For those concerned about global warming, all eyes are on December's UN climate change conference in Copenhagen. The stakes could not be higher. Almost every new report shows that the climate is changing even faster than the most dire projections of the Intergovernmental Panel on Climate Change (IPCC) in their 2007 report.

Yet from my vantage point, internationally negotiated climate agreements are fast becoming obsolete for two reasons. First, since no government wants to concede too much compared with other governments, the negotiated goals for cutting carbon emissions will almost certainly be minimalist, not remotely approaching the bold cuts that are needed.

And second, since it takes years to negotiate and ratify these agreements, we may simply run out of time. This is not to say that we should not participate in the negotiations and work hard to get the best possible result. But we should not rely on these agreements to save civilisation.

Saving civilisation is going to require an enormous effort to cut carbon emissions. The good news is that we can do this with current technologies, which I detail in my book, Plan B 4.0: Mobilizing to Save Civilization.

Plan B aims to stabilise climate, stabilise population, eradicate poverty, and restore the economy's natural support systems. It prescribes a worldwide cut in net carbon emissions of 80% by 2020, thus keeping atmospheric CO2 concentrations from exceeding 400 parts per million (ppm) in an attempt to hold temperature rise to a minimum. The eventual plan would be to return concentrations to 350 ppm, as agreed by the top US climate scientist at Nasa, James Hansen, and Rajendra Pachauri, head of the IPCC.

In setting this goal we did not ask what would be politically popular, but rather what it would take to have a decent shot at saving the Greenland ice sheet and at least the larger glaciers in the mountains of Asia. By default, this is a question of food security for us all.

Fortunately for us, renewable energy is expanding at a rate and on a scale that we could not have imagined even a year ago. In the United States, a powerful grassroots movement opposing new coal-fired power plants has led to a de facto moratorium on their construction. This movement was not directly concerned with international negotiations. At no point did the leaders of this movement say that they wanted to ban new coal-fired power plants only if Europe does, if China does, or if the rest of the world does. They moved ahead unilaterally knowing that if the United States does not quickly cut carbon emissions, the world will be in trouble.

For clean and abundant wind power, the US state of Texas (long the country's leading oil producer) now has 8,000MW of wind generating capacity in operation, 1,000MW under construction, and a huge amount in development that together will give it more than 50,000MWof wind generating capacity (think 50 coal-fired power plants). This will more than satisfy the residential needs of the state's 24 million people.

And though many are quick to point a finger at China for building a new coal-fired power plant every week or so, it is working on six wind farm mega-complexes with a total generating capacity of 105,000 megawatts. This is in addition to the many average-sized wind farms already in operation and under construction.

Solar is now the fastest growing source of energy. A consortium of European corporations and investment banks has announced a proposal to develop a massive amount of solar thermal generating capacity in north Africa, much of it for export to Europe. In total, it could economically supply half of Europe's electricity.

We could cite many more examples. The main point is that the energy transition from fossil fuels to renewables is moving much faster than most people realise, and it can be accelerated.

The challenge is how to do it quickly. The answer is a wartime mobilisation, not unlike the US effort on the country's entry into the second world war, when it restructured its industrial economy not in a matter of decades or years, but in a matter of months. We don't know exactly how much time remains for such an effort, but we do know that time is running out. Nature is the timekeeper but we cannot see the clock.

• Lester R Brown is president of Earth Policy Institute and author of Plan B 4.0: Mobilizing to Save Civilization.