Much has been made of the funding to support clean-energy and climate-adaptation initiatives in developing countries pledged by industrialized countries at the 2010 United Nations Climate Change Conference in Cancún, Mexico (Nature 468, 875–876; 2010). Yet if history is any guide, it is questionable whether these funds will materialize.

Nine years ago in Monterrey, Mexico, the same industrialized nations reaffirmed their commitment to allocate 0.7% of gross national income for official development assistance (ODA). This target was originally mandated by a 1970 UN general resolution that has never been honoured. The ODA peaked in 1982, when it reached just 0.36% of the combined gross national income of countries within the Organisation for Economic Cooperation and Development (OECD).

In 2009, that proportion was languishing at 0.31%. This shortfall in annual funding amounted to US$155 billion, which is substantially more than the Cancún pledge of $100 billion by 2020. If one assumes an average annual growth rate of 2% for OECD economies, by 2020 a further $68 billion of the ODA will still be 'owed' to developing countries.

Even if the Cancún pledges are realized by 2020, they will offset only half of the deficit in the long-promised ODA. Without a more generous and decisive attitude from industrialized countries and legally binding commitments backed up by sanctions, the Cancún pledge will do little to raise the hopes of the world's two billion poorest people.