The use of Nukes by Israel or any other country in the region will have devastating effects.
Depending on the kiloton yield, the outcry would be numbing. 500 kiloton strategic nukes would have global suicide implications, while tactical nukes will have regional implications.
Strategic nukes, at least a dozen of them in the 500 kiloton range would take out the middle east and vaporize around 190 million (3% of the world). Another 200 million in nearby countries would die from radioactive poisoning, and their only crime would be living next door to the Middle East.
Carl Sagan estimated a very low threshold for nuclear winter, a 100 kiloton blast would ignite fires that would cause a nuclear winter....ie, the sun would be blotted out due to the dust and ash from the fires and all plant life would cease to exist....followed shortly thereafter by animal life.
So the option of eliminating the middle east by nukes is global suicide....which is why nukes have been a deterrent to total war for the past 60 years