For more than a year, Rep. Lamar Smith, the chairman of the House Science, Space and Technology Committee, has been hounding federal climate scientists about a landmark scientific study, published in 2015, whose results he didn't like.

Now comes proof from an independent group of scientists that affirms those findings.

The original study, which the new data confirms, was published in the journal Science. It addressed a so-called pause in global warming that scientists had observed from 1998 to 2012. Up until that study, the "warming hiatus" had been a prominent talking point for those arguing that manmade global warming either didn't exist at all, or is less of a problem than most climate scientists make it out to be.

That study, however, said that the global warming slowdown never really happened — it was just an artifact of improperly adjusted surface-temperature data.

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When the NOAA researchers corrected their temperature datasets, the results showed that Earth's climate had warmed by a larger amount than previously assumed.

Climate trends from the 2015 NOAA study that generated controversy on Capitol Hill. Image: noaa

The new NOAA record produced for that study showed nearly twice the warming over the past 18 years than the previous data did.

That finding struck Smith, a Republican from Texas who maintains that human-caused emissions of greenhouse gases are not causing global warming, as suspicious, and he began a dogged effort to determine if the scientists had manipulated data to arrive at politically-motivated results.

“The American people have every right to be suspicious when NOAA alters data to get the politically correct results they want and then refuses to reveal how those decisions were made," Smith said in a statement in 2015.

"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, who has received funding from the oil and gas industry, including ExxonMobil, added.

New NOAA (ERSST v4), old NOAA (ERSST v3) and UK Hadley Center (HADSST3) data differ in recent years. Image: hausfather et al. 2016.

NOAA denied those accusations, and refused to offer up some of the records that Smith asked for, such as all email correspondence about the climate study in question.

Now comes new research that NOAA's data may have been correct. The new study, published in the journal Science Advances on Wednesday, used an independent dataset of ocean temperatures to check the NOAA study.

The new research, from an independent group of scientists, concluded that NOAA's temperature adjustments were accurate.

The research, led by Zeke Hausfather, a climate scientist at the nonprofit organization Berkeley Earth, used different sets of data than the NOAA scientists had.

Hausfather conducted the study with colleagues at York University in the UK, NASA and George Mason University, as well as one independent researcher.

Specifically, the group relied on data from satellite radiometers, floating buoys and robotic Argo floats to create three separate ocean temperature records during the last two decades.

The NOAA surface record, on the other hand, are what is known as composite records, which takes temperature information from a variety of sources — surface weather stations, satellites, ocean buoys and more — and combines them. This can create challenges when making adjustments as methods of recording temperatures change over time, Hausfather said.

Temperature departures from average during fall 2016 in the Arctic. Image: noaa

"We found all three agree almost perfectly with the new NOAA record, [and] show a strong cooling bias in the old NOAA record."

"The challenge with this is that it creates uncertainties and judgement calls about how best to account for and correct changes in instruments (like the changing composition of the shipping fleet) or the change from one instrument to another (e.g., ships to buoy-based measurements)," Hausfather said in an email.

The NOAA study in 2015 had wrestled with just such a change, specifically differences between temperature readings gathered from buoys and those from ships.

The buoy data was more reliable, NOAA's researchers concluded, leading to an adjustment that increased temperatures in recent years, when buoys have become more prevalent.

In an effort to double check if that adjustment was correct, the new study relies on records that were each created from one type of instrument, avoiding the need for any such adjustments.

"We found all three agree almost perfectly with the new NOAA record, [and] show a strong cooling bias in the old NOAA record," Hausfather said. The study also showed that the UK's global surface temperature database and the one maintained by the Japan Meteorological Agency may be underestimating global warming.

"Our results provide a robust validation of NOAA's study. They show that NOAA scientists were not manipulating data or 'cooking the books,' and that their new record is the most accurate composite record over the past two decades," he said.

As for Smith, who has yet to let up in his criticism of NOAA's temperature readings, Hausfather suggests that he ask the National Academy of Sciences to convene a group of researchers to validate the information independently.

"In general, if folks like Lamar Smith think that scientists are getting it wrong, they should ask other scientists (or the National Academy of Sciences) to review and try and replicate their findings, rather than demand scientist emails," he said. "Science advances through replication."

Smith has tried and so far failed to prove any scientific misconduct at NOAA, at one point even issuing a subpoena of the NOAA director, which had never been done in his committee's 56-year history.

The subpoena sought internal NOAA communications related to global temperature datasets and monthly climate reports, among other information that NOAA deemed essential to the unimpeded conduct of its scientific mission.

Scientists denounced Smith's efforts as a witch hunt, and NOAA fought the subpoena, instead meeting with Smith and his staff multiple times to discuss the research. (Mashable reached out to the committee for comment about the new study, but did not hear back by deadline.)

Sat data tells a story climate alarmists don’t want to hear. It doesn’t fit their climate narrative! https://t.co/Myrev2QtW9 — Sci,Space,&Tech Cmte (@HouseScience) January 3, 2017

"Under normal circumstances, this paper would be of interest to very few people — just the people that focus on the details of the instrumental record," said Andrew Dessler, a climate scientist at Texas A&M University. "The only reason this paper is of any interest outside the specialist community is because of Lamar Smith,” he said in an email to Mashable. Dessler was not involved in this study, and said he suspects it was "written specifically to rebut” Smith’s claims, which gained traction among the broader climate denial community.

Another outside researcher, Kevin Trenberth of the National Center for Atmospheric Research, said the conclusions of the paper clearly support NOAA's temperature adjustments, which were led by the top climate official at the agency, Thomas Karl.

"This paper further allays any qualms that there may have been scientific errors or any non-scientific agendas," he said via email. "Lamar Smith owes Tom Karl an apology."

With Smith continuing as the committee chairman in the new Congress, it's possible that this investigation will continue. Posts on the committee’s Twitter account in recent days have continued to raise questions about NOAA’s surface temperature data, this time casting doubt on the claim that 2016 is the warmest year on record, as U.S. and international agencies are set to announce in coming days.

The past year eclipsed the record warmth set in 2015 and 2014, making the last three years the warmest since at least 1880. In addition, levels of carbon dioxide, the longest-lived global warming pollutant, hit record levels this year, at the highest in all of human history.

It’s unlikely such findings will be recognized by the Republican majority on Smith’s panel, however, at least without a fight.