Minnesotans For Sustainability^©

Sustainable:  A society that balances the environment, other life forms, and human interactions over an indefinite time period.

Special Report – Air Temperatures & Dew Points – Great Lakes States

Pat Neuman*
April 16, 2003

 


Air Temperatures
Dew Points
Station Selection and Other Procedures
Procedure
Conclusions
Table 1: Five Year Average Temperature Differences (ºF)
Table 2:  Five Year Average Dew Point and Temperature Differences (ºF)
Table 3: Five Year Average Temperatures (ºF) - Highest of Record
References

 

Great Lakes States: Minnesota, Wisconsin, Michigan, Illinois, Indiana, Ohio, Pennsylvania, and New York.

A five year interval was chosen for this study due to the high annual variability in temperatures and humidity, due to highly variable atmospheric, oceanographic, and other conditions.

Air Temperatures

Temperature data at climate stations within the Great Lakes States are shown in Table 1. The first column shows the 1998 through 2002 average annual temperatures for each station. The second column has historical average annual temperatures based on station records through 1997. Difference values between the periods are shown in the third column. The difference values varied from 1.1 degrees Fahrenheit (F) at Bellefontaine, Ohio to 3.6 degrees F at Spooner, Wisconsin.

Dew Points

Dew point data at airport stations within the Great Lakes States are shown in Table 2. The first column shows the 1998 through 2002 average annual dew points for each station.  The second column has historical average annual dew points based on station records through 1997. Difference values between the periods are shown in the third column. The differences varied from 1.2 F at Columbus, Ohio to 3.8 F at International Falls, Minnesota.

Station Selection and Other Procedures

For airport stations, all stations that had 50 or more years of record were included.  Climate stations are sometimes called National Weather Service (NWS) cooperative stations.  Cooperative observers for the NWS include other government people and private individuals (many farmers).

For the Midwest, many cooperative observers began their record keeping in 1896.  Most of the stations in the East (PA & NY) have records beginning in 1926. Stations were selected that had low percent missing monthly and annual data.

Procedure:

·         Determine stations with highest quality data.

·         Make consistency plots for station temperatures.

·         For each station, determine temperature differences between average temperatures for 1998 through 2002 and average temperatures for historical periods. Historical periods run   from the beginning of record through 1997). Use the differences for the stations with very high quality data to help in the selection of other stations.

·         Select stations for good distribution over Great Lakes States.

·         Make no or limited adjustments in data, use other stations instead.

Conclusions

Annual temperature data at climate stations in the Great Lakes States show that above average annual temperatures occurred from the 1920s through the 1950s and from the 1980s through the year 2002.  Average five year annual temperatures for 1998 through 2002 were the highest of record at many NWS cooperative climate stations.  The majority of the new record five year average temperatures were in the Western Great Lakes States (MN, WI, MI).  The highest five year average temperatures at cooperative stations are shown in Table 3, provisional.

Five year humidity levels (dew points) for 1998 through 2002 were the highest on record at all airport stations in all Great Lakes States.

The airport station data shown in this report represent a large region of the United States.  Near surface humidity has also been shown to have increased at Barrow, Alaska during the latest couple of decades.¹ The 1998 through 2002 humidity has been shown to be higher than any other five year averages in the 1918 through 2002 record of humidity data at Minneapolis, MN.

The largest increases in both temperatures and humidity for the Northeast, Midwest, and Northern Great Plains have been during Winter and early Spring months.^2,3

One of the largest global climate warming fingerprints is that near surface atmospheric humidity (dew points) is increasing. The increase in dew points at stations in this report (Table 2) cannot be a result of increasing evaporation from irrigation because no irrigation occurs during the Winter and early Spring in this area (Great Lakes-Midwest and Great Plains).   It is nearly certain that the increase in humidity, especially during the 1998 through 2002 period, was due to increasing evaporation and transpiration (longer growing seasons) due to global climate warming caused by the accumulation of a higher concentration of greenhouse gases in the atmosphere, and, the higher humidity associated with the 1997-1998 powerful El Nino.  Warmer ocean waters and strong El Ninos, and other warm ocean water oscillations, are linked to having a warmer overall global climate.  As greenhouse gases continue to accumulate in the atmosphere and as ocean waters continue to warm, the buildup of warmth on the planet will continue. The warmth will not be variable as are local and regional day to day and year to year temperature variations.

Summary tables follow.^4,5

    Table 1: Five Year Average Temperature Differences (ºF)

Table 2:  Five Year Average Dew Point and Temperature Differences (ºF)