# Toward Climate-Neutral Heavy Industry: An Analysis of Industry Transition Roadmaps
## 1 Introduction  
Heavy industry sectors involve the extraction and processing of natural resources or scrap into basic materials that can be manufactured or constructed into products [1]. These heavy industry activities are energy-intensive, typically relying on fossil fuel inputs, giving rise to significant CO\({}_{2}\) emissions. For example, emissions from the production of five basic industrial materials--steel, cement, plastic (and other chemicals), paper, and aluminium--account for 20% of global CO\({}_{2}\) emissions, and demand for these materials is only expected to increase as many countries around the world continue to industrialize [2]. As such, there is growing awareness that emissions from heavy industry must be reduced sharply in order for the world to reach the target of the Paris Agreement--to limit global warming to \"well below\" 2 degrees Celsius [3]. Discussions on how to decarbonize heavy industry typically revolve around four interrelated solutions: decarbonizing all energy inputs, increasing energy efficiency, reducing process emissions, and promoting material circularity [4]. For many industries, energy inputs are the main source of emissions; for instance, 67% of emissions in China's chemical industry come from energy inputs [5]. Decarbonizing energy inputs requires reducing direct and indirect energy-related CO\({}_{2}\) emissions, which are often referred to as Scope I License MDP, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ([[https://creativecommons.org/licenses/by/4.0/](https://creativecommons.org/licenses/by/4.0/)]([https://creativecommons.org/licenses/by/4.0/](https://creativecommons.org/licenses/by/4.0/))). Meanwhile, energy efficiency solutions, such as better insulation and using waste heat, can lead to decrease in energy demand, meaning fewer energy inputs to decarbonize in the first place [8]. The Energy Transitions Commission estimates that energy efficiencycould lead to about 30% possible improvements, either through the latest generation of industrial processes or through completely new processes [4]. However, in some industries, such as cement, steel, and chemicals, efforts will also be needed to reduce process emissions that arise during the conversion of raw materials into intermediate or final products [9]. For example, process emissions account for almost two-thirds of total emissions from cement production [10]. Preventing these emissions requires significant shifts in production processes. In steelmaking, this could be via the use of electric arc furnaces or the direct reduction of iron with renewably produced hydrogen instead of coking coal in steelmaking. In cement production, this could be through using alternative binding agents or the use of carbon capture storage (CCS) technology. Lastly, material circularity can help to reduce the demand for brand new industrial products in the first place, meaning less processing in need of decarbonization [11; 12]. Indeed, it has been estimated that circular economy approaches could reduce CO2 emissions from four major industry sectors (plastics, steel, aluminum, and cement) by 40% globally and by 56% in developed economies such as Europe by 2050 [13]. These three solutions entail a transition away from current carbon-intensive patterns of industrial activity and rely significantly on the diffusion of low-carbon innovations into existing industrial systems [14]. Some of the technological and process innovations that form part of these solutions are commercially viable or in pilot stages [15]. Others still require considerable research and development [16]. Some innovations may be incremental--such as energy-efficiency solutions [17; 18]--and others may be more radical--such as electrowinning or 'Hlsarna' approaches to steel making [19]. Either way, significant policy support is considered fundamental to de-risking investment in development, commercialization, and deployment of these innovations [11; 15; 20; 21].