Integrated assessment modelling or integrated modelling is a term used for a type of scientific modelling that tries to link main features of society and economy with the biosphere and atmosphere into one modelling framework. The goal of integrated assessment modelling is to accommodate informed policy-making, usually in the context of climate change though also in other areas of human and social development. While the detail and extent of integrated disciplines varies strongly per model, all climatic integrated assessment modelling includes economic processes as well as processes producing greenhouse gases. Other integrated assessment models also integrate other aspects of human development such as education, health, infrastructure, and governance. These models are integrated because they span multiple academic disciplines, including economics and climate science and for more comprehensive models also energy systemsland-use change, agriculture, infrastructure, conflict, governance, technology, education, and health. The word assessment comes from the use of these models to provide information for answering policy questions. To quantify these integrated assessment studies, numerical models are used. Integrated assessment modelling does not provide predictions for the future but rather estimates what possible scenarios look like. There are two different types of integrated assessment models. First, there are those models that focus on quantifying future developmental pathways or scenarios and provide detailed, sectoral information on the complex processes modelled. Here they are called process-based integrated assessment models. Second, there are models that aggregate the costs of climate change and climate change mitigation to find estimates of the total costs of climate change. Here, these models are called cost-benefit integrated assessment models.
Process-based Integrated Assessment Models
have relied on process-based integrated assessment models to quantify mitigation scenarios. They have been used to explore different pathways for staying within climate policy targets such as the 1.5 °C target agreed upon in the Paris Agreement. Moreover, these models have underpinned research including energy policy assessment and simulate the Shared socioeconomic pathways. Notable modelling frameworks include IMAGE, MESSAGEix, AIM/GCE, GCAM, REMIND-MAgPIE, and WITCH-GLOBIOM. While these scenarios are highly policy-relevant, interpretation of the scenarios should be done with care.
Cost-benefit Integrated Assessment Models
Cost-benefit integrated assessment models are the main tools for calculating the social cost of carbon, or the marginal social cost of emitting one more tonne of carbon into the atmosphere at any point in time. For instance, the DICE, PAGE, and FUND models have been used by the US Interagency Working Group to calculate the social cost of carbon and its results have been used for regulatory impact analysis. This type of modelling is carried out to find the total cost of climate impacts, which are generally considered a negative externality not captured by conventional markets. In order to correct such a market failure, for instance by using a carbon tax, the cost of emissions is required. However, the estimates of the social cost of carbon are highly uncertain and will remain so for the foreseeable future. It has been argued that "IAM-based analyses of climate policy create a perception of knowledge and precision that is illusory, and can fool policy-makers into thinking that the forecasts the models generate have some kind of scientific legitimacy". Still, it has been argued that attempting to calculate the social cost of carbon is useful to gain insight into the effect of certain processes on climate impacts, as well as to better understand one of the determinants international cooperation in the governance of climate agreements. Integrated assessment models have not been used solely to assess environmental or climate change-related fields. They have also been used to analyze patterns of conflict, the Sustainable Development Goals, trends across issue area in Africa,, and food security.
