Edward Barbier grossly underestimates the Adaptation Fund's contribution to sustainable development (Nature 483, 30; 2012). The fund has so far received US$273 million and committed $109 million (see go.nature.com/sgkgr8), not $12.6 million as quoted.

The Adaptation Fund is supported by a carbon market, one of the innovative revenue models Barbier mentions. Under the Clean Development Mechanism of the United Nations Framework Convention on Climate Change, developed countries can trade carbon credits generated by sponsoring emissions-reduction projects in developing countries, helping them to meet their emissions targets under the Kyoto Protocol.

Of the revenue generated by these transactions, 2% goes to the Adaptation Fund for programmes to help developing countries adapt to climate change. These tackle such problems as coastal erosion from sea-level rise, floods from glacial melt and drought-induced falls in crop yields. By January 2012, the fund had spent $30.14 million on such projects.

The carbon market is shrinking because of the global financial crisis and uncertainties over the scale of demand for emissions-reduction credits. However, the Adaptation Fund's structure means it can also accept funds from governments, the private sector and individuals.