California 27 Weather Stations

27 California weather stations are investigated, with the goal of testing the hypothesis that rising CO2 in the atmosphere is causing decreased precipitation (increased drought), and increased incidences of extreme heat. Alphabetically, the stations are located in: Brawley Cedarville

Colfax Cuyamaca

Davis Eureka

Fairmont Friant

Hetch Hetchy Independence

Lindsay McCloud

Oceanside Orland

Orleans Mecca

Needles Newman

Pinnacles N.M. Quincy

San Luis Obispo Santa Barbara

Susanville Tahoe City

Trona Ukiah

Watsonville

These 27 stations were chosen based on geographic spread throughout the state, representation of the seven climate divisions in the state, relatively longterm and complete weather records, quality of station site, and less urbanization.

Pearson correlation coefficients, r, were determined to test the degree of correlation between precipitation data and atmospheric carbon dioxide, as well as between temperature data and carbon dioxide. Pearson correlation coefficients range between -1 (perfect inverse correlation) and +1 (perfect direct correlation), with 0 showing no correlation. The following scale was used to identify degrees of correlation.

Inverse correlations, r is negative Direct correlations, r is positive

r values: -1.0 < -0.7 < -0.5 < -0.3 < -0.1 0 0.1 < 0.3 < 0.5 < 0.7 < 1.0

Summary: In Brawley there is a moderate inverse correlation between incidences of extreme cold and rising CO2 in the atmosphere, but this is the only correlation that is suggested by the data. Correlations with measures of extreme heat or heatwaves, average annual minimum temperatures, average annual maximum temperatures, or annual precipitation are all very weak to none. Evidence supporting a hypothesis that carbon dioxide causes more extreme heat or changes in the amount of rainfall is not found.

Summary: There is no evidence in the data for Cedarville of a correlation between CO2 and precipitation, or between CO2 and average minimum or maximum temperatures. There is at most a weak inverse correlation between CO2 and extremes of cold, and an even weaker inverse correlation between CO2 and extremes of heat.

No evidence is seen in the Cedarville data for CO2 causing more extreme heat or drought.

Summary: Colfax shows a 10 to 20% increase in extreme hot temperatures over the last century, although the hottest daily maximum and heatwave temperatures occured mostly in the 1970s. These increases in the percentages of extreme hot temperatures are moderately to strongly correlated with the rise in CO2 in the atmosphere. In contrast, the average maximum and minimum temperatures over the century are not even moderately correlated with CO2, and annual precipitation has increased slightly, but is not correlated with rising CO2. Colfax data do support the hypothesis that CO2 either causes increases in episodes of extreme heat, or possibly both the rising CO2 and episodes of extreme heat respond to the same outside climate factor. No evidence for decreased precipitation is observed.

Summary: Decreasing precipitation in Cuyamaca weakly correlates with increased CO2 in the atmosphere. Extreme heat temperature events correlate only very weakly or not at all with the rise in CO2, with the 1920s experiencing the most extreme temperature events. However, there is a weak correlation with decreased cold temperature events. Average annual maximum temperatures correlate with CO2 weakly, while average annual minimum temperatures correlate very weakly.

There is only weak evidence in Cuyamaca data for CO2 causing increased drought or extremes of temperature.

Summary: Precipitation in Davis has trended toward an increase of about 0.19 inches per decade, which very weakly correlates with rising CO2. Extreme temperatures of both heat and cold have tended to decrease in Davis between 1 and 2% per decade over the past century, with only a very weak inverse correlation with rising CO2.

Average annual daily maximum temperatures have essentially not changed since records have began to be kept in 1907, while average daily minimum temperatures have trended upward about 0.4 degrees Fahrenheit per decade. Minimum temperatures correlate moderately with rising CO2, while maximum temperatures correlate at most only weakly.

The data show that precipitation has increased in Davis, rather than more drought, and that extreme temperatures have also decreased. CO2 does not correlate with either extreme temperatures or drought in Davis.

Summary: Precipitation in Eureka trends downward about 1.4 inches per century, from about 40 inches in the 1880s to about 38.5 inches in recent years, but this change shows no correlation to the amount of CO2 in the atmosphere.

There has been a significant increase in events of what passes for extreme heat in Eureka, with the percentage of days among the hottest hundred individual days as well as the hottest heatwaves increasing strongly in the recent decades. These changes correlate moderately to strongly with rising CO2 in the atmosphere. However, an extreme heat day in Eureka has a temperature in the 80s Fahrenheit, with the record hottest maximum temperature ever there at 87 degrees. For most Californians, the idea that these are extreme temperatures is a bit ludicrous.

For extreme cold, there is only a very slight rising trend, increasing about 0.5 degrees Fahrenheit per century. This climate change shows no correlation to rising CO2.

Record heat events (comparatively not very extreme though) do correlate with rising CO2 in Cuyamaca's data, supporting the possibility of a cause and effect relationship. No correlation is seen between CO2 and precipitation.

Summary: The trend for precipitation in Fairmont is flat, with no significant change over the past 110 years. There is no correlation between CO2 and precipitation seen in the data.

The number of days of extreme cold have declined in Fairmont, showing a weak correlation with rising CO2.

The number of days of extreme heat have also declined between -0.1 and -0.6% per decade in Fairmont for one day, three day, and six day periods, showing very weak to no correlation with rising CO2. Nine day heatwave incidents, however, have increased by 1.4% per decade, and show a moderately strong correlation with rising CO2 (r=0.697). Annual average maximum temperatures have similarly increased, by about 2.5 degrees Fahrenheit over the last century, correlating moderately with rising CO2 (r=0.56). Average minimum temperatures have increased as well, though not at much, only about 1.2 degrees F over the century, correlating weakly with rising CO2 (r=0.36).

Moderate support for CO2 causing increased extreme heat is seen in Fairmont data, but no support for decreased precipitation is seen.

Friant percent distribution coldest minimum, hottest maximum, and

Note: no data available for the 1920s in the above graph.

Summary: Precipitation in Friant has trended neither up nor down, but remained flat. It shows no correlation with changing CO2 in the atmosphere.

The distribution of the hundred coldest minimums, hottest maximums, and hottest heatwaves show that extreme temperature events of all types in Friant have decreased, between -0.33 and -2.4 percent per decade. Any correlation between extreme temperatures and CO2 is an inverse one.

Average annual maximum and minimum temperatures have increased, by 0.7 F per century for maximums, and by 2.4 F per century for minimums. These changes do correlate with rising CO2, very weakly for maximums (r=0.21) and moderately for minimums (r=0.55).

No support for the hypothesis that CO2 causes increased drought or extreme heat is seen in Friant data.

Hetch Hetchy precipitation data show a longterm rising trend, at 3.7 inches per century, illustrating a very weak correlation with the rise in CO2.

The coldest daily minimum temperatures at Hetch Hetchy have become less common, decreasing about -21.3% over the last century, in a strong inverse correlation with rising CO2 (r = -0.74).

Similarly, incidents of the hottest daily maximum temperatures, as well as 3-day, 6-day, and 9-day heatwaves, have all decreased between 21 and 32% over the century, with moderate to strong inverse correlations with rising CO2 (r = -0.56, r = -0.55, r = -0.51, and r = -0.52, respectively).

Annual averages of daily minimums have increased about 5.2F per century, illustrating a strong correlation with rising CO2 (r = 0.78), while annual averages of daily maximum temperatures have decreased about -1.6F per century, showing a very weak inverse correlation with rising CO2 (r = -0.20).

In sum, Hetch Hetchy data give no support to the hypotheses that CO2 causes increased drought or increased extremes of temperature.

Summary: Precipitation data from Independence shows a slight increasing trend, averaging about 0.6 inches more precipitation now than a century ago. This change have no correlation (or very weak correlation, r = 0.082) with rising CO2.

Extremes of cold temperature have decreased about 16.7% in the last hundred years, exhibiting a weak inverse correlation with rising CO2 (r = - 0.49).

Incidents of extreme hot temperatures have all increased markedly in Independence, rising by about 30% on all measures over the last century. These changes correlate strongly with rising CO2 levels in the atmosphere. Both annual averages of minimum temperatures and of maximum temperatures have also increased: about 2.6 F for minimums (r = 0.56, moderate correlation with CO2) and 5.9 F for maximums (r = 0.74, strong correlation with CO2).

Independence data supports the possibility that CO2 causes increased extreme heat, but the evidence for increased drought is mixed, since more heat contributes to drought conditions, but more precipitation does just the opposite.

Summary: Precipitation data from Lindsay show a trend toward an additional 1.4 inches of precipitation over the past 100 years. There is no significant correlation between this change and rising CO2.

On every measure of extreme temperature, both cold and hot, data from Lindsay shows a decrease in temperature extremes, ranging from 10 to 25% per century. These climate changes are inversely correlated with CO2, ranging from weak to moderate correlations.

The average of annual minimum temperatures has risen by about 3.2 F per century, with a moderate correlation to CO2 (r = 0.65). Averages of annual maximum temperatures have slightly decreased at about -0.21 F per century, with no significant correlation to CO2 (r = 0.09).

There is no evidence in Lindsay's data that CO2 has caused increased extremes of temperature or increased drought.

Precipitation data for McCloud shows a -8.9 inch per annum decreasing trend over the last century, but the total precipitation there is still averaging quite high, at about 42 inches per year. The correlation of this change in precipitation with rising CO2 is very weak, (r = -0.27).

Extremes of cold temperature have decreased almost 9% over the last century, and this change correlates moderately with rising CO2 (r = -0.69).

Extremes of hot temperatures peaked during the period from 2000 to 2010, and have fallen off somewhat since then, though the overall trend in the hottest hundred maximum temperatures has been an increase of about 18% over the last century, and this change correlates strongly with rising CO2 (r = 0.77). The distribution of the hottest heatwaves in McCloud has also trended up by about 10% for 3-day, 6-day, and 9-day periods over the past century, reaching a peak during the 1980s, and falling off since then. With this early peak in the 1980s, the trend in heatwaves correlates only weakly with CO2 rise, (r = 0.24, r = 0.21, and r = 0.18 respectively).

There has been a modest trend in McCloud toward warmer average minimum and maximum temperatures, with minimums rising about 1.8 F per century, and maximums rising 2.1 F per century. These changes correlate only weakly with rising CO2, (r=0.44 for average minimum temperatures, and r =0.36 for maximums).

The precipitation data for McCloud is very weakly supportive of increased drought correlating with increased CO2, and 2014 shows the lowest annual precipitation in the entire record. The possibility of a cause and effect relationship is weakly supported by this data. Extremes of cold have clearly decreased, with a moderate correlation with rising CO2, and extremes of one-day hot temperatures have also increased showing a strong correlation with rising CO2. Heatwaves have also increased, as have average annual minimum temperatures and average annual maximum temperatures, but each of these five effects correlate only very weakly to weakly with rising CO2.

Precipitation records in Mecca over the entire period of record since 1905 show a downward trend of about -1.3 annual inches per century with a very weak inverse correlation with CO2 (r = -0.14), with some breaks in the record 1908-1913 and 1934-1940. The unbroken recordings from 1941 through 2017, however, show a increasing trend of about 1.3 annual inches per century with essentially no correlation with rising CO2 (r=0.013).

The records on percent distribution of the hundred coldest minimum, hottest maximum, and hottest heatwaves seem to show a possible discontinuity between the 1960s and the 1970s. I will look at both the entire record, as well as the record since 1970 to try to make sense of the data.

Over the entire period from 1905 through 2017, the distribution of the coldest minimum temperatures has trended upward at 13.2% per century, with a strong correlation with rising CO2 (r=0.85). However, looking at the period from 1970 through 2017, the trend is much reduced, though still increasing at 3.7% per century, and the correlation of this change with CO2 is very weak (r=0.24). The decade of the 1990s peaks with the most extremely cold days.

Over the entire 1905-2017 period, the distribution of the hundred hottest maximum temperatures by decade shows a rising trend of 15.3% per century, which strongly correlates with rising CO2 (r=0.85). As was the case with the extremely cold minimum temperatures above, the extremely hot maximum temperatures also peaks in the 1990s, and the trend from 1970 through 2017 has a much lower rate of rise, at 4.3% per century, and a very weak correlation with CO2 (r=0.24).

For heatwaves, the entire record from 1905 through 2017 shows increases of from 14 to 16% per century for durations of 3, 6, and 9 days, with moderate to strong correlations with CO2 (r=0.76, r=0.66, and r=0.80 respectively). Looking only at the period from 1970 through 2017, the number of heatwaves in the hottest hundred peaks in the 1980s for 9-day heatwaves, and in the 1990s for 3-day and 6-day heatwaves. The trend from 1970-2017 for all three heatwave durations is negative, with the changes in distribution per century of -6.9% for 3-day, -11.6% for 6-day, and -0.46% for 9-day, with inverse correlations ranging from weak to none with rising CO2 (r=-0.34, r=-0.30, and r=-0.089, respectively).

Average annual minimum temperatures over the entire period of record in Mecca have trended upward 2.3 F per century, while maximum temperatures have trended upward at 3.8 F per century, both with a moderate correlation with CO2 (r=0.64 for minimums, and r=0.59 for maximums). Over the period from 1970 through 2017, the minimum temperature trend has been much higher at 12.7 F per century and correlates strongly with CO2 (r=0.81) while the maximum temperature trend is 4.2 F per century with a weak correlation with CO2 (r=0.33).

In sum, the Mecca precipitation data do not support a hypothesis that rising CO2 causes more drought. The data on extreme temperatures and heatwaves is mixed, some supporting the hypothesis that CO2 might cause more extremes of cold, heatwaves, and possibly extremes of heat as well in Mecca. However, the most recent data during the most rapid rise in CO2 levels (1970-2017) supports those hypotheses only weakly for the case of extreme cold or hot temperatures, and does not at all support the hypothesis of more heatwaves.

Needles, CA Weather data from 7/1/1888 to the present

No significant trend is seen in the precipitation data for Needles, and no correlation with rising CO2 is seen.

Days with extreme cold minimum temperatures have decreased -15% over the last century, with a strong inverse correlation related to rising CO2 (r= -0.78).

Extremely hot daily maximums, and 3-day, 6-day, and 9-day heatwaves have all become more common in Needles between 10 and 15% over the last century. These changes correlate with CO2 rise moderately to strongly (r = 0.65, r = 0.68, r = 0.64, and r = 0.72, respectively).

Annual averages of daily minimum and maximum temperatures have also increase, minimums by about 4.0 F per century, and maximums by 2.0 F per century. These changes correlate moderately with CO2 rise, (r = 0.67 and r = 0.52).

In sum, Needles' data does not support the hypothesis of increased drought due to CO2, but is supportive of the hypothesis of increased extremes of heat, but not extremes of cold.

Precipitation in Newman has trended up about 1.4 inches per century, with a very weak correlation with CO2 (r = 0.12).

Extremes of cold minimum temperatures in Newman have decreased 7.4% over the last century, with a weak inverse correlation to CO2 (r = -0.48). Extremes of hot maximum temperatures as well as heatwave average temperatures have also decreased by small amounts, less than 7% per century, with very weak to no correlation with CO2 ( daily Tmax has r = 0.036, 3-day heatwaves have r = 0.053, 3-day heatwaves have r = 0.13, 9-day heatwaves have r = 0.26).

Annual averages of daily minimum temperatures have risen 2.3 F per century while averages of daily maximums rose 1.6 F per century, both with weak correlations to CO2 ( r = 0.40 and r = 0.39)

In sum, there is no evidence for increased drought or extremes of hot temperatures in Newman correlating with rising CO2. There is an inverse correlation of CO2 with extremes of cold, and a weak direct correlation between CO2 and rising average minimum and maximum temperatures.

Precipitation in Oceanside has trended downward slightly at about -0.66 inches per century. This trend has no correlation with the rise in CO2, (r = -0.042).

There is a strong inverse correlation between CO2 and extremes of cold temperatures in Oceanside (r = -0.82), meaning that if CO2 is causing this effect, it is reducing extreme cold weather events. The agricultural growers of the area are happy about this climate change, as freezes in San Diego County can be very damaging to their crops.

There are only small changes in events of extreme heat over one, three, six, and nine day periods. These changes range from a 5.2% increase in the distribution of the hottest hundred days over the last century, to a 8.2% decrease in the distribution of 9-day heatwaves over the same period. Any correlation between these changes in the distribution of extreme heat events is found to be a weak inverse one, showing, if anything, that rising CO2 decreases the number of high temperature events (r values of -0.14, -0.29, -0.15, and -0.35).

Oceanside's average annual minimum temperatures have trended upward 3.1 degrees Fahrenheit per century, with a moderate correlation with rising CO2, (r = 0.63). At the same time average annual maximum temperatures have trended downward about 0.89 F per century, inversely correlating very weakly with the rising CO2 in the atmosphere, (r = -0.25). Temperatures in Oceanside have moderated, rather than tending toward the more extreme.

In sum, there is no evidence in the data from Oceanside supporting the hypotheses that CO2 increases either drought or extremes of temperature.

Orland rainfall has tended to increase about 4.1 inches per century, a change that correlates only weakly with rising CO2.

The distribution of extreme cold temperatures has shown a small increasing trend since 1903 at +2.5% per century, with a very weak inverse correlation with CO2 (r = -0.16). During the post-1950s time period when CO2 is rising most rapidly, however, the trend has been toward a lower percentage of days in the coldest hundred, as is generally true throughout California.

All of the measures of extreme heat--distribution of the single hottest hundred days, and hottest 3-day, 6-day, and 9-day heatwaves--have all trended downward between about 14 and 27%. All of these trends show a moderate inverse correlation with rising CO2, meaning that if there is any cause and effect relationship, that CO2 is causing incidents of extreme heat to decrease in Orland.

Annual averages of the daily minimum temperatures in Orland have risen slightly, at a rate of about 0.8 F per year, which weakly correlates with rising CO2 (r = 0.38). Annual averages of daily maximum temperatures have trended slightly downward at -0.6 F per century, a change that does not correlate with rising CO2 (r = 0.012).

In sum, increasing rainfall and decreasing hot temperatures in Orland do not support the hypothesis that rising CO2 is causing increased drought or extremes of heat.

Precipitation in Orleans has trended slightly upward, averaging about 2.6 inches per century to the recent average of near 52 inches per annum. No correlation with precipitation is seen relative to rising CO2 (r = 0.018).

Extremes of cold temperature have tended to increase slightly, by about 0.9% over the last century, largely due to a state wide cold snap early in the 1990s. This change, however, only very weakly correlates inversely with rising CO2 (r = -0.18).

Extremes of hot temperatures in Orleans have decreased markedly over the last century, with hot events over one, three, six, and nine day periods falling by nearly 40% per century. These changes inversely correlate with rising CO2 with moderate strength of inverse correlation (r = -0.57, -0.54, -0.50, and -0.49 respectively).

Average annual minimum temperatures have increased about 0.6 F per century, with a weak correlation with rising CO2 (r = 0.31). Average annual maximum temperatures have decreased by about -2.6 F per century, showing a weak inverse correlation with rising CO2 (r = -0.29).

In sum, no convincing evidence of increased drought or extremes of heat or cold is found in the data for Orleans.

Precipitation data from Pinnacles National Monument on California's central coast range show a declining trend in rainfall from an average close to 17 inches in the late 1930s and the 1940s to nearer 15 inches in recent years. This precipitation trend shows a very weak correlation with rising CO2 (r = -0.10). One must conclude there is very weak evidence for a possible cause and effect between rising CO2 and increased drought there.

Extremes of cold at Pinnacles NM trend upward, with about 5.4% more extreme cold incidents recently--particularly in the decade of the 2000s--than from the years including and following 1937. There is a weak correlation between this climate change and rising CO2 (r = 0.41).

Extremes of hot temperatures at Pinnacles trend upward between 4 and 10% per century, largely due to high percentages of the hottest days and heatwaves clustered in the 1950s and expecially the 1960s. But because of the hot cluster in the 1950s and 1960s, and the relatively lower incidences in the 2010s, the correlation between extreme heat and CO2 has been a moderate to weak inverse one. Evidence for CO2 being the causative agent is absent, unless CO2 is causing fewer incidents of extreme heat.

Annual average minimum temperatures have trended downward at about -2.6 F degrees per century, showing a weak inverse correlation with CO2 (r = -0.32). Annual average maximum temperatures have trended upward at 2.1 F degrees per century, weakly correlating with rising CO2 (r = 0.33).

In sum, Pinnacles National Monument data correlations with CO2 show very weak evidence for possible causation of increased drought, weak evidence for possible causation of more extremes of cold, weak to moderate evidence for possible causation of less incidents of extreme heat, and weak evidence for causing declining average minimum temperatures and rising average maximum temperatures, while daily temperature means have remained pretty flat.

Quincy's annual precipitation has trended down over the last century, decreasing about 2.5 inches per year to a recent average around 38 inches per annum. This change does not correlate with rising CO2, though (r = -0.019).

The change in the distribution of the coldest minimum daily temperatures in Quincy has been downward at -11.2% per century, with an inverse correlation with CO2 of moderate strength (r = -0.56).

The percentage of hottest hundred individual maximum temperatures, as well as the hottest 3-day, 6-day, and 9-day heat waves have all increased between 9 and 12% over the last century, but this increase correlates only very weakly to weakly with rising CO2, (r values of 0.34, 0.30, 0.20, and 0.14 respectively).

In sum, the only climate change that correlates even moderately with rising CO2 in Quincy is the decrease in extremely cold temperatures. Evidence for CO2 causing drought is not seen, and for CO2 causing extreme heat the evidence is only weak at best.

Data from San Luis Obispo show declining precipitation over the last century at -1.8 inches per annum, to a recent average around 21 inches a year. The Pearson correlation coefficent for this decline compared to CO2 is near zero, so basically no correlation is seen between these two changes (r = -0.09).

Incidents of extreme cold have also declined there, about -6.9% per century. There is moderate confidence that this change correlates with rising CO2 (r = -0.56). However, the peak of extreme cold temperatures occured in the 1970s rather than in recent decades.

Incidents of the hundred hottest daily maximum temperatures have peaked in the current decade of the 2010s. The trend toward incidents of increased extreme daily maximums above 101 degrees Fahrenheit has trended upward about 11.1% over the last century, and this change strongly correlates with rising CO2 (r = 0.71). The hottest heatwaves have also trended upward, between 7 and 11% per century, but these changes correlate only weakly with rising CO2 (r = 0.39, 0.38, and 0.30 for 3-day, 6-day, and 9-day heatwaves, respectively). Peak percentages of heatwaves are clustered in the 1970s and 1980s.

Both average daily minimum temperatures, and average daily maximum temperatures in San Luis Obispo have trended upward: +1.4 F per century for minimums, and +2.7 F per century for maximums. These changes weakly correlate with rising CO2, (r = 0.40 and 0.42 respectively).

In sum, although there is no evidence for less precipitation correlated with rising CO2 in San Luis Obispo, there is moderate to strong support for CO2-caused decreases in the number of days of extreme cold, and increases in the number of days of extreme heat. There is only weak support for CO2-caused increases in heatwaves.

The precipitation data for Santa Barbara is flat, showing no statistically significant trend either up or down, and exhibits no correlation with rising CO2 (r = -0.002).

The distribution of the coldest minimum temperatures in Santa Barbara has trended downward at -8.3% per century, giving a weak inverse correlation with CO2 (r = -0.35). The distribution of the hottest hundred maximum temperatures, as well as of the hottest hundred heatwaves, have likewise trended downward between -2 and -3% per century, showing either no correlation with rising CO2, or a very weak inverse correlation (r = -0.17 for individual daily maximum temperatures, and for 3-day, 6-day, and 9-day heatwaves r values of -0.12, -0.06, and -0.10).

Trends for average annual minimum temperatures have risen at about 3.8 F per century, a trend correlating strongly with rising CO2 (r = 0.74). Average annual maximum temperatures have risen only slightly, at 0.4 degrees Fahrenheit per century, and does not show a significant correlation with CO2 (r = 0.06).

In sum, data for Santa Barbara gives no support for hypothesized increased extremes of temperature or decreased precipitation caused by rising CO2 in the atmosphere. There is a weak correlation between decreased incidents of extreme cold and CO2, as well as a weak correlation between rising average minimum temperatures and CO2. Temperatures in Santa Barbara have moderated, not become more extreme.

Precipitation in Susanville has strongly trended downward, about -6.3 inches per century since 1893, a trend showing a weak inverse correlation with rising CO2 (r = -0.32). Rather than accelerating during the accelerating rise in CO2 since 1950, this trend has decreased, becoming -4.6 inches per century with a very weak inverse correlation with CO2 (r = -0.18).

Incidents of extreme cold in Susanville have decreased -5.0% per century, with a weak inverse correlation to rising CO2 (r = -0.42). Incidents of on day extreme heat, and extreme heatwaves have also decreased, between 3 and 8% per century, weakly correlating inversely with rising CO2 ( r = -0.31, r = -0.34, r = -0.32, and r = -0.32 for one day, 3-day, 6-day, and 9-day events, respectively).

Annual average daily minimum temperatures have slightly decreased, about -0.5 F per century in this cool, northern, high altitude region of the state, where about 35 F minimums are typical averaged over the year. This trend correlates very weakly with rising CO2 (r = 0.11). Annual average maximums have risen at 1.3 F per century, to typical daily maximums near 65 F, also correlating very weakly with CO2 (r = 0.19).

In sum, Susanville is in a part of California which does show a trend toward less precipitation and thus more drought, and this climate change does show a very weak correlation with rising CO2. Incidents of both extreme cold and extreme heat have declined with the changing climate there, exhibiting a weak inverse correlation with rising CO2. Average minimum temperatures have, however, trended slightly cooler, and average maximums have trended a bit warmer as well.

Precipitation in Tahoe City has increased at a rate of 3.6 inches per century since 1909, showing no correlation to rising CO2 in the atmosphere (r = 0.08). Recently about 33 inches per year is the average.

Incidents of extreme cold have declined about -11.4% per century in Tahoe City, inversely correlating weakly with CO2 (r = -0.48). Incidents of extreme heat have also declined between -5 and -9% for individual days and for heatwaves, showing very weak inverse correlations with rising CO2 (r = -0.17, r = -0.22, r = -0.17, and r = -0.17 for 1-day, 3-day, 6-day, and 9-day events).

Tahoe City's average minimum and maximum temperatures have both risen, up 3.9 F per century for minimums and up 2.0
F per century for maximums, averaging year-round about 30 F (minimums) and 56 F (maximums) in recent years. These changes correlate moderately with rising CO2 for minimums, (r = 0.68) and correlate weakly with maximums (r = 0.45).

In sum, there is no evidence in the precipitation and temperature data for Tahoe City either for increased drought or for increased extremes of temperature caused by rising CO2. Carbon dioxide correlates with increasing rainfall and moderating temperatures, if at all.

Trona rarely gets much precipitation, averaging 3 or 4 inches per year, but the trend in the data shows a decrease of about -0.85 inches per century, which correlates weakly and inversely with rising CO2 (r = -0.11). Looking at the data since 1950, however, when the rate of rise in atmospheric CO2 accelerated, the change in precipitation is an insignificant -0.03 inches per century, with essentially no correlation with the change in CO2 concentration (r = -0.04).

Days of extreme cold in Trona have decreased about -7.8% per century, with a weak inverse correlation to rising CO2 (r = -0.41). Days of extreme heat have also decreased from peak numbers in the 1940s and 1950s, but only slightly, at about -0.5% per year, with no correlation with CO2 (r = -0.001). However, the numbers of hottest heatwaves have generally increased in Trona by between 3 and 11% for 3-day, 6-day, and 9-day heatwaves, with very weak to weak correlations to the rise in CO2 (r = 0.23 for 3-day, r = 0.48 for both 6-day and 9-day heatwaves). Both 6-day and 9-day heatwave events have peaked in the current decade of the 2010s.

Average minimum temperatures in Trona have risen 7.7 F degrees per century, moderately correlating with rising CO2 (r = 0.60), while average maximum temperatures have slightly fallen at -1.3 F per century. Correlation between dropping average maximum temperatures and rising CO2 is very weak and inverse (r = -0.16).

In sum, Trona data do not support the hypotheses that rising CO2 causes increased drought or increased days of extreme cold or heat, but there is some support for a hypothesis linking rising CO2 with more hot heatwave events. However, CO2 also correlates very weakly with decreasing average maximum temperatures, as well, so the data are mixed on this question.

Ukiah precipitation data show annual rainfall of about 38 inches per year decreasing by -0.43 inches per century, a change that does not correlate with rising CO2 (r = -0.03).

Extreme cold days in Ukiah have decreased 11.6% per century, showing a moderate inverse correlation with rising CO2 (r = -0.58). Individual days of extreme heat as well as 3-day, 6-day, and 9-day heatwaves have all decreased as well, by about -3 or -4% per century, showing weak inverse correlations with rising CO2 (r = -0.36, r = -0.40, r = -0.44, and r = -0.35, respectively).

Both annual averages of minimum and of maximum temperatures have risen, minimums by 4.1 F degrees per century, and maximums by 0.24 F degrees per century. The rise in minimums correlates moderately with rising CO2 (r = 0.67), but the rise in maximums does not correlate with CO2 (r = -0.09).

In sum, Ukiah data do not support a hypothesis that CO2 causes either decreased precipitation or increased extremes of temperature.

Precipitation in Watsonville has trended upward, increasing about 2.6 inches per century, with only a very weak correlation to rising CO2 (r = 0.11).

Incidents of extreme cold in Watsonville have decreased about 25% over the last century, a change that weakly correlates with rising CO2 (r = 0.46). Incidents of extreme heat have increased from 10 to 15% per century for individual hot days, as well as heatwaves. These changes correlate moderately to weakly with CO2, (r = 0.67 for individual days, and r = 0.65, r = 0.62, and r = 0.47 for 3-day, 6-day, and 9-day heatwaves, respectively).

Annual average minimum temperatures have trended upward about 5 F degrees per century, correlating moderately with rising CO2 (r = 0.59), however annual average maximum temperatures have been flat, decreasing slightly at -0.05 F degrees over the last century, a trend that only very weakly correlates with CO2 (r = 0.15).

In sum, while Watsonville data does not support a hypothesis that rising CO2 causes decreased precipitation, contributing to drought, it does weakly to moderately support a hypothesis that rising CO2 causes decreased incidents of extreme cold and increased incidents of extreme heat.