We already know from multiple lines of evidence that the planet is warming, so Nova’s post is yet another “Merchant of Doubt” attempt.
Where did they go wrong this time?
The BOM say their temperature records are high quality. An independent audit team has just produced a report showing that as many as 85 -95% of all Australian sites in the pre-Celsius era (before 1972) did not comply with the BOM’s own stipulations. The audit shows 20-30% of all the measurements back then were rounded or possibly truncated. … The BOM are issuing pronouncements of trends to two decimal places like this one in the BOM’s Annual Climate Summary 2011 of “0.52 °C above average” yet relying on patchy data that did not meet its own compliance standards around half the time. It’s doubtful they can justify one decimal place, let alone two?
Unfortunately their poor mathematical knowledge has let them down. Rounding daily temperatures to zero decimal places has almost no effect on a trend over time as shall now be demonstrated. Using the first 100 days from the Sydney BOM data for 2011 (although you could use any station with decimal place data) we can plot the data and the linear trend.
This is what the original data looks like without any rounding, a trend of -0.037.
Round the data to zero decimal places and this is what you get, a trend of -0.036 and a difference in average temperature of 0.004.
The differences reduce as more samples are taken because any single rounding error one way is balanced by rounding errors in the other direction.
If Joanne Nova had basic skills in statistics then she should know this. Instead of advancing the discussion on how best to deal with climate change she wastes time calling for an audit of the BOM. For what purpose?!? Not only can we see that her analysis is flawed, but we already know the evidence for global warming is overwhelming clear.