What are integrated assessment models?

IAMs are computer models that integrate the latest assumptions in economics, energy systems, land use, and climate science to explore what-if futures. The Intergovernmental Panel on Climate Change (IPCC) aggregates hundreds of these future scenarios from IAMs into its assessment reports. Policymakers then use these reports to compare options, estimate costs, and understand how today’s choices ripple through economies and the atmosphere over decades. 

IAMs help answer critical questions, such as:

• What will happen if we take no action on climate change? 

• What is the total energy demand required to limit warming to 1.5 °C? 

• What global carbon price is necessary to limit warming to 1.5 °C?

To answer these questions, IAMs rely on standardized scenarios called shared socioeconomic pathways (SSPs), which include assumptions about population growth, GDP, energy intensity, and more. SSPs allow comparison between models, enabling the IPCC to distill insights for policymakers, who in turn use them to shape global and regional climate targets.

Figure 1: Lifecycle of use-cases for IAMs showing their use in climate policy frameworks and resulting climate goals. NDCs: Nationally Determined Contributions. LTS: Long-term strategies. Source: Carbon Direct.

Representation of carbon removal in IAMs to date

Yet, IAMs underrepresent the diversity of carbon removal technologies. Most scenarios rely heavily on bioenergy with carbon capture and storage (BECCS) and afforestation, while novel and durable approaches, such as direct air capture with carbon storage (DACCS), biochar, and enhanced rock weathering (ERW), have only recently begun to be introduced into models. 

The IPCC’s Sixth Assessment Report (AR6) illustrates the current imbalance. Of the 121 model runs in AR6 scenarios aligned with “well below 2°C” and “above 1.5°C” pathways:

• 120 deployed BECCS,

• 28 deployed DACCS,

• None represented biochar or ERW.

This overreliance on BECCS stems partly from its dual role in producing energy while removing carbon dioxide from the atmosphere.

However, representation of carbon removal in IAMs has also been criticized for failing to consider realistic scale-up constraints on their deployment. This leaves policymakers, environmental advocates, and civil society with distorted cost-optimal pathways and insufficient guidance on how to finance and design markets. 

To achieve global climate targets under the Paris Agreement, even with rapid and deep mitigation, carbon removal is critical for addressing both historical and hard-to-abate emissions. Therefore, accurately modeling future climate mitigation pathways requires expanding and improving how IAMs represent carbon removal.

How IAMs shape national climate commitments

The narrow scope of novel and durable carbon removals in IAMs also shapes many countries’ near-term nationally determined contributions (NDCs) and long-term strategies (LTSs). Most NDCs mention removals only vaguely, and few acknowledge emerging novel and durable technologies such as biochar, DACCS, or ERW (figure 2). 

For example, top emitters like the United States, China, India, and Brazil largely reference emission reductions or nature-based solutions, without notable mention of novel and durable carbon removal. As countries revise NDCs, addressing this gap will be critical. 

Figure 2: Global landscape of carbon removal references within NDCs and LTSs, showing country-level commitments to carbon removal. Data included in this map is the NDCs and LTSs as of May 2024; nations are currently in the process of updating their NDCs (throughout 2025), thus this map is subject to change. As of May 2024, there are no mentions of novel and durable carbon removal in the assessed NDCs. Source: Carbon Direct, adapted from Stuart-Smith RF et al., 2025

Expanding carbon removal in IAMs

To close this gap and represent carbon removal more accurately, Carbon Direct is collaborating with three leading research institutions with well-established IAMs: Pacific Northwest National Laboratory (PNNL), Utrecht University (UU), and the International Institute for Applied Systems Analysis (IIASA). Together, we are updating the latest cost assumptions, learning curves, and growth constraints for existing carbon removal technologies, while adding new representations of DACCS, biochar, and ERW.

Read the full white paper, Carbon Dioxide Removal: Global Goals and Regional Realities →