The scientist at the centre of the storm over mistakes by the UN's climate change panel has broken his silence on the affair to defend his report as "robust and rigorous".

Martin Parry, a climate expert at the Grantham Institute and Centre for Environmental Policy at Imperial College, London, said he was "perplexed" at the way the media has focused on what he called minor points.

Parry was co-chair of the Intergovernmental Panel on Climate Change's (IPCC) working group on impacts, which produced a 2007 report that included the false claim that Himalayan glaciers would melt by 2035.

The discovery of the mistake, and the way it was handled, has produced calls for IPCC chairman Rajendra Pachauri to resign. It has also led to reports of further errors in the report, including that the IPCC wrongly stated that 55% of the Netherlands is below sea level.

In an open letter sent on Saturday to scientists that prepared the 2007 report from IPCC working group two (WG2), which has been the focus of criticism, Parry says: "What began with a single unfortunate error over Himalayan glaciers has become a clamour without substance."

He adds: "It is easy to forget the big picture, which is that the WG2 volume represents a sound and reliable statement of our knowledge, and is the product of robust and rigorous assessment by you all."

Parry said the IPCC had looked into the further alleged mistakes, and that they were "generally unfounded and also marginal to the assessment".

On the Netherlands, he said there were several different figures that could be used, which vary on how the issue is defined. The Dutch Ministry of Transport, he said, uses the figure 60%, which counts land below high water level during storms, while others use 30%, which is land below mean sea level.

Parry also defended IPCC statements on losses due to disasters, projected Amazon forest die-off, African agricultural decline and the use of observations made by climbers of high-altitude ice.

He said many of the criticisms were based on a mistaken belief that the IPCC could not use so-called grey literature – reports from outside academic journals such as from campaign groups and governments.

"Many such reports are intensively reviewed, both internally and externally. Even if not peer-reviewed, there are reports that contain valuable information."

He also defended the time taken by the IPCC to respond to each reported mistake: "Each of the queries raised has involved about a week of investigation and discussion by IPCC authors before a conclusion is published. This is why many colleagues feel our critics are having a 'field day' or 'dream run' and the press are not reflecting a balanced picture. But, is there any other way than for us to take our time and conduct a careful investigation of each query? We have to trust that in the long run common sense will prevail."