The CO2 chart in an Energy Stewards building detail page is taken from the ENERGY STAR system and in fact is a 12-MONTH MOVING TOTAL (that is, an ANNUAL emissions number).
Thus, the CO2 plot on DETAILS page aligns perfectly with the calculations of the ENERGY STAR rating, which is also a 12-MONTH figure. If a building does not have a rating but gets an energy intensity value, it too, is a 12-month calculation (total energy for 12 months divided by square feet).
Energy Stewards takes the CO2 total emissions numbers from ENERGY STAR and plots these. The data display, which is adjusted for weather changes from year to year, provides a simple indication of how a building’s energy use (and the related CO2 contributions) are trending over time.
Here is a plot of the numbers in ENERGY STAR from a Portfolio Manager report for the City of Fitchburg, WI
Here is the Energy Stewards plot:
The thumbnail plots on each building’s HOME PAGE in fact give our estimate of CURRENT MONTH CO2 and are indeed based on a table of estimates internal to Energy Stewards derived from the eGRID system that EPA uses (EPA matches zip code of the building to one of the 26 regions in the eGRID map, Energy Stewards uses a statewide estimate weighted by the area of each state covered by an eGRID region.)