What was done
Working with daily maximum (max), minimum (min) and mean air temperatures (T) from 1062 stations of the U.S. Historical Climate Network, the author computed the slopes of the relationships defined by plots of daily air temperature standard deviation vs. daily mean air temperature for each month of the year for the period 1948-1997.

What was learned
In the words of the author, "for most of the contiguous USA, the slope of the relationship between the monthly mean and monthly standard deviation of daily Tmax and Tmin - the variance response - is either negative or near-zero," which means that "for most of the contiguous USA, a warming climate should produce either reduced air-temperature variability or no change in air-temperature variability."  He also notes that the negative relationships are "fairly strong, with typical reductions in standard deviation ranging from 0.2 to 0.5°C for every 1°C increase in mean temperature."

What it means
Robeson notes that the negative variance response he documented "has the potential to mitigate some of the potential impacts of increasing mean air temperature ... if these impacts are driven by upper-tail temperatures (high values of daily Tmax or Tmin)."  With respect to Tmax, examples of the beneficial consequences he cites include less severe increases in human and crop heat stress and demand for electricity; while with respect to Tmin he notes there would be "fewer severely cold nights during winter."  This latter consequence would be especially important to human health, as we have reviewed several papers that indicate that low temperatures are much more lethal to people than are high temperatures [see Health Effects (Temperature - Cold Weather) in our Subject Index].