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California Climate Division 1:  North Coast

In the following data, Pearson correlation coefficients, r, are determined between atmospheric carbon dioxide and weather factors, including precipitation, average annual temperatures, and the distribution by decade of extreme temperatures.  For these coefficients, the value of r ranges from -1 to +1, with -1 representing a perfect inverse correlation, +1 representing a perfect direct coefficient, and 0 representing no correlation at all.  The author uses the strengths of Pearson Correlation Coefficients as defined by Diana Mindrila, Ph.D and Pheobe Balentyre, M.ED, in Chapter 4 of The Basic Practice of Statistics, (6th Ed.), as illustrated in the following table.

                                                    Value of the Pearson Correlation Coefficient, r        degree of correlation indicated

                                                                   0.7  <|r|                                                   strong correlation

                                                                 0.5 < |r|  < 0.7                                           moderate correlation

                                                                0.3 < |r|  < 0.5                                           weak correlation

                                                                       |r|  < 0.3                                           very weak or no correlation

This author will further subdivide the lowest r values using the following convention

                                                                0.1 < |r|  < 0.3                                           Very weak correlation

                                                                       |r|  < 0.1                                            No correlation

Precipitation Data

Div 1 Prcp.jpg

Over the period of record from 1904 through 2017 for the north coast region of California, There has been a slight trend toward more precipitation at a rate of 0.14 additional inches per decade, with low statistical significance (R squared = 0.0017).  During the period from 1950 through 2017, the trend has been a slight decrease in precipitation at a rate of -0.8 inches per decade, again with low statistical significance (R squared = 0.019).  There is no evidence of a significant change in annual precipitation in the aggregate annual amounts from these three weather stations.

Looking at the Pearson Correlation Coefficient between precipitation and carbon dioxide over the entire period of record 1904-2017 the correlation factor is r = 0.0033, essentially no correlation although the trend is positive toward slightly more precipitation as CO2 levels have risen.  Looking at the same correlation over the period from 1950-2017, there is a very weak negative correlation, with r = -0.14, showing a possible very weak inverse correlation with more CO2 correlating with slightly less precipitation.  No meaningful statistical correlation between rising CO2 and precipitation is evident in this data.

                Extremes of Temperature

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The following table summarizes these extreme temperature trends, and their correlation to rising CO2.

Div 1 extreme temp table.jpg

The trend for all five of these measures of extreme temperature is negative over the entire period of record, showing climate change in the direction of less extreme cold and less extreme heat.   Looking at the trends over the period 1950 through 2017, three of them, the coldest minimum temperatures, and the heatwaves of duration 6 and 9 days do have positive changes, hinting at a possible contribution from rising CO2.

The correlation coefficients between the CO2 and the percent of the hundred coldest extreme temperatures per decade show a very weak inverse correlation over the entire period of the 1900s through 2010s, and a very weak positive correlation over the period post 1950.  Generally, these data show no evidence of increased extreme cold in the northern coast region of California.

Correlation coefficients between CO2 and the four measures of extreme heat over the entire period from the 1900s through the 2010s are all negative, showing that CO2 clearly correlates with climate change in the direction of less extreme heat.  This is particularly true for the distribution of the hottest hundred maximum temperature days, which shows a strong inverse correlation with CO2.  The north coast region of California shows no evidence of increased extremes of temperature, and in fact shows just the opposite.

      Average Annual Maximum and Minimum Temperatures

Div 1 average Tmin mean max vrs CO2.jpg

The aggregate data for these three north coast weather stations in California show that average maximum temperatures have been declining in this climate division at a rate of about -0.015 degrees Fahrenheit per decade.  The aggregate average minimum temperatures have been rising though, at a rate of about 0.018 degrees Fahrenheit per decade.  Both of these results suggest climate change in the direction of less extreme, or more moderate temperatures.

Correlation coefficients between CO2 and maximum temperatures are -0.01 over the entire period of record, and 0.024 in the period from 1950 to 2017, both indicative of no correlation.  There is a weak to moderate correlation between rising CO2 and rising average minimum temperatures, with the correlation coefficient of 0.52 over the entire period of record, and 0.47 over the period since 1950.  Again, the indication is that if CO2 has contributed to climate change in this California climate division, it has been correlated with increased moderation in temperatures.

  California Climate Division 2

Watershed of the Sacramento River

Precipitation Data

Div 2 prcp.jpg

The graph above shows that aggregate average precipitation for weather stations in McCloud, Quincy, Orland, Colfax, and Davis has trended very slightly upward, at a rate of 0.07 inches per decade over the period from 1911 through 2017.  Statistically, the amount of precipitation has not changed at all.  During the period from 1950 to 2017, the precipitation has trended downward -0.8 inches per decade.

The correlation coefficient between CO2 and precipitation from 1911 through 2017 has been -0.028, indicating no correlation.  From 1950 through 2017 the correlation coefficient is -0.15, suggesting a possible very weak inverse correlation.

Extreme Heat in Climate Division 2

Div 2 temp extremes.jpg

The following table summarizes the trends in the graph above, and the correlations between CO2 and the various measures of extreme temperatures.

Div 2 extreme heat table.jpg

The trend in the decadal distribution of extreme cold temperatures has been strongly negative over both the entire period of record, as well as since 1950.  The clear conclusion is that extremely cold temperatures have become much less common in this climate division.  There are strong negative correlations between CO2 and the coldest minimum temperatures, suggesting the CO2 may contribute to significant moderation in extreme cold in this climate division.

The trends measured for more extreme heat show a more mixed message.  The decade of the 1930s has the highest percentage of each of these extreme heat measures, but there is an overall trend of increasing percentage of the hottest maximum temperatures over the entire period of record, 1900s through 2010s.  The percentage of the hottest heatwaves of duration 3-days have increased slightly over the entire period of record, but those of duration 6-days and 9-days, have decreased.

Correlations between CO2 and all of these measures of extreme heat are weak to none over the entire period of record.  Over the decades from the 1950s through 2010s, the correlations are very weak for heatwaves, but there is a strong correlation with the percentage of the hottest hundred maximum temperatures, suggesting a possible contribution to this measure of extreme heat from rising CO2, when the hottest decade of the 1930s is ignored.

Aggregate Average Temperatures in Climate Division 2

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The graph above shows that the aggregate average annual temperatures in McCloud, Quincy, Orland, Colfax, and Davis have increased for maximums, minimums, and mean temperatures.  For maximums, the increase is at a small rate of about 0.04 degrees Fahrenheit per decade, while the rate is more significant for minimums, with an increase of 0.25 F per decade.

Correlation coefficients between these temperatures range from moderate for minimum temperatures (r = 0.58) to very weak for maximum temperatures (r = 0.17).  There is little evidence of CO2 contributing to more extreme temperatures in this data.

       California Climate Division 3:

Great Basin of NE California, Nevada, & Utah

                 Precipitation Data

Div 3 prcp.jpg

The aggregate data for Cedarville, Susanville, and Tahoe City show a nonsignificant decline in annual precipitation in this region of about 0.6 inches over the last century.  The correlation of this decline with rising CO2, while negative, as expected for these factors heading in opposite directions, has correlation factors of r = -0.03 over the entire period of record, and -0.07 over the period from 1950 through 2017, with neither value rising even to the level of a very weak inverse correlation.  There is no evidence that precipitation in this region is correlated with rising CO2 in the atmosphere.

                     Extremes of Temperature

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The following table summarizes the extreme temperature trends in the above graph, and their correlations with the rising CO2 in the atmosphere.

extreme temp table 2.jpg

Extremes of cold temperatures have clearly decreased in this climate region 3, declining at a rate of about -0.74% per decade, since the 1900s, and at about -1.28% per decade since the 1950s.  This decrease in extreme cold shows a moderate to strong correlation with rising CO2 in the atmosphere, showing a potential cause and effect relationship, with more CO2 causing less extremes of cold.

Clearly the 1920s and 1930s showed the most extreme temperature days and heatwaves for this region of California.  Extremes of hot temperatures have trended downward over the entire period of record and since the 1950s for both the hottest hundred daily maximum temperatures, as well as for average temperatures for 3-day heat waves.  6-day heatwaves have trended down in frequency by about 0.8% per decade over the entire period of record, but over the period from the 1950s through the 2010s, ignoring the hot 1920s and 1930s, there has been a slight rise in 6-day and 9-day heatwave extremes.  The correlation with atmospheric CO2 of all four measures of extreme heat used here over the entire period of record is either a weak or very weak inverse relationship--meaning CO2 is correlated with less extreme heat.  The two exceptions to this are for the hottest hundred daily maximums, which over the period from 1950 through 2017 shows no correlation with CO2 at all, and for the hottest hundred 9-day average maximum temperatures, which very weakly correlate with rising CO2.

     Average Annual Maximum and Minimum Temperatures

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The aggregate average annual daily maximum, mean, and minimum temperatures in California climate division 3 have all trended slightly upward, at about 0.4 degrees F per century for maximums, 1.0 degrees F per century for means, and 1.6 degrees F for minimum temperatures.  Correlation factors for these changes related to CO2 are all weak or very weak.  Average minimum temperatures correlate with CO2 over the period from 1900 with r = 0.41, and since 1950 the correlation factor is r = 0.48, both in the weak correlation range.  For average maximum temperatures, the correlation factor from 1900 to 2017 is r = 0.17 (very weak) and for 1950 through 2017 it is r = 0.40 (weak).  In general, data show a weak correlation between these average temperatures and rising CO2.

California Climate Division 4: Central Coast

                           Precipitation Data

Div 4 prcp.jpg

The graph above shows a trend toward decreased precipitation of about -8.4 inches over the last century in aggregate for these three Central Coast locations.  The correlation factor for precipitation with atmospheric CO2 has a value of r = -0.4 both for the period from 1909 to 2017 and for 1950 to 2017, indicating a weak inverse correlation.  There as a possibility that a weak cause and effect relationship could exist between rising CO2 and falling precipitation in this region.

                      Extreme Temperatures

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The table below summarizes the trends and correlations between extreme temperatures and atmospheric CO2 illustrated in the graph above.

Div 4 extreme temp table.jpg

Extremes of daily minimum cold temperatures decreased (-0.85% per decade) in this climate region, as is true in the rest of California.  The correlation factor between these decreased daily minimums and rising CO2 is r = -0.43, in the range of a weak inverse correlation over the entire period since 1909, and there is no correlation over the period from 1950 to 2017. 

The trend in extremes of heat events increases about 1 percent per decade since the 1900s, with the rate of increase dropping somewhat (to between 0.70 and 0.41%) over the period from 1950 to 2017.  The correlation coefficient between the rise in extreme heat and heatwaves range from r = 0.80 (strong correlation) to r = 0.55 (moderate correlation) during the entire period of record, from the 1900s through 2017.  Interestingly, the correlation weakens (ranging from r = 0.77 to r = 0.15, or strong to very weak correlation) during the period when the rate of CO2 increase in the atmosphere is significantly accelerating, from 1950 through 2017.  This weakening casts some doubt on the likelyhood that the correlation represents a cause and effect relationship between rising CO2 and rising numbers of extreme heat events.

      Aggregate Average Annual Temperatures

Div 4 Ave Tmin max.jpg

The graph above illustrates the rise in aggregate average daily minimum, mean, and maximum temperatures.  Daily minimums have risen about 1.7 F over the last century, and maximums have risen about 3.0 F over that period.  These changes have correlation factors with rising CO2 of  r = 0.38 (weak correlation) for minimum temperatures, and r = 0.52 (moderate correlation) with maximum temperatures.  The degree of correlation over the period of accelerating CO2 in the atmosphere from 1950 to 2017 is unchanged from 0.38 (weak correlation) for minimum temperatures, but decreases a bit to r = 0.46 (weak correlation) for maximum temperatures.  The weak to moderate correlation between average minimum and average maximum temperatures in this Central Coast climate region allows (but does not prove of course) a possible weak cause and effect relationship between CO2 and temperatures based on this data.

          California Climate Division 4:

             The San Joaquin Valley

Precipitation Data

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This graph of aggregate precipitation in the San Joaquin Valley region shows a rising trend in annual precipitation of about 1.9 inches per century, with the trend increasing to 2.6 inches per century over the period from 1950 to the present.

When the correlation between rising precipitation and rising CO2 in the atmosphere is tested, a very weak correlation (r = 0.10) is found over the entire period from 1914 through 2017, and no correlation is seen (r = 0.08) over the post 1950 period.

       Temperature Extremes in California Climate Division 5

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The above graph shows the percent distribution of extreme cold and heat events in the southern part of California's central valley.  Major trends apparent are tabulated below.

div 5 extreme temps table.jpg

Extreme cold minimum temperatures have decreased by -1.39% per decade since 1914, and by -1.55% since 1950.  A strong inverse correlation between extreme cold and CO2 is apparent, leading to the possibility that rising CO2 has caused less extremes of cold.

Extremes of heat have decreased as well for all four measures tested here, by more than 1 degree F over the entire period of record.  The decrease since 1950 is smaller in magnitude for the distribution of the hottest hundred daily maximum temperatures and the hottest hundred 3-day heatwaves.  For 6-day and 9-day heatwaves since 1950 they have risen in distribution about 0.2 and 0.3% per decade respectively.  When the correlation between distribution of heat events and CO2 is tested over the entire period of record, only a weak inverse correlation is indicated, and since 1950 the correlation is very weak to none.  No convincing evidence is seen in this data that increased extreme heat events are resulting from rising carbon dioxide.

      Annual Average Maximum and Minimum Temperatures

                    in California Climate Division 5

div 5 Tmax min mean.jpg

The graph above illustrates the changes in aggregate average maximum, mean, and minimum temperatures in these four data sets from California Climate Division 5.  Average daily maximum temperatures have risen about 1.06 F per century, and average minimum temperatures have risen about 4.45 F per century since 1914.  These rates of rise have increased in the period since 1950 to 3.0 F and 5.8 F per century.  When the correlation of these rises in temperature is tested relative to rising CO2, a strong correlation is seen to rising minimum temperatures (r = 0.76 over the period 1914-2017, and r = 0.80 post 1950), but the correlation with rising average maximum temperatures is weak (r= 0.33 from 1914 to 2017, and r = 0.44 from 1950 to 2017).

     California Climate Division 6: South Coast

                     Precipitation Data

Div 6 prcp.jpg

The trend in the graph above shows aggregate average precipitation decreasing at a rate of -4.9 inches per century over the entire period from 1910 to 2017.  The rate of decline in precipitation decreases by half to -2.5 inches per century when measured over the period from 1950 to 2017.  These decreases over both time periods is due to the data from Cuyamaca, as both Santa Barbara and Oceanside average annual precipitation has remained constant or slightly increased.

When the precipitation is correlated to CO2 in the atmosphere, over the entire period from 1910 through 2017 the correlation factor is r = -0.20, or a very weak inverse correlation.  Over the period from 1950 through 2017 the correlation factor is r = -0.09, which means no correlation.  These data do not support a hypothesis that increasing CO2 causes decreased precipitation in climate division 6.

        Extreme Temperatures in California Climate Division 6

Div 6 extreme temp graph.jpg

The data in the above graph is summarized in the table below.

Div 6 extreme temp table.jpg

The distribution of the aggregate coldest minimum temperatures in Santa Barbara, Oceanside, and Cuyamaca has trended to fewer extreme cold events over both 1900s through 2010s (at -0.53% per decade) and 1950s through 2010s (at -1.42% per decade.  The correlations of these cold events with carbon dioxide has a coefficient of r = -0.45 from 1900s through 2010s (weak inverse correlation) and r = - 0.97 for 1950s through 2010s (a strong inverse correlation).  The hypothesis that CO2 causes decreasing extreme cold events is supported (though not proven) by this correlation data.  My experience growing up down in this climate region tells me that a lot of fruit orchard growers in this area are extremely happy about this change in the climate, saving them from using exterior heaters trying to prevent their avocados, oranges, and other fruit trees from freezing.

The distribution of extreme heating events over the period from 1900s through 2010s range from a small increase in the percentage of 6-day heatwaves by about 0.045% per decade, to a decrease in the hottest 9-day heatwaves of -0.28% per decade.  During the period of accelerating concentrations of CO2 in the atmosphere, from 1950 through 2017, the percent of all four measures of extreme heat decreased between 0.1 and 0.9% per decade.  When the changes in percentages of these extreme heat events are compared to the changes in CO2, in every case an inverse correlation is seen, ranging from weak to none in strength.  No evidence of carbon dioxide causing more extreme heat is seen in these data.

   Aggregate Average Minimum and Maximum Temperatures

           in California Climate Division 6

Div 6 Tmax min mean.jpg

The trend line for rising average aggregate maximum temperatures is very nearly flat, rising only 0.45 F over a century, and during the period after 1950, the trend becomes a negative 0.81 F per century.  For minimum temperatures the rise is a bit more, at 2.6 F per century over the entire period of record, and increases to 6.1 F increase per century in the period after 1950.  Tests of the correlation between rising average maximums and rising CO2 show no correlation (r = 0.056) between maximum temperatures and CO2 over the entire period of record, and a very weak inverse correlation (r = -0.11) from 1950 through 2017.  The correlation with minimum temperatures is moderate (r = 0.65) over the entire period of record, and strong (r = 0.74) in the period from 1950 through 2017.  A hypothesis that CO2 raises average minimum temperatures is strongly supported by these data, but a hypothesis that CO2 raises average maximum temperatures in this region is refuted by the data.  If anything, CO2 seems to moderate temperatures, both hot and cold.

    California Climate Division 7: the SW Deserts

Precipitation Data

Div 7 prcp.jpg

The above graph of aggregate annual precipitation in California Climate Division 7 shows a trend of slightly increasing precipitation in the region, rising about 0.14 inches per century between 1921 and 2017 in this desert region.  The increase in precipitation is even more pronounced over the period from 1950 to 2017, with the amount of precipitation rising about 0.94 inches per century.  Testing the correlation between rising precipitation and rising CO2 gives a correlation factor r = 0.0009 (no correlation) over the period from 1921 to 2017, and r = 0.025 (also no correlation) over the period 1950 to 2017.  There is no evidence of increasing CO2 in the atmosphere affecting precipitation in this desert region at all.

Extreme Temperatures in California's Deserts

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Trends and correlations of the extreme temperature measures illustrated in the graph above are shown in the table below.

Div 7 extreme temp table.jpg

The trend in extremely cold days has been toward fewer of the coldest minimum temperatures over time, decreasing by -0.57% per decade since the 1910s, but decreasing half as much, at -0.27% per decade since 1950.   The correlation factors with rising CO2 are r = -0.44 (weak inverse correlation) since the 1910s, and r = -0.36 (also weak inverse correlation) since 1950.  These weak correlations allow at most for only a weak cause and effect relationship between CO2 and less extreme cold.

In all of California the evidence for a strong correlation between rising CO2 and increased extremes of temperature is strongest in this climate region.  Trends for rising 1-day, 3-day, 6-day, and 9-day temperature extremes are evident, ranging from a rate of 0.89% increase per decade for individual days among the hottest hundred, up to 3.79% increases per decade for 9-day heatwaves.   Correlation factors for these extreme temperatures with CO2  range from r = 0.85 to r = 0.96, all quite strong correlations.  While these correlation factors do not prove a cause and effect relationship, they do strongly support the possibility.  The fact that the other California climate divisions tend to give just the opposite result gives reason to doubt a blanket statement that CO2 is causing more extremes of heat in the state.

Average Maximum, Minimum, and Mean Annual Temperatures

            in California Climate Division 7, the SE Deserts

Div 7 Tmax min mean.jpg

Agggregate average temperature trends in climate division 7 trend upward about 3.75 F per century for minimum temperatures, and about 1.62 F per century for maximum temperatures.  These trends are even stronger over the period from 1950 through 2017, with rates of increase of 5.48 F per century and 2.42 F per century respectively.  The correlation factors between these rising temperatures and rising CO2 are r = 0.76 (strong correlation) for minimum temperatures, and r = 0.42 (weak correlation) for maximum temperatures over the entire period of record, values that are virtually the same for the period of 1950 through 2017.  A good case can be made for CO2 causing rising daily minimum temperatures, but the case for causing rising maximum temperatures is weak.

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