frank DC, Friedrich M, Glaser R, Larocque-Tobler I, Nicolussi K, Riemann D (2012) Multi-archive summer temperature reconstruction for the European Alps. AD Quaternary Science Reviews 46: Wetter O, Pfister C, Weingartner R, Luterbacher J, Reist T, Trösch J (2011) The largest floods in the High Rhine basin since 1268 assessed from documentary and instrumental evidence. Hydrological Sciences Journal 56:

35