The Berkeley Earth Project
has used new methods and some new data, but finds the same warming trend seen by groups such as the UK Met Office and Nasa.
The project received funds from sources that back organisations lobbying against action on climate change.
"Climategate", in 2009, involved claims global warming had been exaggerated. Emails of University of East Anglia (UEA) climate scientists were hacked, posted online and used by critics to allege manipulation of climate change data.
The Berkeley group says it has also found evidence that changing sea temperatures in the north Atlantic may be a major reason why the Earth's average temperature varies globally from year to year.
The group includes physicist Saul Perlmutter, a Nobel Prize winner this year
The project was established by University of California physics professor Richard Muller, who was concerned by claims that established teams of climate researchers had not been entirely open with their data.
He gathered a team of 10 scientists, mostly physicists, including such luminaries as Saul Perlmutter, winner of this year's Nobel Physics Prize for research showing the Universe's expansion is accelerating.
Funding came from a number of sources, including charitable foundations maintained by the Koch brothers, the billionaire US industrialists, who have also donated large sums to organisations lobbying against acceptance of man-made global warming.
"I was deeply concerned that the group [at UEA] had concealed discordant data," Prof Muller told BBC News.
"Science is best done when the problems with the analysis are candidly shared."