In a politely worded letter, the director of NASA's Goddard Institute for Space Studies (GISS) has addressed One Nation senator Malcolm Roberts' concerns that the organisation's data on climate change has been manipulated.

In a rare occurrence, director Gavin Schmidt personally wrote a letter in response to Senator Roberts' request for information about the NASA GISTEMP analysis of global surface temperature history.

The GISS Surface Temperature Analysis (GISTEMP) is an estimate of global surface temperature change.

In the letter obtained by Fairfax Media and circulated widely on social media, the NASA scientist directed Senator Roberts to a number of links on the NASA website that published the entirety of NASA's raw data and the code they use to analyse that data.

"However, you appear to hold a number of misconceptions which I am happy to clarify at this time," the letter went on.

The first "misconception" noted by Mr Schmidt related to a graph that Senator Roberts had included in his request.

The graph, as Mr Schmidt pointed out, originated from the Global Historical Climatology Network (GHCN), a project run by the National Ocean and Atmospheric Administration (NOAA).

"Perhaps you might not be aware, but NOAA is a different US Govt. agency than NASA, and questions relating to their activities or products might be more usefully addressed to them," Mr Schmidt said.

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The second "misconception" pertained to Senator Roberts' comments on the effect of homogeneity adjustments on Arctic temperatures "from whatever source".

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The NASA climate scientist continued his letter to Mr Roberts by explaining homogeneity adjustments.

"The claim that GISS has 'removed the 1940s warmth' in the Arctic is not correct," he said.

Mr Schmidt explained that temperature records were homogenised.

This, he said, was a "necessary task to ensure that non-climatic influences in the analysis are minimised as much as possible".

Mr Schmidt urged Senator Roberts if he had any remaining questions, to perform his own analyses.

"Finally, might I suggest that you avail yourself to the resources provided by the Bureau of Meteorology or CSIRO in Australia for further details on this topic," the letter concluded.

This out-of-the-ordinary step taken by the NASA director was not the first time Senator Roberts has come up against a scientist over climate change.

In August, particle physicist Professor Brian Cox took on Senator Roberts on the ABC's Q&A program.

Their exchange involved claims by Senator Roberts that climate data had been corrupted by NASA.