On Thursday, September 28, Mikhail Kovalchuk, a close adviser to Russian president Vladimir Putin, suggested Russia should test “at least” one nuclear weapon at the former nuclear testing site, Novaya Zemlya. A week before Kovalchuk’s statement, CNN released satellite imagery to reveal the expansion of Novaya Zemlya facilities over the past three years to include a new building, along with expansions at former test sites in China and the United States. Kovalchuk’s statement comes amid rising tensions on the ground in Ukraine, with Ukrainian forces attempting to breach Russian defensive lines. Talk of nuclear testing and threats of escalation are part of an ongoing Russian effort to manipulate nuclear risks and deter Western intervention in Ukraine. On October 5, Putin hinted that he might withdraw ratification of the CTBT. If Russia does return to nuclear testing, Putin will have assumed that the international community will be silent or divided on the issue—essentially, he would be betting that Russia can get away with it. But a return to nuclear testing, a well-recognized taboo, could backfire for Moscow. Q1: What would a nuclear test entail? A1: During the Cold War, nuclear possessor states conducted thousands of nuclear tests aboveground and underground. The United States and Russia stopped nuclear testing in 1992, and North Korea is the only country to test in recent years. To ensure nuclear weapons still work, however, nuclear possessors rely on modeling and simulation tools. For example, the U.S. National Ignition Facility (NIF), uses high-energy lasers to create temperatures and pressures similar to those reached during nuclear explosions. The U.S. National Labs also rely on supercomputers, many of which are the fastest in the world. These simulations do not produce a nuclear yield or a chain reaction. Unlike the United States, Russia has largely relied on pit production and warhead replacement, rather than on laser experiments, to continue to certify its stockpile; although Russia is currently developing a “Tsar Laser,” a high-powered laser that can simulate what happens in a nuclear detonation without exploding a weapon, similar to those used by the United States, United Kingdom, China, and France (although if completed, Moscow claims the “Tsar Laser” would be the highest energy of them all). With these high-tech options available, nuclear testing would not necessarily mean a return to high-yield underground tests that could be easily detected, such as those conducted by North Korea on six occasions between 2006 and 2017. The 1997 Comprehensive Test Ban Treaty (CTBT) commits all members “not to carry out any nuclear weapon test explosion or any other nuclear explosion.” The United States, which has signed but not ratified the CTBT, interprets the treaty as “zero-yield,” meaning any modeling and simulation activities cannot generate any nuclear yield. Russia is a member to the CTBT, but in recent years, the United States has raised concerns about Russia’s (and China’s) compliance with the zero-yield international nuclear test ban. The State Department’s 2022 Compliance Report, for example, accuses Russia of conducting supercritical nuclear tests in violation of the zero-yield standard. Because tests can be conducted at low yield, a Russian nuclear test could potentially evade detection. Russia might also deny any allegations of testing, even if there were convincing evidence, as it has done with past arms control violations. Indeed, arms control has been a frequent target of Russian disinformation efforts and could provide plausible deniability for Russia to evade censure for nuclear testing and related activities. Q2: Why would Russia test a nuclear weapon now? A2: Concerns about a Russian return to nuclear testing are not new. In 2019, Lieutenant General Robert P. Ashley, director of the Defense Intelligence Agency, observed, “Russia’s development of new warhead designs and overall stockpile management efforts have been enhanced by its approach to nuclear testing” and not adhering to a zero-yield standard. More recently, in February 2023, Putin suggested the United States was considering a return to testing and indicated that Russia should be ready to return to testing. A month later, Deputy Foreign Minister Sergey Ryabkov said, “If the U.S. does not test, we will not, but we should be prepared for the worst.” There is a technical reason and a political reason Russia might test now. Technically, Russia might want to test to confirm the credibility of its nuclear arsenal after years of nuclear modernization. Moscow may be concerned about the credibility of its existing stockpile. Or it might also return to testing if it is considering new weapons designs, some of which could require expanding beyond existing alternatives to testing. Politically, testing now would send a strong political message that Russia is so committed to winning the war in Ukraine that it is willing to undermine the few remaining international nuclear treaties and norms. Nuclear weapons have cast a shadow over the war, as Russia has relied on implicit (and occasionally explicit) nuclear threats to deter Western intervention. The political impact of a test could somewhat depend on whether Russia formally withdraws from the treaty beforehand or if it instead suspends participation, as it did in February 2023 with the New START Treaty. The CTBT allows for a state’s withdrawal if “extraordinary events” related to the treaty have jeopardized a state’s “supreme national interests.” Again, these tools could provide Russia diplomatic coverage for testing activities. Q3: How would the United States respond to a Russian nuclear test? A3: While the United States is not a full party to the CTBT, it has observed a nuclear testing moratorium since 1992 and is the largest contributor to the CTBT organization, the treaty’s implementation and verification body. Following a 1999 debate, the U.S. Senate voted not to give its ratification and consent to the CTBT due to concerns about whether the United States could verify other states’ compliance with the treaty and ensure the safety and reliability of its stockpile without testing. The United States provides roughly $30 million annually to Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) activities. In a September 28 speech, the U.S. National Nuclear Security Administration (NNSA) offered to open its former test site for inspection to China and Russia to confirm it was not restarting any nuclear testing. Russia and China have not made any similar offers. Various NNSA officials clarified that the U.S. remains committed to a testing moratorium and has offered mutual inspections, but Moscow and Beijing have not responded. The United States would likely respond to a Russian nuclear test by calling for a unified and robust international response. This could entail calls for a UN Resolution, sanctions, and warnings of further political (and potentially military) responses if testing continues. For example, following North Korea’s more recent nuclear tests, the Obama and Trump administrations worked to build international diplomatic and economic pressure on Pyongyang, particularly from China. The Obama administration also used cyber capabilities in an attempt to undermine North Korea’s missile development. And President Trump went so far as to threaten “stopping all trade with any country doing business with North Korea.” Q4: How would the international community respond to a Russian nuclear test? A4: With 187 signatory states, the CTBT is one of the cornerstones of global nuclear order. As such, one would hope the international community would not only respond with indignation and censure to a Russian nuclear test but also speak out to deter Russia from testing in the first place. Regions such as central Asia, the Pacific Islands, and North Africa, along with domestic constituencies, were impacted by the consequences of decades of nuclear testing, including increased rates of cancer and the destruction of local populations and wildlife. But many states in the Global South have been reluctant, if not silent, in calling out Russian nuclear saber-rattling since the invasion of Ukraine in February 2022. For example, at a 2022 Meeting of States Parties of the UN Treaty on the Prohibition of Nuclear Weapons (TPNW), members failed to explicitly call out Russian nuclear threats in a consensus document, which nonetheless condemned “any and all nuclear threats, whether they be explicit or implicit and irrespective of the circumstances.” Many of these states rely on Russia for military support and cheaper access to nuclear energy. A Russian nuclear test would put many of them in a difficult situation of choosing between their loyalty to the TPNW’s mission of nuclear abolition and the practical considerations of partnering with Russia; but failing to condemn further Russian threats, especially if they escalate to nuclear testing, would undermine the TPNW’s legitimacy as a tool for making progress towards disarmament. Q5: How would a nuclear test impact the war in Ukraine? A5: The impact of any Russian nuclear test on the war in Ukraine would depend on a variety of factors. First and foremost would be the nature of the test itself. A verifiable test, confirmed by the CTBTO, would be hard for Russia to deny and be more likely to draw international condemnation. A low-yield test with less evidence would likely lead to a cycle of accusations and denial. But Russia has consistently relied on its nuclear arsenal to sow uncertainty among its Western adversaries. Evidence of a nuclear test would raise further questions among Ukraine and NATO members about Russia’s willingness to use nuclear weapons in the event it is suffering battlefield losses in Ukraine, with the intent of deterring further Western intervention in the crisis and undermining support for Kyiv. Whether or not Russia continues with its nuclear saber-rattling will depend on the potential costs for such risky behavior. One key question is whether India and China would stand by Russia in the event of a nuclear test. China has signed, but not ratified the CTBT. And India, along with Pakistan and North Korea, has neither signed nor ratified. Thus far, Russia’s challenge to nuclear norms and manipulation of nuclear risk has had no significant costs for Moscow. Putin might be inclined to think a nuclear test would not be any different.