The Berkeley study analysed billions of calibrated data points....

The Berkeley study analysed billions of calibrated data points.

Here's a snippet from Wikipedia regarding the data analysis techniques.

" The group uses an algorithm that attaches an automatic weighting to every data point, according to its consistency with comparable readings. The team claims this approach allows the inclusion of outlandish readings without distorting the result and standard statistical techniques were used to remove outliers. The methodology also avoids traditional procedures that require long, continuous data segments, thus accommodating for short sequences, such as those provided by temporary weather stations. This innovation allowed the group to compile an earlier record than its predecessors, starting from 1800, but with a high degree of uncertainty because at the time there were only two weather stations in America, just a few in Europe and one in Asia.[12][18]"

The study was approved and funded by powerful climate denier interests. It has been subject to rigorous peer review.

Some climate deniers seem to believe raw data should never be subject to appropriate adjustment. This is physically impossible and scientifically invalid.