Climate4you update July 2012www.climate4you.com

July 2012 global surface air temperature overview

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July 2012 surface air temperature compared to the average 1998-2006. Green-yellow-red colours indicate areas with higher temperaturethan the 1998-2006 average, while blue colours indicate lower than average temperatures. Data source: Goddard Institute for SpaceStudies (GISS)

Comments to the July 2012 global surface air temperature overview
General: This newsletter contains graphs showing
a selection of key meteorological variables for the
past month. All temperatures are given in degrees
Celsius.

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In the above maps showing the geographicalpattern of surface air temperatures, the period
1998-2006 is used as reference period. The reason
for comparing with this recent period instead of
the official WMO ‘normal’ period 1961-1990, is thatthe latter period is affected by the relatively cold
period 1945-1980. Almost any comparison withsuch a low average value will therefore appear as
high or warm, and it will be difficult to decide if andwhere modern surface air temperatures are
increasing or decreasing at the moment.
Comparing with a more recent period overcomes
this problem. In addition to this consideration, therecent temperature development suggests that thetime window 1998-2006 may roughly represent a
global temperature peak. If so, negative
temperature anomalies will gradually become
more and more widespread as time goes on.
However, if positive anomalies instead gradually
become more widespread, this reference period
only represented a temperature plateau.
In the other diagrams in this newsletter the thinline represents the monthly global average value,
and the thick line indicate a simple runningaverage, in most cases a simple moving 37-monthaverage, nearly corresponding to a three year
average. The 37-month average is calculated fromvalues covering a range from 18 month before to
18 months after, with equal weight for every
month.
The year 1979 has been chosen as starting point inmany diagrams, as this roughly corresponds toboth the beginning of satellite observations and theonset of the late 20th century warming period.
However, several of the records have a much
longer record length, which may be inspected in
grater detail on www.Climate4you.com.

July 2012 average global surface air temperatures
General: Global air temperatures were close to
average for the period 1998-2006, and slightly
lower than the previous month.
The Northern Hemisphere was characterised byrelatively high regional variability, as usual.
Northern and western Europe was relatively cold,
as was eastern Siberia and Alaska. In contrast,
western Siberia and NE North America experienced
relatively warm conditions. The Arctic had a regionof relatively low temperatures spanning from theEuropean sector to Alaska and eastern Siberia,
while regions in western Siberia and northern
Canada experienced relatively high temperatures.
NW Greenland was warm, while most of E
Greenland was cold. In general, however, thedistribution of temperatures in the Arctic to a highdegree reflect the sparse number of observationsin the central part of the Arctic, and the GISS
procedure of extrapolating temperatures measured
at lower latitudes to high latitudes.
Near Equator temperatures conditions in general
were at or below average 1998-2006 temperature
conditions, both for land and ocean. The only clear
exception was represented by the region west ofSouth America, where an El Niño situation isdeveloping.

The Southern Hemisphere was at or below average
1998-2006 conditions. No extensive land areas
experienced temperatures above the 1998-2006
average. Most of South America, Africa andAustralia had below average temperatures. Most of
the oceans in the Southern Hemisphere were nearor below average temperature. The Antarctic
continent generally experienced below average
1998-2006 temperatures. The only warm region
was the peninsula and parts of West Antarctica.
Once again, a temperature contrast is seen
between the two Polar regions.
The global oceanic heat content has been more orless stable since 2003/2004 (page 10).

All diagrams shown in this newsletter and links to original data are available on www.climate4you.com

Lower troposphere temperature from satellites, updated to July 2012

Global monthly average lower troposphere temperature (thin line) since 1979 according to University of Alabama at Huntsville, USA. The
thick line is the simple running 37 month average.

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Global monthly average lower troposphere temperature (thin line) since 1979 according to according to Remote Sensing Systems (RSS),
USA. The thick line is the simple running 37 month average.

Global surface air temperature, updated to July 2012

Global monthly average surface air temperature (thin line) since 1979 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 thick line is the simple running 37 month average.
Please note that this diagram has not been updated beyond June 2012.

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Global monthly average surface air temperature (thin line) since 1979 according to according to the Goddard Institute for Space Studies(GISS), at Columbia University, New York City, USA. The thick line is the simple running 37 month average.

Global monthly average surface air temperature since 1979 according to according to the National Climatic Data Center (NCDC), USA.
The thick line is the simple running 37 month average.

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A note on data record stability:
All the above temperature estimates display
changes when one compare with previous monthly
data sets, not only for the most recent months as aresult of supplementary data being added, but
actually for all months back to the very beginningof the records. Presumably this reflects recognitionof errors, changes in the averaging procedure, andthe influence of other phenomena.

Of the five global records shown above the moststable temperature record seen over time (since2008) is by far the HadCRUT3 series.
You can find more on the issue of temporal stability(or lack of this) on www.climate4you (go to: Global
Temperature, followed by Temporal Stability).

All in one, updated to June 2012

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Superimposed plot of all five global monthly temperature estimates. As the base period differs for the individual
temperature estimates, they have all been normalised by comparing with the average value of the initial 120
months (10 years) from January 1979 to December 1988. The heavy black line represents the simple running 37
month (c. 3 year) mean of the average of all five temperature records. The numbers shown in the lower rightcorner represent the temperature anomaly relative to the individual 1979-1988 averages.

It should be kept in mind that satellite- and surfacebased temperature estimates are derived fromdifferent types of measurements, and thatcomparing them directly as done in the diagram
above therefore in principle may be problematical.
However, as both types of estimate often are
discussed together, the above diagram maynevertheless be of some interest. In fact, thedifferent types of temperature estimates appear toagree quite well as to the overall temperature
variations on a 2-3 year scale, although on ashorter time scale there are often considerable
differences between the individual records.

All five global temperature estimates presently
show an overall stagnation, at least since 2002.
There has been no increase in global air
temperature since 1998, which however wasaffected by the oceanographic El Niño event. This
stagnation does not exclude the possibility that
global temperatures will begin to increase again
later. On the other hand, it also remain a possibility
that Earth just now is passing a temperature peak,
and that global temperatures will begin to decrease
within the coming years. Time will show which ofthese two possibilities is correct.

Global sea surface temperature, updated to late July 20127

Sea surface temperature anomaly at 28 July 2012. Map source: National Centers for Environmental Prediction(NOAA).

Relative warm sea surface water now dominates
the ocean regions near Equator, especially in the
Indian Ocean and in the Pacific. Because of thelarge surface areas involved especially near
Equator, the temperature of the surface water inthese regions significantly affects the global
atmospheric temperature.
An El Niño episode is developing along the west
coast of South America, and the effect of this isseen in the global air temperature estimates (p.35).
The significance of any such short-term warming or
cooling seen in air temperatures should not be overstated. Whenever Earth experiences cold La Niña orwarm El Niño episodes (Pacific Ocean) major heatexchanges takes place between the Pacific Ocean
and the atmosphere above, eventually showing up
in estimates of the global air temperature.
However, this does not reflect similar changes inthe total heat content of the atmosphere-oceansystem. In fact, net changes may be small, as heatexchanges as the above mainly reflect
redistribution of energy between ocean andatmosphere. What matters is the overalltemperature development when seen over anumber of years.

Global monthly average lower troposphere temperature over oceans (thin line) since 1979 according to University of Alabama at
Huntsville, USA. The thick line is the simple running 37 month average.

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Global monthly average sea surface temperature since 1979 according to University of East Anglia's Climatic Research Unit (CRU), UK.
Base period: 1961-1990. The thick line is the simple running 37 month average. Please note that no update beyond April 2012 isavailable at the moment.

Global monthly average sea surface temperature since 1979 according to the National Climatic Data Center (NCDC), USA. Base period:
1901-2000. The thick line is the simple running 37 month average.

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Global ocean heat content, updated to March 2012

Global monthly heat content anomaly (GJ/m2) in the uppermost 700 m of the oceans since January 1979. Data source: National

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Oceanographic Data Center(NODC).

Global monthly heat content anomaly (GJ/m2) in the uppermost 700 m of the oceans since January 1955. Data source: National
Oceanographic Data Center(NODC).

Zonal air temperatures, updated to July 201211

Global monthly average lower troposphere temperature since 1979 for the tropics and the northern and southern extratropics, according
to University of Alabama at Huntsville, USA. Thin lines show the monthly temperature. Thick lines represent the simple running 37 monthaverage, nearly corresponding to a running 3 yr average. Reference period 1981-2010.

Arctic and Antarctic lower troposphere temperature, updated to July 201212

Global monthly average lower troposphere temperature since 1979 for the North Pole and South Pole regions, based on satellite
observations (University of Alabama at Huntsville, USA). Thin lines show the monthly temperature. The thick line is the simple running 37
month average, nearly corresponding to a running 3 yr average.

Arctic and Antarctic surface air temperature, updated to March 2012o

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Diagram showing Arctic monthly surface air temperature anomaly 70-90 N since January 2000, in relation to the WMO reference“normal” period 1961-1990. The thin blue line shows the monthly temperature anomaly, while the thicker red line shows the running 13
month average. Data provided by the Hadley Centre for Climate Prediction and Research and the University of East Anglia's Climatic
Research Unit (CRU), UK.

oDiagram showing Antarctic monthly surface air temperature anomaly 70-90 S since January 2000, in relation to the WMO reference“normal” period 1961-1990. The thin blue line shows the monthly temperature anomaly, while the thicker red line shows the running 13
month average. Data provided by the Hadley Centre for Climate Prediction and Research and the University of East Anglia's Climatic
Research Unit (CRU), UK.

oDiagram showing Arctic monthly surface air temperature anomaly 70-90 N since January 1957, in relation to the WMO reference“normal” period 1961-1990. The year 1957 has been chosen as starting year, to ensure easy comparison with the maximum length of therealistic Antarctic temperature record shown below. The thin blue line shows the monthly temperature anomaly, while the thicker red
line shows the running 13 month average. Data provided by the Hadley Centre for Climate Prediction and Research and the University of
East Anglia's Climatic Research Unit (CRU), UK.

14oDiagram showing Antarctic monthly surface air temperature anomaly 70-90 S since January 1957, in relation to the WMO reference“normal” period 1961-1990. The year 1957 was an international geophysical year, and several meteorological stations were establishedin the Antarctic because of this. Before 1957, the meteorological coverage of the Antarctic continent is poor. The thin blue line shows themonthly temperature anomaly, while the thicker red line shows the running 13 month average. Data provided by the Hadley Centre for
Climate Prediction and Research and the University of East Anglia's Climatic Research Unit (CRU), UK.

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Diagram showing Arctic monthly surface air temperature anomaly 70-90 N since January 1900, in relation to the WMO reference“normal” period 1961-1990. The thin blue line shows the monthly temperature anomaly, while the thicker red line shows the running 13
month average. In general, the range of monthly temperature variations decreases throughout the first 30-50 years of the record,oreflecting the increasing number of meteorological stations north of 70 N over time. Especially the period from about 1930 saw theestablishment of many new Arctic meteorological stations, first in Russia and Siberia, and following the 2nd World War, also in North
America. Because of the relatively small number of stations before 1930, details in the early part of the Arctic temperature record should
not be over interpreted. The rapid Arctic warming around 1920 is, however, clearly visible, and is also documented by other sources of
information. The period since 2000 is warm, about as warm as the period 1930-1940. Data provided by the Hadley Centre for Climate
Prediction and Research and the University of East Anglia's Climatic Research Unit (CRU), UKIn general, the Arctic temperature record appears
to be less variable than the Antarctic record,presumably at least partly due to the higher
number of meteorological stations north of 70oN,
compared to the number of stations south of 70oS.
As data coverage is sparse in the Polar Regions, theprocedure of Gillet et al. 2008 has been followed,
giving equal weight to data in each 5ox5o grid cellwhen calculating means, with no weighting by thesurface areas of the individual grid dells.

Literature:
Gillett, N.P., Stone, D.A., Stott, P.A., Nozawa, T.,
Karpechko, A.Y.U., Hegerl, G.C., Wehner, M.F. andJones, P.D. 2008. Attribution of polar warming tohuman influence. Nature Geoscience 1, 750-754.

Arctic and Antarctic sea ice, updated to July 201216

Graphs showing monthly Antarctic, Arctic and global sea ice extent since November 1978, according to the National Snow and Ice data
Center (NSIDC).

Graph showing daily Arctic sea ice extent since June 2002, to August 15, 2012, by courtesy of Japan Aerospace Exploration Agency(JAXA).

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Northern hemisphere sea ice extension and thickness on 29 July 2012 according to the Arctic Cap Nowcast/Forecast System (ACNFS), US
Naval Research Laboratory. Thickness scale (m) is shown to the right.

Global sea level, updated to April 2012

Globa lmonthly sea level since late 1992 according to the Colorado Center for Astrodynamics Research at University of Colorado at
Boulder, USA. The thick line is the simple running 37 observation average, nearly corresponding to a running 3 yr average.

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Forecasted change of global sea level until year 2100, based on simple extrapolation of measurements done by the Colorado Center for
Astrodynamics Research at University of Colorado at Boulder, USA. The thick line is the simple running 3 yr average forecast for sea levelchange until year 2100. Based on this (thick line), the present simple empirical forecast of sea level change until 2100 is about +18 cm.

Northern Hemisphere weekly snow cover, updated to early August 2012

Northern hemisphere weekly snow cover since January 2000 according to Rutgers University Global Snow Laboratory. The thin line
represents the weekly data, and the thick line is the running 53 week average (approximately 1 year).

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Northern hemisphere weekly snow cover since October 1966 according to Rutgers University Global Snow Laboratory. The thin line
represents the weekly data, and the thick line is the running 53 week average (approximately 1 year). The running average is not
calculated before 1971 because of data gaps in this early period.

Atmospheric CO2, updated to July 201220

Monthly amount of atmospheric CO2 (above) and annual growth rate (below; average last 12 months minus average preceding 12months) of atmospheric CO2 since 1959, according to data provided by the Mauna Loa Observatory, Hawaii, USA. The thick line is thesimple running 37 observation average, nearly corresponding to a running 3 yr average.

Global surface air temperature and atmospheric CO2, updated to July 2012

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Diagrams showing HadCRUT3, GISS, and NCDC monthly global surface air temperature estimates (blue) and the monthly
atmospheric CO2 content (red) according to the Mauna Loa Observatory, Hawaii. The Mauna Loa data series begins inMarch 1958, and 1958 has therefore been chosen as starting year for the diagrams. Reconstructions of past atmospheric
CO2 concentrations (before 1958) are not incorporated in this diagram, as such past CO 2 values are derived by other means(ice cores, stomata, or older measurements using different methodology, and therefore are not directly comparable withdirect atmospheric measurements. The dotted grey line indicates the approximate linear temperature trend, and the boxesin the lower part of the diagram indicate the relation between atmospheric CO 2 and global surface air temperature,negative or positive. Please note that the HadCRUT3 diagram has not yet been updated beyond June 2012.

Most climate models assume the greenhouse gas
carbon dioxide CO2 to influence significantly upon
global temperature. It is therefore relevant tocompare different temperature records withmeasurements of atmospheric CO2, as shown in the
diagrams above. Any comparison, however, should
not be made on a monthly or annual basis, but fora longer time period, as other effects(oceanographic, etc.) may well override thepotential influence of CO2 on short time scales suchas just a few years. It is of cause equally
inappropriate to present new meteorologicalrecord values, whether daily, monthly or annual, as
support for the hypothesis ascribing highimportance of atmospheric CO2 for global
temperatures.
Anysuchshort-period
meteorological record value may well be the resultof other phenomena.
What exactly defines the critical length of a
relevant time period to consider for evaluating thealleged importance of CO2 remains elusive, and is
still a topic for discussion. However, the critical
period length must be inversely proportional to thetemperature sensitivity of CO2, including feedback
effects. If the net temperature effect of
atmospheric CO2 is strong, the critical time period
will be short, and vice versa.

However, past climate research history provides
some clues as to what has traditionally been
considered the relevant length of period overwhich to compare temperature and atmosphericCO2. After about 10 years of concurrent global
temperature- and CO2-increase, IPCC wasestablished in 1988. For obtaining public andpolitical support for the CO2-hyphotesis the 10 year
warming period leading up to 1988 in all likelihood
was important. Had the global temperature instead
been decreasing, politic support for the hypothesis
would have been difficult to obtain.
Based on the previous 10 years of concurrent
temperature- and CO2-increase, many climate

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scientists in 1988 presumably felt that theirunderstanding of climate dynamics was sufficient
to conclude about the importance of CO2 for global
temperature changes. From this it may safely beconcluded that 10 years was considered a period
long enough to demonstrate the effect ofincreasing
atmosphericCO2
onglobaltemperatures.
Adopting this approach as to critical time length (atleast 10 years), the varying relation (positive or
negative) between global temperature andatmospheric CO2 has been indicated in the lower
panels of the diagrams above.

Last 20 year surface temperature changes, updated to June 201224

Last 20 years global monthly average surface air temperature according to Hadley CRUT, a cooperative effort between the
Hadley Centre for Climate Prediction and Research and the University of East Anglia's Climatic Research Unit (CRU), UK.
The thin blue line represents the monthly values. The thick red line is the linear fit, with 95% confidence intervals indicatedby the two thin red lines. The thick green line represents a 5-degree polynomial fit, with 95% confidence intervals indicatedby the two thin green lines. A few key statistics is given in the lower part of the diagram (note that the linear trend is themonthly trend)..

From time to time it is debated if the global surface
temperature is increasing, or if the temperature
has levelled out during the last 10-15 years. The
above diagram may be useful in this context, and it
clearly demonstrates the differences between two

often used statistical approaches to determine
recent temperature trends. Please also note thatsuch fits only attempt to describe the past, andusually have little predictive power.

Climate and history; one example among many

101-106 AD: Bridge constructed across the River Danube at the Iron Gate25

Map showing the location of the Iron Gate (black arrow) in south-east Europe.

An indication of the benign climate of Roman times
with a rather long immunity from cold winters in
Europe may be seen in the building between AD
101 and 106 of a bridge with many stone piers
across the River Danube at the Iron Gate in southeast Europe, between Serbia and the Transylvian
highlands in Romania (cf. Lamb 1995).
The bridge was designed by Appolodorus ofDamascus for the Emperor Trajan for efficientpassage of the Roman armies and administration
across the Danube, preceding Trajan's subsequentconquest of Dacia, a large region broadly
corresponding to modern Romania and Moldova.
Trajan's bridge apparently stood for no less thanabout 170 years Lamb (1977, 1995). This must be
considered an amazing fact, as in any recent
century such a construction would rapidly havebeen carried away by river ice during a cold winter.
In the end the bridge is said to have been
destroyed by the Dacian tribes when the Romans
later withdrew from this part of Europe (Lamb
1977, 1995).

Artistic reconstruction of Trajan's bridge across the river Danube (source: Wikimedia Commons).

Trajan's bridge was 1,135 m in length (the Danube
is about 800 m wide at the place of crossing), 15 m
in width, and 19 m in height above the averagewater level. At each end of the bridge was a Roman
castrum, each built around an entrance to thebridge. In other words, in order to cross the bridge
you had first to pass through a Roman military
camp.
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For the bridge's construction Appolodorus ofDamascus used wooden arches set on twenty
masonry pillars (made of bricks, mortar andpozzolana cement) that spanned 38 m each. The
entire bridge was built quickly within two years
only (between 103 and 105 AD), employing theconstruction of a wooden caisson for each pier. For

more than 1000 years Trajan's bridge was thelongest arch bridge ever constructed, in both total
and span length, and it apparently survived for noless than about 170 years (Lamb 1975, 1977),
before being demolished by the Dacian people.
Although representing an impressive engineeringfeat, relative mild winters with little river ice
presumably contributed to the long survival time of
the bridge.
A relief on Trajan's Column shows the Roman
bridge across the River Danube (see figure below).
Noteworthy on this illustration are the unusuallyflat segmental arches on high-rising concrete piers;in the foreground of the relief Emperor Trajan
sacrificing by the Danube can be seen.

The River Danube and the Kazan gorge at its narrowest point (left), and relief showing the Roman bridge acrossDanube on Trajan's Column in Rome (right). Source: Wikimedia Commons.

The Iron Gate gorge(s) lies between Romania in thenorth and Serbia in the south. At this point, theriver separates the southern Carpathian Mountains
from the northwestern foothills of the Balkan
Mountains. The Romanian, Hungarian, Slovakian,Turkish, German and Bulgarian names literally
mean "Iron Gates" and are used to name the entire
range of gorges. The Romanian side of the gorge
now constitutes the Iron Gates natural park,
whereas the Serbian part constitutes the Đerdap
national park.
The Great Kazan (kazan meaning "boiler") is themost famous and the narrowest gorge of the Iron
Gate route (photo above): the river here narrows
to 150 m and reaches a depth of up to 53 m (174ft). Shortly downstream is the site where theRoman Emperor Trajan had the legendary militarybridge erected between 103 and 105 AD, precedinghis conquest of Dacia. On the right (Serbian) bankof the river a Roman memorial plaque (Tabula
Trajana) commemorates Emperor Trajan's militaryroad into Dacia. The Tabula was originally located
50 meters lower than now. The original site wasflooded with the construction of a majorhydroelectric dam in late 1960s and the monument
was moved to a new position just above thewaterline. On the opposite Romanian bank, at the
Small Kazan, a statue of Trajan's Dacian opponent
Decebalus was carved in rock from 1994 through2004 (see photos below).

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Rock carving showing Decebalus on the Romanian side of the Iron Gate (left), and a plate commemorating theroman Emperor Trajan on the Serbian bank (right). Source: Wikimedia Commons.

The twenty pillars carrying Trajan's bridge were stillvisible in 1856, when the level of the Danube hit arecord low. In 1906, the International Commissionof the Danube however decided to destroy two of
the pillars, to ensure safe navigation on the river. In
1932, there were 16 remaining pillars underwater,
but in 1982 archaeologists only manage to find 12of these. Presumably the missing four had been
swept away by river ice following the relative cold

period 1960-1980 in Europe. Today, only theentrance pillars are visible on either bank of the
Danube.
In 1979, Trajan's Bridge was added to theMonument of Culture of Exceptional Importance,
and in 1983 it was added to the ArchaeologicalSites of Exceptional Importance list, and by that it isprotected by Republic of Serbia.

Sources and References:Lamb, H.H. 1977. Climate, present, past and future. Volume 2. Climatic history and the future. Methuen & Co
Ltd., London, 835 pp.
Lamb, H.H. 1995. Climate, History and the Modern World. Routledge, London, 2nd edition, 433 pp.

*****

All the above diagrams with supplementary information, including links to data sources and previous
issues of this newsletter, are available on www.climate4you.com

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Yours sincerely, Ole Humlum (Ole.Humlum@geo.uio.no)
August 19, 2012.