Trend Data

I did some work with excel to create a graph that would show the slope of a linear regression for each year through the present.  Essentially, the data point at a certain year Y shows the trend in temperature from year Y to the present.  This “trend” is not derived from just taking the endpoints and finding the change in temperature, but instead by finding the slope using all data points in the given time interval. Below is a graph representing what I have been describing.  As the year approaches the present, there is less data to work with, so the trends become increasingly eratic and of large magnitude.

Below is a graph that extends only through 2003, so it is easier to see the trends before 2003.

As you can see, it is safe to say that the temperature trend is upward from 1980-1998 to the present.  In 1998, the Earth underwent a massive El Nino, raising global temperatures and creating approximately an even trend in temperature during the past decade.  We can also say that the temperature trend has been even since 2001, and downward since 2002, 2003, 2004, etc.  This is important because of claims of recent of “global cooling” or that global warming has stopped.  Certainly, global warming has stopped since 2001, making 7 years without warming.  We can take it a step farther and say that “global cooling” has occured since 2002, making it 6 years of cooling. 

So the next question is, how statistically significant is a 7 year stable temperature trend and a 6 year cooling trend.  I chose UAH (University of Alabama at Huntsville) data for two reasons: 1) It is sattelite based, and thus not effected by urbanization bias. 2)  It covers the period of 1980 to the present, which exhibits warming that some claim has been caused by CO2 emissions.  Therefore, to answer my question about statistical significance, I need to go into the full 28 years of data to see if the 7 year stable temperature and 6 year cooling trend exist.  I am guessing that they do.  Below is graph of actual UAH temperature.

As you can see, it is very likely that a 6 year cooling trend (remember, using linear regression not endpoints) exists elsewhere in the data.  In fact, it appears that an 8 year cooling trend exists from 1980-1988.  Therefore, recent claims about “global cooling” and that “global warming has stopped” may be statistically insignificant, unless the case can be made the climate as a whole is showing signs of stablization, which may very well be the case.  Based upon changes in oceanic circulation (the PDO recently going negative) and projected weak solar intensity over the next two solar cycles, this current trend of “global cooling” may continue and become statistically signifiant.

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