Pakistan and India may have 400 to 500 nuclear weapons by 2025 with yields from tested 12- to 45-kt values to a few hundred kilotons. If India uses 100 strategic weapons to attack urban centers and Pakistan uses 150, fatalities could reach 50 to 125 million people, and nuclear-ignited fires could release 16 to 36 Tg of black carbon in smoke, depending on yield. The smoke will rise into the upper troposphere, be self-lofted into the stratosphere, and spread globally within weeks. Surface sunlight will decline by 20 to 35%, cooling the global surface by 2° to 5°C and reducing precipitation by 15 to 30%, with larger regional impacts. Recovery takes more than 10 years. Net primary productivity declines 15 to 30% on land and 5 to 15% in oceans threatening mass starvation and additional worldwide collateral fatalities.

ing the exact number of nuclear weapons in the world. Nuclear weapon states shield details about their arsenals and generally have only imprecise knowledge about the size and composition of other countries' inventories; this creates uncertainty, mistrust, and misunderstandings. More transparency would alleviate this, and in fact, Britain, France, and the United States have recently taken steps to provide additional nuclear data to the public. We estimate that the world's nine nuclear weapon states possess nearly 22,400 intact nuclear warheads. The vast majority of these weapons-approximately 95 percent-are in the U.S. and Russian arsenals. Nearly 8,000 warheads-nearly one-third of the worldwide total-are operational to some degree (not necessarily fully operational) and ready to launch on relatively short notice. We estimate that approximately 1,880 warheads are on different levels of alert: Russia, 960 warheads; United States, 810; France, 64; and Britain, 48. The stockpiles of the nations that are not recognized as nuclear weapon states under the Nuclear Non-Proliferation Treaty-Israel, India, Pakistan, and North Korea-are minuscule in comparison with those of Russia and the United States and are especially difficult to estimate. India and Pakistan have a combined total of approximately 150 nuclear warheads, just a few more than what is carried on a single U.S. Trident submarine. Though Israel has not acknowledged it possesses nuclear weapons, the U.S. intelligence community estimates that it has an arsenal of approximately 80 warheads. North Korea remains a mystery, but it may have enough

The authors calculate that some 125,000 nuclear warheads have been built since 1945, about 97 percent of them by the United States and the Soviet Union and Russia. The nine nations with nuclear weapons now possess more than 10,000 nuclear warheads in their military stockpiles, the authors estimate, with several thousand additional US and Russian retired warheads in storage, awaiting dismantlement. The nuclear stockpiles of China, as well as Pakistan, India, Israel, and North Korea, are minuscule in comparison with the US and Russian arsenals, but more difficult to estimate. Still, the authors believe that ChinaÕs nuclear weapons stockpile has surpassed Great BritainÕs. Although the total number of nuclear warheads in the world is decreasing because of US and Russian reductions, all the nations with nuclear weapons continue to modernize or upgrade their nuclear arsenals.