Jun 2, 2016

Detection of anthropogenic influence on a summertime heat stress index

by
Thomas R. Knutson, Jeffrey J. Ploshay
,
Climatic Change
  • Examines whether there are now detectable changes in summertime heat stress over land regions
  • Uses a simplified wet bulb globe temperature (WBGT) index as a heat stress metric 
  • Compares observed trends in WBGT (1973–2012) to trends from CMIP5 historical simulations (eight-model ensemble) using either anthropogenic and natural forcing agents combined or natural forcings alone
  • Analysis suggests that there has been a detectable anthropogenic increase in mean summertime heat stress since 1973, both globally and in most land regions analyzed
  • Finds a detectable increase over a larger fraction of land for WBGT than for temperature, as WBGT summertime means have lower interannual variability than surface temperature at gridbox scales
  • Finds, notably, that summertime WBGT over land has continued increasing in recent years--consistent with climate models--despite the apparent ‘hiatus’ in global warming and despite a decreasing tendency in observed relative humidity over land since the late 1990s