In the 2006 film Children of Men, set in the near future, a sudden failure of human fertility has led to global political violence, social collapse and forced migration. Britain is one of the few countries with a still functioning government, but in response to the refugee crisis it has become a semi-fascist society. There is constant propaganda warning citizens not to shelter refugees, and the police round-up and imprison foreigners in huge detention camps.

It is a powerful film on several levels. But it also strikes me as a chillingly plausible vision of Britain's response to a major refugee crisis. Unfortunately, according to all the available evidence, we are on course for the greatest refugee crisis the world has ever seen within the next two or three decades.

In the last few months there have been riots and political disturbances in countries from Haiti to West Africa, Egypt, Burma and Indonesia; triggered by huge increases in food and fuel prices. As the economic and political effects of climate change and resource-scarcity continue to intensify over coming years, we can expect to see forced migration on a massive scale. The human suffering involved is almost unimaginable. The effect of such a refugee crisis on our own society is, however, quite easy to imagine; especially if you have seen Children of Men.

In a recent article on the website climatedenial.org, the writer George Marshall reported an interesting experiment: "You can measure how seriously an organisation takes an issue by finding how many times it mentions it on their website", he claims. By using a Google search, he finds that leading human rights and refugee organisations' websites contain more references to donkeys than to climate change.

"In doing this they are reflecting a wider social denial strategy, noted in several academic studies", Marshall argues. "The large majority of people, whilst noting that climate change is a serious issue, will admit to never talking about it in their daily life ... Ironically this strategy mimics a common social response to human rights abuses: when asked, people admit that they heard the screams in the night or they noticed that people had disappeared, but, through a socially negotiated compact, they never discussed what they know to be happening with each other."

I don't think we can afford to ignore the probable effects of climate change on our society's response to refugees. If we want to avoid drifting towards a xenophobic "Fortress Britain" we need to act now to revitalise a commitment to offering sanctuary as one of the most precious aspects of our culture. This is the aim of the City of Sanctuary movement, a national network of local groups committed to welcoming people seeking sanctuary in their communities.

I would also like to see this commitment to sanctuary adopted explicitly by those organisations which are working towards a more sustainable future, such as the Transition Towns movement.

I don't believe that a future Britain like that portrayed in Children of Men is inevitable; unless we allow it to become so through our inaction. To use a Transition Towns slogan, "We are the ones we've been waiting for."

Read more on the City of Sanctuary movement here