Scientists at the University of Auckland in New Zealand analyzed the first 10 years of global cloud-top height measurements (from March 2000 to February 2010) from the Multi-angle Imaging SpectroRadiometer (MISR) instrument on NASA’s Terra spacecraft. The study, published recently in the journal Geophysical Research Letters, revealed an overall trend of decreasing cloud height. Global average cloud height declined by around one percent over the decade, or by around 100 to 130 feet (30 to 40 meters). Most of the reduction was due to fewer clouds occurring at very high altitudes.which also illustrates the fact that once an instrument is available to measure something, it will be measured and analyzed and its entrails examined.
Supposedly, this demonstrates that cloud heights are getting lower and that this is a sign of global cooling. Now, cloud heights may indeed be getting lower and the world may indeed be cooling since the great El Niño of 1998, but that MLT on the graph is almost entirely an artifact of the Big Dip ca. 2008.
|Engineering location benchmark,|
sometimes mistaken for rifle scope
Suppose a drill is set up to make a hole at the x-y location shown on the left. Normal machine vibrations will cause deflections in both the x- and y-directions, resulting in a cloud of points around the targeted location. Since the vibration is commonly present, this pattern is called common cause variation. If however, the machine is damaged in some way that the spindle comes down off the perpendicular, we will get holes outside the normal pattern of random deflections. This is called special cause variation.
- by successive differences (i.e., between consecutive pieces off the drill press)
- by rational subgroups (i.e., samples from a larger stream for which machine, operator, environment, material, etc. were essentially constant)
|A process experiencing only random variation|
Upper and lower control limits (UCL/LCL) are calculated from
estimates of short-term variation, such as the range between
|A process experiencing assignable variation|
Special causes generally knock data outside the control limits,
which represent three standard deviations of random variation
At about 2001, there is a step-change, or "shift." The mean residual cloud height (called by climate scientists for some reason the mean "anomaly") was running an average of about 30 then dropped to a mean of around 10. Mentally superimpose a set of control limits like unto the first chart above onto the first year's data, then onto the second year's data. Both seem to be stationary series around 30 and 10, resp.
Except for the Big Dip (and possibly a Small Dip, 2003) the remainder of the chart seems remarkably stable. IOW, you could fair a median through the remainder of the data, calculate control limits and get something a bit like the second chart above: a stationary series with spikes and outliers. Without the raw data, more cannot be said. But, block the first year and the Dip with your hands and see what you think.