Tom Kram

A new scenario framework for Climate Change Research: scenario matrix architecture

This paper describes the scenario matrix architecture that underlies a framework for developing new scenarios for climate change research. The matrix architecture facilitates addressing key questions related to current climate research and policy-making: identifying the effectiveness of different adaptation and mitigation strategies (in terms of their costs, risks and other consequences) and the possible trade-offs and synergies. The two main axes of the matrix are: 1) the level of radiative forcing of the climate system (as characterised by the representative concentration pathways) and 2) a set of alternative plausible trajectories of future global development (described as shared socio-economic pathways). The matrix can be used to guide scenario development at different scales. It can also be used as a heuristic tool for classifying new and existing scenarios for assessment. Key elements of the architecture, in particular the shared socio-economic pathways and shared policy assumptions (devices for incorporating explicit mitigation and adaptation policies), are elaborated in other papers in this special issue.

A new scenario framework for climate change research: background, process, and future directions

The scientific community is developing new global, regional, and sectoral scenarios to facilitate interdisciplinary research and assessment to explore the range of possible future climates and related physical changes that could pose risks to human and natural systems; how these changes could interact with social, economic, and environmental development pathways; the degree to which mitigation and adaptation policies can avoid and reduce risks; the costs and benefits of various policy mixes; and the relationship of future climate change adaptation and mitigation policy responses with sustainable development. This paper provides the background to and process of developing the conceptual framework for these scenarios, as described in the three subsequent papers in this Special Issue (Van Vuuren et al., 2013; O’Neill et al., 2013; Kriegler et al., Submitted for publication in this special issue). The paper also discusses research needs to further develop, apply, and revise this framework in an iterative and open-ended process. A key goal of the framework design and its future development is to facilitate the collaboration of climate change researchers from a broad range of perspectives and disciplines to develop policy- and decision-relevant scenarios and explore the challenges and opportunities human and natural systems could face with additional climate change.

A new scenario framework for climate change research: the concept of shared climate policy assumptions

The new scenario framework facilitates the coupling of multiple socioeconomic reference pathways with climate model products using the representative concentration pathways. This will allow for improved assessment of climate impacts, adaptation and mitigation. Assumptions about climate policy play a major role in linking socioeconomic futures with forcing and climate outcomes. The paper presents the concept of shared climate policy assumptions as an important element of the new scenario framework. Shared climate policy assumptions capture key policy attributes such as the goals, instruments and obstacles of mitigation and adaptation measures, and introduce an important additional dimension to the scenario matrix architecture. They can be used to improve the comparability of scenarios in the scenario matrix. Shared climate policy assumptions should be designed to be policy relevant, and as a set to be broad enough to allow a comprehensive exploration of the climate change scenario space.

Global and Regional Greenhouse Gas Emissions Scenarios

This article presents a set of 30 greenhouse gas (GHG) emissions scenarios developed by six modeling teams. The scenarios describe trajectories up to 2100 by four world regions. Today the distribution of both income and GHG emissions is very unbalanced between various world regions. Furthermore, the relative importance of individual gases and sources of emission differ from region to region. A feature shared by all scenarios is higher growth rates of population, income and GHG emissions in the current developing countries (DEV) than in industrialized countries (IND). Today the DEV regions account for about 46% of all emissions, but by 2100 no less they contribute 67–76% of the global total. By that same year the total income generated in the DEV regions reaches 58–71% from only 16% in 1990. As a result of these two developments, GHG emissions per unit of income converge over time. Carbon emitted from fossil fuel use remains the primary source of GHG emissions over the next century; by 2100 CO2 makes up 70 to 80% of total GHG emissions. The role of sulfur warrants special attention. Contrary to many earlier studies, all scenarios presented here assume that sulfur emissions are controlled in all regions sooner or later, and to various degrees. As sulfur plays a role in cooling of the atmosphere through formation of sulfate aerosols, a local effect, this abatement constitutes a relative local warming effect. The decrease of sulfur emissions is already observed the IND regions, and is expected also in ASIA after an initial rise.

Drivers and patterns of land biosphere carbon balance reversal

The carbonbalance of the landbiosphere is the result of complex interactions between land, atmosphere andoceans, including climatic change, carbondioxide fertilization and land-use change.While the land biosphere currently absorbs carbondioxide from the atmosphere, this carbonbalancemight be reversed under climate and land-use change (‘carbonbalance reversal’). A carbonbalance reversalwould render climatemitigationmuchmoredifficult, as net negative emissionswould beneeded to even stabilize atmospheric carbondioxide concentrations.We investigate the robustness of the landbiosphere carbon sinkunderdifferent socio-economicpathwaysby systematically varying climate sensitivity, spatial patterns of climate change and resulting land-use changes. For this,we employ amodelling frameworkdesigned to account for all relevant feedbackmechanismsby coupling the integrated assessmentmodel IMAGEwith theprocess-baseddynamic vegetation, hydrology and crop growthmodel LPJmL.Wefind that carbon balance reversal can occurunder a broad range of forcings and is connected to changes in tree cover and soil carbonmainly innorthern latitudes. These changes are largely a consequence of vegetation responses to varying climate andonly partially of land-use change and the rate of climate change. Spatial patterns of climate change as deduced fromdifferent climatemodels, substantially determinehowmuchpressure in termsof globalwarming and land-use change the landbiospherewill tolerate before the carbonbalance is reversed.A reversal of the landbiosphere carbonbalance canoccur as early as 2030, although at very low probability, and shouldbe considered in thedesign of so-calledpeak-and-decline strategies. Introduction: the land biosphere carbon sink The land biosphere presently absorbs substantial amounts of carbon dioxide (CO2) from the atmosphere, partially compensating CO2 emissions from fossil fuel combustion and land use change and thus slowing anthropogenic climate change. Over the last three decades, land surfaces have absorbed about 2.3±0.8 Pg carbon (C) per year. Over the same period, land use change has led to average emissions of 1.0±0.5 Pg C yr, leaving a net carbon sink of 1.3 Pg C yr (Le Quéré et al 2014). This net carbon flux from the atmosphere to the land biosphere is a prominent negative (dampening) feedback mechanism in the Earth system (Friedlingstein et al 2006) that slows the rate of increase of atmospheric CO2. The interannual variability of the land–atmosphere carbon flux reflects its sensitivity to changes in precipitation in sensitive ecosystems (Schwalm et al 2012, Gatti et al 2014, Poulter et al 2014) as well as to variations in temperature (Lucht et al 2002). Land carbon uptake is projected to increase under climate change, mainly driven by the positive effects of CO2 fertilization of photosynthesis (Sitch et al 2008, Friend et al 2014), which are subject to large uncertainties (Schimel et al 2015). However, under high emission scenarios and severe climate change, some studies have found that the OPEN ACCESS

A new toolkit for developing scenarios for climate change research and policy analysis

WWW.ENVIRONMENTMAGAZINE.ORG VOLUME 56 NUMBER 2 Y ogi Berra succinctly captured how economic growth, technology change, demographic change, and climate change are altering visions of what the future could bring: “the future ain’t what it used to be.”1 Understanding the range and character of possible futures is critical to furthering assessment of climate change, including the potential risks to physical, natural, and human systems in the context of different development pathways, and mitigation and adaptation options to avoid, prepare for, and manage those risks. Because concerns about climate change span the current to the far future, the field has a long history of using scenarios to explore and evaluate the extensive uncertainties associated with future climate change and development pathways. Projecting possible impacts under different futures and identifying the trade-offs and synergies of adaptation and mitigation policies require scenarios that include (1) the drivers of greenhouse gas emissions, (2) the resulting emissions, (3) assumptions about other drivers of socioeconomic development that will affect the magnitude and pattern of impacts, and/or the ability to avoid, prepare for, cope with, and recover from climate change, and (4) the adaptation and mitigation policy environment.

Towards pathways bending the curve terrestrial biodiversity trends within the 21st century

Unless actions are taken to reduce multiple anthropogenic pressures, biodiversity is expected to continue declining at an alarming rate. Models and scenarios can be used to help design the pathways to sustain a thriving nature and its ability to contribute to people. This approach has so far been hampered by the complexity associated with combining projections of pressures on, and subsequent responses from, biodiversity. Most previous assessments have projected continuous biodiversity declines and very few have identified pathways for reversing the loss of biodiversity without jeopardizing other objectives such as development or climate mitigation. The Bending The Curve initiative set out to advance quantitative modelling techniques towards ambitious scenarios for biodiversity. In this proof-of-concept analysis, we developed a modelling approach that demonstrates how global land use and biodiversity models can shed light on wedges able to bend the curve of biodiversity trends as affected by land-use change, the biggest current threat to biodiversity. In order to address the uncertainties associated with such pathways we used a multi-model framework and relied on the Shared Socioeconomic Pathway/Representative Concentration Pathway scenario framework. This report describes the details of this modelling approach.