Managing the risks of missing international climate targets

Journal of The Air & Waste Management Association, 2009

Anthropogenic emissions of greenhouse gases, especially carbon dioxide, CO 2, have led to increasing atmospheric concentrations, the primary cause of the 0.8 ºC warming the earth has experienced since the industrial revolution. With industrial activity and population expected to increase for the rest of the century, large increases in greenhouse gas emissions are projected, with substantial global additional warming predicted. While much literature exists on various aspects of this subject, this paper aims to provide a succinct integration of the projected warming the earth is likely to experience in the decades ahead, the emission reductions that may be needed to constrain this warming, and the technologies needed to help achieve these emission reductions.

Proceedings of the National Academy of Sciences, 2009

Avoiding ''dangerous anthropogenic interference with the climate system'' requires stabilization of atmospheric greenhouse gas concentrations and substantial reductions in anthropogenic emissions. Here, we present an inverse approach to coupled climatecarbon cycle modeling, which allows us to estimate the probability that any given level of carbon dioxide (CO 2) emissions will exceed specified long-term global mean temperature targets for ''dangerous anthropogenic interference,'' taking into consideration uncertainties in climate sensitivity and the carbon cycle response to climate change. We show that to stabilize global mean temperature increase at 2°C above preindustrial levels with a probability of at least 0.66, cumulative CO 2 emissions from 2000 to 2500 must not exceed a median estimate of 590 petagrams of carbon (PgC) (range, 200 to 950 PgC). If the 2°C temperature stabilization target is to be met with a probability of at least 0.9, median total allowable CO 2 emissions are 170 PgC (range, ؊220 to 700 PgC). Furthermore, these estimates of cumulative CO 2 emissions, compatible with a specified temperature stabilization target, are independent of the path taken to stabilization. Our analysis therefore supports an international policy framework aimed at avoiding dangerous anthropogenic interference formulated on the basis of total allowable greenhouse gas emissions.

Energy Strategy Reviews, 2016

There is now a wealth of model-based evidence on the technology choices, costs and other impacts (such as fossil fuel demand) associated with mitigation towards stringent climate targets. Results from over 900 hundred scenarios have been reviewed in the latest Intergovernmental Panel on Climate Change Assessment Report (IPCC AR5) including baseline scenarios under which no mitigation action is taken, as well as those under which different limits to global warming are targeted. A number of additional studies have been undertaken in order to assess the implications of global mitigation action. The objective of the paper is to provide a concise overview and comparison of major input assumptions and outputs of recent studies focused on mitigating to the most stringent targets explored, which means around the 2°C level of global average temperature increase by 2100. The paper extracts key messages grouped into four pillars: mitigation costs, technology uncertainty, policy constraints, and co-benefits. The principal findings from this comparison are that, according to the models, mitigation to 2°C is feasible, but delayed action, the absence or limited deployment of any of a number of key technologies (including nuclear, CCS, wind and solar), and limited progress on energy efficiency, all make mitigation more costly and in many models infeasible. Further, rapid mitigation following delayed action leads to potentially thousands of idle fossil fuel plants globally, posing distributional and political economy challenges. * The reported time horizon for these models is 2050 instead of the usual 2100; however the pathways to 2050 are in agreement with a 2°C target in 2100.

2018

This chapter examines mitigation pathways consistent with limiting warming to 1.5°C above preindustrial levels. In doing so, it explores the following key questions: What is the remaining budget of CO2 emissions to stay below 1.5°C? To what extent do 1.5°C scenarios involve overshooting and returning to below 1.5°C by 2100? {2.2, 2.6} How is the carbon budget affected by non-CO2 emissions? {2.2, 2.3, 2.4, 2.6} What do 1.5°C pathways imply about transitions in energy, land use and sustainable development? {2.3, 2.4} How do policies in the near term affect the ability to limit warming to 1.5°C? {2.3, 2.5} What are the strengths and limitations of current modelling tools? {2.6} There is very high risk that under current emission trajectories or current national pledges the Earth will warm more than 1.5°C above preindustrial levels. Limiting warming to 1.5°C would require a rapid phase out of net global carbon dioxide (CO2) emissions and deep reductions in non-CO2 drivers of climate change such as methane. Such ambitious mitigation pathways are put at risk by high population growth, low economic development, and limited efforts to reduce energy demand. In comparison to a 2°C limit, required transformations are qualitatively similar but more pronounced and rapid over the next decades (high confidence) {2.3.1, 2.3.5, 2.5.1}. It is possible to define consistency with limiting warming to 1.5°C in different ways, including pathways that keep global average temperature below 1.5°C and those that overshoot 1.5°C and return later in the century. These different types of pathways come with very different implications and risks, including for sustainable development. For the purposes of this chapter, any scenario (non-overshoot and overshoot) with a greater than 50% probability of limiting warming to 1.5°C in 2100 is referred to as a "1.5°C scenario", with variations highlighted where appropriate. {2.3.1, 2.2.3, 2.5.3} This assessment evaluates the temperature outcome from quantitative model descriptions of emissions associated with the energy system, land use and the economy. While such model results provide insight into the consequences of policy options and their interplay with socioeconomic and technological development, the models are constrained by multiple underlying assumptions. For this reason, their results are complemented in this assessment with other types of studies and evidence. {2.1.3, 2.2.1, 2.6.1, 2.6.2} Remaining Carbon Budgets of 1.5°C pathways This assessment explores two types of remaining carbon budgets. The first is the Threshold Peak Budget (TPB), defined as cumulative CO2 emissions from 1 January 2016 until global mean temperature peaks. The second is the Threshold Return Budget (TRB), defined as cumulative CO2 emissions until global mean temperature returns to 1.5 or 2°C after a temporary temperature overshoot. Budgets are computed assuming that warming is limited to 1.5 or 2°C with either 50% likelihood or 66% likelihood, and accounting for non-CO2 drivers. Current emissions are ~40 GtCO2 yr-1 , which means budgets from 2019 onwards will be ~120 GtCO2 lower than counting from the start of 2016. The range accompanying budget calculations are based on available scenarios and cover physical uncertainty as well as variations in non-CO2 emissions. Values are presented in Table ES1. {2.2.2} Do Not Cite, Quote or Distribute 2-5 Total pages: 143 long-lived greenhouse gases (predominantly nitrous oxide from agriculture). Such pathways also reduce emissions of short-lived climate forcers (particularly methane) as much as possible. {2.2.2} Remaining uncertainties in the Earth system, including feedbacks and radiative forcings, primarily increase rather than decrease the risk of exceeding 1.5°C of warming (medium confidence). Uncertainties in radiative forcing and revisions in methane forcing allow only medium confidence in the assessed likely range. Most uncertainties in the Earth system, including permafrost feedbacks and the saturation of carbon uptake by the biosphere, are expected to reduce available carbon budgets and, therefore, increase the risk of exceeding 1.5°C of warming. In addition, budgets are sensitive to uncertainties in estimating temperature change since preindustrial times, current land-use emissions, climate sensitivity, and the impact of non-CO2 forcers (especially aerosols). {2.2.2, 2.6.2} The risk of passing 1.5°C and the requirements for urgent action Even with emissions reductions in line with countries' pledges under the Paris Agreement, known as Nationally-Determined Contributions (NDCs), a large share of the TPB would be exhausted by 2030 (median confidence). This means there is high risk that warming will exceed 1.5°C during the 21 st century and remain above it by 2100 if emissions are reduced only to the level of current commitments, or remain above them. Current NDCs are estimated to result in greenhouse gas emissions of ~49-56 GtCO2-eq yr-1 in 2030. In contrast, 1.5°C scenarios available to this assessment show an interquartile range of 14 to 48 GtCO2-eq yr-1 in 2030. If current pledges are followed to 2030, there are no model scenarios in which average warming is kept below 1.5°C. The large majority of models also fail to return warming to below 1.5°C by the end of the 21 st century if global emissions reduce in line with NDCs but no further. There is a high risk, therefore, that even if current NDCs are met, the post-2030 transformations that would be required to limit warming to 1.5°C are too steep and abrupt to be achieved even by the large portfolio of mitigation options that is considered in models (high confidence). {2.3.1.1, 2.3.5, Table 2.7, Cross-chapter Box 4.1} Delayed action or weak near-term policies increase the risk of exceeding 1.5°C and stranded investment in fossil-based capacity, leading to higher long-term mitigation challenges (high confidence). Historical emissions and policies already mean that pathways with at least a 66% likelihood of holding global warming below 1.5°C are out of the reach of models (medium confidence; Table ES1). Failure to achieve near-term emissions reductions would mean faster rates of change afterwards to stay consistent with 1.5°C, as well as generally higher cumulative CO2 emissions until carbon neutrality is reached (global net zero CO2 emissions). This, in turn, implies a larger requirement for carbon dioxide removal (CDR), and a higher and longer exceedance of the 1.5°C temperature limit. A lack of near-term policy commitment and regulatory credibility hinders mitigation investments and increases abatement costs. (high confidence) {2.1.3, 2.3.2, 2.5.1, 2.5.2} Strong carbon pricing mechanisms are necessary in 1.5°C scenarios to achieve the most cost-effective emissions reductions (high confidence). Discounted carbon prices for limiting warming to 1.5°C are three to seven times higher compared to 2°C, depending on models and socioeconomic assumptions (medium confidence). Carbon pricing can be usefully complemented by other policy instruments in the real world. For example, technology policies can also have an important role in the near term. {2.5.1, 2.5.2} Adopting a 1.5°C rather than 2°C pathway implies faster socio-technical transitions and deployment of mitigation measures. The shift from 2°C to 1.5°C also implies more ambitious, internationally cooperative and transformative policy environments in the short term that target both supply and demand (very high confidence). To keep the target of limiting warming to 1.5°C within reach, the stringency and effectiveness of policy portfolios is critical, as well as their diversity beyond carbon pricing. Pathways that assume stringent demand-side policies, and thus lower energy intensity and limited energy demand, reduce the risks of exceeding 1.5°C. {2.5, 2.5.1, 2.5.2} Limiting warming to 1.5°C requires a marked shift in investment patterns (high confidence), implying a financial system aligned with mitigation challenges. Studies reveal a gap between current investment patterns and those compatible with 1.5°C (or 2°C) scenarios. Whereas uncertainties exist regarding the extent of required investments (1.4-3.8 trillion USD annually on the supply side for 2016-2050), studies Do Not Cite, Quote or Distribute 2-7 Total pages: 143 confidence). Since some non-CO2 warming agents are emitted alongside CO2, particularly in the energy and transport sectors, non-CO2 emissions can be addressed through CO2 mitigation as well as through specific measures, for example to target agricultural methane, black carbon from kerosene lamps or HFCs (such as the Kigali Amendment). (high confidence) Every tenth of a degree of warming that comes from non-CO2 emissions reduces the remaining carbon budget for 1.5°C by ~150 GtCO2, increasing the risk of exceeding 1.5°C (medium confidence). Mitigating non-CO2 emissions can carry large benefits for public health and sustainable development, particularly through improved air quality. (high confidence) {2.2.2, 2.3.1, 2.4.2, 2.5.1} Properties of transitions in mitigation pathways before mid-century In 1.5°C scenarios, mitigation options are deployed more rapidly, at greater scale, and with a greater portfolio of options than in 2°C scenarios. Key technical and behavioural options are sector and region specific but generally include efficiency improvements, reduction in demand and switching to lower-carbon sources of energy (including renewables and/or nuclear) (high confidence). End-use electrification replacing fossil fuels plays a major role in the buildings, industry and transportation sectors. {2.3.4, 2.4.1, 2.4.2, 2.4.3} 1.5°C scenarios include rapid electrification of energy end use (about two thirds of final energy by 2100 alongside rapid decreases in the carbon intensity of electricity and of the residual fuel mix (high confidence). The electricity sector is fully decarbonized by mid-century in 1.5°C pathways, a feature shared with 2°C pathways....

San Francisco Global Climate Action Summit, 2018

This presentation summarizes the results of global climate models which have been developed and employed to predict annual increases in greenhouse gases and their effect on average global temperature increases from year-end 2016 to year-end 2031. These models predict that average global temperatures could reach 1.50 degrees C (+2.72 degrees F) by year-end 2025 and 2.09 degrees C (+3.76 degrees F) by year-end 2031 compared to the average global temperatures at year-end 1970. Therefore, the initiation of a global climate “tipping point” has a reasonable probability of occurring before 2031. The predicted atmospheric increases in water vapor and reductions in surface albedo, due to increasing global temperatures, are projected to significantly modify global weather patterns and escalate extreme precipitation in some areas concurrent with drought periods in other regions. The expected increases of greenhouse gases and global temperatures originally predicted from the 2016 model are compared with published data at the end of 2021. To date, this model has accurately predicted the average temperature increases and increased atmospheric concentrations of CO2, N2O, CH4, and H2O, as well as Albedo (Earth’s surface reflectivity) from year-end 2016 to 2021. Although the average global temperature has increased by 1.23 degrees C (2.22 degrees F) from 1970-2021, many areas have experienced a much greater temperature increase. For example, the average temperature increases from 1970-2021 during the summer in California has been 3.5 degrees C (6.3 degrees F). Several mitigation approaches are described that may help delay the timing for this impending potential “tipping point.” Recommended approaches include the efficient and economical conversion of CO2 emissions and CO2 captured from ambient air; CH4 emissions from oil wells; and waste biomass into low-carbon fuels and hydrocarbon feedstocks for plastic production. This presentation was originally developed in support of the Under2Coalition, which was established between California and Germany’s state of Baden-Württemberg in 2015, and which currently encompasses members from more than a third of the world’s economies.

Climate Policy

Since the mid-1990s, the aim of keeping climate change within 2 8C has become firmly entrenched in policy discourses. In the past few years, the likelihood of achieving it has been increasingly called into question. The debate around what to do with a target that seems less and less achievable is, however, only just beginning. As the UN commences a two-year review of the 2 8C target, this article moves beyond the somewhat binary debates about whether or not it should or will be met, in order to analyse more fully some of the alternative options that have been identified but not fully explored in the existing literature. For the first time, uncertainties, risks, and opportunities associated with four such options are identified and synthesized from the literature. The analysis finds that the significant risks and uncertainties associated with some options may encourage decision makers to recommit to the 2 8C target as the least unattractive course of action.

Sustainability Science, 2018

We have assessed the risks associated with setting 1.5, 2.0, or 2.5 °C temperature goals and ways to manage them in a systematic manner and discussed their implications. The results suggest that, given the uncertainties in climate sensitivity, "net zero emissions of anthropogenic greenhouse gases in the second half of this century" is a more actionable goal for society than the 2 or 1.5 °C temperature goals themselves. If the climate sensitivity is proven to be relatively high and the temperature goals are not met even when the net zero emission goal is achieved, the options left are: (A) accepting/adapting to a warmer world, (B) boosting mitigation, and (C) climate geoengineering, or any combination of these. This decision should be made based on a deeper discussion of risks associated with each option. We also suggest the need to consider a wider range of policies: not only climate policies, but also broader "sustainability policies", and to envisage more innovative solutions than what integrated assessment models can currently illustrate. Finally, based on a consideration of social aspects of risk decisions, we recommend the establishment of a panel of "intermediate layer" experts, who support decision-making by citizens as well as social and ethical thinking by policy makers.

Nature Climate Change, 2011

Long-term future warming is primarily constrained by cumulative emissions of carbon dioxide 1-4 . Previous studies have estimated that humankind has already emitted about 50% of the total amount allowed if warming, relative to pre-industrial, is to stay below 2 • C (refs 1,2). Carbon dioxide emissions will thus need to decrease substantially in the future if this target is to be met. Here we show how links between nearterm decisions, long-term behaviour and climate sensitivity uncertainties constrain options for emissions mitigation. Using a model of intermediate complexity 5,6 , we explore the implications of non-zero long-term global emissions, combined with various near-term mitigation rates or delays in action. For a median climate sensitivity, a long-term 90% emission reduction relative to the present-day level is incompatible with a 2 • C target within the coming millennium. Zero or negative emissions can be compatible with the target if medium to high emission-reduction rates begin within the next two decades. For a high climate sensitivity, however, even negative emissions would require a global mitigation rate at least as great as the highest rate considered feasible by economic models 7,8 to be implemented within the coming decade. Only a low climate sensitivity would allow for a longer delay in mitigation action and a more conservative mitigation rate, and would still require at least 90% phase-out of emissions thereafter.

Global climate change, driven largely by the combustion of fossil fuels and by deforestation, is a growing threat to human well-being in developing and industrialized nations alike. Significant harm from climate change is already occurring, and further damages are a certainty. The challenge now is to keep climate change from becoming a catastrophe. There is still a good chance of succeeding in this, and of doing so by means that create economic opportunities that are greater than the costs and that advance rather than impede other societal goals. But seizing this chance requires an immediate and major acceleration of efforts on two fronts: mitigation measures (such as reductions in emissions of greenhouse gases and black soot) to prevent the degree of climate change from becoming unmanageable; and adaptation measures (such as building dikes and adjusting agricultural practices) to reduce the harm from climate change that proves unavoidable. Avoiding the Unmanageable Human activities have changed the climate of the Earth, with significant impacts on ecosystems and human society, and the pace of change is increasing. The global-average surface temperature is now about 0.8°C above its level in 750, with most of the increase having occurred in the 20th century and the most rapid rise occurring since 970. Temperature changes over the continents have been greater than the global average and the changes over the continents at high latitudes have been greater still. The pattern of the observed changes matches closely what climate science predicts from the buildup in the atmospheric concentrations of carbon dioxide (CO 2), methane (CH 4), and other greenhouse gases (GHGs), taking into account other known influences on the temperature. The largest of all of the human and natural influences on climate over the past 250 years has been the increase in the atmospheric CO 2 concentration resulting from deforestation and fossil-fuel burning. The CO 2 emissions in recent decades (Figure ES.), which have been responsible for the largest part of this buildup, have come 75% to 85% from fossil fuels (largely in the industrialized countries) and 5% to 25% from deforestation and other land-cover change (largely from developing countries in the tropics). A given temperature change in degrees Celsius (ºC) can be converted into a change in degrees Fahrenheit (ºF) by multiplying by .8. Thus, a change of 0.8ºC corresponds to a change of 0.8 x .8 = .44ºF.

Science

Lecture Notes in Energy, 2012

Contents 1 Introduction 1 2 The Ultimate Objective of Climate Response Strategies, and a Desirable and Feasible International Framework 2.1 The Ultimate Objective (Article 2 of the UNFCCC), and the 2 Degree Target 2.1.1 Brief History of Article 2 2.1.2 Interpretation of Article 2 10 2.1.3 2 Degree Target at the G8 Summit and International Negotiations 16 2.2 2 Degree Target from the Viewpoint of Vertical Balance: What Does It Mean7 2.2.1 Is a 2 Degree Increase Dangerous 7 2.2.2 No Adaptation Is Unrealistic 2.2.3 Catastrophe and 2 Degree Target 2.2.4 Feasibility of 2 Degree Target 21 2.2.5 Uncertainty and 2 Degree Target 2.2.6 2 Degree Target from a Cost and Benefit Perspective. 2.3 2 Degree Target from the Viewpoint of Horizontal Balance: Efficient Allocation of Scarce Resources 2.4 What Kind of International Framework Will Be Desirable and Feasible' 2.4.1 Current Situation 2.4.2 Does a Legally Binding Treaty Work Well') 34 2.4.3 Pledge and Review Is the Best Way for the First Step .. 2.4.4 Common but Differentiated Responsibilities 36 2.4.5 Taking Various Factors-Adaptation, Technology Innovation and Diffusion, and Funding-into Account. 37 2.4.6 Geo-engineering as an Insurance 38 2.5 Concluding Remarks 39 References 39 xi xii Contents 3 Mitigation Targets and Effort-Sharing Among Regions and Countries 3.1 Climate Change Mitigation Targets in the Context of Mitigation and Damage Costs, and Sustainable Development 3.1.1 Climate Change Mitigation Targets in the Context of Balancing Climate Change Mitigation and Damages. .

Proceedings of the National Academy of Sciences, 2009

have already committed the planet to an increase in average surface temperature by the end of the century that may be above the critical threshold for tipping elements of the climate system into abrupt change with potentially irreversible and unmanageable consequences. This would mean that the climate system is close to entering if not already within the zone of ''dangerous anthropogenic interference'' (DAI). Scientific and policy literature refers to the need for ''early,'' ''urgent,'' ''rapid,'' and ''fast-action'' mitigation to help avoid DAI and abrupt climate changes. We define ''fast-action'' to include regulatory measures that can begin within 2-3 years, be substantially implemented in 5-10 years, and produce a climate response within decades. We discuss strategies for short-lived non-CO 2 GHGs and particles, where existing agreements can be used to accomplish mitigation objectives. Policy makers can amend the Montreal Protocol to phase down the production and consumption of hydrofluorocarbons (HFCs) with high global warming potential. Other fast-action strategies can reduce emissions of black carbon particles and precursor gases that lead to ozone formation in the lower atmosphere, and increase biosequestration, including through biochar. These and other fastaction strategies may reduce the risk of abrupt climate change in the next few decades by complementing cuts in CO 2 emissions. biosequestration ͉ black carbon ͉ hydrofluorocarbons ͉ tipping points ͉ tropospheric ozone

Nature Climate Change

he Paris Agreement sets the framework for international climate action. Within that context, countries are aiming to hold warming well below 2 °C and pursue limiting it to 1.5 °C. How such global temperature outcomes can be achieved has been explored widely in the scientific literature 1-4 and assessed by the IPCC, for example, in its Fifth Assessment Report (AR5; ref. 5) and its Special Report on Global Warming of 1.5 °C (SR1.5; ref. 6). Studies explore aspects of the timing and costs of emissions reductions and the contribution of different sectors 3,7,8. However, there has been critique that, with the exception of a few notable studies 9-12 , the scenarios in the literature first exceed the prescribed temperature limits in the hope of recovering from this overshoot later through net-negative emissions 13-16. Some pioneering studies 10-12 have explored implications of limiting overshoot through, for example, zero emissions goals, or have looked into the role of bioenergy with carbon capture and storage (BECCS) in reaching different temperature targets 9. All these studies have relied on one or two models and/or a limited set of temperature targets. We bring together nine international modelling teams and conduct a comprehensive modelling intercomparison project (MIP) on this topic. Specifically, we explore mitigation pathways for reaching different temperature change targets with limited overshoot. We do this by adopting the scenario design from ref. 11 and contrast scenarios with a fixed remaining carbon budget until the time when net-zero CO 2 emissions (net-zero budget scenarios) are reached with scenarios that use an end-of-century budget design. The latter carbon budget for the full century permits the budget to be temporarily overspent, as long as net-negative CO 2 emissions (NNCE)

World Futures Review, 2016

At this time, most climate researchers are only using a limited range of futures approaches: for example, Intergovernmental Panel on Climate Change (IPCC) future scenarios have been developed primarily with empirical predictive methods that extrapolate trends. These seriously underestimate the risk of nonlinear developments and critical failures. This article examines the Paris Climate Conference (COP) 21 agreement on climate mitigation; explains why current efforts are based on false assumptions and likely to fail; argues that holistic, integrative methods are needed to avoid disaster; and uses these methods to develop a practical strategy for accelerating systemic transformation. Despite the impressive diplomatic achievements of the Paris Agreement, there is a dangerous lag between the pace of political, economic, and technological change and the rapid (nonnegotiable) rate of climate change. The challenge is to find ways to manage the conflict between the need to work within exist...