The US National Oceanic and Atmospheric Administration (NOAA) has refused to comply with lawmakers’ attempts to subpoena internal communications relating to a recent climate-change study by its scientists.

The analysis, published in Science in June1, analyzed NOAA's temperature records and found that global warming has continued apace in the early twenty-first century. The study contradicts previous findings — often cited by global-warming sceptics — suggesting that warming has slowed since the 1990s.

Representative Lamar Smith, the Texas Republican who leads the House of Representatives Committee on Science, Space, and Technology, asked NOAA in July for the data used in the study and for any internal communications related to it. NOAA has provided the committee with the publicly available data and has briefed committee staff on the research, but the agency has not turned over the communications.

Although NOAA’s latest response to the committee skirted the issue, the agency suggests in a 27 October statement to Nature that it has no intention of handing over documents that reveal its internal deliberations.

“Because the confidentiality of these communications among scientists is essential to frank discourse among scientists, those documents were not provided to the Committee,” the agency said. “It is a long-standing practice in the scientific community to protect the confidentiality of deliberative scientific discussions.”

In response to queries from Nature, Smith released a statement accusing NOAA of rigging its temperature records and stonewalling the House committee.

“NOAA needs to come clean about why they altered the data to get the results they needed to advance this administration’s extreme climate change agenda,” Smith said. “The Committee intends to use all tools at its disposal to undertake its Constitutionally-mandated oversight responsibilities.”

NOAA spokeswoman Ciaran Clayton denies the accusations. She notes that the agency’s study was peer-reviewed and published in a respected scientific journal, and that the agency has provided the committee with temperature data and briefings on the research.

“We stand behind our scientists, who conduct their work in an objective manner,” Clayton says. "We have provided all of the information the Committee needs to understand this issue."

Temperatures rise

The NOAA study, led by Thomas Karl, director of the National Centers for Environmental Information in Asheville, North Carolina, corrected biases in the agency’s global temperature record.

Karl and his colleagues adjusted for known biases in ocean temperature readings from ships and buoys, while also adding measurements from other land-based monitoring stations — expanding the range of those stations into the Arctic. The revised record showed temperatures rising consistently.

Smith’s subpoena came to light on 23 October when the highest-ranking Democrat on the science committee, Representative Eddie Bernice Johnson of Texas, released a letter accusing Smith and his fellow Republicans of using the subpoena to advance a “fishing expedition”. Democrats on the committee, Johnson wrote, “won’t be complicit in the illegitimate harassment of our Nation’s research scientists”.

Andrew Rosenberg, a former NOAA employee who now heads the Center for Science and Democracy at the Union of Concerned Scientists, an advocacy group based in Cambridge, Massachusetts, says that Smith’s investigation confounds government science with politics. He adds that Karl and his colleagues were merely updating their records with the best available science, not acting to advance political means.

“There’s absolutely no implication that there is malfeasance of any kind,” Rosenberg says. “You could ask these questions anytime anybody updates an analysis, but you are only picking the ones where you really don’t like the answer."