It wasn't supposed to work that way. States' rights was a rallying cry for conservatives for much of the 20th century, first in allowing segregation and racial discrimination across the south and then in allowing environmental destruction around the west. Rightwingers have usually believed in a weak federal government - except when they run it; and that weakness, or rather the strength of the local, has been one of the bright spots during the seven bleak years of life under Bush.

The changes operate on all scales. Across the country, quite a lot of cities and towns have passed measures condemning the Iraq war or calling for the troops to be brought home. A handful of California counties have banned GM agriculture, and others have tried but been defeated by industry money - but may try again. North Dakota farmers created so powerful a pact against the use of Monsanto's GM wheat that the corporation eventually gave up on commercialising the invention worldwide.

My own city, San Francisco, has made plans to issue identity cards to undocumented immigrants, attempted to legalise same-sex marriage a few years back, and as of November 20 2007 banned plastic grocery bags in supermarkets and pharmacies as a step towards banning them altogether. San Francisco, which is as much a peninsular republic unto itself as an irritation on the left edge of the superpower, has also gone for solar energy in a big way, kerbside compost pick-up as part of a successful programme to radically reduce landfill, and various other green programmes (though affluence itself is environmentally devastating, and we also have lots of big cars and air traffic). We are also trying out a universal healthcare plan.

Since a 2005 national mayors' conference, more than 500 mayors from around the country have vowed to make their cities comply with or exceed the Kyoto accords, even while the federal government stalls. Any bleak picture you may have of the American hinterland as a vast sprawl of big-box stores, soulless suburbs and mindless consumption isn't wrong, but is incomplete. Eating locally, starting community gardens in the inner city, supporting and spreading farmer's markets, growing organically, promoting bicycle use, creating denser, more alternative, transport-friendly housing, increasing solar and wind technology, and building greener are all proliferating parts of the contemporary landscape too. Portions of New Orleans, for example, are being rebuilt to be energy efficient, use alternative energy and generally be green. Detroit is full of community gardens and experiments with local economies. As Los Angeles becomes a more and more Latino city, it develops more neighbourhoods of small businesses and lively pedestrian life.

From abroad, viewers mostly see this country as its federal government, the government that brought on a belligerent foreign policy while refusing to address the crises of climate change. It's more than fair to say that the federal government could not behave this way without implicit consent from the majority of the governed. And from afar, it's hard to see how tacit that consent is, or how much dissent is part of the landscape - it's a big part, especially on climate change.

Alexis de Tocqueville noted about 160 years ago that Americans had a talent for congregating in groups and organisations, so there's nothing new about the way that existing environmental groups and new grassroots organisations have taken up that issue. But it is exciting. Last year in Vermont the environmental writer Bill McKibben and a few college students started a walk across the state, something that grew into a thousand-person march to demand positive action on climate change. This push went for federal legislation to stipulate a reduction of 80% in climate-change gases by 2020, a far more radical standard than most have yet broached. A weaker federal bill is under consideration, and, pushed by his constituents, the Vermont senator, Bernie Sanders, continues to work towards far tougher regulations. However, the big changes may be made by an end run around the federales.

Since 2002, California has been battling the federal government for the right to set emissions standards for vehicles within the state. Since more than 10% of the nation's population lives in California, any such regulation could change the face of the domestic auto industry, and so both car-makers and the White House have tried to defeat the measures. Happily, they have lost.

One step came when Massachusetts sued to get the Environmental Protection Agency to stop saying that it didn't have the power to regulate greenhouse gas emissions; the state won in the supreme court in the autumn of 2006. Another landmark came in November when a federal circuit court for the west struck down national vehicle mileage standards that increase efficiency by one mile per gallon, which California's attorney general called "pathetic". Soon afterwards, the attorney general joined 16 states in demanding that Congress prevent the Bush administration from blocking its 2002 motor vehicle greenhouse-gas emissions law. Change for the better largely comes from the bottom up, and in a decentralised country it doesn't always have to reach the top to matter. These changes that are afoot across the US suggest that the federal government may become increasingly irrelevant on many issues.

The centre cannot hold, Yeats wrote; his next line is "Mere anarchy is loosed upon the world". Anarchism in the contemporary sense of decentralised direct democracy is on the loose, and that's the rest of the good news. Globally, as the nation-state becomes increasingly less meaningful - a provider of positive goods and more and more just an army and some domestic enforcement - people are withdrawing to shape and support more localised forms of organisation and power. To the extent that it's part of that civilised and localising world, the same is true of the US.

· Rebecca Solnit is the author of Hope in the Dark: The Untold History of People Power comment@theguardian.com