The top priority in addressing climate change is to reduce net emissions of greenhouse gases to zero as swiftly as possible. Among the policy instruments for achieving this goal: carbon markets and carbon taxes; subsidies and incentives for energy conservation and for developing renewable energy technologies; building a new network of advanced nuclear reactors to provide carbon-free energy; imposing restraints on deforestation and planting large numbers of new trees; developing powerful new technologies for removing carbon dioxide from the atmosphere; incentivizing private citizens to reduce the carbon footprint of their lifestyles; and introducing new governmental policies for decarbonizing national economies. By combining all these strategies, humankind could realistically reach net zero emissions by the middle years of this century. From that point forward, it can start actively removing existing accumulations of carbon dioxide, eventually bringing global warming to a halt and reversing some of the damage that’s already been done.

To a hard-nosed “realist” reader, the scenarios of growing international coordination and pragmatic institution-building described in the preceding chapters will no doubt seem like an idealistic fantasy. From such a reader’s perspective, we are likely to see a very different sort of future unfold in the second half of the twenty-first century – a geopolitics based on continued rivalry, arms races, and frantic competition for dominance among China, the United States, and Russia, alongside the restless jockeying of new powers like India, Brazil, Japan, and perhaps a more tightly consolidated EU. Some prominent scholars of international relations subscribe to this view, and this chapter summarizes their arguments about the prospects of geo-strategic affairs over the coming decades. In such a scenario of “business as usual,” unfortunately, the planet-level instruments for managing our four mega-dangers would be distressingly weak, and the opportunities for large coalitions of nations to come together successfully in coordinated, long-range projects will be rare.

This chapter describes five “action areas” in which politically achievable changes over the coming two decades could render humankind a lot safer than it is today. For climate change, these include urgent measures for rapid decarbonization, coupled with ramped-up research on technologies for carbon removal and for solar radiation management; new international pacts among small groups of nations for emissions reductions with mutual accountability and incentives; and pre-adaptation measures for dealing effectively with unavoidable harms caused by global warming. For nuclear weapons, these include preparing contingency plans for major or limited nuclear wars, as well as risk-reduction measures than can be implemented today. For pandemics, experts point to four sensible and affordable measures that would greatly reduce the harms of future pandemics. For AI, an immediate challenge will be to prepare for chronic mass unemployment due to rising levels of automation. Finally, the chapter proposes the creation of a new federal agency, the Office for Emerging Biotechnology, to oversee and regulate cutting-edge developments in this field.

The argument presented in the coming chapters rests on one basic premise: the cumulative power of small, incremental changes over time. I maintain that a much better system of global governance can gradually emerge over the coming century and a half, allowing humankind to successfully manage the dangers that threaten our survival. Part III describes what might be accomplished in the next 10 to 20 years; Part IV is tuned to the last decades of this century, around the year 2100; and Part V sketches a full-fledged global framework that might perhaps emerge by the mid-twenty-second century.

Who will supply the “purpose” in this process? Who will steer the boat? No one in particular – or, more accurately, all of us at once. Here I need to make a brief digression on the question of whether history has a deeper goal or directionality.

A global federal government would be a mighty instrument – and lots of power-hungry leaders and groups from around the planet will no doubt vie with each other to manipulate it to their parochial ends. The global institutions will therefore need to incorporate robust mechanisms to ensure that they remain rigorously accountable, fully transparent, and genuinely independent and impartial in their basic functioning. Four features would therefore be important to include in such a government: strong subsidiarity, the separation of powers, an executive branch with plural leadership, and a high bar of supermajority voting before major action can occur in the world legislature. A second key goal for this government will be to reduce the gross disparities in wealth and opportunity that divide the world’s peoples. One plausible mechanism for achieving this would be a UN-run system of Guaranteed Minimum Income, implemented globally. Such a government could also adopt pragmatic policies to nudge the world’s autocratic nations toward higher degrees of democratization and respect for human rights.

Despite significant reductions in nuclear arsenals after the Cold War, the world’s nuclear nations still are pointing thousands of warheads at each other, using systems that are vulnerable to human error, miscalculation, or cyberwarfare. Over the past decades, humankind has come hair-raisingly close in several well-documented instances to unleashing full-scale nuclear war. The logic of arms races makes it very hard for nations to resist the temptation of modernizing and building up their arsenals. On the other hand, new designs for nuclear reactors – whether for fission or fusion processes – hold out the tantalizing possibility of safe, cheap, and abundant electricity. Nuclear-generated electricity does not release greenhouse gases, and therefore could play a key role in creating a sustainable energy system over the coming century.

This chapter offers the story of the green movement since the 1950s as a case study in how to bring about deep and lasting societal change in the absence of full political consensus. Over the past 60 years, green activists have not succeeded in fully realizing their goal of a sustainable economic system, but they have succeeded in bringing pervasive changes to modern economic, social, and energy systems. By pursuing an eclectic, decentralized, and multifaceted set of strategies over many decades, they have made a significant positive impact. A similar strategy is likely to work best for building new systems of global governance for mega-dangerous technologies. Climate change may prove to be a uniquely potent unifying factor for humankind over the coming decades, allowing effective mobilization for incremental reforms. The reasons for this are threefold: climate change is not subject to the logic of arms races; it threatens to bring tangible harms that affect all human beings; and its disasters will escalate gradually over the coming decades, giving people a chance to wake up and respond constructively.

Given the weakness of today’s UN as an instrument for tackling global challenges, we need to rely on treaties and diplomacy for urgent safety measures at the international level: a new pact on restricting bioweapons and synthetic biology, with inspections for verification; a treaty on AI and cyberwarfare; and a treaty to restrain the arms race for weapons in the oceans and outer space. After creating an Office for Emerging Biotechnology in the US, we should promote the creation of similar offices in as many other nations as possible, building a network of global regulatory capabilities. Finally, we can undertake a series of moderate reforms to beef up the effectiveness of the UN: enlarging the Security Council; restricting the use of the veto; and adding new Peacebuilding roles to the General Assembly.

Tapping the power of fossil fuels over the past century and a half has propelled a massive expansion of human enterprise and prosperity, yet it has also released toxic amounts of carbon dioxide into the atmosphere, thereby endangering the future viability of human civilization. If global average temperatures rise 4 to 6 degrees above the level of preindustrial times, climate scientists nearly unanimously conclude that severe disruptions of global ecosystems will result. These disruptions include: self-reinforcing spirals of global warming caused by feedback factors like melting permafrost, ice loss, water vapor, and wildfires; acidification of ocean waters and flooding of coastal regions as sea level rises by as much as one foot per decade; growing frequency of severe weather events such as droughts, floods, superstorms, and heat waves; the spread of tropical diseases into temperate regions; and the collapse of agriculture in many parts of the planet, leading to waves of desperate climate refugees.

Building and maintaining a global federal government won’t be easy: plenty of things could go awry along the way, and plenty more could go sour even after the government was up and running. The world’s peoples may respond to severe climate change by retrenching into regional or national enclaves. The global legislature could become gridlocked in a manner similar to the UN during the Cold War. One nation or group of nations could succeed in gaining unilateral control over the global government, resulting either in an Orwellian superstate or in a catastrophic planetary civil war. These scenarios form a perfectly real and plausible possibility for our collective future – and the coming generations will need to be ever-vigilant in their efforts to prevent them from happening.

The path-breaking achievements of the past century offer grounds for cautious hope. Over the coming decades, economic and technological interdependence will continue to intensify, binding the interests of the world’s peoples even more tightly together than today. As nations and regions find themselves increasingly “in the same boat,” win-win solutions among them are likely to become more self-evidently attractive. To be sure, the possibility of failure is ever-present and very real. Building more effective instruments for planet-level governance will prove exceedingly hard, and we can expect plenty of disheartening setbacks along the way. But the evidence from the past, and the plausible trajectory of challenges and incentives that await us in the coming century, suggest that it can be done.

Over the coming decades, artificial intelligence and robotics will continue to grow rapidly in power and scope, exerting a transformative impact on our lives. Seven trends are likely: the machines will become progressively more versatile and multifunctional in their capabilities; they will be designed to improve their own software and hardware over time, as they interact with their environment; the line between AI and robots will gradually blur, as machines come to permeate our society at all levels; these machines will be entrusted with complex practical tasks that require them to develop sophisticated commonsense knowledge about the human social world; the machines will be interconnected in functional networks that multiply their powers; such machines will need to be able to refuse to obey certain kinds of human commands, raising fundamental questions about who controls their actions; and the logic of arms races will apply to such machines, impelling nations and corporations to develop increasingly powerful machines as quickly as possible, with only a secondary concern for caution and safety.