Mauna Loa and Mount Washington Updated through 2021
Below are updated graphs based on temperature measurements from the Mauna Loa and Mount Washington Observatories. More detailed information about the observatories was provided in the original posts:
Mauna Loa Temperature Trend – 2016 February 24
Mount Washington Temperature Trend – 2016 February 16
Mauna Loa Temperature Trends
There are three different temperature measurement sites at the Mauna Loa Observatory. The longest running is the US Historical Climate Network (HCN) site with measurements back to 1955. The HCN site only measures daily maximum and minimum temperatures and since September 1992 only operates on federal work days (no weekends or holidays). Since inception, the HCN site has been moved to several different locations at the observatory, which could affect measurement representativeness and continuity. The next longest record is from the National Center for Atmospheric Research (NCAR) site with continuous measurements that are reported as hourly averages since 1977. Most recently in 2006 a US Climate Reference Network (CRN) site was added at the observatory and it reports daily minimum and maximum temperatures as well as 5-minute and hourly averages. For the graphs below, the daily maximum and minimum temperatures were used to compile daily, monthly, and annual averages. For NCAR, the daily maximum and minimum were based on hourly averages.
Below is a graph of the annual temperature averages from all three of the sites. It is not clear why they diverge suddenly in 2011. The last HCN site move was in 2009 and the other two sites have not moved. The HCN site moves occurred in 1956 on May 1, in 1957 on November 1, in 1996 on November 20, in 2002 on July 22, and in 2009 on December 16.
Below is a look at the HCN annual temperature averages, including 5-year and 15-year running averages as well as a linear trend fit.
Notice that a linear fit to the HCN annual temperatures shows a downward trend since 1980 as shown below. If this 40-year trend persisted for 100 years (which is unlikely) it would show a decrease of -0.87C.
The NCAR annual temperature averages show an upward trend since 1977.
The CRN annual temperature averages show an upward trend since 2006.
Below are versions of the same graphs above, but using monthly averages and including running 12-month averages. The next graph shows the monthly HCN temperature averages since 1955.
The monthly HCN temperatures since 1980 also show a downward trend like the annual HCN averages.
The NCAR monthly temperature averages since 1977 show an upward trend.
And the CRN monthly averages show an upward trend since 2006.
The next graph shows monthly temperature differences between the three sites.
It’s not clear why the measurement differences suddenly decrease in 2018. There was a gap in the NCAR data in June 2018, possibly indicating an instrument change.
These differences illustrate how changing influences over time, most likely from a variety of causes, can create substantial uncertainty in trying to establish a temperature trend even from well documented and quality assured measurements.
Mount Washington Temperature Trends
The Mount Washington HCN weather station has been providing daily minimum and maximum temperature measurements since 1948. Annual averages from the weighted means of monthly averages are graphed below.
Since 1998 the temperature trend shows a slight increase.
The graph below includes 5-year and 15-year running averages along with the annual averages. Notice that the 5-year average for 2016-2020 is only 0.36C higher than the first 5-year average for 1948-1952, indicating that the overall temperature now is about the same as it was around 1950.
The next graph shows monthly HCN temperature averages since 1948, along with running 12-month averages and a linear fit. Notice that winter temperatures are much more variable from year to year than the summer peaks.
As with the annual averages, the monthly averages show a slight increase since 1998.
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