It sounds like science fiction: A nuclear weapon exploded at high altitude above the United States interacts with the Earth's atmosphere, ionosphere, and magnetic field to produce an electromagnetic pulse. This pulse radiates to the Earth and creates massive electrical currents, blowing out electronics, shorting electrical systems, and frying information systems. Cascading infrastructure failures cripple the financial, food distribution, trade, and medical systems. The threat is real and has existed since the birth of nuclear weapons and is now evolving, according to the Commission to Assess the Threat to the United States from Electromagnetic Pulse (EMP) Attack. The means to create such pulses may be in the hands of terrorists and rogue states, and the United States is vulnerable due to its reliance on electronic, telecommunication, energy, and information networks. The good news, says the commission, is that an EMP catastrophe is preventable. Strategies include limiting the proliferation of nuclear weapons and making attempts to acquire them carry severe consequences. Also key is reducing the country's vulnerabilities. "By protecting key elements in each critical infrastructure and by preparing to recover essential services, the prospects for a terrorist or rogue state being able to achieve larger-scale, long-term damage can be minimized," the commission says in a report now on SM Online.