Using data from direct observations, experimental mesocosms, field experiments, and complex computer models, the IPCC has made a very strong case supporting the hypothesis that human behavior is leading to rapid and substantial climate change. One important anthropogenic effect is changes to the carbon cycle, primarily greater CO2 export into the atmosphere from industrial activity. In recent years, both oceans and terrestrial sources have taken up some of this excess CO2, but ocean uptake is particularly problematic, because it leads to acidification. There are many other important greenhouse gases that influence Earth’s surface temperatures, including methane, nitrous oxide, ozone, and a diverse group of halocarbons. Though less abundant, these gases have a much greater global warming potential than CO2, on a per molecule basis. Many effects of greenhouse gases on global climate are complex; for example, a particular halocarbon can increase and decrease surface temperatures via different mechanisms. There are many different types of climate models that use the movement of the atmosphere around Earth, and the interaction of the atmosphere with the oceans and with biological processes, to project future climate. Though there are quantitative differences between the projections of each model, these models all project a much warmer and wetter global climate over the next century, with northern latitudes experiencing the greatest impact of climate change.

Chapter 1 offers a historical examination of the causes and discovery of global heating and the development of the scientific consensus that it is human-caused and can be curtailed only by cutting greenhouse gas emissions and describes how those developments nonetheless failed to lead to extensive action.

This is our climate change status check, and the first three things to understand are that climate change is real, anthropogenic (i.e., caused by humans), and dangerous. To drive home those points, this chapter relies heavily on the science of the landmark IPCC climate assessments and particularly the most recent AR5 report. We drill down on a key figure from the AR5 to clarify the observed data since 1850 in respect of global average surface temperatures, sea level rise, atmospheric concentrations of several greenhouse gases, and annual CO2 emissions. With a second figure we examine the sources of climate forcing since 1950 and clarify the degree to which they are caused by humanity or by nature. We then divert to key facets that we don’t yet fully understand about climate change, including tipping points, “climate sensitivity” and the likely emissions pathway that humanity will choose over the remainder of the century. We conclude with the observation that irrespective of how these mysteries play out, substantial climate change is in our future. It’s coming.

Climate change is now a significant concern for almost every government, many major international organizations, industries of every variety, thousands of nongovernmental organizations and many millions of people around the world. Climate change has moved from being a minor scientific issue in international relations, national politics and human affairs to being, as we move through the 2020s, one of the most high-profile political issues globally. In short, climate change is now high politics. Governments have negotiated agreements to study climate change and to put in place policies that limit the greenhouse gas pollution that causes it. All of this has been driven to a great extent by climate science. However, despite the high profile of climate change and actions around the world to address it, the responses of countries and other actors, including businesses and individuals, have failed to keep up with the increasing pace of change. Special interests and climate denial have gotten in the way.

To exercise its responsibilities effectively in the global interest, the legislative function in a reformed United Nations will require supporting advisory mechanisms for specialized scientific, technical and other expertise. Moreover, a strong civil society voice including nongovernmental organizations has been shown to contribute constructively to global policy-making; a Chamber of Civil Society could thus play a central advisory role to the General Assembly. The goal will be to ensure an effective UN decision-making capacity, based on the best available knowledge and analysis, to address global challenges. Additional supporting mechanisms are necessary to support this process; advisory bodies made up of individuals with established expertise would initially focus their efforts on several pressing global catastrophic risks, including climate change, the deterioration of the environment, nuclear proliferation and the peace and security challenges this raises. An excellent precedent in this area is the Intergovernmental Panel on Climate Change (IPCC). In the scientific domain beyond pressing global catastrophic risks, the General Assembly will need to have a number of general advisory mechanisms to provide additional specialized expertise, supplemented by an ethical advisory process in an Office of Ethical Assessment, to provide analysis of the ethical implications of issues under consideration.

Because of its transboundary effects and because states will be the primary actors, large-scale solar geoengineering and its governance are matters of international law. This is the first of four chapters that consider rules from custom, treaty, and principles as well as international organizations. Although there are no international instruments that are legally binding, in force, and specific to solar geoengineering, international law provides both a substantial extant governance framework and a foundation upon which future norms, rules, procedures, and institutions specific to solar geoengineering could be built. This chapter introduces how international law operates and discusses several general international legal principles that would guide its interpretation and development with respect to solar geoengineering. It describes one source of binding international law – that of states’ customary behavior – and what it might mean for solar geoengineering, emphasizing procedural obligations. The chapter reviews some relevant nonbinding multilateral environmental agreements and activities of intergovernmental organizations, such as the Intergovernmental Panel on Climate Change.