Tuesday, March 31, 2015

Strange adjustments to the climate data

People are looking at the climate databases, and strange and unnatural acts are being performed on the data:
The Melbourne temperature record is one of the “long time” instrumental records of Australian temperature. It starts in 1855 and continues to the present day.
This is exactly the sort of record you want to have, long term and (until recently) well-sited.
The maximum temperature, which generally occurs in the middle of the afternoon, shows almost no trend at all until about 1995. However the minimum temperature, which generally occurs in the early morning before sunrise, shows an upward trend starting at about 1945. With no sunlight on the ground, the night air cools but the heat emitted by buildings and human activities, the “urban heat island” effect, lessens the cooling.
We've seen this before here.  Here comes the unnatural act:
The third temperature series in each of Figures 2 and 3 is of the average annual temperatures recorded in the ACORN-SAT data[3] which has been “homogenized” by the Bureau of Meteorology. A comparison of the measured and adjusted temperature increases from 1944 to 2013 is shown in Table 1.

...

Two conclusions can be drawn from this analysis:
  • There is a clear heat island effect in central Melbourne that is detectable in the minimum temperature measurements.       It may be as much as 0.2 degrees per decade (or 1 degree over 50 years!).
  • The adjustments made to obtain the homogenised ACORN-SAT Melbourne data reduce the apparent long-term temperature increases. So these adjustments compensate somewhat for the urban warming but by increasing the temperatures of the earlier years!
The adjustments are not done on a station-by-station basis, to correct for specific data collection issues (say, moving a station to a new location or upgrading the equipment).  Rather, they are statistical calculations and manipulations which have some pretty serious drawbacks:
In more detail, the ACORN-SAT Melbourne minimum temperatures before 1990 are shifted up relative to the raw data. The stepped adjustments would suggest instrument changes but the BOM records show thus is not the case. Further, there is no sign of the step changes in the direct Melbourne temperature records. An upward correction is also applied to the maximum temperatures, but is applied only to the past, before 1990, and not the present.

A step adjustment does not compensate for a gradual rise due to an urban heat island effect.
So multiply this single station by 1000, for the surface record.  How accurate is the "homogenised" data?  What are the error bars?  Just how confident should we be in a measurement showing a tenth of a degree or two per decade?

Me, I like the satellite record because it avoids all of this statistical nonsense.  Unfortunately, it only dates back to 1979.

If you're like me, you'll take the whole ZOMGTHERMAGEDDON!!eleventy! thing with a big grain of salt.

8 comments:

Archer said...

"If you're like me, you'll take the whole ZOMGTHERMAGEDDON!!eleventy! thing with a big grain of salt."

And a slice of lime. And a shot of tequila. ;)

Personally, I laugh at the whole "The Science is Settled!" crowd. Any true scientist knows that in any day, it's always possible, however unlikely, that a new theorem or hypothesis will pop up that revolutionizes our fundamental understanding of (with all respect to Douglas Adams) Life, the Universe, and Everything. The cry of "The Science is Settled!" has been heard throughout human history, from people who couldn't or wouldn't accept that their view of the world was wrong.

Anyone who uses it without taking another long, hard look at the issue - and really testing the new idea - is no scientist.

2cents said...
This comment has been removed by the author.
burt said...

Everyone KNOWS that the sun and heavens revolve around the earth. The science is settled!

drjim said...

The whole thing reminds me of "The N-Ray Affair"....

Weetabix said...

I've not looked because I don't care that much, but several questions occur to me:
- what is the length of the record of climate temperature data?
- what is the temporal distribution of stations? That is, how many were online in 1900? 1920? 1940, and so on?
- what is the spatial distribution of stations? That is, do we have a good, weighted distribution such that cities, suburbs, rural, and undeveloped areas each have a number of stations proportional to the total area of the planet that they represent? I'm certain that the answer to that is no.

I think the data we have to date is very skewed. The last time I read about the climate models, there were about 9 parameters used. 3 had no effect on the model and the other six had wide margins of error.

Ah, the beauties of extrapolation! You can get any result you want.

ProudHillbilly said...

Heh. Those of us that grew up in an urban area ecperienced "climate change". And then some of us moved... I didn't run my AC a single night last year. Because I don't live in the city anymore.

ProudHillbilly said...

Heh. Those of us that grew up in an urban area ecperienced "climate change". And then some of us moved... I didn't run my AC a single night last year. Because I don't live in the city anymore.

Will said...

Somewhere out there is a photo record of the environmental change of one of the temp stations. Starts in a field, 100+years ago, with scattered trees (orchard?). Trees go away, buildings start to appear. Then a blacktop parking lot surrounds it, with more buildings. Still in use! I think it was connected with one of the universities.