I referred previously to the Chicxulub Event about 65 million years ago that wiped out the dinosaurs. THAT rock was about 10 km/6 miles in size. The Wabar object was quite a bit smaller - only a rock the size of a large living room. It smacked in the middle of the driest desert in the world (the temperature reached 61C/142 F one mid-morning while I ran a magnetometer over the biggest two craters).
While small by comparison, this object still caused immense damage. Geologic and geophysical mapping show that it raised a mushroom cloud of molten glass to at least the Stratosphere; molten glass rained down at least 850 meters/900 yards away. The object broke up in the lower atmosphere and created at least three craters that we can still see between the moving Saif dunes. Calculations show that the rock (94% iron and 4% nickel, plus copper, cobalt, and iridium) brought with it a kinetic energy equivalent to, or bigger than, the Hiroshima atom bomb. The Wabar impact site is similar to the Sedan and other bomb craters in the Nevada Test Site, save one: there is no radiation. There is shocked quartz, an asymmetric ejecta field, and there are other minerals that suggest temporary temperatures reaching over 10,000 C. If you could have seen it, you would not have likely survived the experience.
Here's the crucial point: Wabar happened in 1863. Gene Shoemaker and I mapped the field site together and we made a bet. We both agreed that the site was very young. If it was older than a Qu'ranic reference to 'Ubar, I owed him a steak dinner. If it was younger than that, HE owed ME a Thai dinner with a coconut sticky-rice dessert. Sadly, Gene was killed in a horrific car-wreck 300 km north of Alice Springs in Australia in 1996, before the thermoluminescence dating results (from sand we had carefully gathered at night below the impact rim of one of the craters) came back. Result: less than 250 years. Details for the 1863 date are in the SciAm article.
Whew. A "city buster" hitting the Earth less than 150 years ago? Imagine that.
Another crucial point: I have partial records that suggest that "city busters" like this hit the Earth in 1863, 1908, 1930, 1935, and 1947. And that's just on land. By a miracle, every one of these fell in very remote areas. I published another article in 2002 (Wynn, J.C., 2002, Mapping an iron meteorite impact site with a magnetometer, and implications for the probability of a catastrophic impact on Earth: Journal of Environmental & Engineering Geophysics, vol. 7, no. 4 (December 2002), pp. 143-150.) that showed that these things happen far more frequently than even a radical like Gene Shoemaker had ever suspected.
About 80% of the human population now lives within 100 km/60 miles of the ocean. At least 70% of the Earth's surface is ocean. Something like 20,000+ tons of TNT equivalent detonating under an ocean is your classic Mogi Source - the perfect Tsunami-maker. If it just hit your city, it would be a relatively clean death for everyone around it by comparison.
One final point: we cannot easily "see" these things coming. They have to be really big before enough light scatters off them to be picked up by Earth-based telescopes, and you would need many "picks" before you could calculate a reliable orbit. By the time you could see a Wabar-sized object, it would already be over. Since the Earth has substantial gravity, one of these things flying even close to the planet will be drawn towards it, gravity being what it is. We can't use radar to spot these, either. The energy of a radar beam falls off as the distance squared, and even if the beam was 100% reflected, the return beam would have energy falling off as the return distance squared. Mankind doesn't have radar beams with enough energy to do this; if they did, it would fry everything in the sky flying through its beam.
What does this all mean? It means we are helpless beneath the sky. It means we do not control our future. You can get good warning of a volcanic eruption, a shorter warning for a hurricane, a really short warning for a tornado, and NO warning for an earthquake or one of these bombs from the sky.
You can store a year's supply of food and water to help you and your neighbors survive a near hit.