China's most senior negotiator on climate change said today he was keeping an open mind on whether global warming was man-made or the result of natural cycles.

Xie Zhenhua said there was no doubt that warming was taking place, but more and better scientific research was needed to establish the causes.

Xie, Premier Wen Jiabao's special representative on climate change, was speaking in Delhi at the end of a two-day meeting of ministers from four of the most powerful emerging economies – China, India, Brazil and South Africa.

The four countries, known as the Basic group, called on rich nations to ensure that $10bn pledged to combat climate change was handed over before the end of the year. South Africa's environment minister accused the US of lagging behind at Copenhagen and said it had a moral obligation to take a lead on the issue.

The group pledged to pass on details of their own voluntary actions on the environment to the UN framework convention on climate change by 31 January.

Xie's comments caused consternation at the end of the post-meeting press conference, with his host, the Indian environment minister, Jairam Ramesh, attempting to play down any suggestions of dissent over the science of climate change.

Ramesh refused to accept China had stepped out of line, although he conceded: "We still need more science to understand whether global warming is causing glacial melt or whether it is the natural cycles."

Responding to a question about the controversy over the melting of Himalayan glaciers and to fresh doubts cast on the link between global warming and extreme weather events, Xie said there were still "disputes" in the scientific community over the causes.

"Now the mainstream view is according to the review reports by the IPCC," he said. "There is one starkly different view, that the climate change or climate warming issues is caused by the cyclical element of nature itself. I think we need to adopt an open attitude to the scientific research, that we need to have as inclusive as possible all kinds of views concerning this aspect, because we want our views to be more scientific and to be more consistent."

Asked later to clarify his remarks, he said: "It is already a solid fact that the climate is already warming. The scientists have already shown that te global climate is warming.

"Due to the climate change influences, the countries that have been actively impacted most are those developing countries, in particular those small island countries. And the major reason of this climate change issue is the unconstrained emissions produced by developed countries in the process of their industrialisation. That is the mainstream view and we need to make responses concerning these views. There are some uncertain views but our attitude is open, that we need to have more studies. But this shall not impede our efforts in combating the climate change."

The Basic group played a key role in drawing up the Copenhagen accord in December. Ramesh said they had agreed that rich nations should demonstrate their credentials by ensuring that the $10b pledged at Copenhagen was paid this year.

"That is the basic minimum," he said. "If $10bn as promised in the Copenhagen accord does not flow to Africa, to small island states and to the LDCs [least developed countries] we believe that frankly the developed countries are not serious. That is the first milestone that has to be achieved. You have to put money on the table, you have to identify the projects and money has to start flowing."