By Danny Wood
BBC News, Madrid
The United Nations has approved a 10-year strategic plan to tackle desertification, but has failed to reach an accord on the budget.
Most of those who will suffer will be in Africa, the UN says
The meeting of the UN Convention to Combat Desertification has ended in Madrid and is expected to move on to New York to try to sort out funding.
The UN says desertification caused by climate change and unsuitable farming is a crisis of global proportions.
In 10 years it could drive 50 million people from their homes, it says.
Most of those will be in Africa.
The UN's top climate change official, Ivo de Boer, said there was a "very close interaction" between climate change and desertification.
"Climate change is having an impact on deserts and at the same time, because carbon is captured in soils, desertification also has an interaction with climate change.
"So it's something that works both ways which is why it's important to address the issue in combination."
Before this conference in Madrid, there was considerable scepticism about the convention's capacity to deal with desertification.
The convention was adopted a decade ago but environmental groups say not one of nearly 200 signatory countries is keeping to its commitments.
Spanish news reports say the problem of reaching an agreement at this meeting was caused by Japan.
The surprise resignation of the Japanese prime minister left Japan's delegates at the conference unable to get authorisation to approve the budget.
Spain's director of biodiversity, Jose Herranz, says the new strategic plan does set concrete objectives that will help fight desertification.
But without an approved budget, environmental groups described this conference as a failure.
Mr de Boer said the convention was trying to deal with its financial issues and was "making every effort" to become more cost effective.
He said it was "looking very critically at itself, at its functioning, how it is using its money".