Two things, after half a lifetime of trying to understand America, come suddenly together. One is the curious, seemingly mindless obsession with regulation that infects the land of the free. (A few weeks ago they detained a babe in arms at airport departure because his name was on their terrorist-suspect list.) The other is a perennial sense of looming disaster. But let's come to Katrina and Rita in a second. Meanwhile, other signs point the way.For years - a silly little holiday hobby - we've gone round the States taking pictures of the municipal notices they put up. "Have fun and enjoy Santa Monica beach," for instance."No fires or fireworks; dogs not permitted at any time; ball playing in designated areas only; must obey lifeguards' direction; no dressing or undressing; no tents or enclosures permitted; no sleeping midnight to 5am; must place rubbish in trash can; no alcoholic beverages; no glass containers; no percussion instruments" - with the relevant city ordinance numbers tabulated down the side. (No percussion instruments, rule 4204C.)So "fun" is a carefully limited concept. And that, in part, is because inanimate objects can wreak havoc. "Caution: nails, splinters, uneven deck, gaps between planks, bare feet and high-heel shoes are DANGEROUS." It is also because nature itself heaves with threat. A scarlet skull and crossbones posted by the Grand Canyon reads: "Danger: Extreme heat conditions exist in the canyon - Hiking may lead to Life Threatening Injury or Death!!"But, of course, the great, swilling sea means maximum menace. "Swim near a lifeguard - Beware of rip currents, uneven ocean bottom, rocks, piers / pilings, jettys / groins. No diving in shallow water." And more danger still dogs hundreds of miles of the Pacific: "This coastline is naturally dynamic - crashing waves and crumbling cliffs. Rocks are slippery. Large, unexpected waves sweep people off their feet. Play it safe - don't climb rocks or go into the water and risk getting carried out to sea."In Oregon, a few weeks ago, you saw full Hollywood horror lurking on the horizon. "If you feel an earthquake - Protect yourself until the earthquake is over - Move quickly inland to high ground - Do not pack or delay - A tsunami may be coming in a few minutes ... " Play it safe? Only, perhaps, by staying at home.Can such notices of imminent extinction be taken seriously, though - especially when, as on Venice Beach, they're close to an athletic centre where "The ethics of paddle tennis and good sportsmanship shall prevail" by similarly gruff decree? Not really. Too much bureaucracy douses any sense of fear. A warning ritually repeated is no warning at all. You forget what this big country is like.Now it's time to remember as Rita piles more debris along the Gulf and pushes New Orleans back into Katrina's ooze. In Hertford, Hereford and Hampshire, hurricanes hardly happen. But along America's south and east coasts, they have their regular lashing season of destruction. To the west, tsunamis may come, and come again, hours later. Blizzards spread from the north. Tornados from nowhere beat through Oklahoma. The San Andreas fault shifts sullenly, waiting for its moment. Mount St Helens never sleeps.Nature, in short, is a hostile force and repeated enemy. Most of Europe's disasters are man-made: mountain tunnels imploding, planes crashing, wars, hatreds. Most of America's, by contrast, are natural nightmares. And there's one gap in understanding.Did New Orleans react so sluggishly to Katrina because it was warned and warned again, warned into apathy? Perhaps, a little. Was Rita quite the monster a once-bitten met office warned against? Perhaps, not quite. But the struggle for perspective is constant. We can sit on more tranquil sidelines and cry "global warming". Yet America's next disaster may burst from beneath the earth or sea and have nothing to do with Kyoto.Did the BBC "gloat" over Katrina? Not that I saw. But that tired, glib line about "the world's only superpower" assumes that any power on earth can somehow staunch natural disasters. Not so. We are humbled time and again, from Sri Lanka to San Francisco. Our defences come down. Mortality engulfs the Big Easy as swiftly as Thailand. Stand on the slopes of Mount St Helens and, 25 years on, the dead forests of blasted trees bear witness to our impotence. Millions flee.And there, perhaps, the noticeboards of life and death come together, not just as bureaucracy striving for order, but as something Old Testament apocalyptic. The ten commandments of Santa Monica beach, with one commandment added for luck. Never forget plagues, pestilences and our terrible vulnerability. Be humble (and observe the due ethics of paddle tennis).