British Foreign Secretary William Hague has described climate change as “perhaps the twenty-first century’s biggest foreign policy challenge”. He has stressed that “a world which is failing to respond to climate change is one in which the values embodied in the United Nations will not be met”. Indeed, the UN Charter makes clear that a central purpose of that organisation is to “achieve international co-operation in solving international problems of an economic, social, cultural or humanitarian character”.

Climate change is just such a problem – and its impacts and costs fall disproportionally on developing countries. That is deeply unfair. So it is only right that in Cancun last December the 16th Conference of the Parties to the United Nations Framework Convention on Climate Change reaffirmed the commitment from developed countries in Copenhagen in December 2009 jointly to mobilise $100bn of climate finance a year by 2020, to address the adaptation needs of developing countries and help them to limit their carbon emissions.

The UK takes this commitment very seriously and recognises the need for urgent action. The British Government has therefore allocated £2.9bn of Overseas Development Assistance (ODA) to international climate finance for the period 2011/12 to 2014/15 (including our Fast Start commitment). This will be administered through our International Climate Fund (ICF), which has just been formally established.

We expect to spend about 50% of the total on adaptation in poor and vulnerable countries, with around 30% for work to reduce carbon emissions and 20% for forestry.

We have three overall priorities for ICF funding, which we will deliver through both bilateral and multilateral channels in a way which maximises its impact and value for money:

- To show that building low carbon, climate resilient growth at scale is both feasible and desirable;

- To support adaptation in poor countries and help build an effective international framework on climate change;

- To drive innovation, creating new partnerships with the private sector to support low carbon climate resilient growth;

One important avenue for ICF funding is the Climate Development and Knowledge Network (CDKN) (www.cdkn.org), which will receive £50m over the next five years from the UK and £11.8m from the Netherlands. CDKN offers advice, technical assistance, research, strategic knowledge sharing and partnership building to developing countries, to enable them to make long term policy and investment decisions which are climate change resilient and help low carbon development.

The ICF will also fund the climate element of an Advocacy Fund to support the poorest countries to take part more effectively in international negotiations; this will be formally established later this year.

This UK funding will play an important role in helping to mobilise ambitious global action on climate change. But the UK is the only major donor so far to have made specific finance commitments up to 2015. More is needed to meet the Copenhagen commitment of $100bn a year by 2020.

We look to other donors too to make significant and ambitious financial pledges, and we look to business to play an important role, since we expect the target to be reached through a mix of public and private finance. As the Stern Review in 2006 made clear, the clock is ticking. With every passing year, the global cost of effective action to tackle climate change grows greater. The time to act is now.

This is an op-ed by John Rankin, British High Commissioner to Sri Lanka