Editing IPCC:AR6/SR15/Chapter-4 (section)

== 4.6 Knowledge Gaps and Key Uncertainties ==

<div id="article-4-6-block-1"></div>

The global response to limiting warming to 1.5°C is a new knowledge area, which has emerged after the Paris Agreement. This section presents a number of knowledge gaps that have emerged from the assessment of mitigation, adaptation and carbon dioxide removal (CDR) options and solar radiation modification (SRM) measures; enabling conditions; and synergies and trade-offs. Illustrative questions that emerge synthesizing the more comprehensive Table 4.13 below include: how much can be realistically expected from innovation, behaviour and systemic political and economic change in improving resilience, enhancing adaptation and reducing GHG emissions? How can rates of changes be accelerated and scaled up? What is the outcome of realistic assessments of mitigation and adaptation land transitions that are compliant with sustainable development, poverty eradication and addressing inequality? What are life-cycle emissions and prospects of early-stage CDR options? How can climate and sustainable development policies converge, and how can they be organized within a global governance framework and financial system, based on principles of justice and ethics (CBDR-RC), reciprocity and partnership? To what extent would limiting warming to 1.5°C require a harmonization of macro-financial and fiscal policies, which could include central banks? How can different actors and processes in climate governance reinforce each other, and hedge against the fragmentation of initiatives?

These knowledge gaps are highlighted in Table 4.13 along with a cross-reference to the respective sections in the last column.

<div id="article-4-6-block-2"></div>

<span id="table-4.13"></span>
'''Table 4.13'''

<span id="knowledge-gaps-and-uncertainties"></span>
'''Knowledge gaps and uncertainties'''

Knowledge Area

Mitigation

Adaptation

Reference

1.5°C Pathways and Ensuing Change

* Lack of literature specific to 1.5°C on investment costs with detailed breakdown by technology
* Lack of literature specific to 1.5°C on mitigation costs in terms of GDP and welfare
* Lack of literature on distributional implications of 1.5°C compared to 2°C or business-as-usual at sectoral and regional levels
* Limited 1.5°C-specific case studies for mitigation
* Limited knowledge on the systemic and dynamic aspects of transitions to 1.5°C, including how vicious or virtuous circles might work, how self-reinforcing aspects can be actively introduced and managed

* Lack of literature specific to 1.5°C on adaptation costs and need
* Lack of literature on what overshoot means for adaptation
* Lack of knowledge on avoided adaptation investments associated with limiting warming to 1.5°C, 2°C or business-as-usual
* Limited 1.5°C-specific case studies for adaptation
* Scant literature examining current or future adaptation options, or examining what different climate pathways mean for adaptation success
* Need for transformational adaptation at 1.5°C and beyond remains largely unexplored

4.2

Options to Achieve and Adapt to 1.5°C

Energy Systems

* The shift to variable renewables that many countries are implementing is just reaching a level where large-scale storage systems or other grid flexibility options, e.g., demand response, are required to enable resilient grid systems. Thus, new knowledge on the opportunities and issues associated with scaling up zero-carbon grids would be needed, including knowledge about how zero-carbon electric grids can integrate with the full-scale electrification of transport systems
* CCS suffers mostly from uncertainty about the feasibility of timely upscaling, both due to lack of regulatory capacity and concerns about storage safety and cost
* There is not much literature on the distributional implications of large-scale bioenergy deployment, the assessment of environmental feasibility is hampered by a diversity of contexts of individual studies (type of feedstock, technology, land availability), which could be improved through emerging meta-studies

* Relatively little literature on individual adaptation options since AR5
* No evidence on socio-cultural acceptability of adaptation options
* Lack of regional research on the implementation of adaptation options

4.3.1

Land &amp; ecosystems

* More knowledge would be needed on how land-based mitigation can be reconciled with land demands for adaptation and development
* While there is now more literature on the underlying mechanisms of land transitions, data is often insufficient to draw robust conclusions, and there is uncertainty about land availability
* The lack of data on social and institutional information (largest knowledge gap indicated for ecosystems restoration in Table 4.11), which are therefore not widely integrated in land use modelling
* Examples of successful policy implementation and institutions related to land-based mitigation leading to co-benefits for adaptation and development are missing from the literature
* There is relatively little scientific literature on the effects of dietary shifts and reduction of food wastage on mitigation, especially regarding the institutional, technical and environmental concerns

* Regional information on some options does not exist, especially in the case of land-use transitions
* Limited research examining socio-cultural perspectives and impacts of adaptation options, especially for efficient irrigation, coastal defence and hardening, agroforestry and biodiversity management
* Lack of longitudinal, regional studies assessing the impacts of certain adaptation options, such as conservation agriculture and shifting to efficient livestock systems
* More knowledge is needed on the cost-effectiveness and scalability of various adaptation options. For example, there is no evidence for the macro-economic viability of community-based adaptation (CbA) and biodiversity management, or on employment and productivity enhancement potential for biodiversity management and coastal defence and hardening.
* More knowledge is needed on risk mitigation and the potential of biodiversity management
* Lack of evidence of the political acceptability of efficient livestock systems
* ''Limited evidence'' on legal and regulatory feasibility of conservation agriculture and no evidence on coastal defence and hardening
* For transparency and accountability potential, there is ''limited evidence''  for conservation agriculture and no evidence for biodiversity management, coastal defence and hardening and sustainable aquaculture
* No evidence on hazard risk reduction potential of conservation agriculture and biodiversity management

4.3.2

Urban &amp; infrastructure systems

* ''Limited evidence'' on relationship between toxic waste and public transport
* ''Limited evidence'' on the impacts of electric vehicles and non-motorized urban transport, as most schemes are too new
* As changes in shipping and aviation have been limited to date, ''limited evidence'' of social impacts
* Knowledge about how to facilitate disruptive, demand-based innovations that may be transformative in urban systems, is needed
* Understanding of the urban form implications of combined changes from electric, autonomous and shared/public mobility systems, is needed
* Considering distributional consequences of climate responses is an on-going need
* Knowledge gaps in the application and scale up of combinations of new smart technologies, sustainable design, advanced construction techniques and new insulation materials, renewable energy and behaviour change in urban settlements
* The potential for leapfrog technologies to be applied to slums and new urban developments in developing countries is weak.

* More evidence would be needed on hot-spots, for example the growth of peri-urban areas populated by large informal settlements
* Major uncertainties emanate from the lack of knowledge on the integration of climate adaptation and mitigation, disaster risk management, and urban poverty alleviation
* There is ''limited evidence'' on the institutional, technological and economic feasibility of green infrastructure and environmental services and for socio-cultural and environmental feasibility of codes and standards
* In general, there is no evidence for the employment and productivity enhancement potential of most adaptation options.
* There is ''limited evidence'' on the economic feasibility of sustainable water management

4.3.3

Industrial systems

* Lack of knowledge on potential for scaling up and global diffusion of zero- and low-emission technologies in industry
* Questions remain on the socio-cultural feasibility of industry options, including human capacity and private sector acceptance of new, radically different technologies from current well-developed practices, as well as distributional effects of potential new business models
* As the industrial transition unfolds, lack of knowledge on its dynamic interactions with other sectors, in particular with the power sector (and infrastructure) for electrification of industry, with food production and other users of biomass in case of bio-based industry developments, and with CDR technologies in the case of CC(U)S
* Life-cycle assessment-based comparative analyses of CCUS options are missing, as well as life-cycle information on electrification and hydrogen
* Impacts of industrial system transitions are not well understood, especially on employment, identity and well-being, in particular in the case of substitution of conventional, high-carbon industrial products with lower-carbon alternatives, as well as electrification and use of hydrogen

* Very ''limited evidence'' on how industry would adapt to the consequences of 1.5°C or 2°C temperature increases, in particular large and immobile industrial clusters in low-lying areas as well as availability of transportation and (cooling) water resources and infrastructure
* There is ''limited evidence'' on the economic, institutional and socio-cultural feasibility of adaptation options available to industry

4.3.4

Overarching adaptation options

* There is no evidence on technical and institutional feasibility of educational options
* There is ''limited evidence'' on employment and productivity enforcement potential of climate services
* There is ''limited evidence'' on socio-cultural acceptability of social safety nets
* There is a small but growing literature on human migration as an adaptation strategy. Scant literature on the cost-effectiveness of migration

4.3.5

Short-lived climate forcers

* ''Limited evidence'' of co-benefits and trade-offs of SLCF reduction (e.g., better health outcomes, agricultural productivity improvements)
* Integration of SLCFs into emissions accounting and international reporting mechanisms enabling a better understanding of the links between black carbon, air pollution, climate change and agricultural productivity

4.3.6

Carbon dioxide removal

* A bottom-up analysis of CDR options indicates that there are still key uncertainties around the individual technologies. Ocean-based options will be assessed in depth in the IPCC Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC)
* Assessments of environmental aspects are missing, especially for ‘newer’ options like enhanced weathering or direct air carbon capture
* In order to obtain more information on realistically available and sustainable removal potentials, more bottom-up, regional studies, also taking into account also social issues, would be needed. These can better inform the modelling of 1.5°C pathways
* Knowledge gaps on issues of governance and public acceptance, the impacts of large-scale removals on the carbon cycle, the potential to accelerate deployment and upscaling, and means of incentivization
* Knowledge gaps on integrated systems of renewable energy and CDR technologies such as enhanced weathering and DACCS
* Knowledge gaps on under which conditions the use of captured CO <sub>2</sub> is generating negative emissions and would qualify as a mitigation option

4.3.7

Solar radiation modification (SRM)

* In spite of increasing attention to the different SRM measures and their potential to keep global temperature below 1.5°C, knowledge gaps remain, not only with respect to the physical understanding of SRM measures but also concerning ethical issues
* We do not know how to govern SRM in order to avoid unilateral action and how to prevent possible reductions in mitigation (‘moral hazard’)

4.3.8

Enabling Conditions

Governance

* As technological changes have begun to accelerate, there is a lack of knowledge on new mechanisms that can enable private enterprise to mainstream this activity, and reasons for success and failure need to be researched
* Research is thin on effective multilevel governance, in particular in developing countries, including participation by civil society, women and minorities
* Gaps in knowledge remain pertaining to partnerships within local governance arrangements that may act as mediators and drivers for achieving global ambition and local action
* Methods for assessing contribution and aggregation of non-state actors in limiting warming to 1.5°C
* Knowledge gap on an enhanced framework for assessment of the ambition of NDCs

* The ability to identify explanatory factors affecting the progress of climate policy is constrained by a lack of data on adaptation actions across nations, regions, and sectors, compounded by an absence of frameworks for assessing progress. Most hypotheses on what drives adaptation remain untested
* Limited empirical assessment of how governance affects adaptation across cases
* Focus on ‘success’ stories and leading adaptors overlooks lessons from situations where no or unsuccessful adaptation is taking place

4.4.1

Institutions

* Lack of 1.5°C-specific literature
* Role of regulatory financial institutions and their capacity to guarantee financial stability of economies when investments potentially face risks, both because of climate impacts and because of the systems transitions if lower temperature scenarios are pursued
* Knowledge gaps on how to build capabilities across all countries and regions globally to implement, maintain, manage, govern and further develop mitigation options for 1.5°C.
* While importance of indigenous and local knowledge is recognized, the ability to scale up beyond the local remains challenging and little examined
* There is a lack of monitoring and evaluation (M&amp;E) of adaptation measures, with most studies enumerating M&amp;E challenges and emphasising the importance of context and social learning. Very few studies evaluate whether and why an adaptation initiative has been effective. One of the challenges of M&amp;E for both mitigation and adaptation is a lack of high quality information for modelling. Adaptation M&amp;E is additionally challenged by limited understanding on what indicators to measure and how to attribute altered vulnerability to adaptation actions

4.4.2

Lifestyle and behavioural change

* Whereas mitigation pathways studies address (implicitly or explicitly) the reduction or elimination of market failures (e.g., external costs, information asymmetries) via climate or energy policies, no study addresses behavioural change strategies in the relationship with mitigation and adaptation actions in the 1.5°C context
* Limited knowledge on GHG emissions reduction potential of diverse mitigation behaviour across the world
* Most studies on factors enabling lifestyle changes have been conducted in high-income countries, more knowledge needed from low- and middle-income countries, and the focus is typically on enabling individual behaviour change, far less on enabling change in organizations and political systems

* Knowledge gaps on factors enabling adaptation behaviour, except for behaviour in agriculture.
* Little is known about cognitive and motivational factors promoting adaptive behaviour.
* Little is known about how potential adaptation actions might affect behaviour to influence vulnerability outcomes

4.4.3

Lifestyle and behavioural change

* Limited understanding and treatment of behavioural change and the potential effects of related policies in ambitious mitigation pathways, e.g., in Integrated Assessment Models

4.4.3

Lack of insight on what can enable changes in adaptation and mitigation behaviour in organizations and political systems

Technological innovation

* Quantitative estimates for mitigation and adaptation potentials at economy or sector scale as a result of the combination of general purpose technologies and mitigation technologies have been scarce, except for some evidence in the transport sector
* Evidence on the role of international organizations, including the UNFCCC, in building capabilities and enhancing technological innovation for 1.5°C, except for some parts of the transport sector
* Technology transfer trials to enable leapfrog applications in developing countries have ''limited evidence''

4.4.4

Policy

* More empirical research would be needed to derive robust conclusions on effectiveness of policies for enabling transitions to 1.5°C and on which factors aid decision-makers seeking to ratchet up their NDCs

* Understanding of what policies work (and do not work) is limited for adaptation in general and for 1.5°C in particular, beyond specific case studies

4.4.5

Finance

Knowledge gaps persist with respect to the instruments to match finance to its most effective use in mitigation and adaptation

4.4.5

Synergies and Trade-Offs Between Adaptation and Mitigation

* Strong claims are made with respect to synergies and trade-offs, but there is little knowledge to underpin these, especially of co-benefits by region
* Water–energy conservation relationships of individual conservation measures in industries other than the water and energy sectors have not been investigated in detail
* There is no evidence on synergies with adaptation of CCS in the power sector and of enhanced weathering under carbon dioxide removal
* There is no evidence on trade-offs with adaptation of low- and zero-energy buildings, and circularity and substitution and bio-based industrial system transitions
* There is no evidence of synergies or trade-offs with mitigation of CbA
* There is no evidence of trade-offs with mitigation of the built environment, on adaptation options for industrial energy, and climate services

4.5.4

<span id="faqs-frequently-asked-questions"></span>