Matthew Gidden

International Institute for Applied Systems Analysis | IIASA · Energy

Carbon dioxide removal (CDR) involves capturing CO2 from the atmosphere and storing it for decades to millennia. Alongside deep emissions reductions, CDR is required for meeting the temperature goal of the Paris Agreement (IPCC 2022). However, parties to the agreement do not currently distinguish CDR from emissions reductions in their climate pledg...

Previous phases of the Coupled Model Intercomparison Project (CMIP) have primarily focused on simulations driven by atmospheric concentrations of greenhouse gases (GHGs), for both idealized model experiments and climate projections of different emissions scenarios. We argue that although this approach was practical to allow parallel development of...

Carbon fluxes from land use are key to the Paris Agreement. However, data comparability issues persist between countries’ inventories and targets (Nationally Determined Contributions, NDCs), which generally include direct and indirect anthropogenic net emissions, and what models provide as Paris-aligned benchmarks (direct net emissions only). As a...

Global emission reduction efforts continue to be insufficient to meet the temperature goal of the Paris Agreement¹. This makes the systematic exploration of so-called overshoot pathways that temporarily exceed a targeted global warming limit before drawing temperatures back down to safer levels a priority for science and policy2–5. Here we show tha...

The 6th Assessment Report from the Intergovernmental Panel on Climate Change lacked sufficient land-sector scenario information to estimate total carbon dioxide removal deployment. Here, using a dataset of land-based carbon dioxide removal based on the scenarios assessed by the Intergovernmental Panel on Climate Change, we show that removals via af...

The State of CDR reports are intended to regularly inform researchers, policymakers and practitioners on the state of progress, by systematically collecting and analysing the vast amount of data and developments in many parts of the world. The second edition continues the assessment of CDR development, expanding geographical coverage and including...

Current emissions trends are likely to deplete a 1.5°C consistent carbon budget soon after the year 2030, resulting in a period of overshoot. To navigate responsibilities for and during this period we contrast ‘fair’ allocations of a remaining carbon budget with projected carbon emissions trends until net-zero. We term this measure the ‘net-zero ca...

Rapid emissions reductions, including reductions in deforestation-based land emissions, are the dominant source of global climate mitigation potential in the coming decades. However, carbon dioxide removal (CDR) will also have an important role to play. Despite this, it remains unclear whether current national proposals for CDR align with temperatu...

Ensembles of mitigation pathways, produced by multiple different models, are becoming increasingly influential as the world seeks to define climate goals and implement policy to meet them. In this context a range of open-source code has been developed to standardise and facilitate the systematic and robust analysis of mitigation pathways. We introd...

Carbon dioxide removal (CDR) is a critical component of any strategy to limit global warming to well below 2°C and rapidly gaining attention in climate research and policymaking. Despite its importance, there have been few attempts to systematically evaluate the scientific evidence on CDR. Here we use an approach rooted in artificial intelligence t...

We review how the international modelling community, encompassing Integrated Assessment models, global and regional Earth system and climate models, and impact models, have worked together over the past few decades, to advance understanding of Earth system change and its impacts on society and the environment, and support international climate poli...

The IPCC 6th Assessment Report lacked sufficient land sector scenario information to estimate total carbon dioxide removal (CDR) deployment. Using a new dataset, we show that land CDR plays an important near-term role and novel removal technologies scale to multi-gigatonne levels by 2050 and beyond to balance residual emissions and draw down warmin...

Taking stock of global progress towards achieving the Paris Agreement requires consistently measuring aggregate national actions and pledges against modelled mitigation pathways¹. However, national greenhouse gas inventories (NGHGIs) and scientific assessments of anthropogenic emissions follow different accounting conventions for land-based carbon...

Previous phases of the Coupled Model Intercomparison Project (CMIP) have primarily focused on simulations driven by atmospheric concentrations of greenhouse gases (GHGs), both for idealized model experiments, and for climate projections of different emissions scenarios. We argue that although this approach was pragmatic to allow parallel developmen...

The Emissions Gap Report is UNEP's spotlight report launched annually in advance of the annual Climate negotiations. The EGR tracks the gap between where global emissions are heading with current country commitments and where they ought to be to limit warming to 1.5°C. Each edition explores ways to bridge the emissions gap.

Carbon Dioxide Removal (CDR) is a key element of any mitigation strategy aiming to achieve the long-term temperature goal of the Paris Agreement, as well as national net-zero and net-negative greenhouse gas emissions targets. For robust CDR policy, the credibility of certification schemes is essential.

Rapid emissions reductions, including reductions in deforestation-based land emissions, are the dominant source of global mitigation potential in the coming decades 1 . But in addition, carbon dioxide removal (CDR) will have an important role to play. Here we benchmark proposed CDR in the Nationally Determined Contributions (NDCs) and the long-term...

Questions around the technical and political feasibility of deep mitigation scenarios assessed by the Intergovernmental Panel on Climate Change have increasingly been raised as have calls for more directly analyzing and incorporating aspects of justice and fairness. Simultaneously, models are increasing the technical representation of novel carbon-...

Addressing questions of equitable contributions to emission reductions is important to facilitate ambitious global action on climate change within the ambit of the Paris Agreement. Several large developing regions with low historical contributions to global warming have a strong moral claim to a large proportion of the remaining carbon budget (RCB)...

A global, independent scientific assessment of Carbon Dioxide Removal

The 2015 Paris Agreement sets the objectives of global climate ambition as expressed in its long-term temperature goal and mitigation goal. The scientific community has explored the characteristics of greenhouse gas emission reduction pathways in line with the Paris Agreement. However, when categorizing such pathways, the focus has been put on the...

The implementation of a carbon pricing policy to comply with GHG emission targets faces opposition in small economies. An integrated modeling exercise was carried out for Israel to assess the cost-effectiveness of GHG emission reduction options. Alternative policies in terms of carbon pricing and policy standards are evaluated. The results show tha...

While the Intergovernmental Panel on Climate Change (IPCC) physical science reports usually assess a handful of future scenarios, the Working Group III contribution on climate mitigation to the IPCC's Sixth Assessment Report (AR6 WGIII) assesses hundreds to thousands of future emissions scenarios. A key task in WGIII is to assess the global mean te...

Scientifically rigorous guidance to policy makers on mitigation options for meeting the Paris Agreement long-term temperature goal requires an evaluation of long-term global-warming implications of greenhouse gas emissions pathways. Here we employ a uniform and transparent methodology to evaluate Paris Agreement compatibility of influential institu...

While the IPCC’s physical science report usually assesses a handful of future scenarios, the IPCC Sixth Assessment Working Group III report (AR6 WGIII) on climate mitigation assesses hundreds to thousands of future emissions scenarios. A key task is to assess the global-mean temperature outcomes of these scenarios in a consistent manner, given the...

The 2015 Paris Agreement sets the objectives of global climate ambition as expressed in its long-term temperature goal and mitigation goal. The scientific community has explored the characteristics of greenhouse gas emission reduction pathways in line with the Paris Agreement. However, when categorizing such pathways, the focus has been put on the...

King et al. raise important issues, several of which pertain to the broader policy discourse surrounding international climate negotiations and countries’ climate pledges rather than the modeling conducted in our Policy Forum. We agree with King et al. that the updated Paris Agreement pledges could paint an overly optimistic picture of the future,...

The expected growth in the demand for passenger and freight services exacerbates the challenges of reducing transport GHG emissions, especially as commercial low-carbon alternatives to petroleum fuels are limited for shipping, air and long-distance road travel. Biofuels can offer a pathway to significantly reduce emissions from these sectors, as th...

Without additional support policies, clean cooking could become unaffordable for about 470 million people by 2030 if a post-pandemic recovery is slow, and about 200 million people by 2030 under ambitious climate mitigation action. Acceleration of clean cooking transitions by tapping into pandemic recovery and climate funds to target the poorest peo...

As part of the 2015 Paris Agreement, countries agreed to regularly revisit and enhance their national climate strategies and, every 5 years, to offer new emissions targets in the form of nationally determined contributions (NDCs) (1). This year’s 26th Conference of Parties provides a waypoint in this updating process as countries have been offering...

Slow progress in expanding clean cooking access is hindering progress on health, gender, equity, climate and air quality goals globally. Despite a rising population share with clean cooking access, the number of cooking poor remains stagnant. In this study we explored clean cooking access until 2050 under three reference scenarios, a COVID-19 recov...

National net zero emission targets could, if fully implemented, reduce best estimates of projected global average temperature increase to 2.0–2.4 °C by 2100, bringing the Paris Agreement temperature goal within reach. A total of 131 countries are discussing, have announced or have adopted net zero targets, covering 72% of global emissions. These ta...

The open-source Python package pyam provides a suite of features and methods for the analysis, validation and visualization of reference data and scenario results generated by integrated assessment models, macro-energy tools and other frameworks in the domain of energy transition, climate change mitigation and sustainable development. It bridges th...

The open-source Python package pyam provides a suite of features and methods for the analysis, validation and visualization of reference data and scenario results generated by integrated assessment models, macro-energy tools and other frameworks in the domain of energy transition, climate change mitigation and sustainable development. It bridges th...

The open-source Python package pyam provides a suite of features and methods for the analysis, validation and visualization of reference data and scenario results generated by integrated assessment models, macro-energy tools and other frameworks in the domain of energy transition, climate change mitigation and sustainable development. It bridges th...

Since its adoption in 2015, governments, international agencies and private entities have increasingly recognized the implications of the Paris Agreement’s 1.5°C long-term temperature goal (LTTG) for greenhouse gas emissions reduction planning in both the near- and long-term. Governments have submitted or are preparing updates of their Nationally D...

The Shared Socioeconomic Pathways (SSPs) represent five narratives of future development used for climate change research. They include quantified projections of socioeconomic variables such as population, income levels, inequalities, and emissions over the twenty-first century. The SSP’s population projections embody explicit, pathway-specific int...

This report explores three key unresolved issues in international negotations on the rules for international carbon markets under Article 6 of the Paris Agreement: achieving an overall mitigation in global emissions (OMGE), collecting a share of proceeds (SOP) for adaptation and the transition of the Clean Development Mechanism into the Paris Agree...

Equity is one of the key principles underpinning the global climate regime and is all the more essential given the heterogenous, self-differentiated nature of the Paris Agreement. The scientific community has proposed several effort-sharing schemes to operationalise equity – reflecting not only the multi-faceted nature of the problem but also a lon...

Achieving the 1.5°C temperature target of the Paris Agreement requires rapid and significant reductions in emissions. There is strong evidence that electricity generation from coal must rapidly decrease to achieve this goal, but a large range of uncertainty over a potential bridging role of natural gas in the electricity sector. Using the integrate...

Limiting global warming to 1.5°C requires far-reaching transformations across power generation, buildings, industry, transport, land use, coastal zone management, and agriculture, as well as the immediate scale-up of technological carbon removal and climate finance. This report translates these transitions into 40 targets for 2030 and 2050, with me...

The wave of national net zero CO 2 and greenhouse gas emission targets could, if fully implemented, reduce best estimates of projected global average temperature increase to 2.1–2.4°C by 2100 and could bring achievement of the Paris Agreement within reach. 127 countries are discussing, have announced or have adopted net zero targets, which together...

We present an overview of results from 11 integrated assessment models (IAMs) that participated in the 33rd study of the Stanford Energy Modeling Forum (EMF-33) on the viability of large-scale deployment of bioenergy for achieving long-run climate goals. The study explores future bioenergy use across models under harmonized scenarios for future cli...

This paper explores the potential role of bioenergy coupled to carbon dioxide (CO2) capture and storage (BECCS) in long-term global scenarios. We first validate past insights regarding the potential use of BECCS in achieving climate goals based on results from 11 integrated assessment models (IAMs) that participated in the 33rd study of the Stanfor...

Bioenergy is expected to play an important role in long-run climate change mitigation strategies as highlighted by many integrated assessment model (IAM) scenarios. These scenarios, however, also show a very wide range of results, with uncertainty about bioenergy conversion technology deployment and biomass feedstock supply. To date, the underlying...

A modest fraction of current global stimulus funds can put the world on track to achieve Paris Agreement goals

The global response to the COVID-19 pandemic has led to a sudden reduction of both GHG emissions and air pollutants. Here, using national mobility data, we estimate global emission reductions for ten species during the period February to June 2020. We estimate that global NOx emissions declined by as much as 30% in April, contributing a short-term...

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

The Paris Agreement long-term temperature goal is to be achieved on the basis of equity. Accomplishing this goal will require carbon dioxide removal (CDR), yet existing plans for CDR deployment are insufficient to meet potential global needs, and equitable approaches for distributing CDR responsibilities between nations are lacking. Here we apply t...

Anthropogenic increases in atmospheric greenhouse gas concentrations are the main driver of current and future climate change. The integrated assessment community has quantified anthropogenic emissions for the shared socio-economic pathway (SSP) scenarios, each of which represents a different future socio-economic projection and political environme...

To achieve the Paris Agreement’s long-term temperature goal, current energy systems must be transformed. Australia represents an interesting case for energy system transformation modeling: with a power system dominated by fossil fuels and, specifically, with a heavy coal component, there is at the same time a vast potential for expansion and use of...

Proposed emission reduction targets and the scarcity of fossil fuel resources make a transition of the energy system towards an emission-free electricity supply necessary. Australia represents an interesting case for energy system transformation modelling. While it currently has a power system dominated by fossil fuels, and specifically with a heav...

Many countries have implemented national climate policies to accomplish pledged Nationally Determined Contributions and to contribute to the temperature objectives of the Paris Agreement on climate change. In 2023, the global stocktake will assess the combined effort of countries. Here, based on a public policy database and a multi-model scenario a...

Exploring potential future pathways for developing Asia’s energy consumption, CO2 emissions and infrastructure investment needs is essential to understanding how the countries of this rapidly growing region may contribute to the global climate targets set out in the 2015 Paris Agreement. To this end, this study employs the state-of-the-art global i...

Spatially distributed anthropogenic and open burning emissions are fundamental data needed by Earth system models. We describe the methods used for generating gridded datasets produced for use by the modeling community, particularly for the Coupled Model Intercomparison Project Phase 6. The development of three sets of gridded data for historical o...

Anthropogenic increases of atmospheric greenhouse gas concentrations are the main driver of current and future climate change. The Integrated Assessment community quantified anthropogenic emissions for the Shared Socioeconomic Pathways (SSP) scenarios, each of which represents a different future socio-economic projection and political environment....