Warming turns every impact.

The impacts of global climate change on international security could be of historic proportion, challenging those of previous global threats such as nuclear weapons proliferation, the Great Depression, and terrorism [1]. For instance, global economic damages from natural catastrophes, many of them climate related, have doubled every ten years and reached trillions of dollars per year in total damages over the past two decades [2]. The climate-change risks faced by developing countries are even more staggering in magnitude, including vulnerability to extreme weather, deteriorating national security, and degraded public health, among others [3,4]. More explicitly, melting glaciers could flood river valleys in Kashmir and Nepal, and reduced rainfall could aggravate water and food security so that 182 million people could die of disease epidemics and starvation attributable to climate change [5]. Under the most severe of these projections, if the Greenland Ice Sheet would melt, sea levels could rise by 6 m – enough to inundate almost all low lying island states as well as coastal areas from San Francisco and New York to Amsterdam and Tokyo [6]. Military analysts have therefore suggested that climate change acts as a “threat multiplier” to national-security concerns, something that takes existing problems and makes them worse, impinging on global stability [7].

But while the evidence base surrounding the security impacts of climate change are fairly well-understood and with such understanding ever improving, less is known about the security risks around the deployment of emergent climate technologies. In this study, we focus on the geopolitical, security [8], and military risks facing negative emissions and solar geoengineering options. We term this the “next climate war” with inspiration from Mann [9], who argued that the first “climate war” was a soft war about ideas and knowledge. That political war was waged over ideas and knowledge about climate change itself, and fuelled by a “thirty-year campaign to deflect blame and responsibility and delay action on climate change.” Our study, by contrast, points out how the next climate war, a second one, would not necessarily be a cold war, and could very well involve active military conflict or hybrid warfare, even a "hot war" or global nuclear conflagration.

Although controversial, negative emissions and geoengineering options could become the future backbone of a low-carbon or net-zero society, given that they avoid the need for coordinated or global action (and can be deployed by a smaller group of actors, even non-state actors) [10]. Negative emissions technologies may already be necessary to account for committed emissions resulting from economic activity (and “locked in” global warming) and gaps in implementation facing the Paris Agreement [11]. For these reasons, some of the the climate-science literature suggests that negative emissions options “are essential” [12] for reaching climate targets, represent “an inevitable component” [13] of technology portfolios, and are “physically needed” to curtail global warming [14]. Solar geoengineering options are also being heralded as ways to “buy time” for mitigation and negative-emissions options to be scaled up [15], and to help address unknown and potentially dangerous tipping points in the climatic system [16]. Some suggest that solar geoengineering “must be considered” as a feasible option for supplementing carbon abatement [17].

In this study, we utilize a large and diverse expert interview exercise (N = 125) to critically examine the geopolitical, security, and military issues associated with ten negative emission options (or greenhouse gas removal technologies) and ten solar geoengineering options (or solar radiation management technologies). We ask: What geopolitical considerations does deployment give rise to? What particular military applications exist? What risks do these options entail in terms of weaponization, misuse, and miscalculation? We examine such existing and prospective security risks by means of a novel conceptual framework that captures a far broader spectrum of security concerns than those which exist in the extant literature (see Section 2) and which go well beyond insights derived from climate modelling and game theory by drawing on a novel, rich, and original dataset of expert perceptions.