What was done
The urban heat island (UHI) of Houston, Texas was evaluated from 82 nighttime sets of radiation data obtained using the split-window infrared channels of the Advanced Very High Resolution Radiometer on board the NOAA-9 satellite during March 1985 through February 1987 and from 125 sets of similar data obtained from the NOAA-14 satellite during July 1999 through June 2001.

What was learned
In the words of the author, "over the course of 12 years, between 1987 and 1999, the mean nighttime surface temperature heat island of Houston increased 0.82 ± 0.10 [°C]."  It was also pointed out that "the growth of the UHI, both in magnitude and spatial extent, scales roughly with the increase in population, at approximately 30%."  In addition, it was noted that the mean rural temperature measured during the second interval was "virtually identical to the earlier interval."

What it means
This extremely well designed study has probably characterized the development of the urban heat island of Houston, Texas better than has ever been done before for any city on earth; and, in so doing, it has demonstrated that the growth of the UHI "scales roughly with the increase in population."  What is more, it demonstrates that this phenomenon is huge.  In just 12 years, the UHI of Houston grew by more than the IPCC calculates the mean surface air temperature of the earth rose over the entire past century, over which period the earth's population rose by some 280% or nearly an order of magnitude more than the 12-year population growth experienced by Houston.

Clearly, the impact of population growth on the urban heat island effect is very real and significant, vastly overshadowing the effects of nature itself.  It has been demonstrated by Oke (1973), for example, that towns with as few as 1,000 inhabitants typically create a warming of the air within them that is over twice as great as the increase in mean global air temperature believed to have occurred since the end of the Little Ice Age, while the urban heat islands of the great metropolises of the world rival the temperature differences that exist between full-fledged ice ages and interglacials.

Given these facts, it is presumptuous in the extreme to believe that the global surface air temperature record of the last two decades of the 20th century -- when world population rose by over 35% -- could ever be accurately enough "massaged" to provide a realistic assessment of what the planet's non-urban-affected surface air temperature really did over that period.  Hence, like it or not, we are essentially forced to rely on the satellite record when it comes to evaluating contemporary global climate change; and that record suggests that the warming of that period -- if there truly was any at all -- was a far cry from the "unprecedented" status that climate alarmists are fond of attaching to it.

Reference
Oke, T.R.  1973.  City size and the urban heat island.  Atmospheric Environment 7: 769-779.