Diplomacy is traditionally a game of alliance and compromise. Yet in the early hours of Saturday 11 December, Bolivia found itself alone against the world: the only nation to oppose the outcome of the United Nations climate change summit in Cancún. We were accused of being obstructionist, obstinate and unrealistic. Yet in truth we did not feel alone, nor are we offended by the attacks. Instead, we feel an enormous obligation to set aside diplomacy and tell the truth.

The "Cancún accord" was presented late Friday afternoon, and we were given two hours to read it. Despite pressure to sign something – anything – immediately, Bolivia requested further deliberations. This text, we said, would be a sad conclusion to the negotiations. After we were denied any opportunity to discuss the text, despite a lack of consensus, the president banged her gavel to approve the document.

Many commentators have called the Cancún accord a "step in the right direction." We disagree: it is a giant step backward. The text replaces binding mechanisms for reducing greenhouse gas emissions with voluntary pledges that are wholly insufficient. These pledges contradict the stated goal of capping the rise in temperature at 2C, instead guiding us to 4C or more. The text is full of loopholes for polluters, opportunities for expanding carbon markets and similar mechanisms – like the forestry scheme Redd – that reduce the obligation of developed countries to act.

Bolivia may have been the only country to speak out against these failures, but several negotiators told us privately that they support us. Anyone who has seen the science on climate change knows that the Cancún agreement was irresponsible.

In addition to having science on our side, another reason we did not feel alone in opposing an unbalanced text at Cancún is that we received thousands of messages of support from the women, men, and young people of the social movements that have stood by us and have helped inform our position. It is out of respect for them, and humanity as a whole, that we feel a deep responsibility not to sign off on any paper that threatens millions of lives.

Some claim the best thing is to be realistic and recognise that at the very least the agreement saved the UN process from collapse.

Unfortunately, a convenient realism has become all that powerful nations are willing to offer, while they ignore scientists' exhortations to act radically now. The UN's Intergovernmental Panel on Climate Change has found that in order to have a 50% chance of keeping the rise in temperature below 1.5C, emissions must peak by 2015. The attempt in Cancún to delay critical decisions until next year could have catastrophic consequences.

Bolivia is a small country. This means we are among the nations most vulnerable to climate change, but with the least responsibility for causing the problem. Studies indicate that our capital city of La Paz could become a desert within 30 years. What we do have is the privilege of being able to stand by our ideals, of not letting partisan agendas obscure our principal aim: defending life and Earth. We are not desperate for money. Last year, after we rejected the Copenhagen accord, the US cut our climate funding. We are not beholden to the World Bank, as so many of us in the south once were. We can act freely and do what is right.

Bolivia may have acted unusually by upsetting the established way of dealing with things. But we face an unprecedented crisis, and false victories won't save the planet. False agreements will not guarantee a future for our children. We all must stand up and demand a climate agreement strong enough to match the crisis we confront.

• Pablo Solon is the ambassador of the Plurinational State of Bolivia to the United Nations.