Sunday, September 14, 2014

New paper links Arctic sea ice extent to absorption of sunlight by clouds

A new paper published in the Journal of Geophysical Research Atmospheres finds Arctic sea ice concentrations at the low of each summer are related to absorption of sunlight by cloud cover at the top of the atmosphere in early summer, a phenomenon "not represented in most of current climate models."

According to the authors, 
"absorbed solar radiation at the top of the atmosphere in early summer (May–July) plays a precursory role in determining the Arctic sea ice concentration in late summer (August–October)"   
"this intimate delayed...relationship is not represented in most of current climate models. Rather, the models tend to over-emphasize internal sea ice processes in summer."
Alarmists focus on Arctic sea ice as the supposed canary in the coal mine for CAGW, but many papers have demonstrated natural variability is more likely responsible for the trends in Arctic sea ice than man-made CO2, including the natural Atlantic Multidecadal Oscillation, wind and storm activity. This new paper suggests another way that natural variability controls Arctic sea ice extent via cloud cover, another possible solar amplification mechanism  via the cosmic ray theory of climate.

Alarmists ignore the unspeakable all-time record highs in Antarctic sea ice extent broken over each of the past three years, as do climate models, which laughably predicted the opposite of a decrease in Antarctic sea ice extent more so than Arctic sea ice. 

Alarmists also claim current Arctic sea ice changes are "unprecedented" while ignoring proxy data indicating Arctic sea ice was much less than present-day during the Holocene Climate Optimum ~6,000 years ago, Arctic temperatures were warmer than the present multiple times over past 1357 years, the Medieval Warming Period in the Arctic was warmer than the present, Alaskan glaciers are about the same size as during the Medieval Warm Period, etc., etc.



Connecting early summer cloud-controlled sunlight and late summer sea ice in the Arctic


Yong-Sang Choi, Baek-Min Kim, Sun-Kyong Hur, Seong-Joong Kim, Joo-Hong Kim, Chang-Hoi Ho

This study demonstrates that absorbed solar radiation (ASR) at the top of the atmosphere in early summer (May–July) plays a precursory role in determining the Arctic sea ice concentration (SIC) in late summer (August–October). The monthly ASR anomalies are obtained over the Arctic Ocean (65°N–90°N) from the Clouds and the Earth's Radiant Energy System during 2000–2013. The ASR 
[absorbed solar radiation] changes primarily with cloud variation. We found that the ASR [absorbed solar radiation] anomaly in early summer is significantly correlated with the SIC [Arctic sea ice concentration] anomaly in late summer (correlation coefficient, r ≈ −0.8 with a lag of 1 to 4 months). The region exhibiting high (low) ASR anomalies and low (high) SIC anomalies varies yearly. The possible reason is that the solar heat input to ice is most effectively affected by the cloud shielding effect under the maximum TOA solar radiation in June and amplified by the ice-albedo feedback. This intimate delayed ASR-SIC relationship is not represented in most of current climate models. Rather, the models tend to over-emphasize internal sea ice processes in summer.

New paper predicts Antarctica will only contribute a tiny -.87 to +2.5 inches of sea level rise by 2100

A new paper published in Climate Dynamics models the future contribution of the Antarctic ice sheet to global mean sea level in 2100 and predicts a range from a decrease in sea level [due to ice accumulation] of -22 mm or negative 0.87 inches to a slight increase in sea levels of 63 mm or 2.5 inches. The median of this range is a tiny 1.6 inches of sea level contribution from Antarctica by the year 2100, hardly of concern.

Further, this estimate based upon conventional climate model assumptions of climate sensitivity to CO2, falsified as exaggerated at confidence levels exceeding 98%. 

The authors also conclude that "sea-level change has driven the deglaciation of the ice sheet" over the past 21,000 years since the peak of the last ice age. Global sea levels have been naturally rising for ~20,000 years and have decelerated over the past 8,000 years, decelerated over the 20th centurydecelerated 31% since 2002 and decelerated 44% since 2004 to less than 7 inches per century. There is no evidence of an acceleration of sea level rise, thus no evidence of any effect of mankind on sea levels. Since sea-level rise is not man-made, and based upon the findings of this paper, there is therefore no evidence of any effect of man on Antarctic glacier loss in the past. 

Antarctica holds over 80% of the ice on Earth, with most of the remainder in the Greenland ice sheet, which has also been demonstrated to be resistant to thaw and "insensitive" to surface melting from warming, thus further lowering sea level rise projections. Lowered sea level contributions from both Antarctica and Greenland effectively call off the alarm on future sea levels. 



A model study of the effect of climate and sea-level change on the evolution of the Antarctic Ice Sheet from the Last Glacial Maximum to 2100

M. N. A. Maris, J. M. van Wessem, W. J. van de Berg, B. de Boer, J. Oerlemans


Due to a scarcity of observations and its long memory of uncertain past climate, the Antarctic Ice Sheet remains a largely unknown factor in the prediction of global sea level change. As the history of the ice sheet plays a key role in its future evolution, in this study we model the Antarctic Ice Sheet from the Last Glacial Maximum (21 kyr ago) until the year 2100 with the ice-dynamical model ANICE. We force the model with different temperature, surface mass balance and sea-level records to investigate the importance of these different aspects for the evolution of the ice sheet. Additionally, we compare the model output from 21 kyr ago until the present with observations to assess model performance in simulating the total grounded ice volume and the evolution of different regions of the Antarctic Ice Sheet. Although there are some clear limitations of the model, we conclude that sea-level change has driven the deglaciation of the ice sheet, whereas future temperature change and the history of the ice sheet are the primary cause of changes in ice volume in the future. We estimate the change in grounded ice volume between its maximum (around 15 kyr ago) and the present-day to be between 8.4 and 12.5 m sea-level equivalent and the contribution of the Antarctic Ice Sheet to the global mean sea level in 2100, with respect to 2000, to be −22 to 63 mm.

New paper debunks the "wet gets wetter, dry gets drier" meme

A new paper published in Nature Geoscience finds the "wet gets wetter, dry gets drier" meme derived from climate models is an oversimplification of climate change not supported by observational data, and that the opposite pattern of "dry gets wetter, and wet gets drier" is almost as likely to occur. According to the authors,
"assessments of observed continental dryness trends yield contradicting results. The concept that dry regions dry out further, whereas wet regions become wetter as the climate warms has been proposed as a simplified summary of expected as well as observed changes over land, although this concept is mostly based on oceanic data. 
We find that over about three-quarters of the global land area, robust dryness changes cannot be detected. Only 10.8% of the global land area shows a robust ‘dry gets drier, wet gets wetter’ pattern, compared to 9.5% of global land area with the opposite pattern, that is, dry gets wetter, and wet gets drier. We conclude that aridity changes over land, where the potential for direct socio-economic consequences is highest, have not followed a simple intensification of existing patterns."
The paper joins at least one other finding the "wet gets wetter and dry gets drier" meme is false on local scales, although this belief is still commonly held in the climate science community. American Meteorological Society President Dr. Marshall Shepherd tweeted a few months ago that one of his "toughest challenges" is "explaining to linear thinkers that dry/drier, wet/wetter is expected. They want either or" :
  1. one my toughest challenges. Explaining to linear thinkers that dry/drier, wet/wetter is expected. They want either or.

These two papers demonstrate that this meme is a gross oversimplification as about as likely as the reverse to occur, with no change in aridity found in ~80% of global land area observations from 1948-2005. Likewise, the common assumption that dry and wet areas will become more extreme is also premature and potentially false. 

Article describing the new paper below



Global assessment of trends in wetting and drying over land


Nature Geoscience
 
 
doi:10.1038/ngeo2247
Received
 
Accepted
 
Published online
 
Changes in the hydrological conditions of the land surface have substantial impacts on society12. Yet assessments of observed continental dryness trends yield contradicting results34567. The concept that dry regions dry out further, whereas wet regions become wetter as the climate warms has been proposed as a simplified summary of expected8910 as well as observed1011121314changes over land, although this concept is mostly based on oceanic data810. Here we present an analysis of more than 300 combinations of various hydrological data sets of historical land dryness changes covering the period from 1948 to 2005. Each combination of data sets is benchmarked against an empirical relationship between evaporation, precipitation and aridity. Those combinations that perform well are used for trend analysis. We find that over about three-quarters of the global land area, robust dryness changes cannot be detected. Only 10.8% of the global land area shows a robust ‘dry gets drier, wet gets wetter pattern, compared to 9.5% of global land area with the opposite pattern, that is, dry gets wetter, and wet gets drier. We conclude that aridity changes over land, where the potential for direct socio-economic consequences is highest, have not followed a simple intensification of existing patterns.


UPDATE: Science Daily article on this paper:

Rules of thumb for climate change turned upside down: Wet and dry regions recalculated

Date:
September 14, 2014
Source:
ETH Zurich
With a new analysis of land regions, ETH climate researcher are challenging the general climate change precept that dry regions are getting drier and wet regions are getting wetter. In some regions they are encountering divergent trends.
Based on models and observations, climate scientists have devised a simplified formula to describe one of the consequences of climate change: regions already marked by droughts will continue to dry out in the future climate. Regions that already have a moist climate will experience additional rainfall. In short: dry gets drier; wet gets wetter (DDWW).
However, this formula is less universally valid than previously assumed. This was demonstrated by a team of ETH climate researchers led by Peter Greve, lead author of a study recently published in Nature Geoscience. Traditional analyses use technology that can comprehensively describe climate characteristics above the ocean, but is problematic over land. While this fact was mentioned in said studies, scientific and public discourse has neglected this aspect so far. In their new study, the ETH researchers in the group headed by Sonia Seneviratne's, professor for land-climate dynamics, take into account the specific climatic properties of land surfaces, where the amount of available water is limited when compared with the ocean.
In her analysis, the climate scientists made use of measured data compiled solely on land, such as rainfall, actual evaporation and potential evaporation. The data derived from various sources was combined by Greve and his co-authors -- this allowed them to extract trends in terms of a region's humidity and dryness. Furthermore, the researchers compared data from between 1948 and 1968 and 1984 to 2004.
Half of the surface areas show divergence
The evaluation shows no obvious trend towards a drier or wetter climate across three-quarters of the land are. There are solid trends for the remaining quarter. However, only half of this surface area follows the DDWW principle, i.e. one-eighth of the total landmass, while the trends seem to contradict this rule over the other half.
In some regions, the climate has developed contrary to the general climate formula 'dry gets drier; wet gets wetter' over the past 70 years. (Chart: from Greve et al, 2014)
Some regions which should have become wetter according to the simple DDWW formula have actually become drier in the past -- this includes parts of the Amazon, Central America, tropical Africa and Asia. On the other hand, there are dry areas that have become wetter: parts of Patagonia, central Australia and the Midwestern United States.
Nevertheless, the 'wet gets wetter' rule is largely confirmed for the Eastern United States, Northern Australia and northern Eurasia. 'Dry gets drier' also corresponds to indications in the Sahel region, the Arabian Peninsula and parts of Central Asia and Australia.
However, the DDWW principle does still applies to the oceans. "Our results emphasise how we should not overly rely on simplifying principles to asses past developments in dryness and humidity," Greve explains. This can be misleading, as it cannot do justice to the complexity of the underlying systems.
Story Source:
The above story is based on materials provided by ETH ZurichNote: Materials may be edited for content and length.
Journal Reference:
  1. Greve P, Orlowsky B, Müller B, Sheffield J, Reichstein M, Seneviratne SI. Global assessment of trends in wetting and drying over landNature Geoscience, 14th September 2014 DOI: 10.1038/ngeo2247

Paper could explain why Mann had to "hide the decline" & relationship of solar activity to tree growth

A paper published in New Phytologist finds "the growth of British spruce trees appears to follow a cosmic pattern, with trees growing faster when high levels of cosmic rays arrive from space." The level of cosmic rays is in turn controlled by solar activity and the strength of the solar wind, which blocks cosmic rays from the Earth.

The authors find

"during a number of years, the trees' growth also particularly slowed. These years correlated with periods when a relatively low level of cosmic rays reached the Earth's surface. When the intensity of cosmic rays reaching the Earth's surface was higher, the rate of tree growth was faster. The effect is not large, but it is statistically significant. 
The intensity of cosmic rays also correlates better with the changes in tree growth than any other climatological factor, such as varying levels of temperature or precipitation over the years. 
"The correlation between growth and cosmic rays was moderately high, but the correlation with the climatological variables was barely visible," Ms Dengel told the BBC.
The paper, which was published the month before Climategate in 2009, may ironically explain the mystery behind the so-called "divergence problem" that led Michael Mann et al to use his "trick to hide the decline" in tree-ring proxy temperatures, one of the largest scientific scandals of the whole Climategate affair. 

Solar activity reconstructions have demonstrated that solar activity in the latter half of the 20th century was at the highest levels of the past 3,000 - 9,400 years. Since increased solar activity increases the solar wind which blocks cosmic rays from space, cosmic rays were at relatively low levels during the latter 20th century. According to this paper, this decrease in cosmic rays may have accounted for a decrease in tree growth in the latter 20th century, which corresponds to the "decline" in tree-ring sizes that Mann et al tried to "hide" after 1960. Further, the authors did not find any statistically-significant correlation between tree-ring size and temperature or precipitation, which is what Mann et al falsely assumed and thus, had to conveniently hide.

Thus, given the findings of this paper, it could well be that the high solar activity of the latter 20th century explains both the global warming and the decline in tree growth ["the divergence problem"] that Mann used his "trick to hide" because it didn't support "the cause" of Mann-made global warming. 

The authors attribute the correlation between cosmic rays and tree growth to the Svensmark et al cosmic ray theory of climate, one of many solar amplification mechanisms described in the literature.

"We tried to correlate the width of the rings, i.e. the growth rate, to climatological factors like temperature. We also thought it would be interesting to look for patterns related to solar activity, as a few people previously have suggested such a link," explains Ms Dengel. 
"We found them. And the relation of the rings to the solar cycle was much stronger than it was to any of the climatological factors we had looked at. We were quite hesitant at first, as solar cycles have been a controversial topic in climatology."

"As for the mechanism, we are puzzled." 
Ms Dengel's team proposes two main hypotheses as to how cosmic ray particles could influence the growth of trees. 
The first idea is that cosmic rays ionise gases in the atmosphere, creating molecules around which clouds condense, therefore increasing cloud over.[Svensmark's cosmic ray theory of climate]
One study published in 2006 suggested it may account for as little as 2% of the variation in cloud cover across the UK.[Note a mere 1-2% change in cloud cover is sufficient to cause global warming or cooling] 
But if it does occur, then an increase in cloud cover and haze would diffuse the amount of solar radiation reaching the trees. 
As diffuse radiation penetrates forest canopies better than direct light, it would increase the amount of radiation that plants capture, and increase photosynthesis by trees, boosting growth.

Mann's Climategate "trick to hide the decline" in tree-ring growth affair is explained and lambasted by warmist Dr. Richard Mueller in this highly recommended short lecture excerpt:





and hilariously parodied by Minnesotans for Global Warming:



From the full paper here


By Matt Walker BBC News 10/19/09
Editor, Earth News
Tree rings
Cosmic record

The growth of British trees appears to follow a cosmic pattern, with trees growing faster when high levels of cosmic radiation arrive from space.
Researchers made the discovery studying how growth rings of spruce trees have varied over the past half a century.
As yet, they cannot explain the pattern, but variation in cosmic rays impacted tree growth more than changes in temperature or precipitation.
The study is published in the scientific journal New Phytologist.
"We were originally interested in a different topic, the climatological factors influencing forest growth," says Ms Sigrid Dengel a postgraduate researcher at the Institute of Atmospheric and Environmental Science at the University of Edinburgh.
 The relation of the rings to the solar cycle was much stronger than to any climatological factors 
Sigrid Dengel
University of Edinburgh
To do this, Ms Dengel and University of Edinburgh colleagues Mr Dominik Aeby and Professor John Grace obtained slices of spruce tree trunks.
These had been freshly-felled from the Forest of Ae in Dumfriesshire, Scotland, by Forest Research, the research branch of the UK's Forestry Commission.
The trees had been planted in 1953 and felled in 2006.
The researchers froze the trunk slices, to prevent the wood shrinking, then scanned them on to a computer and used software to count the number and width of the growth rings.
As the trees aged, they showed a usual decline in growth.
However, during a number of years, the trees' growth also particularly slowed. These years correlated with periods when a relatively low level of cosmic rays reached the Earth's surface.
Sitka spruce (Picea sitchensis)
Reaching for the stars
When the intensity of cosmic rays reaching the Earth's surface was higher, the rate of tree growth was faster.
The effect is not large, but it is statistically significant.
The intensity of cosmic rays also correlates better with the changes in tree growth than any other climatological factor, such as varying levels of temperature or precipitation over the years.
"The correlation between growth and cosmic rays was moderately high, but the correlation with the climatological variables was barely visible," Ms Dengel told the BBC.
Here comes the Sun
Cosmic rays are actually energetic particles, mainly protons, as well as electrons and the nuclei of helium atoms, that stream through space before hitting the Earth's atmosphere.
The levels of cosmic rays reaching the Earth go up and down according to the activity of the Sun, which follows an 11-year cycle.
 As for the mechanism, we are puzzled 
Sigrid Dengel
University of Edinburgh
Every 11 years or so, the Sun becomes more active, producing a peak of sunspots. These sunspots carry a magnetic field that blocks and slows the path of energetic particles.
When the researchers looked at their data, they found that tree growth was highest during periods of low sunspot activity, when most cosmic rays reached Earth.
But growth slowed during the four periods of cosmic ray-blocking high sunspot activity, which have occurred between 1965 and 2005.
"We tried to correlate the width of the rings, i.e. the growth rate, to climatological factors like temperature. We also thought it would be interesting to look for patterns related to solar activity, as a few people previously have suggested such a link," explains Ms Dengel.
"We found them. And the relation of the rings to the solar cycle was much stronger than it was to any of the climatological factors we had looked at. We were quite hesitant at first, as solar cycles have been a controversial topic in climatology."
Tree trunk slices
Sliced for examination
"As for the mechanism, we are puzzled."
Ms Dengel's team proposes two main hypotheses as to how cosmic ray particles could influence the growth of trees.
The first idea is that cosmic rays ionise gases in the atmosphere, creating molecules around which clouds condense, therefore increasing cloud over.[Svensmark's cosmic ray theory of climate]
This mechanism is hotly debated among scientists, and evidence for it is weak.
One study published in 2006 suggested it may account for as little as 2% of the variation in cloud cover across the UK.[note a mere 1-2% change in cloud cover is sufficient to cause global warming or cooling]
But if it does occur, then an increase in cloud cover and haze would diffuse the amount of solar radiation reaching the trees.
As diffuse radiation penetrates forest canopies better than direct light, it would increase the amount of radiation that plants capture, and increase photosynthesis by trees, boosting growth.
Explaining the unexplained
"Or there is some direct effect," says Ms Dengel.
What that might be is unknown, but experiments in space have shown that cosmic rays can have some positive impacts on biological materials.
Ms Dengel says that much more work needs to be done to investigate the effect further, and their results have received a mixed reaction from other scientists.
"We sent the paper to 161 international colleagues. We are still harvesting the emails. We've identified four groups who would like to work with us on this.
"Locally, one of our colleagues is a cloud physicist. He was encouraging but sceptical at the same time."
If further research backs up the team's findings, the implications could be significant.
"We want to repeat this work for larger data sets, and understand the mechanism better, before we speculate," says Ms Dengel.
But the influence of cosmic rays could resolve other as yet unexplained cycles in tree growth found in studies in North America.
It also suggests the amount of aerosols that humans emit into the atmosphere could impact tree growth, as high levels of aerosols cause "global dimming", an effect that occurs when the levels of light reaching the Earth's surface fall.
"If it is true that the mechanism is all about rays enhancing diffuse radiation, it would mean that 'global dimming' and 'global brightening' would have a big effect on tree growth and therefore on the absorption of carbon dioxide," warns Ms Dengel.

Saturday, September 13, 2014

New paper finds water vapor in the troposphere controlled by natural processes, not CO2

A new paper published in the Journal of Geophysical Research Atmospheres finds water vapor & relative humidity in the upper troposphere [where the non-existent 'hot spot' is supposed to be] is "primarily determined by its temperature change during recent vertical movement, i.e. cooling during ascent/expansion and warming during descent/compression." [i.e. via the adiabatic lapse rate]. 

Conventional AGW greenhouse theory assumes, however, that the primary greenhouse gas water vapor is instead controlled by man-made CO2, which allegedly amplifies [via "positive feedback"] the greenhouse effect of CO2 by a factor of 3-5 times. This new paper torpedoes that theory by demonstrating that the natural adiabatic lapse rate [which is dependent only upon atmospheric mass, gravity, and atmospheric heat capacity at constant pressure, and is completely independent of CO2 levels] instead controls the relative humidity/water vapor content of air masses as they rise/expand/cool/dry and then fall/compress/warm in an infinite cycle due to the gravity field. 

Catastrophic global warming theory is additionally torpedoed by overwhelming observational evidence that water vapor feedback is negative, not positive, and therefore counteracts any warming effect of CO2 via a self-regulating homeostatic mechanism. The wet adiabatic lapse rate is only one-half the dry adiabatic lapse rate, proving that water vapor acts as a negative-feedback cooling agent, not as a positive-feedback warming agent.


Processes controlling water vapor in the upper troposphere / lowermost stratosphere: An analysis of eight years of monthly measurements by the IAGOS-CARIBIC observatory

A. Zahn et al


An extensive set of in situ water vapor (H2O) data obtained by the IAGOS-CARIBIC passenger aircraft at 10–12 km altitude over eight years (2005 – 2013) is analyzed. A multifaceted description of the vertical distribution of H2O from the upper troposphere (UT) via the extra-tropical tropopause mixing layer (exTL) into the lowermost stratosphere (LMS) is given. Compared to longer-lived trace gases, H2O is highly variable in the UT and exTL. It undergoes considerable seasonal variation, with maxima in summer and in phase from the UT up to ~4 km above the tropopause. The transport and dehydration pathways of air starting at the Earth's surface and ending at 10–12 km altitude are reconstructed based upon (i) potential temperature (θ), (ii) relative humidity with respect to ice (RHi), and (iii) back trajectories as a function of altitude relative to the tropopause. RHi [relative humidity with respect to ice] of an air mass was found to be primarily determined by its temperature change during recent vertical movement, i.e. cooling during ascent/expansion and warming during descent/compression. The data show with great clarity that H2O and RHi at 10–12 km altitude are controlled by three dominant transport/dehydration pathways: (i) the Hadley circulation, i.e. convective uplift in the tropics and pole-ward directed subsidence drying from the tropical tropopause layer (TTL) with observed RHi down to 2%, (ii) warm conveyor belts and mid-latitude convection transporting moist air into the UT with observed RHi usually above 60%, and (iii) the Brewer-Dobson shallow and deep branches with observed RHi down to 1%.

Thursday, September 11, 2014

Review finds global biomass production continues to rise at a remarkable rate

A new review by SPPI and CO2 Science:

global_temp_biosphere_prod
[Illustrations, footnotes and references available in PDF version]
Excerpts:
Among the many climate-alarmist fears of CO2-induced global warming is the concern that the productivity of the biosphere will decline if global temperatures rise to the extent predicted by computer models. Yet, for many alarmists, the future is the present. Since 1980, for example, the Earth has weathered three of the warmest decades in the instrumental temperature record, a handful of intense and persistent El Niño events, large-scale deforestation, "unprecedented" forest fires, and the eruption of several volcanoes. Concurrently, the air's CO2 content increased by 16%, while human population grew by 55%. So just how bad is the biosphere suffering in response to these much-feared events? Or, is it even suffering at all?
In spite of climate-alarmist claims that the temperatures of the latter part of the 20th century and on through the present were unprecedented over the past one to two millennia (which is highly debatable) and that atmospheric CO2 concentrations were the highest they had been for several hundred millennia (which is true), as well as the fact that mankind yearly harvests and/or destroys much of the planet's natural vegetation, the total yearly production of terrestrial vegetative biomass for the globe as a whole continues to rise, and at a remarkable rate. Why is this so? Perhaps it is because the twin evils of the radical environmentalist movement are not the devilish developments they are made out to be, but are actually blessings in disguise, benefiting earth's biosphere in spite of all of the political attempts to severely curtail the CO2 emissions of humanity.

New excuse for 'pause' #52: 'Unusual climate anomaly' of unprecedented deceleration of secular warming trend

Added as #52 to the list of excuses for the 18-26 year "pause" of global warming, the researchers ask whether "the global climate sensitivity [to CO2] has recently changed" [i.e. decreased]?: 

Last decade's slow-down in global warming enhanced by an unusual climate anomaly

JRC News [EU "in-house science service", Sept. 10, 2014]:

A hiatus in global warming ongoing since 2001 is due to a combination of a natural cooling phase, known as multidecadal variability (MDV) and a downturn of the secular warming trend. The exact causes of the latter, unique in the entire observational record going back to 1850, are still to be identified, according to a JRC article which analysed the phenomena.

Since 2001, surface temperatures have not risen at the same rate as higher atmospheric radiative forcing.
The earth hasn't warmed at the same pace during the 20th century. The noticeable temperature increases during some periods interspersed with fairly stable or decreasing levels during others have been explained as a combination of secular global warming (likely manmade) and natural climate variability. We are currently, in the early 21st century, experiencing a hiatus period, during which surface temperatures have not risen at the same rate as higher atmospheric radiative forcing.

JRC scientists analysed surface temperature data records – which began in 1850 – to separate natural variations from secular (i.e., long-term) trends. They identified three hiatus periods (1878-1907, 1945-1969 and 2001 to date), during which global warming slowed down. These hiatus periods coincide with natural cooling phases – the multidecadal variability (MDV), most likely caused by natural oceanic oscillations. The scientists therefore conclude that the MDV is the main cause of these hiatus periods during which global warming decelerated.

GraphHadCRUT4 Temperature Anomaly 1850-2013 (°C) (blue and red bars). Secular trend (red line), multidecadal variability (green line) and reconstructed signal from the statistical analysis (black line). Hiatus periods are indicated with grey bars in the x-axis.
© EU, 2014

However, they found that the current hiatus period is, for the first time, particularly strongly influenced by changes in the secular trend, which shows a strong acceleration from 1992-2001 and a deceleration from 2002 to 2013. Such rapid and strong fluctuations in the secular warming rate are unprecedented.

This unique fluctuation in the recent secular warming rate could have several causes, such as recent changes in the tropical Pacific Ocean, the accelerated melting of Arctic ice, changes in the deep ocean heat storage or the increasing content of aerosols in the stratosphere. The authors recommend further scientific investigation of the causes and consequences of this change, in order to address whether the global climate sensitivity has recently changed. Such research is crucial to understanding current climate conditions and creating plausible scenarios of future climate evolution.

Abstract & open access paper here:


Figure 3. Global warming rate analysis.

a) Warming rates (°C year−1) obtained from the different signals identified in the SSA: ST (red line), MDV (blue line) and reconstructed signal (black line). The dashed thin red lines are the confidence intervals for the warming rate associated with the ST obtained from each individual month’s time series. b) Zoom on the last 25 years of the time series.

Figure 4. SSA reconstructed signals for Northern Hemisphere surface temperature.
a) HadCRUT4 annual surface temperature (gray line), multidecadal variability (MDV, blue line), secular trend (ST, red line) and reconstructed signal (MDV+ST, black line). The dashed thin red lines indicate the range of variability of the ST obtained by applying SSA to the temperature time series obtained for each individual month. b) Warming rates (°C year−1) obtained from the different signals identified in the SSA for the Northern Hemisphere. The dashed thin red lines are the confidence intervals for the warming rate associated with the ST obtained from each individual month’s time series. c) Zoom on the last 25 years of the warming rate time series.

Application of the Singular Spectrum Analysis Technique to Study the Recent Hiatus on the Global Surface Temperature Record


Global surface temperature has been increasing since the beginning of the 20th century but with a highly variable warming rate, and the alternation of rapid warming periods with ‘hiatus’ decades is a constant throughout the series. The superimposition of a secular warming trend with natural multidecadal variability is the most accepted explanation for such a pattern. Since the start of the 21st century, the surface global mean temperature has not risen at the same rate as the top-of-atmosphere radiative energy input or greenhouse gas emissions, provoking scientific and social interest in determining the causes of this apparent discrepancy. Multidecadal natural variability is the most commonly proposed cause for the present hiatus period. Here, we analyze the HadCRUT4 surface temperature database with spectral techniques to separate a multidecadal oscillation (MDV) from a secular trend (ST). Both signals combined account for nearly 88% of the total variability of the temperature series showing the main acceleration/deceleration periods already described elsewhere. Three stalling periods with very little warming could be found within the series, from 1878 to 1907, from 1945 to 1969 and from 2001 to the end of the series, all of them coincided with a cooling phase of the MDV. Henceforth, MDV seems to be the main cause of the different hiatus periods shown by the global surface temperature records. However, and contrary to the two previous events, during the current hiatus period, the ST shows a strong fluctuation on the warming rate, with a large acceleration (0.0085°C year−1 to 0.017°C year−1) during 1992–2001 and a sharp deceleration (0.017°C year−1 to 0.003°C year−1) from 2002 onwards. This is the first time in the observational record that the ST shows such variability, so determining the causes and consequences of this change of behavior needs to be addressed by the scientific community.

Spectral Analysis says Natural Variations Cause Pause

11.09.2014 19:53 Age: 5 min   Reporting Climate Science



Click to enlarge. HadCRUT4 Temperature Anomaly 1850-2013 (°C) (blue and red bars). Secular trend (red line), multidecadal variability (green line) and reconstructed signal from the statistical analysis (black line). Hiatus periods are indicated with grey bars in the x-axis. Courtesy: EU.

A hiatus in global warming ongoing since 2001 is due to a combination of a natural cooling phase, known as multidecadal variability (MDV) and a downturn of the secular warming trend. The exact causes of the latter, unique in the entire observational record going back to 1850, are still to be identified, according to a JRC article which analysed the phenomena.

The earth hasn't warmed at the same pace during the 20th century. The noticeable temperature increases during some periods interspersed with fairly stable or decreasing levels during others have been explained as a combination of secular global warming (likely manmade) and natural climate variability. We are currently, in the early 21st century, experiencing a hiatus period, during which surface temperatures have not risen at the same rate as higher atmospheric radiative forcing.

JRC scientists analysed surface temperature data records – which began in 1850 – to separate natural variations from secular (i.e., long-term) trends. They identified three hiatus periods (1878-1907, 1945-1969 and 2001 to date), during which global warming slowed down. These hiatus periods coincide with natural cooling phases – the multidecadal variability (MDV), most likely caused by natural oceanic oscillations. The scientists therefore conclude that the MDV is the main cause of these hiatus periods during which global warming decelerated.

However, they found that the current hiatus period is, for the first time, particularly strongly influenced by changes in the secular trend, which shows a strong acceleration from 1992-2001 and a deceleration from 2002 to 2013. Such rapid and strong fluctuations in the secular warming rate are unprecedented.

This unique fluctuation in the recent secular warming rate could have several causes, such as recent changes in the tropical Pacific Ocean, the accelerated melting of Arctic ice, changes in the deep ocean heat storage or the increasing content of aerosols in the stratosphere. The authors recommend further scientific investigation of the causes and consequences of this change, in order to address whether the global climate sensitivity has recently changed. Such research is crucial to understanding current climate conditions and creating plausible scenarios of future climate evolution.


Global surface temperature has been increasing since the beginning of the 20th century but with a highly variable warming rate, and the alternation of rapid warming periods with ‘hiatus’ decades is a constant throughout the series. The superimposition of a secular warming trend with natural multidecadal variability is the most accepted explanation for such a pattern. Since the start of the 21st century, the surface global mean temperature has not risen at the same rate as the top-of-atmosphere radiative energy input or greenhouse gas emissions, provoking scientific and social interest in determining the causes of this apparent discrepancy. Multidecadal natural variability is the most commonly proposed cause for the present hiatus period. Here, we analyze the HadCRUT4 surface temperature database with spectral techniques to separate a multidecadal oscillation (MDV) from a secular trend (ST). Both signals combined account for nearly 88% of the total variability of the temperature series showing the main acceleration/deceleration periods already described elsewhere. Three stalling periods with very little warming could be found within the series, from 1878 to 1907, from 1945 to 1969 and from 2001 to the end of the series, all of them coincided with a cooling phase of the MDV. Henceforth, MDV seems to be the main cause of the different hiatus periods shown by the global surface temperature records. However, and contrary to the two previous events, during the current hiatus period, the ST shows a strong fluctuation on the warming rate, with a large acceleration (0.0085°C year−1 to 0.017°C year−1) during 1992–2001 and a sharp deceleration (0.017°C year−1 to 0.003°C year−1) from 2002 onwards. This is the first time in the observational record that the ST shows such variability, so determining the causes and consequences of this change of behavior needs to be addressed by the scientific community.

Application of the Singular Spectrum Analysis Technique to Study the Recent Hiatus on the Global Surface Temperature Record by Diego Macias, Adolf Stips, Elisa Garcia-Gorriz published in Plos One. DOI: 10.1371/journal.pone.0107222

Read the abstract and read the open access paper here.

European Commission news release here.