How should humanity share the cost of action on climate change? Without an answer to this question, the world will not secure a strong and binding deal on the climate at Copenhagen next month, and we will continue on a path towards an increasingly inhospitable world. As many key players have warned, there is a real chance of failure. The Swedish prime minister, Fredrik Reinfeldt, warns that negotiations are faltering because the west is unwilling to offer financing to emerging economies, and the developing world won't budge without the promise of cash.

US Senators on both sides of the aisle are doing all they can to block action with talk of danger to jobs and the US economy. Countries in eastern Europe say that contributing too much will wreck their fragile economies, and wealthier westerners are unwilling to fix numbers, hoping to translate silence into a stronger bargaining position with the US and Japan. No one wants to pay too much, and everyone wants someone else to pay more. This is only rational, isn't it, just part of getting a fair deal for all? It depends on how one counts the cost of climate change.

Some insist that the options on the table are simply too expensive. No deal is better than a deal which costs us too much. Money is the determining factor – not warnings about a grim future or something as wishy-washy as concern for the poor. As idiotic as this sounds, it nevertheless gets you where you live, right in the wallet, and many people actually fall for it. Recall Bush's excuse for pulling the US out of Kyoto, the world's first failed opportunity for a climate deal: "complying with those mandates would have a negative economic impact, with layoffs of workers and price increases for consumers." He does at least speak plainly. Relieved of some of the fanfare, the climate talks are in danger of stalling because of thoughts not too distant from plain words like these. Serious action on climate change will damage our current wealth, so we won't do it.

There is something fundamentally vicious about putting money at the heart of the negotiations. No doubt matters are excruciatingly complex, and reasonable people can argue about how best to spend money on climate change and the world's other ills, but that's not what's happening. We are in danger of failing to act simply because some maintain that the cost of action is too high. Think about the relevant causes and effects of climate change: our easy lives of high-energy consumption and the damage we are doing to the planet. Consider the human beings who will suffer because of our easy lives. Avoiding meaningful action on climate change just because it might be too expensive is on a moral par with harming other people for money. Call it what it is: keeping money in exchange for the suffering of others.

Ethics sometimes has to trump economics. If you have a moral obligation to take action, you don't get out of it with talk of expense. Would you forgive someone for avoiding a moral duty because he thought it might cost him too much? He'd rather not abandon plans for a festive weekend in Spain, so those child care payments will have to wait. No judge would let a father get away with that. Sometimes we have to tighten our belts and do the right thing, even if it costs us more than we'd like.

The west has a long history of industrialisation, and it has done the most damage to our world. Therefore the west has the largest moral obligation to take action. No doubt all countries, even those industrialising much later, have moral responsibilities too, but the point is that our obligations click in no matter what the rest of the world does, no matter what other countries pay. We have to pay for our fair share of the damage, not fight hard for the cheapest way out.

Some think that talking about moral obligations just makes us feel guilty, and we've had enough of that. Others collapse in the face of complexity, groaning that we can't do enough in the short time that we have. Don't believe a word of it. Human beings can move mountains in an instant when they see that something is wrong – the obvious examples are the right ones to think about. If our representatives have forgotten the moral demand for action on climate change, it's up to the rest of us to do something – maybe remind them that they've mistaken money for the things which really matter.

• James Garvey is secretary of the Royal Institute of Philosophy and author of The Ethics of Climate Change