New paper finds US extreme heat waves have decreased since the 1930's

A paper published today in the Journal of Applied Meteorology and Climatology finds that US extreme heat waves have decreased over the period from 1930-2010. According to the authors, "Several daily maximum [Extreme Heat Events] near the 1930’s led to 1930-2010 trends of daily maximum [Extreme Heat Events] decreasing" and "Maps indicated negative trends in the interior of the [continental United States] and positive trends in coastal and southern areas. Continental scale increases between 1970 and 2010 were mostly offset by the decreases between 1930 and 1970." In other words, the overall trend of US extreme heat waves was a decrease from the 1930's to the ice age scare of the 1970's, and then a return to levels still shy of those in the 1930's.

Note: The confusing sentence in the abstract below is easier to understand if broken down into the 2 components:

1. Several daily maximum EHEs [Extreme Heat Events] near the 1930’s led to 1930-2010 trends of daily maximum  EHEs [Extreme Heat Events] decreasing. 

2. Several daily (minimum) EHEs [Extreme Heat Events] near the (2000’s) led to 1930-2010 trends of daily (minimum) EHEs [Extreme Heat Events] (increasing). 

Source: Hansen Convicts Himself Of Data Tampering

Journal of Applied Meteorology and Climatology 2013 ; e-View

doi: http://dx.doi.org/10.1175/JAMC-D-13-071.1

A trend analysis of the 1930-2010 extreme heat events in the continental U.S.

Evan M. Oswald¹ and Richard B. Rood

Atmospheric Oceanic and Space Sciences, University of Michigan, Ann Arbor, USA

Abstract

Extreme heat events (EHEs) are linked to mortality rates, making them an important research subject in both the climate and public health fields. This study evaluated linear trends in EHEs using the United States Historical Climatology Network (USHCN) version 2.0 dataset and quantified the longer-term EHE trends across the continental United States (CONUS).
The USHCN-daily version 1 dataset was integrated with the homogenized USHCN-monthly version 2.0 dataset to create daily data for trend analysis. Time series and estimated trends in multiple characteristics of EHEs (e.g. number, total days, mean duration, etc) were calculated as were the continental means and spatial maps. The differences between EHEs based on daily maximum temperatures, minimum temperatures and both minimum and maximum temperatures were explored. In order to focus on warming and cooling periods the trends were also estimated separately over the first half and second half of the study period (1930-2010).

The results indicated the trends for different EHE characteristics were coherent (e.g. temporally correlated, similar spatial pattern of trends). Maps indicated negative trends in the interior of the CONUS [continental United States] and positive trends in coastal and southern areas. Continental scale increases between 1970 and 2010 were mostly offset by the decreases between 1930 and 1970. Several daily maximum (minimum) EHEs near the 1930’s (2000’s) led to 1930-2010 trends of daily maximum (minimum) EHEs decreasing (increasing). Lastly, the results suggest linear trends depend on which daily temperature extreme is required to exceed the threshold.