Contents:

1

Page 2:

Year 2023 global surface air temperature overview versus last 10 years

Page 3:

Year 2023 global surface air temperature overview versus year 2022

Page 4:

Comments to the Year 2023 global surface air temperature overview

Page 5:Lower troposphere temperature from satellites, updated to year 2023

Page 6:

Global surface air temperature, updated to year 2023

Page 7:

Reflections on the significance of the 2023 global annual temperature

Page 8:Comparing surface air temperatures with data from satellites at the end of 2023

Page 9:Global satellite temperature trends calculated for different periods

Page 9:Global surface air temperature trends calculated for different periods

Page 10: Troposphere and stratosphere temperatures from satellites at the end of 2022
Page 11: Sea surface temperature anomaly at the end of year 2023 and 2022
Page 12: Ocean temperatures, uppermost 1900 m, updated to December 2020
Page 13: La Niña and El Niño episodes, updated to October-December 2023
Page 14: PDO - Pacific Decadal Oscillation, updated to 2023
Page 15: AMO (Atlantic Multidecadal Oscillation) Index, updated to 2022
Page 16: Tropical storm and hurricane accumulated cyclone energy (ACE)Page 19: Arctic and Antarctic sea ice extension, updated to December 2023
Page 20: Northern Hemisphere snow cover, updated to December 2023
Page 21: Atmospheric specific humidity, updated to December 2023
Page 22: Atmospheric CO2, updated to December 2023
Page 24: Number of daily sunspots since 1900, updated to December 31, 2023
All diagrams in this newsletter as well as links to the original data are available on www.climate4you.com

Year 2023 global surface air temperature overview versus average last 10 years

2

FIGURE 1. Annual 2023 average surface air temperature compared to the annual average of the last 10 years. Green-yellow-red colours
indicate areas with higher temperature than the 10-year average, while blue colours indicate lower than average temperatures. Data
source: Remote Sensed Surface Temperature Anomaly, AIRS/Aqua L3 Monthly Standard Physical Retrieval 1-degree x 1-degree V006
(https://airs.jpl.nasa.gov/), obtained from the GISS data portal (https://data.giss.nasa.gov/gistemp/maps/index_v4.html).

Year 2023 global surface air temperature overview versus year 2022

3

FIGURE 2. 2023 annual surface air temperature compared to year 2022. Green-yellow-red colours indicate regions where the present year
was warmer than last year, while blue colours indicate regions where the present year was cooler than last year. Variations in annual
temperature from one year to the next has no tangible climatic importance but may nevertheless be interesting to study. Data source:
Remote Sensed Surface Temperature Anomaly, AIRS/Aqua L3 Monthly Standard Physical Retrieval 1-degree x 1-degree V006
(https://airs.jpl.nasa.gov/), obtained from the GISS data portal (https://data.giss.nasa.gov/gistemp/maps/index_v4.html).

Comments to the Year 2023 global surface air temperature overview
The present newsletter contains graphs showing a
selection of key meteorological variables for theyear 2023. All temperatures are given in degrees
Celsius.
In the above maps showing the geographical patternof surface air temperatures, the last previous 10
years (2013-2022) are used as reference period.
The rationale for comparing with this recent period
instead of various ‘normal’ periods defined for partsof the past century, is that such reference periods
often will be affected by past cold periods, like, e.g.,
1945-1980. Most modern comparisons with suchreference periods will inevitably appear as warm,
and it will be difficult to decide if modern
temperatures are increasing or decreasing.

4

Comparing instead with the last previous 10 years
overcomes this problem and clearer displays themodern dynamics of ongoing change. This decadal
approach also corresponds well to the usual
memory horizon for many people and is now also
adopted as reference period by other institutions,e.g., the Danish Meteorological Institute (DMI).
Traditionally, a 30 -year reference period is often
used by various meteorological institutions forcomparison purposes. However, this is a mostunfortunate time interval, as observations clearly
demonstrate that various global climate parameters(see, e.g., page 15) are influenced by periodic
changes of 60-70 years. The often used 30-yr
reference period is roughly half this period and istherefore extremely unsuited as a good referencetime interval.

The average global surface air temperature for2023.
According to the AIRS remote sensed surface
temperature anomaly the global average surface airtemperature for year 2023 was very high. The year
2023 was affected by a strong El Niño episode(Pacific Ocean, see diagrams p. 3, 11 and 13).
In the Northern Hemisphere Canada and western
Russia was characterised by annual temperatures

above the average for the last 10 years, whilenorthern Europe, Siberia, Alaska, and western USA
had annual temperatures below the 10-yr average.
Ocean wise, The North Atlantic was relatively cold
north of 15-25oN, but relatively warm west ofnorthern Africa. In the Pacific the annual surface airtemperature was relatively high around 35oN, but
cold north of this. In the Arctic, the European andSiberian sectors were relatively cold, while theCanadian and Russian sectors were relatively warm.
Near the Equator surface air temperatures weregenerally near or above the average for the previous
10 years. Especially in Pacific Ocean warm
conditions reflect the ongoing El Niño episode. See
also reflections on p.7.
In the Southern Hemisphere annual surface airtemperatures in 2023 were near or below theaverage for the previous 10 years. Especially SouthAmerica and most of southern Africa and Australia
were cool compared to the previous 10 years. Ocean
wise, temperatures were near or below the 10-yr
average, with exception of the southern parts of theSouth Atlantic, which were relatively warm.
The ocean around the Antarctic continent was
generally characterised by relatively high annual
surface air temperatures in 2023. Only the ocean
beyond parts of West Antarctic was relatively cold.
Most of the Antarctic continent was relatively cold.
Only parts of the Atlantic sector of East Antarctic
were relatively warm.
Summing up for 2023, using AIRS remote sensed
surface temperatures the global average airtemperatures were very high when seen in a long
instrumental time scale (150 years). In fact,according to all temperature databases referred toin this newsletter, the year 2023 was the warmest
year on record. In contrast, the two previous years
2021 and 2022, were influenced by a cold La Niña
episode in the Pacific Ocean. Thus, the global
surface air temperature record in 2023 continues tobe substantially influenced by oceanographic
phenomena.

Lower troposphere temperature from satellites, updated to year 2023

5

FIGURE 3. Mean annually lower troposphere temperature anomaly (thin line) since 1979 according to University of Alabamaat Huntsville, USA. The average for 1979-2008 (30 years) has been set to zero, to make comparison with other temperature
data series easy.

FIGURE 4. Mean annual lower troposphere temperature anomaly (thin line) since 1979 according to according to Remote
Sensing Systems (RSS), USA. The average for 1979-2008 (30 years) has been set to zero, to make comparison with othertemperature data series easy.

Global surface air temperature, updated to year 2023

6

FIGURE 5. Mean annual global surface air temperature (thin line) since 1850 according to according to the Hadley Centre for
Climate Prediction and Research and the University of East Anglia's Climatic Research Unit (CRU), UK. The average for 19792008 (30 years) has been set to zero.

FIGURE 6. Mean annual global surface air temperature since 1880 according to according to the National Climatic Data
Center (NCDC), USA. The average for 1979-2008 (30 years) has been set to zero, to make comparison with other temperature
data series easy.

FIGURE 7. Mean annual global surface air temperature (thin line) since 1880 according to according to the Goddard Institutefor Space Studies (GISS), at Columbia University, New York City, USA. The average for 1979-2008 (30 years) has been set tozero, to make comparison with other temperature data series easy.

7

Reflections on the significance of the 2023 global annual surface air temperature

According to the surface stations 2023 (initiating
1850 and 1880) ranks as a record warm year. Also,
according to the satellite records (since 1979) 2023
was a record warm year.
The last strong El Niño terminated during 2017.
Often a warm El Niño episode is followed by a cool
oceanographic reversal, known as La Niña, which
also will influence global air temperatures, but thentowards lower values. In fact, a La Niña episodeestablished itself in late 2017, lasting until early2018. Towards the end of 2018, however a new,moderate El Niño initiated and affected global air
temperatures toward their high average values in2019 and 2020. Towards the end of 2020, a new as
La Niña episode established itself, influencing global
air temperatures toward lower values in both 2021
and 2022. In 2023 a new and strong El Niño
established itself (Fig. 12 and 14), causing the
average global air temperature to increase. The
temperature effect of this oceanic phenomenon isclearly seen on figure 1 and 2.

El Niño and La Niña is playing near the Equator,
which explains the large effect on the average global
air temperature, also in 2023. In fact, no less than
50% of planet Earth’s surface area is located within
30oN and 30oS. In contrast to this, relative coolinghas played out during 2023 in the North Atlantic
along the main track of the Gulf Stream and theNorth Atlantic Current.
Air temperature changes do not only play out at thesurface, but also at higher levels in the atmosphere(see Fig. 11). The current CO2 hypothesis projects
that the initial temperature increase should affectthe upper Troposphere, at 6-8 km altitude.
However, since 1979 the earth's surface has
warmed faster than the upper Troposphere,
implying that the surface heating observed is notpredominantly due to added atmospheric CO2, but islargely caused by variations in other factors(insolation, cloud cover, oceans, land use, etc.).

Comparing surface air temperatures with data from satellites at the end of 2023

8

FIGURE 8. Plot showing the average of monthly global surface air temperature estimates (HadCRUT4, GISS and
NCDC) and satellite-based temperature estimates (RSS MSU and UAH MSU). The thin lines indicate the monthly
value, while the thick lines represent the simple running 37-month average, nearly corresponding to a running
3-yr average. The lower panel shows the monthly difference between surface air temperature and satellite
temperatures. As the base period differs for the different temperature estimates, they have all been normalisedby comparing to the average value of 30 years from January 1979 to December 2008.

Global satellite temperature trends calculated for different periods until end of 2023

FIGURE 9. Diagram showing the latest 5, 10, 20 and 30 yr linear annual global temperature trend, calculated as
the slope of the linear regression line through the data points, for two satellite-based temperature estimates(UAH MSU and RSS MSU).

9Global surface air temperature trends calculated for different periods until end of 2023

FIGURE 10. Diagram showing the latest 5, 10, 15, 20, 30, 50, 70 and 100-year linear annual global temperature trend,
calculated as the slope of the linear regression line through the data points, for three surface-based temperature estimates(GISS, NCDC and HadCRUT3).

Troposphere and stratosphere temperatures from satellites at the end of 2023

10

FIGURE 11. Global monthly average temperature in different according to University of Alabama at Huntsville, USA. The thinlines represent the monthly average, and the thick line the simple running 37-month average, nearly corresponding to arunning 3-year average.

Sea surface temperature anomaly at the end of year 2023 and 2022

11

FIGURE 12. Sea surface temperature anomaly in late December 2023 and 2022, upper and lower panel,
respectively. Reference period: 1977-1991. Map source: Plymouth State Weather Center.

Ocean temperatures, uppermost 1900m, updated to December 2021

12

FIGURE 13. Diagram showing average 0-1900m depth ocean temperatures in selected latitudinal bands, using
Argo-data. The thin line shows monthly values, and the stippled line shows the running 13-month average.
Source: Global Marine Argo Atlas. Please note that the Argo data series is not yet updated beyond December
2021.

La Niña and El Niño episodes, updated to October-December 2023

13

FIGURE 14. Warm (>+0.5oC) and cold (<0.5oC) episodes for the Oceanic Niño Index (ONI), defined as 3 month running meanof ERSST.v3b SST anomalies in the Niño 3.4 region (5oN-5oS, 120o-170oW)]. Base period: 1971-2000. For historical purposes
cold and warm episodes are defined when the threshold is met for a minimum of 5 consecutive over-lapping seasons.

Year 2023 was characterized by a strong El Niño episode developing in the Pacific Ocean. At the end of theyear, the index persists at high values, as shown by Figure 14 above. This diagram also shows that the previous
2015-16 El Niño is among the strongest El Niño episodes since the beginning of the record in 1950. Considering
the entire record, however, recent variations between El Niño and La Niña episodes are not unusual.

PDO - Pacific Decadal Oscillation, updated to 2023

Typical wintertime Sea Surface Temperature (colors),Sea Level Pressure (black lines) and surface wind stress(arrows) anomaly patterns during warm and cool phases of PDO.

14

FIGURE 15. Annual values of the Pacific Decadal Oscillation (PDO) according to the Joint Institute for the Study of the
Atmosphere and Ocean (JISAO), a Cooperative Institute between the National Oceanic and Atmospheric Administration andthe University of Washington. The PDO is a long-lived El Niño-like pattern of Pacific climate variability, and the data series
goes back to January 1900. The thin line indicates annual PDO values, and the thick line is the simple running 7-year average.

AMO (Atlantic Multidecadal Oscillation) Index, updated to 2022

15

FIGURE 16. Annual Atlantic Multidecadal Oscillation (AMO) detrended index values since 1856. The thin line indicates theannual values, and the thick line is the simple running 11-year average. Data source: Earth System Research Laboratory at
NOAA.

The Atlantic Multidecadal Oscillation (AMO; Fig. 40)
is a mode of variability occurring in the North
Atlantic Ocean sea surface temperature field. The
AMO is basically an index of North Atlantic Sea
surface temperatures (SST).
The AMO index appears to be correlated to air
temperatures and rainfall over much of theNorthern Hemisphere. The association appears tobe high for northeastern Brazil, African Sahel rainfall
and North American and European summer climate.
The AMO index also appears to be associated withchanges in the frequency of North American
droughts and is reflected in the frequency of severe
Atlantic hurricanes.

As one example, the AMO index may be related tothe past occurrence of major droughts in the US
Midwest and the Southwest. When the AMO is high,these droughts tend to be more frequent or
prolonged, and vice-versa for low values of AMO.
Two of the most severe droughts of the 20th century
in US occurred during the peak AMO values between
1925 and 1965: The Dust Bowl of the 1930s and the1950s droughts. On the other hand, Florida and thePacific Northwest tend to be the opposite; highAMO is here associated with relatively highprecipitation.
A Fourier-analysis (not shown here) show the AMO
record to be controlled by an about 67-year long
cycle, and to a lesser degree by a 3.5-year cycle.

Tropical storm and hurricane accumulated cyclone energy (ACE), updated to 2020
Accumulated cyclone energy (ACE) is a measure used by the National Oceanic and Atmospheric Administration(NOAA) to express the activity of individual tropical cyclones and entire tropical cyclone seasons. ACE is
calculated as the square of the wind speed every 6 hours and is then scaled by a factor of 10,000 for usability,
using a unit of 104 knots2. The ACE of a season is the sum of the ACE for each storm and considers the number,strength, and duration of all the tropical storms in the season.

16

FIGURE 17: The diagram above shows the annual global tropical storm and hurricane accumulated cyclone energy(ACE) 104 Knots2, since 1970. Data source: Maue ACE data.

The damage potential of a hurricane is proportional to the square or cube of the maximum wind speed, and thus
ACE is therefore not only a measure of tropical cyclone activity, but also a measure of the damage potential of

an individual cyclone or a season. Existing records (Fig. 17) do not suggest any abnormal cyclone activity in recent
years.
The global ACE data since 1970 display a variable pattern over time (Fig. 17), but without any clear trend, as are
the diagrams for the Northern- and Southern Hemisphere (panels in Fig. 17). A Fourier analysis (not shown here)
shows a significant period of about 3.6 year in the ACE data, and furthermore suggests the existence of a 11.5year period, but the data series is still too short to conclude anything decisively on this.
The period 1989-1998 was characterised by high values, other peaks were seen 2004, 2015 and 2018, while theperiods 1973-1988, 1999-2003 and 2006-2014 were characterised by low values. The peaks in 1997/98 and 2016
coincide with strong El Niño events in the Pacific Ocean (Fig. 14). The ACE data and ongoing cyclone dynamics
are detailed in Maue (2011). The Northern Hemisphere ACE values (central panel in figure 17) dominates theglobal signal (lower panel in figure 17) and therefore show similar peaks and lows as displayed by the global data,
without any clear trend for the entire observational period. The Northern Hemisphere main cyclone season is
June-November. The Southern Hemisphere ACE values (upper panel in Fig. 17) are generally lower than for the
Northern Hemisphere, and the main cyclone season is December-April.

17

FIGURE 18: Accumulated cyclonic energy (ACE; Atlantic basin) per year since 1850 AD. Thin lines show annual ACE
values, and the thick line shows the running 7-year average. Data source: Atlantic Oceanographic andMeteorological Laboratory (AOML), Hurricane research Division. Please note that these data are not yet updated
beyond 2018.

The Atlantic Oceanographic and Meteorological Laboratory ACE data series goes back to 1850. A Fourier analysis
for the Atlantic Basin (Fig. 18) show the ACE series to be strongly influenced by a periodic variation of about 60
years’ duration. At present, since 2002, the Atlantic ACE series is displaying an overall declining trend, but withlarge interannual variations. The North Atlantic hurricane season often shows above average activity when La
Nina conditions are present in Pacific during late summer (August-October), as was the case in 2017 (Johnstone
and Curry, 2017).
Golany (2021) presents many additional observations and reflections on recent storm and hurricane activity.

Golany, I.M. 2021: Impacts of Climate Change Perception and Reality. The Global Warming Policy Foundation,
report 46, 44pp. https://www.thegwpf.org/content/uploads/2021/02/Goklany-EmpiricalTrends.pdf

18Arctic and Antarctic sea ice extension, updated to December 2023

19

FIGURE 19. Global and hemispheric 12 month running average sea ice extension since 1979, the satellite-era.
The October 1979 value represents the monthly average of November 1978 - October 1979, the November 1979
value represents the average of December 1978 - November 1979, etc. The stippled lines represent a 61-month(ca.5 years) average. Last month included in the 12-month calculations is shown to the right in the diagram.
Data source: National Snow and Ice Data Center (NSIDC).

Northern Hemisphere snow cover, updated to December 2023

20

FIGURE 20. Northern Hemisphere seasonal snow cover since 1972 according to Rutgers University Global Snow
Laboratory.

Atmospheric specific humidity, updated to December 2023

21

FIGURE 21. Specific atmospheric humidity (g/kg) at three different altitudes in the lower part of the atmosphere(the Troposphere) since January 1948 (Kalnay et al. 1996). The thin blue lines show monthly values, while thethick blue lines show the running 37-month average (about 3 years). Data source: Earth System ResearchLaboratory (NOAA).

Water vapour is the most important greenhouse gas in Earth’s atmosphere, considerably more important than
CO2.

Atmospheric CO2, updated to December 2023

22

FIGURE 22. Monthly amount of atmospheric CO2 (upper diagram) and annual growth rate (lower diagram); average last 12 months minus
average preceding 12 months, thin line) of atmospheric CO2 since 1959, according to data provided by the Mauna Loa Observatory, Hawaii,USA. The thick, stippled line is the simple running 37-month average, nearly corresponding to a running 3-year average.

23

FIGURE 23. Visual association between annual growth rate of atmospheric CO 2 (upper panel) and Oceanic Niño Index (lower
panel). See also Figure 14 and 21, respectively.

Number of daily sunspots since 1900, updated to December 31, 2023

24

FIGURE 24. Daily observations of the number of sunspots since 1 January 1900 according to Solar Influences
Data Analysis Center (SIDC). The thin blue line indicates the daily sunspot number, while the dark blue line
indicates the running annual average.

***************All above diagrams with supplementary information (including links to data sources and previous issues of thisnewsletter) are available on www.climate4you.com

Yours sincerely,
Ole Humlum(Ole.Humlum@gmail.com)
Arctic Historical Evaluation and Research Organisation, Longyearbyen, Svalbard
24 January 2024.