Alternative metrics for measuring surface heating trends

One use of the term “global warming” has been to describe observed surface temperature increases during the last century. However, surface warming, requires using surface heat content to monitor this aspect of the climate system. The real changes in heat content of the surface air temperature, however, are not fully described by temperature alone. Surface observation site microclimates highlight the influence of land surface characteristics on surface heat trends, and since moist enthalpy is more sensitive to surface vegetation properties and more accurately depicts surface heating than temperature, this is a more accurate metric of surface warming or cooling. Temperature and moist enthalpy (expressed as equivalent temperature) trends from 1982-1997 are examined for sites in the eastern United States. Overall, surface trends show slight cooling in temperatures and slight warming in equivalent temperatures. Surface equivalent temperature trends are generally smaller in magnitude than temperature trends. Seasonally, surface trends show the most warming in winter and the most cooling in fall. Equivalent temperature trends during the winter and fall are generally identical in sign to, and larger than, temperature trends, but opposite in sign during the spring and summer. Trend patterns vary widely, however, between individual sites. Local land cover has a large influence on heating trends. Urban sites show more warming, or less cooling, than rural sites. Continued work with alternative heating metrics will increase understanding of microclimate influences and surface-troposphere connections.