A nuclear weapon is a certain thing-atomic or hydrogen, fission or fusion, bomb or missile, so many megatons-but nothing could be more uncertain than the consequences of using one.
In fact, more than 500 above ground nuclear weapon tests have provided volumes of information about the consequences of nuclear detonations. See, for example, a recent article published by the Bulletin of the Atomic Scientists, "What would happen if an 800-kiloton nuclear warhead detonated above mid-town Manhattan." On a clear day with average weather conditions, the enormous heat and light from the mile-diameter fireball created by the detonation of this single warhead would almost instantly ignite fires over a total area of about 152 square miles. No one within the fire zone would survive.
Perhaps Lepore was not referring to the immediate effects of a nuclear weapon detonation, but rather the long-term environmental consequences of a war fought with hundreds or thousands of nuclear weapons. Lepore does trace the history of the studies that observed and predicted these long term effects, focusing upon the work of Carl Sagan and the first studies on nuclear winter. But the peer-reviewed research on nuclear winter did not stop in the 1980s. See, for example, the latest Public Interest Report published by the Federation of American Scientists (Winter 2016/2017, Volume 69, Number 3), which contains a detailed examination of 21st century nuclear winter research in the article "Turning a Blind Eye Towards Armageddon - US Leaders Reject Nuclear Winter Studies.
While it is true that nuclear weapons stockpiles have been greatly reduced since the mid-1980s, the peer-reviewed studies tell us that the remaining US and Russian strategic nuclear arsenals are still fully capable of killing most human and animal life that inhabits the Earth. Sadly, these studies continue to be ignored by the leaders of the nuclear weapon states, who prefer to focus on the dangers of nuclear terrorism but avoid the existential threats posed by the their own nuclear arsenals.
The central issue in Lepore's article is a very real and important one: the reality of uncertainty in almost all science—especially in science based on modeling rather than direct, reproducible empirical findings—and the challenges this poses for responsibly invoking scientific findings in charged public policy debates. The importance of insisting on respect for facts is essential for any rational debate about any policy issue. This is perhaps most essential in regard to nuclear weapons, since there is no uncertainty that the survival of human civilization is at stake.