Well... an EMP is an Electromagnetic Pulse, so temperatures attainable on Earth would not stop it. About the only way to do it with temperature would be to freeze it to absolute zero (0 degrees kelvin or -271 degrees Celsius), and you'd have much bigger problems at those temperatures! Not to mention the unstable way in which matter works in a Bose-Einstein condensate... :lol:
An EMP is a side effect of a nuclear bomb. How bad it is depends on how high up in the atmosphere it is detonated. For example, it would only take the high altitude airburst of 3 nuclear weapons in key places above the US to destroy EVERY piece of solid state electronics in the entire country- without anyone experiencing the devastating effects of a nuclear bomb's blast wave. No cars made after the mid 80's, gas pumps, calculators, computers, internet, telephones, power grid, etc. would work. It would ALL be destroyed, sending us back to the 1800's technologically. While there was older technology which could function fine with no transistors, it has virtually all been scrapped in favor of microprocessor controlled technology. For an example of what would happen, research the nuclear weapon detonated in space over the pacific which blacked out much of the Pacific rim back in the 1960's. There wasn't much damage back then because of the state of technology. If it were to happen today, it would destroy the world's economy.