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> Temperature change
post Feb 2 2006, 08:36 PM
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When the NWS reports climate change, they always report how much the average temperature differs from climate norms. For example, for 2005, they recently reported that average temperature were 1.2 degrees higher than 1895-2004 climate normals.

One thing I wondered was are high and low temperatures rising equally, or is high rising much higher, but lows moving down, etc? I had never seen reported how much high and low temperatures differed from climate normals.

Here at ForecastWatch we use the 1971-2000 climate normals as a benchmark unskilled forecast, so calculating the accuracy of that forecast gives us the difference between that normal and the actual temperatures.

For the United States, for 800 non-random stations (located at airports usually near population centers), the results are interesting. Highs were 0.03 degrees lower than the recent (1971-2000) climate normals, on average, but lows were 2.38 degrees warmer than climate normals. If you assume that average temperature is the average of highs and lows, the average temperature would be about 1.18 degrees above 1971-2000 climate normals. That number is similar to the 1.2 degree anomaly reported by the NWS against the 1895-2004 climate normals.

2004 was similar. Highs for those 800 stations were 0.63 degrees below climate normals, and low temperatures were 2.41 degrees above climate normals. This averages to 0.89 degrees above the average 1971-2000 climate normal temperatures. This is similar to the 0.7 degree anomaly reported by the NWS for 2004 against 1895-2003 climate normals.

I thought this was an interesting statistic, but I don't know what it means. I'd like to hear your thoughts. Is a climatologically steady high, but increasing low expected? What might cause that? Obviously, average temperature is very important in modelling climate change, but does an increasing low affect weather differently than if both were rising equally?

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post Feb 2 2006, 10:25 PM
Post #2


Interesting data!! An analysis of the causes of the disparity in the deltas of high and low temps should answer several questions:

- Do heat island effects near population centers (where many weather
stations are located) affect low and high temps equally?
- Given that narrowing the differences between low and high temps
can be a result of higher humidities, is there more moisture in the
air on average, and is it evidenced by increased cloud cover?
- How does this data correlate with the increases in greenhouse
gases that are touted as causes of global warming?
- What role does particulate air pollution (again, highest near
population centers) play in the differing increase?

This is a short list, not comprehensive by any means. The data is significant, tho'!
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post Feb 3 2006, 11:14 AM
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They also examined the daily maximum and minimum temperatures from the United States, China, and the former Soviet Union and found a general decline in the intra-monthly temperature variability. As reported in the SAR, a related analysis by Karl et al. (1995b) found reduced day-to-day variability during the 20th century in the Northern Hemisphere, particularly in the United States and China. Recently, Collins et al. (2000) has identified similar trends in Australia. By analysing a long homogenised daily temperature index for four stations in Northern Europe, Moberg et al. (2000) also found a progressive reduction in all-seasons inter-daily variability of about 7% between 1880 and 1998. Balling (1998) found an overall decrease in the spatial variance of both satellite-based lower-tropospheric measurements from 1979 to 1996 and in near-surface air temperatures from 1897 to 1996.



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