The rain still pours down like Noah's flood. If it's still raining on July 15, St Swithin's day, legend says there'll be another 40 days of it afterwards. Meteorologists say there's not a word of statistical truth in that, but St Swithin was a 10th century bishop who knew no better. What of the Bishop of Carlisle? He said this weekend that the Yorkshire floods are a judgment on society's moral degradation. "This is a strong and definite judgment", says the antedeluvian Rt Rev Graham Dow. It's a judgment on pro-gay laws that undermine marriage. "The sexual orientation regulations are part of a general scene of permissiveness. We are in a situation where we are liable for God's judgment which is intended to call us to repentance." So there you have it: hang the gays and save the planet. The Muslim terrorists who want to blow up nightclubs are on the same wavelength. It's only a small step from calling down God's wrath on those you hate to becoming an implement of His will.

Draw what lessons you choose from the current floods, but one thing strikes me forcibly. Seven people are dead and 27,000 homes have been flooded, along with 5000 businesses. Maybe 100,000 people in all will return to stinking, filthy homes where the electricity and water doesn't work, the drains have backed up, the stink has seeped into the plaster which needs ripping out and floors buckle. Some people are only just returning home now in Carlisle from the 2005 floods. Last week's victims will live with the dank stench indefinitely and at least £1bn of damage has been done.

Newspapers and television bulletins enjoy pictures of boats in streets and old ladies carried to safety by gallant firemen, with a frisson of schadenfreude in the sight of someone's kitchen waist-high in water. But essentially this disaster has had low key coverage, though it is far worse than foot and mouth in its human effects. The farming lobby is good at making a noise, but this calamity happened in urban areas of Hull, Sheffield and places up north where national journalists rarely venture. Imagine if the Thames had burst its banks at Westminster, Chelsea and Fulham. It wouldn't have been a weather story but a full-scale national emergency. The north-south wealth and influence divide is deep on every measurement, despite the revival of northern cities and inner London containing the poorest boroughs of all. Psychologically, Londoncentricity is getting worse as media fascination with billionaire celebrity, City mega-wealth and the extravagance of Knightsbridge and Mayfair distorts the image of the whole country.

London is the only really well-defended part of Britain, where the Thames barrier is built to withstand everything below a once in 2000-year freak flood. London's value to the nation was always the prime priority. But it will take disasters happening in rich cities before the reality of climate change forces opinion-makers to put it at the top of the world's agenda. Hollywood films about New York under water are scary entertainment: when the real thing happens in black New Orleans, nothing changes.

Floods cause real hardship. At least a quarter of homes have no contents insurance. Those who don't have the £150 for basic protection are usually the least able to afford repairs and replacements. The Association of British Insurers reckons that replacing a low income household's furnishings and goods would cost at least £5000. The uninsured are also least likely to have friends with space to put them up or families with money to spare. The Environment Agency says it is mainly the most deprived postcodes that are the most flood-prone. Historic social topography shows that in towns the poor live by the river near industrial areas, while the rich are up on the hill. Guess who is destined for the Thames Gateway flood plain.

Many homes were caught not by rivers but by flash floods from torrential downpours that rose up through overflowing drains. Extreme weather means drains need redesigning for events that used to only happen every 250 years. Sheffield has one of the oldest weather records, starting in 1820. There has been no rainfall like it since. This episode may or may not be a climate change symptom - only patterns tell the story, not single events. The expectation is for more ferocious winter rain and parched summers. The Environment Agency says there is still a risk of drought as this torrential rain pours off into the sea, not into the water table.

Barbara Young, chief executive of the agency, says this is a warning of the huge defences needed to cope with climate change. It is too late now to stop extreme weather worsening, even if - and that's a big if - urgent international action is taken in time to stop planet meltdown. Consider, she says, the electricity substations and generators, the police and fire stations, telephone exchanges, the roads and railways lines and all vital services that need to be moved or climate-proofed. The country's economic success will depend on adapting, and that now unavoidable cost suddenly looks stupendous.

But as ever, one important question is who will pay the heaviest price, and who will be best placed to avoid the consequences? The same question arises over every policy in a nation as profoundly as unequal as ours. If everything needs to be climate change-proofed then everything needs to be class-proofed too. Internationally, climate change will hit the poorest hardest, from Bangladesh and the Pacific atolls to the Sahara, while the west has the money to protect itself. But New Orleans showed how within the rich countries, the way it strikes will emphasise all the existing social inequalities.

Next weekend at Wembley stadium Live Earth links up with seven other mega-concerts around the world, and millions will sign Al Gore's seven-point climate change pledge. They will promise to demand their country joins international agreements to cut carbon emissions, to reduce their personal emissions, offset the rest, plant trees and buy from sustainable businesses. Rock concerts are easy politics that risk suggesting everything can be fixed with no hard choices. But they do raise awareness. There is a sense now that everyone knows they should take action, but why do it if no one else is? People are waiting for governments to tell them they must: it requires a guarantee of collective action. Maybe this week's smoking ban will remind nervous politicians that people will do what they should, but only when everyone else does too.

polly.toynbee@theguardian.com