At its core, the Treaty on the Prohibition of Nuclear Weapons (TPNW), also known as the nuclear ban treaty, makes the argument that the humanitarian consequences of nuclear weapons are too grave and their risks too high for nuclear deterrence to be a sustainable basis for international security. This is underpinned by a growing body of new scientific evidence, which demonstrates how these consequences would be more global, cascading and catastrophic than previously understood. The same goes for the -increasing- complexity of risks associated with nuclear weapons. All States and peoples anywhere on Earth are at risk of becoming collateral damage in a multitude of ways of even a "limited" regional nuclear exchange. The Treaty's conclusion is, thus, that the nuclear deterrence security paradigm is not only highly precarious, fragile and not sustainable but also seriously affects and diminishes the security of non-nuclear states and, ultimately, all humanity. This concern is not only justified, given that global nuclear risks are on the rise, it also expresses a legitimate and evidence-based security perspective. TPNW supporters have highlighted this perspective countless times, in the treaty itself, though national or joint statements and in the declarations adopted at their First and Second Meetings of States Parties.

Nevertheless, the belief that nuclear weapons and nuclear deterrence provide an "ultimate security guarantee" reigns supreme in nuclear armed states and many of their allies. This is the main reason that hinders actual progress toward nuclear disarmament and progress towards a world without nuclear weapons. If we actually want to see such progress, a paradigm shift is required and the discourse about nuclear weapons needs to change. It needs to move beyond the assumption of nuclear deterrence stability and that nuclear weapons will in the end not be used in a conflict to a critical and evidence-based challenge of these assumptions and the concrete consideration of the humanitarian consequences of nuclear deterrence failing.

This was the focus of the so-called Humanitarian Initiative, which was the precursor of the TPNW. It focussed on an international discussion of the humanitarian consequences of nuclear weapons explosions and to assess in concrete terms and based on scientific evidence what happens when nuclear weapons are used and on the complexity of risks are associated with these weapons.

From 2012-2015, several international conferences took place dedicated to presenting new evidence on the humanitarian impact of nuclear weapons and understanding the risks of these weapons. One particularly important element on the humanitarian consequences was the new evidence that even a so-called limited nuclear war -using a small fraction of today's arsenals- could lead to a nuclear winter. Huge amounts of soot would be transported by firestorms that would result from nuclear explosions into high layers of the atmosphere. This would disperse across the globe leading to a nuclear winter lasting several years with significant temperature drops in most moderate climate areas. Staple food production would be severely impacted globally. This new scientific research -a spin off from the climate change science- had a great impact. If a nuclear war between two states in the northern hemisphere leads to a famine in the southern hemisphere, say sub-Saharan Africa, this raises profound legal and ethical issues and questions about the legitimacy of the nuclear status quo.

Not only, is it impossible to appropriately address the immediate humanitarian emergency and long-term consequences of nuclear weapon detonations, the new science highlighted that these consequences would be truly global. In short, this was new scientific evidence that the practice of nuclear deterrence -if it goes wrong even in a so-called "limited nuclear conflict"- means that all humanity and the world as a whole ends up as collateral damage in much more severe ways than previously understood.

Similarly, understanding the complexities of nuclear risks featured prominently in these conferences. Most states were shocked to learn historical cases that demonstrated how risky and vulnerable nuclear weapons system appeared to be and how often humanity escaped from nuclear disaster or accidents mostly through good fortune.

Maybe the most consequential aspect, however, was to give a voice to survivors of nuclear weapons use and testing. Hibakusha attended the conferences and gave witness accounts of their harrowing experiences. Victims of past nuclear testing campaigns, such as from the Pacific or from Kazakhstan did the same. This moved the discussion from being an abstract topic that is difficult to understand or imagine very much to a concrete human experiences. This new discussion about the humanitarian consequences and risks of nuclear weapons generated enormous momentum among non-nuclear weapon states. By 2015, 159 States supported a joint statement in the UN expressing their deep concern about the humanitarian consequences of nuclear weapons. 138 States supported a Pledge that Austria had presented - to "fill the legal gap for the prohibition of nuclear weapons (...) due to their unacceptable humanitarian consequences and associated risks" and generated the momentum for the negotiation and adoption in 2017 in the United Nations on a ban treaty.

The TPNW is still a young treaty. As of this writing, 93 countries have signed the treaty, with 70 having ratified it. The ban treaty has already had a significant impact by giving voice to the majority of countries that are largely disenfranchised by the global nuclear order. The universalization of the TPNW and the debate on the prohibition of nuclear weapons are key objectives of the treaty. TPNW signatories, together with civil society organizations, will continue to pursue this goal gradually and steadily. This entails convincing more countries to join the treaty, as every ratification and signature of the TPNW strengthens its normative value on a global scale. At the same time, it is equally important to continue the promotion of the underlying rationale regarding the humanitarian consequences and risks of nuclear weapons, which underscores the urgency of seeing progress on nuclear disarmament and moving away from the precarious nuclear deterrence paradigm.

The TPNW's multilateral effort points to an alternative approach to the problem of nuclear weapons and security. While it cannot coerce anyone to give up its nuclear weapons, the treaty can provide a convincing rationale for the lack of legitimacy, legality, and sustainability of nuclear weapons through strong arguments and evidence. The ban treaty can lay the groundwork for when nuclear-armed countries are ready to engage in concrete steps toward nuclear disarmament and away from the precarious nuclear deterrence paradigm.

When most nuclear developments point in the opposite direction of nuclear disarmament and the leadership of nuclear-armed countries on this issue has all but disappeared, the TPNW is an indispensable and potentially consequential ray of hope against an otherwise very bleak backdrop of currently failing leadership on nuclear disarmament.