Suchergebnisse

To keep the risks of climate change in check, the international community has agreed on the long-term target of limiting the increase of global mean temperature to no more than 2 °C above pre-industrial levels. This target is, however, so far not underpinned by commensurate near-term policy measures. Given the commons nature of the climate problem, the solution will eventually require concerted actions on the international level. To this end, negotiations have been conducted under the United Nations Framework Convention on Climate Change, but so far only made little progress towards tangible emission reductions consistent with the 2 °C limit. Instead, policy initiatives enacted so far have been regionally fragmented, incomprehensive and generally not ambitious enough to hold the stated 2 °C limit in a cost-effective manner. Starting from this observation, this dissertation aims to answer the following three main questions: 1. What are the implications of a further delay of comprehensive climate policies? 2. What are the crucial determinants of adverse lock-ins and path-dependencies in the energy system induced by delayed action? 3. Which policy portfolio can keep the door to achieving ambitious targets at moderate costs open? The answer to the first question is an important prerequisite to informing policy makers about the appropriate policy stringency today, weighing current and future risks and opportunities against each other. To provide a comprehensive evaluation, our analysis not only considers the traditionally used aggregated cost metric, but complements it with three other metrics that better represent the distributional and dynamic dimension of the problem. The answer to the second question helps to identify the most adverse impacts of delayed climate policies on the energy system's climate change mitigation potentials. It thus also informs the choice about priorities for policies to bridge into a low-carbon future, as addressed in the third question. The idea here is to go beyond a one-dimensional option space of more or less near-term policy ambition, but to explore to which extent different policy instruments have a beneficial effect beyond their near-term effect on emissions, thus helping to keep long-term targets within reach. As recent experience has shown, governments have much less difficulty to implement technology policies than to implement carbon pricing. Therefore we analyze different policies regulating high-carbon and supporting low carbon technologies as well as a reform of subsidies and taxes for fossil fuels. Beyond the evaluation of the individual effects of these policies, an important contribution is to quantify the interactions among these instruments, as well as the interactions of these with two carbon pricing mechanisms, a carbon tax and a cap-and-trade scheme. The research presented here is mainly based on the analysis of quantitative scenarios of large scale detailed numerical models of the global energy-economy system. This dissertation makes use of both the detailed analysis of larger number of scenarios produced from one model as well as the comparative analysis of harmonized scenario sets across different models. Five different research articles published in peer-reviewed scientific journals form the core five chapters of this thesis, preceded by an introduction chapter laying out the wider background and methods. A discussion with the overall conclusions from the aggregate research plus an outlook to future research concludes. ; Die internationale Gemeinschaft hat sich zum Ziel gesetzt, den Anstieg der globalen Durchschnittstemperatur auf unter 2 °C gegenüber dem vorindustriellen Niveau zu begrenzen, so dass die Risiken umgebremsten Klimawandels vermieden werden. Bis jetzt ist dieses Ziel aber noch nicht mit adäquaten kurzfristigen Politikmassnahmen unterfüttert. Aufgrund der Allmendestruktur des Klimaproblems wird es sich langfristig nur mit koordiniertem Vorgehen auf internationaler Ebene lösen lassen. Daher werden auf UN Ebene seit mehr als zwei Jahrzehnten Verhandlungen geführt, die bisher allerdings noch keine signifikanten Emissionsreduktionen bewirken konnten. Stattdessen sind umgesetzte Politikinitiativen regional und sektoral fragmentiert und im Allgemeinen nicht ambitioniert genug, um die gesetzte 2 °C-Grenze auf kosteneffektive Weise einzuhalten. Aufbauend auf dieser Beobachtung behandelt diese Dissertation die drei folgenden Kernforschungsfragen: 1. Was sind die Konsequenzen einer weiteren Verzögerung von umfassender Klimapolitik? 2. Welches sind die entscheidenden Trägheiten und Pfadabhängigkeiten im Energiesystem in Szenarien mit verzögerter Klimapolitik? 3. Welches Portfolio an Politikinstrumenten kann ambitionierte Ziele bei moderaten Kosten erreichbar halten? Die Beantwortung der ersten Frage bildet eine wichtige Grundinformation für eine ausgewogene Entscheidung über das passende Ambitionsniveau jetziger Klimatpolitik, unter Abwägung sowohl heutiger als auch zukünftiger Risiken und Chancen. Unsere Analyse betrachtet nicht nur die typischerweise verwendete Metrik aggregierter Kosten, sondern stellt dieser drei weitere Metriken zur Seite, die adäquater die Verteilungsaspekte und zeitliche Dimension des Problems beleuchtet. Die Antwort auf die zweite Frage hilft bei der Identifizierung von Effekten verzögerter Politik, die sich negativ auf die Vermeidungsoptionen im Energiesystem auswirken. Dadurch liefert sie auch entscheidende Hinweise zu prioritären Politikoptionen zur Vorbereitung zukünftiger Emissionsneutralität, die in der Analyse der dritten Frage untersucht werden. Bei dieser ist der Ansatz, den eindimensionalen Optionsraum von mehr oder weniger Politikambition zu erweitern. Wir untersuchen, in welchem Maße verschiedene Politikinstrumente einen positiven Effekt haben, der über den Einfluss auf kurzfristige Emissionen hinausgehen, so dass langfristige Ziele erreichbar bleiben. Wie die jüngere Vergangenheit gezeigt hat, ist es für Regierungen wesentlich einfacher, Technologiepolitiken einzuführen als CO2-Bepreisung. Daher analysieren wir verschiedene Politiken zur Beschränkung emissionsintensiver Technologien, zur Förderung von sauberen Technologien, wie auch die Reform von Subventionen und Steuern auf fossile Energieträger. Neben der Betrachtung der individuellen Effekte dieser Politiken ist ein wichtiger Beitrag dieser Arbeit, dass auch die Interaktionen zwischen diesen Politiken sowie die Interaktionen dieser Politiken mit zwei Methoden der CO2-Bepreisung, einer CO2-Steuer und eines Emissionshandelssystems, quantifiziert werden. Die vorgestellte Forschung basiert hautpsächlich auf der Analyse quantitativer Szenarien von detaillierteren numerischen Modellen des globalen Wirtschafts-Energie-Systems. Die Dissertation besteht sowohl aus mehreren Analysen einer großen Anzahl von Szenarien in einem Modell als auch aus der vergleichenden Analyse harmonisierter Szenariensätze in verschiedenen Modellen. Nach einem Einleitungskapitel, das Hintergrund und Methoden einführt, bilden fünf verschiedene Forschungsaufsätze, die in begutachteten Wissenschaftszeitschriften veröffentlicht wurden, die fünf Kernkapitel dieser Arbeit. Abschließend folgt darauf eine übergreifende Diskussion der Ergebnisse und Schlussfolgerungen, sowie ein Ausblick auf mögliche weiterführende Forschungsfragen.

"Governance Schools" lassen sich als multidisziplinäre, praxisorientierte Ausbildungseinrichtungen verstehen, die Studierende unmittelbar für den Berufsalltag in einem weit verstandenen Feld von "Politik" in Staat, Wirtschaft und Zivilgesellschaft qualifizieren wollen. Bildungspolitisch stellen sie keine Konkurrenz, sondern eine Ergänzung zu den stärker wissenschaftlich-disziplinären Angeboten der öffentlichen Universitäten dar und können dabei allenfalls den Anspruch erheben, ein wenig "Hefe" im derzeit – aus guten Gründen – stark gärenden "Teig" der deutschen Bildungslandschaft zu sein. Gleichwohl könnten Governance Schools als Hochschulen mit großer Autonomie als Impulsgeber in der gegenwärtigen Reformdiskussion fungieren. Hinsichtlich der möglichen Effekte auf die Elitenrekrutierung sollten Governance Schools angesichts des derzeitigen Standes der Zugangsstrukturen insbesondere zu öffentlichen Leitungspositionen in Deutschland nicht dramatisiert werden. Statt der befürchteten, selbstreferentiellen Abschottung politischer Eliten mit homogenen Ausbildungshintergrund können sie u.U. sogar dem Leistungsprinzip Vorschub leisten, dass sowohl unter Effektivitäts- als auch unter Legitimitätsgesichtspunkten zu einer Verbesserung gegenüber dem Status quo führt. Angesichts der noch immer in den meisten Bereichen existierenden Juristendominanz und der zentralen Rolle der Parteien in der Elitenrekrutierung wollen "Governance Schools" in Deutschland zunächst andere Vereinseitigungen der politischen Elitenrekrutierung aufbrechen. Der Blick auf die negativen Auswüchse von "Schulen der Macht" in anderen Ländern Europas macht gleichwohl deutlich, dass erstens eine Umkehrung der Verhältnisse im Sinne eines fast vollständigen Monopols der Elitenausbildung durch entsprechende Einrichtungen nicht wünschenswert sein kann und dass zweitens den Aufnahmeverfahren besondere Aufmerksamkeit zu widmen ist, um den Offenheitsanspruch des Leistungsprinzips in der Elitenrekrutierung aufrecht zu erhalten.

The employment implications of decarbonizing the energy sector have received far less attention than the technology dimension of the transition, although being of critical importance to policymakers. In this work, we adapt a methodology based on employment factors to project future changes in quantity and composition of direct energy supply jobs for two scenarios - (1) relatively weak emissions reductions as pledged in the nationally determined contributions (NDC) and (2) stringent reductions compatible with the 1.5 °C target. We find that in the near-term the 1.5°C-compatible scenario results in a net increase in jobs through gains in solar and wind jobs in construction, installation, and manufacturing, despite significant losses in coal fuel supply; eventually leading to a peak in total direct energy jobs in 2025. In the long run, improvements in labour productivity lead to a decrease of total direct energy employment compared to today, however, total jobs are still higher in a 1.5 °C than in an NDC scenario. Operation and maintenance jobs dominate future jobs, replacing fuel supply jobs. The results point to the need for active policies aimed at retraining, both inside and outside the renewable energy sector, to complement climate policies within the concept of a "just transition".

Deutsch-französischer Neuanfang in der militärischen Zusammenarbeit. Wie kann - rechtzeitig zum 40. Jahrestag des Elysée-Vertrages - dem deutsch-französischen Verhältnis und zugleich auch der Europäischen Sicherheits- und Verteidigungspolitik (ESVP) ein neuer Schub gegeben werden? Durch die zunehmende europäische Verflechtung wird eine enge deutsch-französische Zusammenarbeit nicht etwa weniger wichtig, sondern effektiver. Dies gilt auch im Bereich militärischer Zusammenarbeit. Hier behinderten bisher unterschiedliche Einstellungen zur Atlantischen Allianz und inkompatible Streitkräfte-Strukturen ein enges Zusammenwirken. Den entscheidenden Anstoß zur "Europäischen Sicherheits- und Verteidigungspolitik" (ESDP) gab nicht zufällig eine britisch-französische Initiative. Inzwischen jedoch ist der europäische Elan in Verteidigungsfragen erlahmt. Einen neuen Anstoß könnten Deutschland und Frankreich geben, indem sie in ihrer militärischen Zusammenarbeit vorangehen und damit anderen EU-Partner ein Beispiel setzen. Da die Nato in der Global-Strategie der USA heute eine weniger zentrale Rolle spielt, werden auch die Schwierigkeiten verringert, die der unterschiedliche Allianz-Status Frankreichs und Deutschlands für ein gemeinsames Vorgehen mit sich bringt. Er tritt dadurch in den Hintergrund, daß sich die Streitkräfte-Strukturen beider Länder mittlerweile angenähert haben - weg von traditioneller Landesverteidigung, hin zu Krisen-Prävention und -Intervention. Vor diesem Hintergrund werden folgende konkrete Maßnahmen deutsch-französischer Zusammenarbeit empfohlen: - In der strategischen Aufklärung setzen beide Länder auf unterschiedliche Programme - Frankreich auf Helios II, Deutschland auf SAR-Lupe. Es sollte eine gemeinsame Einrichtung zur Auswertung der von beiden Systemen übermittelten Informationen eingerichtet werden, so daß sie zusammen den Kern eines europäischen satellitengestützten Aufklärungsverbundes bilden würden. - Jeder größere europäische Militäreinsatz erfordert ein gemeinsames, mobiles Hauptquartier mit ...

We estimate the cumulative future emissions expected to be released by coal power plants that are currently under construction, announced, or planned. Even though coal consumption has recently declined and plans to build new coal-fired capacities have been shelved, constructing all these planned coal-fired power plants would endanger national and international climate targets. Plans to build new coal-fired power capacity would likely undermine the credibility of some countries' (Intended) Nationally Determined Contributions submitted to the UNFCCC. If all the coal-fired power plants that are currently planned were built, the carbon budget for reaching the 2 °C temperature target would nearly be depleted. Propositions about 'coal's terminal decline' may thereby be premature. The phase-out of coal requires dedicated and well-designed policies. We discuss the political economy of policy options that could avoid a continued build-up of coal-fired power plants.

We estimate the cumulative future emissions expected to be released by coal power plants that are currently under construction, announced, or planned. Even though coal consumption has recently declined and plans to build new coal-fired capacities have been shelved, constructing all these planned coal-fired power plants would endanger national and international climate targets. Plans to build new coal-fired power capacity would likely undermine the credibility of some countries' (Intended) Nationally Determined Contributions submitted to the UNFCCC. If all the coal-fired power plants that are currently planned were built, the carbon budget for reaching the 2 °C temperature target would nearly be depleted. Propositions about 'coal's terminal decline' may thereby be premature. The phase-out of coal requires dedicated and well-designed policies. We discuss the political economy of policy options that could avoid a continued build-up of coal-fired power plants.

While the international community has agreed on the long-term target of limiting global warming to no more than 2°C above pre-industrial levels, only a few concrete climate policies and measures to reduce greenhouse gas (GHG) emissions have been implemented. We use a set of three global integrated assessment models to analyze the implications of current climate policies on long-term mitigation targets. We define a weak-policy baseline scenario, which extrapolates the current policy environment by assuming that the global climate regime remains fragmented and that emission reduction efforts remain unambitious in most of the world's regions. These scenarios clearly fall short of limiting warming to 2°C. We investigate the cost and achievability of the stabilization of atmospheric GHG concentrations at 450 ppm CO2e by 2100, when countries follow the weak policy pathway until 2020 or 2030 before pursuing the long-term mitigation target with global cooperative action. We find that after a deferral of ambitious action the 450 ppm CO2e is only achievable with a radical up-scaling of efforts after target adoption. This has severe effects on trans-formation pathways and exacerbates the challenges of climate stabilization, in particular for a delay of cooperative action until 2030. Specifically, reaching the target with weak near-term action implies (a) faster and more aggressive transformations of energy systems in the medium term, (b) more stranded investments in fossil-based capacities, (c) higher long-term mitigation costs and carbon prices and (d) stronger transitional economic impacts, rendering the political feasibility of such pathways questionable.

This study assesses Japan's mid-century low-emission pathways using both national and global integrated assessment models in the common mitigation scenario framework, based on the carbon budgets corresponding to the global 2 °C goal. We examine high and low budgets, equal to global cumulative 1600 and 1000 Gt-CO2 (2011–2100) for global models, and 36 and 31 Gt-CO2 (2011–2050) in Japan for national models, based on the cost-effectiveness allocation performed by the global models. The impacts of near-term policy assumption, including the implementation and enhancement of the 2030 target of the nationally determined contribution (NDC), are also considered. Our estimates show that the low budget scenarios require a 75% reduction of CO2 emissions by 2050 below the 2010 level, which is nearly the same as Japan's governmental 2050 goal of reducing greenhouse gas emissions by 80%. With regard to near-term actions, Japan's 2030 target included in the NDC is on track to meet the high budget scenario, whereas it is falling short for the low budget scenario, which would require emission reductions immediately after 2020. Whereas models differ in the type of energy source on which they foresee Japan basing its decarbonization process (e.g., nuclear- or variable renewable energy-dependent), the large-scale deployment of low-carbon energy (nuclear, renewable, and carbon capture and storage) is shared across most models in both the high and low budget scenarios. By 2050, low-carbon energy represents 44–54% of primary energy and 86–97% of electricity supply in the high and low budget scenarios, respectively. © 2019, The Author(s).

Cost-effective achievement of the Paris Agreement's long-term goals requires the unanimous phase-out of coal power generation by mid-century. However, continued investments in coal power plants will make this transition difficult. India is one of the major countries with significant under construction and planned increase in coal power capacity. To ascertain the likelihood and consequences of the continued expansion of coal power for India's future mitigation options, we use harmonised scenario results from national and global models along with projections from various government reports. Both these approaches estimate that coal capacity is expected to increase until 2030, along with rapid developments in wind and solar power. However, coal capacity stranding of the order of 133–237 GW needs to occur after 2030 if India were to pursue an ambitious climate policy in line with a well-below 2 °C target. Earlier policy strengthening starting after 2020 can reduce stranded assets (14–159 GW) but brings with it political economy and renewable expansion challenges. We conclude that a policy limiting coal plants to those under construction combined with higher solar targets could be politically feasible, prevent significant stranded capacity, and allow higher mitigation ambition in the future.

Hopes are high that removing fossil fuel subsidies could help to mitigate climate change by discouraging inefficient energy consumption and levelling the playing field for renewable energy. In September 2016, the G20 countries re-affirmed their 2009 commitment (at the G20 Leaders' Summit) to phase out fossil fuel subsidies and many national governments are using today's low oil prices as an opportunity to do so. In practical terms, this means abandoning policies that decrease the price of fossil fuels and electricity generated from fossil fuels to below normal market prices. However, whether the removal of subsidies, even if implemented worldwide, would have a large impact on climate change mitigation has not been systematically explored. Here we show that removing fossil fuel subsidies would have an unexpectedly small impact on global energy demand and carbon dioxide emissions and would not increase renewable energy use by 2030. Subsidy removal would reduce the carbon price necessary to stabilize greenhouse gas concentration at 550 parts per million by only 2-12 per cent under low oil prices. Removing subsidies in most regions would deliver smaller emission reductions than the Paris Agreement (2015) climate pledges and in some regions global subsidy removal may actually lead to an increase in emissions, owing to either coal replacing subsidized oil and natural gas or natural-gas use shifting from subsidizing, energy-exporting regions to non-subsidizing, importing regions. Our results show that subsidy removal would result in the largest CO 2 emission reductions in high-income oil- and gas-exporting regions, where the reductions would exceed the climate pledges of these regions and where subsidy removal would affect fewer people living below the poverty line than in lower-income regions.

Climate policy needs to account for political and social acceptance. Current national climate policy plans proposed under the Paris Agreement lead to higher emissions until 2030 than cost-effective pathways towards the Agreements' long-term temperature goals would imply. Therefore, the current plans would require highly disruptive changes, prohibitive transition speeds, and large long-term deployment of risky mitigation measures for achieving the agreement's temperature goals after 2030. Since the prospects of introducing the cost-effective policy instrument, a global comprehensive carbon price in the near-term, are negligible, we study how a strengthening of existing plans by a global roll-out of regional policies can ease the implementation challenge of reaching the Paris temperature goals. The regional policies comprise a bundle of regulatory policies in energy supply, transport, buildings, industry, and land use and moderate, regionally differentiated carbon pricing. We find that a global roll-out of these policies could reduce global CO2 emissions by an additional 10 GtCO2eq in 2030 compared to current plans. It would lead to emissions pathways close to the levels of cost-effective likely below 2 °C scenarios until 2030, thereby reducing implementation challenges post 2030. Even though a gradual phase-in of a portfolio of regulatory policies might be less disruptive than immediate cost-effective carbon pricing, it would perform worse in other dimensions. In particular, it leads to higher economic impacts that could become major obstacles in the long-term. Hence, such policy packages should not be viewed as alternatives to carbon pricing, but rather as complements that provide entry points to achieve the Paris climate goals.

Governments worldwide have agreed that international climate policy should aim to limit the increase of global mean temperature to less than 2oC with respect to pre-industrial levels. The purpose of this paper is to analyse the emission reductions and related energy system changes in various countries in pathways consistent with the 2oC target. We synthesize and provide an overview of the national and regional information contained in different scenarios from various global models published over the last few years, as well as yet unpublished scenarios submitted by modelling teams participating in the MILES project (Modelling and Informing Low-Emission Strategies). We find that emissions in the mitigation scenarios are significantly reduced in all regions compared to the baseline without climate policies. The regional cumulative CO2 emissions show on average a 76% reduction between the baseline and 450 scenario. The 450 scenarios show a reduction of primary energy demand in all countries of roughly 30-40% compared to the baseline. In the baseline scenario, the contribution of low-carbon energy technology remains around 15%, i.e. similar as today. In the mitigation scenario, these numbers are scaled up rapidly towards 2050. Looking at air quality, sulphur dioxide and black carbon emissions are strongly reduced as a co-benefit of greenhouse gas emission reductions, in both developing and developed countries. However, black carbon emissions increase in countries that strongly rely on bioenergy to reach mitigation targets. Concerning energy security, energy importing countries generally experience a decrease in net-energy imports in mitigation scenarios compared to the baseline development, while energy exporters experience a loss of energy export revenues.

International audience ; Non-technical summary We summarize some of the past year's most important findings within climate change-related research. New research has improved our understanding about the remaining options to achieve the Paris Agreement goals, through overcoming political barriers to carbon pricing, taking into account non-CO 2 factors, a well-designed implementation of demand-side and nature-based solutions, resilience building of ecosystems and the recognition that climate change mitigation costs can be justified by benefits to the health of humans and nature alone. We consider new insights about what to expect if we fail to include a new dimension of fire extremes and the prospect of cascading climate tipping elements. Technical summary A synthesis is made of 10 topics within climate research, where there have been significant advances since January 2020. The insights are based on input from an international open call with broad disciplinary scope. Findings include: (1) the options to still keep global warming below 1.5 °C; (2) the impact of non-CO 2 factors in global warming; (3) a new dimension of fire extremes forced by climate change; (4) the increasing pressure on interconnected climate tipping elements; (5) the dimensions of climate justice; (6) political challenges impeding the effectiveness of carbon pricing; (7) demand-side solutions as vehicles of climate mitigation; (8) the potentials and caveats of nature-based solutions; (9) how building resilience of marine ecosystems is possible; and (10) that the costs of climate change mitigation policies can be more than justified by the benefits to the health of humans and nature. Social media summary How do we limit global warming to 1.5 °C and why is it crucial? See highlights of latest climate science.

International audience ; Non-technical summary We summarize some of the past year's most important findings within climate change-related research. New research has improved our understanding about the remaining options to achieve the Paris Agreement goals, through overcoming political barriers to carbon pricing, taking into account non-CO 2 factors, a well-designed implementation of demand-side and nature-based solutions, resilience building of ecosystems and the recognition that climate change mitigation costs can be justified by benefits to the health of humans and nature alone. We consider new insights about what to expect if we fail to include a new dimension of fire extremes and the prospect of cascading climate tipping elements. Technical summary A synthesis is made of 10 topics within climate research, where there have been significant advances since January 2020. The insights are based on input from an international open call with broad disciplinary scope. Findings include: (1) the options to still keep global warming below 1.5 °C; (2) the impact of non-CO 2 factors in global warming; (3) a new dimension of fire extremes forced by climate change; (4) the increasing pressure on interconnected climate tipping elements; (5) the dimensions of climate justice; (6) political challenges impeding the effectiveness of carbon pricing; (7) demand-side solutions as vehicles of climate mitigation; (8) the potentials and caveats of nature-based solutions; (9) how building resilience of marine ecosystems is possible; and (10) that the costs of climate change mitigation policies can be more than justified by the benefits to the health of humans and nature. Social media summary How do we limit global warming to 1.5 °C and why is it crucial? See highlights of latest climate science.

International audience ; Non-technical summary We summarize some of the past year's most important findings within climate change-related research. New research has improved our understanding about the remaining options to achieve the Paris Agreement goals, through overcoming political barriers to carbon pricing, taking into account non-CO 2 factors, a well-designed implementation of demand-side and nature-based solutions, resilience building of ecosystems and the recognition that climate change mitigation costs can be justified by benefits to the health of humans and nature alone. We consider new insights about what to expect if we fail to include a new dimension of fire extremes and the prospect of cascading climate tipping elements. Technical summary A synthesis is made of 10 topics within climate research, where there have been significant advances since January 2020. The insights are based on input from an international open call with broad disciplinary scope. Findings include: (1) the options to still keep global warming below 1.5 °C; (2) the impact of non-CO 2 factors in global warming; (3) a new dimension of fire extremes forced by climate change; (4) the increasing pressure on interconnected climate tipping elements; (5) the dimensions of climate justice; (6) political challenges impeding the effectiveness of carbon pricing; (7) demand-side solutions as vehicles of climate mitigation; (8) the potentials and caveats of nature-based solutions; (9) how building resilience of marine ecosystems is possible; and (10) that the costs of climate change mitigation policies can be more than justified by the benefits to the health of humans and nature. Social media summary How do we limit global warming to 1.5 °C and why is it crucial? See highlights of latest climate science.