Many in the rich world demonise the increasing population in the poor world as the central issue we need to tackle in our attempts to mitigate climate change. Whilst not denying the importance of population stabilisation, examining the relative environmental impacts of different communities allows us to view the burgeoning global population in a broader context. Taking carbon emissions (footprints) to be a useful measure of an individual's environmental impact, we can get an insight into the responsibility for this impact among different populations. The average carbon footprint in Europe is 10 tonnes per person per annum, in North America 20 tonnes, in China 5, in India 2, and in Sub Saharan Africa 1.

So at the present time, one American consumer has the same carbon impact as 20 Tanzanian consumers. It follows that reducing the carbon emissions of those in wealthy countries must have the same priority as stabilising the population. Reducing carbon emissions is the essence of the Contraction component of our favoured policy response to climate change, Contraction and Convergence.

 There is no secret about the best way to achieve the demographic transition necessary to stabilise populations. Societies in which  women get secondary education , and in which all have ready access to contraception, undergo rapid transitions to replacement levels of population,the magic average of 2.1 children per couple who are able to conceive. Resourcing poor societies is a necessary fist step on this path, and the Convergence element of Contraction and Convergence will lead to billions of dollars being transferred to those living in poor countries. 

There are three essential ingredients to Contraction and Convergence which ensures that its implementation will have the combined effects of stabilising populations and reducing carbon.

First is to make the scientifically determined amount of carbon emissions which will keep keep our globes temperature within  collectively agreed limits the legally binding constraint within which all fossil fuel based activity can occur. This is considerably less than at present, so there needs to be a Contraction of carbon emissions. 

Second is to allocate this carbon amount as equal entitlements to each person presently living on the globe. Within the constraints outlined above, high emitters will have less entitlement than their present emissions, low emitters more, leading to a convergence of carbon entitlements. The low emitters will be able to sell their unused entitlements to the high emitters thus getting the necessary resources to enable population stabilisation.

Third, to get maximum benefit from their limited entitlements, everyone will have compelling financial reasons to go about their lives in low carbon ways. So all will have major incentives to create the low carbon economies upon which our future depends.  

Getting this framework in place is thus the imperative. Important discussions on whether we should put in place fiscal and other policies to encourage  one child  or indeed no child families, should take place in the context of the globally implemented framework of Contraction and Convergence.