The Norwegian island of Jan Mayen lies in the Arctic Circle approximately 600 km northeast of Iceland, 500 km east of Greenland and almost 1000 km from the coast of Norway. It is just over 50 km long and is inhabited only by a few Norwegian military and meteorological personnel on six month deployments. It does, though, have two weather stations (BE ID: 16234 and BE ID: 157312 with 735 and 1113 months of data respectively) that provide the only temperature data for over 500 km in all directions (see Fig. 122.1 below).
Fig. 122.1: The (approximate) locations of the two longest weather station records in Jan Mayen. Those stations with a high warming trend between 1911 and 2010 are marked in red while those with a cooling or stable trend are marked in blue.
The mean temperature anomaly (MTA) for Jan Mayen is shown in Fig. 122.1 below. From 1920 to 1990 the temperature trend is downward with temperatures falling by about 0.7°C according to the best fit line (red line) or 1.5°C according to the 5-year moving average (yellow line). After 1990 the temperature increases by up to 2°C. Both of these changes are less than the natural variation seen in the 5-year average (yellow curve) so it is impossible to definitively attribute them to climate change.
Fig. 122.2: The mean temperature change for Jan Mayen since 1920 relative to the 1971-2000 monthly averages. The best fit is applied to the monthly mean data from 1921 to 2000 and has a negative gradient of -0.93 ± 0.25 °C per century.
The MTA in Fig. 122.2 is the average of anomaly data from two stations (see Fig. 122.3 below) and was determined using the usual method as outlined in Post 47. The anomalies were determined relative to monthly reference temperatures (MRT) with the MRTs calculated using data from 1971-2000.
Fig. 122.3: The number of station records included each month in the mean temperature anomaly (MTA) trend for Jan Mayen in Fig. 122.2.
Repeating the averaging process using data that has been adjusted by Berkeley Earth (BE) yields the temperature curve shown in Fig. 122.4 below. In this case the 10-year average (orange curve) is broadly similar in shape to the yellow curve in Fig. 122.2, but the temperature fall before 1990 and the rise after are both slightly larger. In both cases, however, the temperatures in 2010 are less than 0.5°C higher than in 1930.
Fig. 122.4: Temperature trends for Jan Mayen based on Berkeley Earth adjusted data. The best fit linear trend line (in red) is for the period 1921-2000 and has a negative gradient of -1.04 ± 0.11°C/century.
The similarity in the two sets of data (Fig. 122.2 and Fig. 122.4) is reflected in the scale of the adjustments made to the original data by Berkeley Earth. The magnitudes of these adjustments are shown graphically in Fig. 122.5 below. The blue curve is the difference in MTA values between adjusted (Fig. 122.4) and unadjusted data (Fig. 122.2), while the orange curve is the contribution to those adjustments arising solely from breakpoint adjustments. In this case neither are particularly large, with data after 1950 being adjusted down by about 0.18°C. The only significant adjustment is for data between 1960 and 1976 which is adjusted upwards by about 0.9°C. The effect of this is to reduce the size of the temperature dip before 1970 seen in Fig. 122.2.
Fig. 122.5: The contribution of Berkeley Earth (BE) adjustments to the anomaly data in Fig. 122.4 after smoothing with a 12-month moving average. The blue curve represents the total BE adjustments including those from homogenization. The linear best fit (red line) to these adjustments for the period 1921-2000 has a slight negative gradient of -0.07 ± 0.04 °C per century. The orange curve shows the contribution just from breakpoint adjustments.
Summary
According to the raw unadjusted temperature data, the climate of Jan Mayen has remained fairly stable since 1930 (see Fig. 122.2).
Over the same period adjusted temperature data from Berkeley Earth appears to show similar climate variations (see Fig. 122.5).
The patterns seen in the temperature data for Jan Mayen in Fig. 122.2 (decline before 1990 and warming after) are similar to those seen previously for nearby islands of Greenland (Fig. 119.1 in Post 119), Iceland (Fig. 120.1 in Post 120) and the Faroes (Fig. 121.1 in Post 121).
Acronyms
BE = Berkeley Earth.
MRT = monthly reference temperature (see Post 47).
MTA = mean temperature anomaly.
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