Read here. A peer-reviewed study documents the extremely warm temperatures of the Medieval Period that occurred in the California Sierra Nevada range. Scientists, working with dead tree trunks located above the current treeline, affirm California's Medieval extreme warm temperature history, which still remains unprecedented.
"Working with dead tree trunks located above the current treeline on tephra-covered slopes of Whitewing Mountain and San Joaquin Ridge.....the five researchers say "the Medieval forest on Whitewing was growing under mild, favorable conditions (warm with adequate moisture)," as indicated by "extremely low mean sensitivities [to stress] and large average ring widths." More specifically, they conclude, as reported in their abstract, that annual minimum temperatures during the Medieval Climatic Anomaly in the region they studied were "significantly warmer" (+3.2°C) "than present,".....Once again, we have another example of a paleoclimate study in which the Medieval Warm Period is determined to have been significantly warmer than it is currently....."
Read here. Basic common sense suggests solar influences are driving all climate change instead of a minuscule trace gas such as CO2. In a National Science Foundation (NSF) funded peer-reviewed study of Chinese lake sediment cores, researchers find climate change cycles strongly associated with solar output oscillations.
"The authors find “The carbonate percentage and ostracode abundance show a consistent pattern with ~200 year moisture oscillations during the last 1000 years.” The variations appear to be related to periodicities of solar output – Zhao et al. conclude “Higher solar output corresponds to a stronger monsoon, which intensifies the uplift of air mass on the high Tibetan Plateau and strengthens the subsidence of air mass over the QB. The reverse is true during the period of lower solar output. Thus, high solar activity is correlated with dry climate in QB and increased precipitation in monsoonal areas.”.....As was the case in the first article, the 200 year quasi “cycle” is again linked to a similar cycle in solar activity. Zhao et al. speculate that “The ~200-yr time spacing between wet and dry climate periods indicated by the A/C ratio variations suggests a possible solar forcing of effective moisture changes in the region.” The authors also note that the basin was especially dry “around AD 1600 during the first few centuries of the Little Ice Age”. So much for any argument that the Little Ice Age was somehow confined to Europe....."
Read here. A new peer-reviewed study finds that global cooling climate change leads to major social instabilities (due to worsening weather/climate conditions), including outbreaks of devastating war. In essence, Chinese data and historical records indicate temperature warming leads to paradise and cooling to hell. This study refutes the speculative, catastrophic predictions of AGW alarmists regarding the impact of warming on society.
[Zhibin Zhang et al] "Here, using historical records and palaeoclimatic reconstructions during AD 10–1900, we demonstrate that war frequency, price of rice, locust plague, drought frequency, flood frequency and temperature in China show two predominant periodic bands around 160 and 320 years where they interact significantly with each other. Temperature cooling shows direct positive association with the frequency of external aggression war to the Chinese dynasties.....with the frequency of internal war within the Chinese dynasties through drought and locust plagues. The collapses of the agricultural dynasties of the Han, Tang, Song and Ming are more closely associated with low temperature. Our study suggests that food production during the last two millennia has been more unstable during cooler periods....."
Read here. Climate alarmists are fond of claiming that global warming causes an increase in storm frequency and intensity. There is not much, if any, actual empirical evidence backing up these claims, unless one believes speculative IPCC climate model predictions. What does the actual data say?
Recently, peer-reviewed research out of the New Zealand region confirms that modern warming itself has not generated an increase in storminess or raised storm's severity. In fact, the researchers found over the last 7,000+ years that increases in frequency/severity are usually associated with cooling periods, not warming.
"Working with sediment cores extracted from Lake Tutira on the eastern North Island of New Zealand, Page et al. developed a 7200-year history of the frequency and magnitude of storm activity.....they say that over the course of their record, "there are 25 periods with an increased frequency of large storms," the onset and cessation of which stormy periods "was usually abrupt, occurring on an inter-annual to decadal scale." They also note that the duration of these stormy periods "ranged mainly from several decades to a century," .....while "intervals between stormy periods range from about thirty years to a century." In addition, they find that millennial-scale cooling periods tend to "coincide with periods of increased storminess in the Tutira record, while warmer events match less stormy periods.".....as is demonstrated by the results of their work in the real world, the sudden occurrence of a string of years -- or even decades -- of unusually large storms is something that can happen at almost any time on its own, or at least without the necessity of being driven by human activities such as the burning of fossil fuels."
Read here and here. A peer-reviewed study confirming that Medieval Warming temperatures were considerably warmer than those experienced during modern era. The research reveals that modern temperatures are not "unprecedented" as claimed, and that significant natural warming does happen without the influence of human CO2 emissions. (click on image to enlarge)
"The Jämtland multi-millennial tree-ring width chronology is comprised of living and subfossil Scots pines (Pinus sylvestris L.) sampled close to the present tree-line in the central Scandinavian Mountains.....Several periods of anomalously warm and cold summers were noted throughout the record: (1) 550 to 450 BC (Roman Warm Period), when summer temperatures were the warmest of the entire record, exceeding the 1961-1990 mean by more than 6°C, (2) AD 300 to 400 (Dark Ages Cold Period), which was "the longest period of consecutive cold summers," averaging 1.5°C less than the 1961-1990 mean, (3) AD 900 to 1000, a warm era corresponding to the Medieval Warm Period, and (4) AD 1550 to 1900, a cold period known as the Little Ice Age..... With respect to the latter portion of the tree-ring record, which encompasses the period of modern global warming, Linderholm and Gunnarson declare that this phenomenon "does not stand out as an anomalous feature in the 3600-year record, in fact other periods show more rapid warming and also higher summer temperatures." What should be even more embarrassing to the world's climate alarmists is the fact that the last half of the 20th century actually experienced cooling."
Read here. Map source here. Scientists studied the extended warm period (interglacial) prior to the last major ice age. That prior warm period happened some 125 thousand years ago. Using a sediment core from a German lake, the scientists analyzed the quantity of pollen grains found in the core. Approximately every 1,500 years during the ancient interglacial, the climate changed from a warming phase to a cooling phase. The current interglacial, since the end of the last ice age about 15 thousand years ago, shares this same, every 1,500 year oscillation of warming-to-cooling climate changes.
The scientists involved in the study suggest this natural 1,500 year oscillation, found in both the ancient interglacial and the one we live in, is likely due to solar forces.
"The results of the authors' analysis revealed the presence of 11 major cold events having an average recurrence time of approximately 1450 years over the course of the last interglacial, which periodicity is essentially identical to the millennial-scale oscillation of climate throughout the current interglacial (Bond et al., 1997, 2001; deMenocal et al., 2000; McDermott et al., 2001; Gupta et al., 2003; Hu et al., 2003).....This study adds to the growing body of evidence that earth's climate oscillates in a well-defined manner on a timescale of approximately 1500 years. This knowledge is very important, for it suggests that something other than the historic buildup of carbon dioxide in the atmosphere may be responsible for 20th-century warming..... Indeed, there is absolutely no evidence for any concomitant oscillation in the air's CO2 content accompanying the 1500-year oscillation of climate that was responsible for the warmings that produced the prior Medieval Warm Period and the still earlier Roman Warm Period,"
Read here. Map source here. Using sediment cores and two different techniques of analysis, scientists confirm in a peer-reviewed study that Medieval Warming peak sea surface temperatures adjacent to Greenland were some 3°C higher than modern temperatures, both in the winter and summer. No wonder Erik the Red found Greenland so agreeable and attractive.
"The authors developed a high-resolution record of ocean and climate variations during the late Holocene in the Fram Strait.....based on detailed analyses of a sediment core recovered.....sea surface temperature (SST) histories were "nearly identical and show oscillations between -1°C and 5.5°C in winter and between 2.4°C and 10.0°C in summer,".....the mean SSTs of summers were warmer than those of the present about 80% of the time, while the mean SSTs of winters exceeded those of current winters approximately 75% of the time.....The highest temperatures of all were recorded in the vicinity of 1320 cal. years BP, during a warm interval that persisted from about AD 500 to 720 during the very earliest stages of the Medieval Warm Period"
Read here. In the broad realm of empirical evidence for Medieval Warming, there is one unique indicator that does not require a Phd to appreciate and understand - that would be tree lines. In general, if the climate is warmer, the tree line will move farther north and/or to higher elevations. As scientists discovered in the Ural Mountains, the modern tree line is at a much lower elevation than the Medieval tree line.
"Most importantly, Mazepa reports that "a large number of well-preserved tree remains can be found up to 60-80 meters above the current tree line, some dating to as early as a maximum [our italics] of 1300 years ago," and that "the earliest distinct maximum in stand density [our italics] occurred in the 11th to 13th centuries, coincident with Medieval climatic warming.".....Noting that "dead trees located above the current tree-line ecotone provide evidence of the dynamic behavior in the location of the tree line in the recent past (Shiyatov, 1993, 2003)," Mazepa reports that "previous studies have concluded that increases in tree-line elevation, and associated increases in tree abundance within the transient tree-line ecotone, are associated with extended warm periods"
Read here. Map source here. Government funded climate scientists and Gore-led warming alarmists constantly attempt to mislead the public by implying that any present climate change is "unprecedented." Unfortunately for the alarmistas, the preponderance of peer-reviewed research documents significant climate change shifts over the last 5,000 years, with many of the shifts being of far larger magnitude. From this study of Alberta, Canada sediment cores, comes more irrefutable evidence of natural climate change prior to human CO2 emissions.
"Periods of both increasing and decreasing grain size (moisture availability) were noted throughout the 4000-year record at decadal, centennial and millennial time scales. The most predominant departures included several-centuries-long epochs that corresponded to the Little Ice Age (about AD 1500-1900), the Medieval Warm Period (about AD 700-1300), the Dark Ages Cold Period (about BC 100 to AD 700) and the Roman Warm Period (about BC 900-100).....The Pine Lake sediment record convincingly demonstrates the reality of the non-CO2-induced millennial-scale climatic oscillation that alternately brings several-century periods of dryness and wetness to the southern Alberta region of North America during concomitant periods of relative hemispheric warmth and coolness, respectively. It also demonstrates there is nothing unusual about the region's current moisture status"
Read here. As common sense science would surmise, the Antarctic region follows a natural cycle of cooling and warming. As the scientists have now found, new peer-research confirms these type of dominant Antarctic warming/cooling cycles - and human CO2 emissions are found not to be the relevant driving force.
"Historical records for the western Antarctic Peninsula (WAP) show that it is particularly prone to rapid climate change—change that occurs in cycles of ~200 years and ~2500 years.....ice in the Antarctic region undergoes periodic episodes of rapid melting—and it is all entirely natural, not because of human activity. The new paper echos these findings: “Paleo-records show that analogous climate variations have occurred in the past 200 to 300 years, and over longer 2500-year cycles, with rapid (decadal) transitions between warm and cool phases in the WAP."....."Their conclusion was that “variability of these parameters demonstrates the significance of both short-term cycles, which recur approximately every 200 yr, and longer term events (~2500 yr cycles) that are most likely related to global climatic fluctuations.”"
Read here. Map source here. Scientists construct temperatures over the last 1,000 years from Scottish fjord sediment cores. The past temperatures of some 500 years ago reveal a rate of change warming and absolute temp levels that equal those of the late 20th century. Again, another peer-reviewed study confirms the natural state of constant temperature and climate change regardless of low/high CO2 atmospheric levels.
Summary: Today's temperatures are not unusual, nor unprecedented.
"The results of the two researchers' most recent efforts revealed that the most distinctive feature of the Loch Sunart temperature record was an abrupt warming at AD 1540 that led to a temperature anomaly of 1.1°C above the long-term mean from AD 1540-1600.....Noting that "the rate and magnitude of the inferred warming at AD 1540... is similar to the rate of change and magnitude observed during the late twentieth century," Cage and Austin concluded that "changes in twentieth century marine climate cannot yet be resolved from a background of natural variability over the last millennium," which is another way of saying that late 20th-century warming was not unusual enough to validly ascribe it to the concomitant increase in the air's CO2 content."
Read here. IPCC scientists still claim that the Medieval Warming was limited to the northern European region despite all the evidence otherwise. Adding to that 'otherwise,' researchers documented a confirmed Medieval warming and associated dry precipitation levels within the Panama region, near the Equator.
"The authors conclude that "the correspondence between warm medieval temperatures and dry hydrologic anomalies in Panama supports a large-scale Medieval Climatic Anomaly that may have been global in extent, and involved atmospheric circulation reorganizations that are linked to ENSO.".....noting that such reorganizations of earth's climate system are not dependent on rising atmospheric CO2 concentrations to trigger them, and, therefore, that the development of the Modern Warm Period likely was largely unrelated to the concomitant increase in the air's CO2 concentration"
Read here. Map source here. Scientists, using sediment cores, determine that all the historical, major climate changes have impacted the Southern Hemisphere at approximately the same times as impacting the Northern Hemisphere.
"Signy Island [in Southern Ocean, near Antarctica] is seen to have experienced the relative warmth of the last vestiges of the Roman Warm Period...Then comes the Dark Ages Cold period...after which the Medieval Warm Period appears at the same point in time and persists for the same length of time that it does in the vicinity of Ireland, whereupon the Little Ice Age sets in just as it does in the Northern Hemisphere. Finally, there is an indication of late 20th century warming, but with still a long way to go before conditions comparable to those of the Medieval Warm Period are achieved..... it demonstrates that the global warming of the past century, which led to the demise of the Little Ice Age, is but the most recent phase of a natural climatic oscillation that is totally unrelated to the increase in the air's CO2 content that just happened to coincide with its occurrence."
Read here. The research keeps being conducted, providing further scientific evidence that the Medieval Warming was considerably warmer that the current period warming of the late 20th and early 21st century. The irrefutable climate data continues to mount regarding the extreme variation in historical temperatures, as this chart indicates. (click on image to enlarge)
"Kobashi et al. (2010)constructed a history of the last thousand years of central Greenland surface air temperature, based on values of isotopic ratios of nitrogen and argon...from air bubbles trapped in the GISP2 ice core that had been extracted from central Greenland...results reveal that the latter part of the Medieval Warm Period was approximately 1.67°C greater than the temperature of the last decades of the 20th century, which climate alarmists claim to have been the warmest of the past millennium."
Read here. Map
Why do we say "huge" for the post-Roman period? Climate alarmistas are in
an existential panic about a global temperature change of 0.7°C since
1880, per the National Climate Data Center (NCDC) data. A fair amount of that
increase in temperatures since 1880 is natural versus the small AGW
increase since 1970; and, the total 0.7 temperature change is significantly less
than the post-Roman 2.0 degree change - 2.0 is huge versus 0.7.
The historical evidence
points to past periods experiencing much greater temperature variation
and associated climate change, and the South China Sea is yet another
Sr/Ca ratios of two Porites corals from the coast of Leizhou
Peninsula in the northern South China Sea were measured.....From the
Dark Ages Cold Period portion of the coral record, Wei et al. determined
that the average annual SST was approximately 2.0°C colder than that of
the last decade of the 20th century (1989-2000), while from the Roman
Warm Period portion of the record they obtained a mean annual
temperature that was identical to that of the 1989-2000 period as
measured at the Haikou Meteorological Station.....As has been
demonstrated many times before in a number of places throughout the
world, these data indicate that the last decade of the 20th century did
not display unusual or unprecedented warmth. Indeed, there were prior
times within both the Medieval Warm Period and Roman Warm Period when
temperatures were equally as warm as, or actually warmer than, what
they have been recently; and all of these earlier warm periods occurred
at times when the air's CO2 concentration was fully 100 ppm less than
what it is today"
Map source here. Read here. Anderson et al. used sea core sediments to reconstruct temperatures of the Norwegian Sea surface over the last 3,000 years. Research clearly identified the Roman warming, Dark Ages cooling, Medieval warming and the Little Ice Age cooling. Research also showed historical temperatures warmer than those experienced in the Norwegian Sea during the modern era.
"The climate history derived from this study is remarkably similar to that derived by McDermott et al. (2001) from a high-resolution speleothem ð18O record obtained from a stalagmite discovered in a cave in southwestern Ireland. At the beginning of the 3000-year-long Voring Plateau record, both regions were clearly in the end-stage of the long cold period that preceded the Roman Warm Period...both regions begin their descent into the Dark Ages Cold Period, which held sway until the increase in temperature that produced the Medieval Warm Period...Last of all, the Little Ice Age is evident, with cold periods centered at approximately 400 and 100 years BP.....Andersson et al. report that "surface ocean conditions warmer than present were common during the past 3000 years."
Read here. Scientists who base their livelihoods on global warming research funding claim that late 20th century warming was "unprecedented." This specific claim is embarrassingly false, and more peer-research science (study of fossil dinoflagellate cysts and pollen from sediment cores) from the Chesapeake Bay waters confirms that.
"The authors report that "several dry periods ranging from decades to centuries in duration are evident in Chesapeake Bay records." The first of these periods of lower-than-average precipitation, which spanned the period 200 BC-AD 300, occurred during the latter part of the Roman Warm Period,.....The next such period (~AD 800-1200), in the words of the authors, "corresponds to the 'Medieval Warm Period',..... First, it [Willard et al. research] demonstrates the reality of the millennial-scale hydrologic cycle that accompanies the millennial-scale temperature cycle that is responsible for producing alternating warm and cold intervals such as the Roman Warm Period, Dark Ages Cold Period, Medieval Warm Period, Little Ice Age and Modern Warm Period. Second, it [research] demonstrates that the global warming of the 20th century has not produced unusually strong wet and dry periods, contradicting climate-alarmist claims that warming will exacerbate extreme climate anomalies."
Read here. Scientists using the latest analysis techniques, conducted a high resolution analysis of the ice core retrieved from Antarctica's Dome C station. The Dome C is located on the eastern half of Antarctica, on the polar plateau with an elevation of 10,607 feet. (The more well-known Vostok polar station is located on the same plateau at a similar elevation, ~ 3,200 meters.)
What did this new high resolution analysis determine?
The Medieval Warming period had temperatures that approached 1°C higher than current temperatures, in spite of lower CO2 levels.
The Minoan Warming period had temperatures that possibly exceeded current temperatures by 1°C, in spite of lower CO2 levels.
The previous interglacial period, approximately 130,000 years ago, had temperatures in excess of 4°C versus current temperatures, in spite of lower CO2 levels.
Clearly, the new ice core data indicates that natural climate variations caused huge temperature variations in the past. Based on this empirical climate science, it would be safe to conclude that current climate changes are predominantly driven by natural forces (see this chart and post also), not human CO2 trace gas emissions. (click on image to enlarge)
This high resolution ice core data ends at the year 1912. The similarly situated Vostok polar station temperature record was used as proxy to assess polar plateau temperature increase/decrease over the last 60 years. As the Vostok temperature data reveals, current temperatures may actually be lower than what the Antarctica plateau experienced during the 1950's. In addition, peer-reviewed studies indicate Antarctica temperature change to be minimal over last two centuries.
Download this newest Dome C ice core research, source here.
Read here. Much has been made by global warming alarmists about the warming of Alaska since the 1970's and thus inferring it is due to human CO2 emissions. What they conveniently fail to mention is that most of the warming was due to a major PDO (Pacific Decadal Oscillation) shift to a warming phase that took place during the late 70's.
And, they always fail to point out that peer-reviewed research shows that the Alaskan climate was both warmer and cooler than the current climate over the last 2,000 years. (click on image to enlarge)
"In commenting on these findings, Hu et al. remark that "the warmth before AD 300 at Farewell Lake coincides with a warm episode extensively documented in northern Europe whereas the AD 600 cooling is coeval with the European 'Dark Ages'." They also say that "the relatively warm climate AD 850-1200 at Farewell Lake corresponds to the Medieval Climatic Anomaly, a time of marked climatic departure over much of the planet." And they say that "these concurrent changes suggest large-scale teleconnections in natural climatic variability during the last two millennia, likely driven by atmospheric controls.""....."Noting that "20th-century climate is a major societal concern in the context of greenhouse warming," Hu et al. conclude by reiterating that their record "reveals three time intervals of comparable warmth: AD 0-300, 850-1200, and post-1800," and they say that "these data agree with tree-ring evidence from Fennoscandia, indicating that the recent warmth is not atypical [it's not unusual] of the past 1000 years,"
The U.S. has sponsored much climate research over recent decades, including the study of ice cores from Greenland. The National Climate Data Center (NCDC), a NOAA organization, maintains the Greenland ice core temperature data, which can be downloaded from their web site.
Fortunately, this Greenland ice core temperature data allows for an analysis of temperature change from minimum (trough) temperature to maximum temperature (peak) over extended time spans. Likewise, temperature change from maximum to minimum can also be analyzed. Sooo, what does that NCDC ice core temperature data actually indicate about temperature change?
1. Huge temperature swings have occurred naturally over thousands of years, prior to any human CO2 emissions.
2. The Modern warming increase (see pink arrow/dot on chart) since the bottom of the Little Ice Age (around 1840) has been minuscule versus all previous warming period temperature changes when compared to their respective cooling period trough that preceded.
3. Over the 9,000 years, the average temperature increase from the trough of the preceding cooling period to the next temperature peak has exceeded 2.0°C. In contrast, the Modern warming has barely reached a 0.7°C increase since the Little Ice Age cooling trough.
4. There have been nine significant warming trends leading to temperature peaks over last 9,000 years; and, all exceed the Modern warming trend in terms of absolute degree change (increase).
5. There have been nine significant cooling periods over the same time span. Many cooling periods have seen temperatures decline by over 2.0°C.
6. The average number of years between temperature warming peaks is approximately 990 years. Since the last peak around 1040 A.D., it has now been 970 years, which suggests the current warming period is close to peaking before the next natural cooling period dominates.
7. All scientists agree that all extreme temperature changes prior to the 20th century were of natural origin. In contrast, it's only climate alarmist scientists who believe that the temperature change since the Little Ice Age is all man-made (see pink arrow/dot).
(click on image to enlarge)
Note: The Greenland ice core data ends in early 20th century; the pink arrow and dot have been added to indicate the "consensus" temperature increase through 2009 since the LIA end mid-19th century.
Read here (also read the comments for further information). It would seem that an Ohio State global warming advocate scientist, in association with researchers at Michael Mann's Penn State climate group, conducted a study of previous studies on Arctic sea ice. This Ohio State study makes the very vague claim that sea ice loss "appears to be unmatched over at least the last few thousand years,”.
The researchers comments about their study suggests that science and statistical techniques they utilized may be of 'Mannian' nature, which have proven to be black magic, at best.
"When we look carefully at various chemical and biological components of the sediment, and how the sediment is distributed — then, with certain skills and luck, we can reconstruct the conditions at the time the sediment was deposited.”....."They searched for patterns in the proxy data that fit together like pieces of a puzzle."
Any science that is based on "certain" skills and some "luck", while only seeking data that "fit together like pieces of a puzzle" and thus rejecting data that does not conform to the IPCC global warming hypothesis, sounds an awful lot like the discredited hockey-stick style of science.
The Greenland ice cores provide the best evidence of Arctic cooling and warming, which would be an excellent indicator of likely past sea ice conditions. It would appear the Ohio State researchers in choosing their "puzzle pieces" rejected the best data available, the non-conforming ice core data. (click on images to enlarge)
Per the Greenland ice cores, current Arctic temperatures are well within the range of past warming events. In fact, current Arctic warming has not reached the levels of past historical and ancient warming. These images and other historical temperature charts can be found here. Other climate history postings. Modern temperature charts.
Scientists involved with the study of ancient and historical climates
are well aware of the impact that nature's major cooling and warming
oscillations have on the environment. Cold periods, such as the Little
Ice Age (LIA), can be very destructive to plant life, literally causing
vegetation to shift southward in the Northern Hemisphere seeking warmth.
Once natural warming returns though, vegetation will shift back to its
previous northern boundaries.
This is exactly what happened with
the forests of northern Canada. After the LIA, the tree line shifted in
some areas up to 200 kilometers farther north.(click image to enlarge)
1772: “I have observed during my several journeys in those parts that
all the way to the north of Seal River the edge of the wood is faced
with old withered stumps, and trees which have been flown (sic) down by
the wind….Those blasted trees are found in some parts extend to a
distance of twenty miles from the living woods, and detached patches of
them are much farther off; which is proof that the cold has been
increasing in these parts for some ages. Indeed some of the older
Northern Indians have assured me that they have heard their fathers and
grandfathers say, they remembered the greatest part of those places
where the trees are now blasted and dead, in a flourishing state.”
Read here. The Roman Warming was an extended period of atypical warmth associated with low levels of atmospheric CO2. Neither alarmists nor climate models have any explanation for this period of natural warming. Typical alarmist response is that Roman Warming was just a regional condition, despite a slew of peer-reviewed research finding it was of global nature.
"Hence, they cannot stomach the thought that the Medieval Warm Period of a thousand years ago could have been just as warm as, or even warmer than, it has been recently, especially since there was so much less CO2 in the air a thousand years ago than there is now. Likewise, they are equally loath to admit that temperatures of the Roman Warm Period of two thousand years ago may also have rivaled, or exceeded, those of the recent past, since atmospheric CO2 concentrations at that time were also much lower than they are today. As a result, climate alarmists rarely even mention the Roman Warm Period, as they are happy to let sleeping dogs lie."
Read here. Well....the scientists didn't really use the term 'crap' but the terminology 'beaver-pond deposits' sounds awful suspicious, no? Anyways, beavers habitat is adversely affected by drought conditions, which occurred in Yellowstone during both the Roman and Medieval warmings. It became so dry during these warming periods that beaver activity in Yellowstone was severely diminished.
"Persico and Meyer report that "gaps in the beaver-pond deposit record from 2200-1800 and 700-1000 cal yr BP are contemporaneous with increased charcoal accumulation rates in Yellowstone lakes and peaks in fire-related debris-flow activity, inferred to reflect severe drought and warmer temperatures (Meyer et al., 1995)." In addition, they note that "the lack of evidence for beaver activity 700-1000 cal yr BP is concurrent with the Medieval Climatic Anomaly, a time of widespread multi-decadal droughts and high climatic variability in Yellowstone National Park (Meyer et al., 1995) and the western USA (Cook et al., 2004; Stine, 1998; Whitlock et al., 2003)," while we note that the lack of evidence for beaver activity 2200-1800 cal yr BP is concurrent with the Roman Warm Period...Once again, these findings suggest there is nothing unusual, unnatural or unprecedented about the degree of warmth and drought of the Current Warm Period, in contrast to what climate alarmists continually claim."
Read here. Map source. Scientists analyze lake sediment core stretching back some 1,500 years. The core reveals extreme warmth of Medieval Warming and the cold of the Little Ice Age.
"The authors inferred the thermal conditions of Smreczynski Staw Lake in the Tatra Mountains of southern Poland via analyses of the distributions of various cladocera, chironomid and diatom species they identified and quantified in a sediment core they had extracted from the center of the lake in the spring of 2003, which contained sediments that had accumulated there over the prior 1500 years...once again we have another demonstration of the fact that the peak warmth of the late 20th-century and the early 21st-century has not been as unprecedented as the world's climate alarmists have typically claimed it to be."
The AGW hypothesis states that human CO2 emissions will cause the world
to warm, with the the globe's polar areas being especially vulnerable to
rapid warming, due to CO2. The evidence from the last 1,000 years plus does not support the hypothesis.
Previously, we examined the data from Antarctica. Now we look at the actual Arctic area data (see chart below) and find that like the Antarctic, the northern polar regions have temperature swings unrelated to the CO2 levels. From peak to valley, Arctic temperatures changed more than 1.6 degrees Celsius while CO2 levels remained fairly stable. (click on image to enlarge)
Despite the alarmist claims of polar regions melting due to CO2-induced warming, there is no evidence to support that claim, either historically or currently. In fact, the highest temperatures reached over the last 1,000+ years were during the Medieval Period (about 1,000 years before present) when CO2 levels were close to being their lowest, based on the ice core data.
Temperature data is from the Greenland GISP II ice core, which ends in year 1905. CO2 levels are from the same dataset used in the previous Antarctica graph.
Read here. Researchers discovered sediment core evidence that the Little Ice Age in Africa was likely to have been driven by solar changes. Multiple lakes, including Masoko, Malawi, Chilwa, Chiuta, and Tanganyika, indicate a solar impact at work over 500 years, not human CO2 emissions.
"In the words of the ten researchers who conducted the work, "magnetic, organic carbon, geochemical proxies and pollen assemblages indicate a dry climate during the 'Little Ice Age' (AD 1550-1850), confirming that the LIA in eastern Africa resulted in marked and synchronous hydrological changes...In discussing their findings, the African and French scientists note that the Little Ice Age in Africa appears to have had a greater thermal amplitude than it did in the Northern Hemisphere... In addition, the group of scientists emphasizes that the positive correlation of Lake Masoko hydrology with various solar activity proxies "implies a forcing of solar activity on the atmospheric circulation and thus on the regional climate of this part of East Africa.""
Read here. Map source. Researchers document that this area of the Himalayas experienced a Roman warming period similar in temperatures to recent modern warming; and, the same area experienced higher than modern temperatures during the Medieval Period.
"The authors developed a relative history of atmospheric warmth and moisture covering the last 1800 years for the region surrounding Paradise Lake -- which is located in the Northeastern Himalaya based on pollen and carbon isotopic (δ13C) analyses of a one-meter-long sediment profile they obtained from a pit "dug along the dry bed of the lakeshore...Bhattacharyya et al. report that their climatic reconstruction revealed a "warm and moist climate, similar to the prevailing present-day conditions," around AD 240 -- which would represent the last part of the Roman Warm Period -- as well as another such period that turned out to be "more warmer 1100 yrs BP (around AD 985) corresponding to the Medieval Warm Period...occurring at times when the atmosphere's CO2 concentration was more than 100 ppm less than it is today."
Read here. Recently, Phil Jones in an interview with the BBC: "...he agreed that the debate had not been settled over whether the
Medieval Warm Period was warmer than the current period." Why would he make such a statement after so many years claiming the opposite?
As Phil Jones knows full well from his own research, the Medieval Warming Period was highly likely to have experienced warmer temperatures than current temperatures per the proxy reconstructions (below graph represents proxy reconstructions only). In a 2003 study that he published with Mann, the proxy reconstructed temperatures clearly show warmer historical temperatures (see blue and green lines on graph below) and that modern temperatures were not accelerating (note steepness of slope of red curve at different points in time) as quickly as they had done in the past.
In addition, when viewing the graphical representation of the proxy temperatures (minus any instrumental temperature records) the claim that modern warming is solely a result of human-CO2, versus all previous historical warmings being the result of only natural forces, is obviously ludicrous to assert. (click on image to enlarge)
"First of all, granting them almost everything they have done, it can readily be seen from their own graph of their own results that the end point of their reconstructed global mean temperature history is not the warmest period of the prior 1800 years. In fact, their treatment of the data depicts three earlier warmer periods: one just prior to AD 700, one just after AD 700 and one just prior to AD 1000...as tree-ring data comprise the bulk of the proxy temperature information employed by Mann and Jones, their reconstructed global mean temperature history must possess a non-temperature-induced pseudo-warming signal driven by CO2- and nitrogen-induced increases in growth that make 20th century warming appear significantly greater than it really is....Their data, however, speak for themselves in clearly demonstrating that late 20th century global warmth was not unprecedented over the past two millennia."
Read here and here (PDF). Scientists produced a temperature reconstruction from a cave's stalagmite. Roman and Medieval warmings found to range from 1.1°C to 2.3°C higher than the 3,000 year mean. The Little Ice Age climate temperatures documented to have been 1.2°C lower than mean. In summary, the stalagmite records reveal a climate range of temperature changes of 3.5°C, prior to any industrial/consumer CO2 emissions from fossil fuels.
"The climate record derived from China's Jingdong Cave is just another example of what is being found in paleoclimate studies all around the world. There is an externally-forced millennial-scale climatic oscillation of probable solar origin that periodically brings the world relatively warmer and colder conditions, irrespective of whatever may or may not be happening to the air's CO2 content. The Modern Warm Period would thus appear to be nothing more than the most recent expression of this phenomenon."
Read here. IPCC global warming scientists and their climate models have been predicting more floods due to human-caused, CO2 warming. Like most predictions by climate model scientists, their predictions are not based on actual scientific evidence. When the proper research was done, scientists discovered that floods occur with significantly more frequency during global cooling periods, such as the Little Ice Age.
"Benito et al. report that the combined palaeoflood and documentary records indicate that past floods were clustered during particular time periods: AD 950-1200 (10), AD 1648-1672 (10), AD 1769-1802 (9), AD 1830-1840 (6), and AD 1877-1900 (10), where the first time interval coincides with the Medieval Warm Period and the latter four time intervals all fall within the confines of the Little Ice Age; and calculating mean rates of flood occurrence over each of the five intervals, we obtain a value of 0.40 floods per decade during the Medieval Warm Period, and an average value of 4.31 floods per decade over the four parts of the Little Ice Age, which latter value is more than ten times greater than the mean flood frequency experienced during the Medieval Warm Period."
The AGW hypothesis states that human CO2 emissions will cause the world to warm, with the the globe's polar areas being especially vulnerable to rapid warming, due to CO2. Without any hesitation, not waiting for any actual empirical evidence, global-warming scientists and activists predicted that Antarctica will melt, causing incredible sea level increases.
It has not come true, and is not about to happen based on real world, scientific reality. (click on image to enlarge)
Luckily for the world's inhabitants, the CO2-crazed "scientists," alarmists and gore-profiteers have been spectacularly wrong. The historical Antarctica temperatures and atmospheric CO2 levels provide proof that temperatures change significantly without a direct relationship to CO2 levels.
Per the Vostok ice cores, southern polar temperatures have made swings of 3 degrees Celsius during historical times while related CO2 levels have barely budged. And when 20th century human CO2 emissions increased dramatically? Vostok polar ice sheet temperatures have stayed flat. (Note: The mean temperature for Vostok over the ice core history has been a minus 55 degrees Celsius. The ice sheet won't be melting even if there were swings in temperature of 20 degrees.)
Note: More evidence that the climate has experienced wide temperature changes prior to any industrial/consumer CO2 emissions, similar to what the Vostok ice cores reveal.
During U.S. Senate testimony (2005), evidence was presented that revealed multiple studies supporting a consensus that the Medieval Period experienced extreme warming that matches or exceeds any modern, post-1970's warming. The multi-graph below represents the research from major climate researchers that was presented at the Senate testimony. It's of interest to note that none of these scientists are considered global warming "skeptics." (Source of multi-graph from 2005 testimony.)
Besides these studies, hundreds of scientists have conducted research that more often than not, confirm that Medieval Warming was unprecedented. For a quick review of historical climate charts that show this, go here. In addition, C3 has compiled a page that includes climate-history postings, with and without charts. (click on image to enlarge)
"According to the six scientists, we understand, for the most part, the shape of long-term climate fluctuations better than their amplitudes. For instance, nearly all 1000-year temperaturereconstructions capture the major climatic episodes of the Medieval Warm Period, Little Ice Age and Current Warm Period; but for various reasons they exhibit differences in the degree of climatic warming or cooling experienced in the transitions between them, which for decadal means may amount to as much as 0.4 to 1.0°C...knowledge of the correct amplitude of the major climatic episodes of the past millennium is "critical for predicting future trends." Why? Because if it can be shown that the amplitudes of the major historical climate episodes were as large as, or even greater than, that of 20th-century global warming, there would be a "redistribution of weight towards the role of natural factors in forcing temperature changes, thereby relatively devaluing the impact of anthropogenic emissions and affecting future predicted scenarios.""
Read here, PDF, here, here and here. Way back in 1997, researchers published a paper that was based on data from 6,000 plus borehole sites from all the continents. The reconstructed temperatures clearly showed a Medieval Period warming that was, and is, unprecedented. The data also makes clear that subsequent warming began well before the growth of human CO2 emissions and this natural rebound would obviously lead to temperatures similar to the Medieval Period.
A year later, the infamous Mann hockey-stick temperature chart was published to wild acclaim by the IPCC and AGW-centric activists. So popular did the Mann chart become, the 6,000+ borehole chart was completely ignored since its data refuted the Mann study. The borehole scientists then decided to re-publish their study with primarily only the blue-side (the typical AGW-favored data cherry-picking) of the chart below. This repackaged borehole study became accepted by the AGW-centric scientists as it seemed to support their cause and the Mann's hockey-stick. (click on image to enlarge)
"The authors searched the large database of terrestrial heat flow measurements compiled by the International Heat Flow Commission of the International Association of Seismology and Physics of the Earth's Interior for measurements suitable for reconstructing an average ground surface temperature history...Based on a total of 6,144 qualifying sets of heat flow measurements obtained from every continent of the globe, they produced a global climate reconstruction, which, they state, is "independent of other proxy interpretations [and] of any preconceptions or biases as to the nature of the actual climate history."...From their reconstruction of "a global climate history from worldwide observations," the authors found strong evidence that the Medieval Warm Period was indeed warmer than it is now."
"Quite suddenly, the same borehole authors - Pollack, Huang, Shen published a new, two-page-long paper in Nature: it appeared in October 1998. The paper contained a rather different graph than the graph from 1997...The new paper was using temperatures and 358 sites only instead of the 6000 sites used in 1997 (94 percent of sites eliminated) and it has erased 19,500 years out of 20,000 years (97.5 percent of the time interval eliminated) from the paper written in 1997 in order not to contradict Mann et al....That's what they call "independence". Moreover, if someone wanted to extend the record as far as possible while avoiding any hints of a warmer period in the past such as the medieval warm period, he would have made the same cut: 500 years ago. What a coincidence."
Read here. Map here. France's Burgundy region farmers, famous for their wines, also had the foresight to record grape harvest data going back to the ending of the Medieval Warming Period. Using that evidence, researchers constructed a temperature record revealing a very slight cooling since the hot temperatures of the Medieval Warming.
Clearly, this unique record reveals that modern era temperatures are in no manner "unprecedented," especially when compared to the warmth of the lengthy period that stretches from 1370 through the 1600's. There is an exceptional modern year, though. During summer of 2003 (very last data point on chart), France experienced the late summer extreme, freak heat wave that was later found to have a non-global warming basis. (click on image to enlarge)
"In this respect, the Chuine et al. temperature history forcefully rebuts the hockeystick-derived claim of the world's climate alarmists that air temperatures of the last two decades of the 20th century were unprecedented over the past millennium and possibly over the past two millennia (Mann and Jones, 2003)...great importance of the Chuine et al. findings is that if it was warmer than it is now during parts of the 1300s, 1400s and 1600s, when there was far less CO2 in the air than there is currently (perhaps as much as 100 ppm less), it is reasonable to believe that whatever was responsible for the warmth of those earlier times may be responsible for much of the warmth of the present era (or perhaps even all of it)"
Read here. Map here. Studying the fossil remains of trees located under a Swiss glacier, scientists verify that the treeline was some 200 meters higher than the current one. This indicates that Medieval Warming Period (MWP) was not only warmer, but lasted an extended period.
"Based on radiocarbon dating of the fossil wood remains of eight larch fragments found one meter beneath the surface of the ground at the base of the front of the Piancabella rock glacier,... the authors determined that the wood was formed somewhere between AD 1040 and 1280 ...Then, based on this information and "geomorphological, climatological and geophysical observations," they inferred that "the treeline in the Medieval Warm Period was about 200 meters higher than in the middle of the 20th century, which corresponds to a mean summer temperature as much as 1.2°C warmer than in AD 1950."...adjusting for warming between 1950 and the present, we calculate that the MWP was about 0.5°C warmer than the peak warmth of the CWP."
Read here. Climate alarmist scientists claim that global warming will unleash weather related natural disasters with a severity the world has never experienced before, and it's already started. This specific type of alarmism is entirely fabricated with no relationship to reality and past experience. Most severe weather events and related natural disasters occur during a climate cooling condition, not warming, as recent Chinese peer-reviewed research shows:
Speaking of the last of the overbank flooding episodes, they note that it "corresponds with the well documented 'Little Ice Age,' during which there were frequent natural disasters including catastrophic floods, droughts, dust storms, heat waves, migratory locusts and frequent famines and plagues in the middle-lower reaches of the Yellow River drainage basin," when "climate departed from its long-term average conditions and was unstable, irregular, and disastrous," which is pretty much like the Little Ice Age has been described in many other parts of the world as well.
Read here. This must have been extremely painful to those scientists claiming modern temperatures are "unprecedented," and had devoted a portion of their career towards fabricating "hockey stick" confirmations, as revealed by the Climategate emails.
As for what this result implies, the researchers conditionally -- and rather amusingly -- state that further warming of present day Greenland climate "will result in temperature conditions that are warmer than anything seen in the past 1400 years." But, of course, their work more directly and unconditionally implies that late 20th-century and early 21st-century weather has not yet been warm enough to confer "unprecedented" status upon Greenland air temperatures. What is more, Vinther et al. readily admit that the independent "GRIP borehole temperature inversion suggests that central Greenland temperatures are still somewhat below the high temperatures that existed during the Medieval Warm Period."
Read here. Across the globe, more evidence is being found that indicates that the Medieval warming temperatures were definitely higher than the current "unprecedented" temperatures mistakenly(?) claimed by politicians. The latest peer-reviewed research out of China confirms this.
...they say that "regional proxy temperature series with lengths of 500-2000 years from China have been reconstructed using tree rings with 1-3 year temporal resolution, annually resolved stalagmites, decadally resolved ice-core information, historical documents with temporal resolution of 10-30 years, and lake sediments resolving decadal to century time scales,"...Since portions of two of the four sections of China for which temperature reconstructions extended far enough back in time to sample the Medieval Warm Period exhibited temperatures comparable to those of the late 20th century, and since portions of two other sections actually revealed parts of the Medieval Warm Period to have been warmer than the late 20th century, it is clear that there is nothing unusual, unnatural or unprecedented about the country's current level of warmth. Hence, by the reasoning set forth by Ge et al. in the introduction to their study, there is no compelling reason to attribute late 20th-century warmth in that sprawling country to 20th-century increases in the air's CO2 concentration...
Read here. Despite its name, Iceland was a very hot spot during the Medieval Period.
Even with its volcanoes now awakening, Iceland is still a chilly place compared to 1,000 years ago. Source of map here. (click on images to enlarge)
Working with biogenic silica (BSi) and total organic carbon (TOC) data obtained from two sediment cores retrieved from Haukadalsvatn (65°03.064'N, 21°37.830'W) -- a lake in northwest Iceland -- and a 170-year instrumental temperature history that was obtained from Stykkisholmur (50 km distant), the authors identified "a broad peak in BSI and lack of a trend in TOC between ca. 900 and 1200 AD," which they described as being indicative of "a broad interval of warmth" that was "coincident with the Medieval Warm Period," and which clearly exhibited much greater warmth than was observed at any time during the Current Warm Period.
Read here. The extreme warmth and global existence of the Medieval Warming is again highlighted in the peer-research conducted in the Gulf of California's Pescadero Basin. No doubt about it: Medieval temps were hot and not just a northern Europe climate condition. (click on image to enlarge)
Researchers developed high-resolution records of diatoms and silicoflagellate assemblages spanning the past 2000 years from analyses of a sediment core extracted from Pescadero Basin in the Gulf of California (24°16.78'N, 108°11.65W). Results indicated that the relative abundance of Azpeitia nodulifera (a tropical diatom whose presence suggests the occurrence of higher sea surface temperatures), was found to be far greater during the Medieval Warm Period than at any other time over the 2000-year period studied, while during the Modern Warm Period its relative abundance was actually lower than the 2000-year mean.
Map source. Read here. Researchers continue their quest to fill in the historical temperature/climate gaps, which will help policy makers and the public better understand how past climate differs and resembles modern times.
As with almost all non-tree ring temperature reconstructions, the evidence grows that the Medieval Warming produced temperatures higher than current modern ones. In addition, the MWP evidence points to an extended period of warming during Medieval times. (click on image to enlarge)
Working with two replicate sediment cores extracted from the central point of Lake WB02 in the Wynniatt Bay region of Canada's Northern Victoria Island, the authors developed an 8,000-year history of the area's mean July air temperature, based upon the modern analogue technique (MAT) and weighted averaging partial least squares (WAPLS) regression, utilizing chironomid species assemblage data. As best we can determine from their graphical results, late-Holocene temperatures peaked about 1100 years ago in both reconstructions, at values that were (1) approximately 3.8°C warmer than the peak temperature of the Current Warm Period (CWP), which occurs at the end of their record in the AD 1990s in their MAT analysis, and (2) approximately 1.0°C warmer than the peak temperature of the CWP, which also occurs at the end of their record in their WAPLS analysis.
Read here. Across the globe, researchers have found a wide range of evidence indicating the extreme warm temperatures and impact of the Medieval Warming. One of the many characteristics of extreme warming is the change in precipitation levels of the northern latitudes, which experience less precipitation. These regions become much more vulnerable to drought conditions that the extreme warming of climate change brings. For more information on droughts and severe weather, go here.
As peer reviewed research has found, the extreme warming of the Medieval Warming Period is unique and unprecedented, as indicated by the drier (drought) conditions that Finland trees experienced. (click on image to enlarge)
Helama et al. developed what they describe as "the first European dendroclimatic precipitation reconstruction," based on data obtained from hundreds of moisture-sensitive Scots pine tree-ring records originating in southern Finland, using regional curve standardization (RCS) procedures. This work revealed, as they describe it, a "distinct and persistent drought, from the early ninth century AD to the early thirteenth century AD," which interval, in their words, "precisely overlaps the period commonly referred to as the Medieval Climate Anomaly, due to its geographically widespread climatic anomalies both in temperature and moisture.
Read here. The Indo-Pacific ocean area represents the warmest volume of water known to exist naturally. Soooo, is that pool of warm water the warmest it's ever been? Is it experiencing the "unprecedented" warmth that alarmists always speak of? Nope, not even close - it's "lukewarm" compared to the Roman and Medieval warming eras. (click on image to enlarge)
Oppo et al. derived a continuous sea surface temperature (SST) reconstruction from the Indo-Pacific Warm Pool (IPWP), which they describe as "the largest reservoir of warm surface water on the earth and the main source of heat for the global atmosphere."....spans the past two millennia and, as they describe it, "overlaps the instrumental record, enabling both a direct comparison of proxy data to the instrumental record and an evaluation of past changes in the context of twentieth century trends." Reconstructed SSTs were, in their words, "warmest from AD 1000 to AD 1250 and during short periods of first millennium." From the authors' Figure 2b, adapted below, we calculate that the Medieval Warm Period was about 0.4°C warmer than the Current Warm Period.
Read here. This peer-reviewed Gulf of California research uses temperature proxy evidence (sediment core diatoms and silicoflagellate assemblages) that reveals modern global warming not to be very global, nor very robust. Actual, but inconvenient thermometer evidence corroborates both conditions.
Additional temperature proxies, such as tree-rings, also indicated that modern global warming was mild to non-existent. In fact, the weak tree-ring data used by the infamous Climategate scientists is what eventually led to the fraudulent 'hide-the-decline' fiasco, which then resulted in this famous, entertaining and toe-tapping video (new version of video here).
Back to the science....below is Gulf of California data. (click on image to enlarge)
"Barron and Bukry developed high-resolution records of diatoms and silicoflagellate assemblages spanning the past 2000 years from analyses of a sediment core extracted from Guaymas Basin in the Gulf of California. Results indicated that the relative abundance of Azpeitia nodulifera (a tropical diatom whose presence suggests the occurrence of higher sea surface temperatures), was found to be far greater during the Medieval Warm Period than at any other time over the 2000-year period studied, while during the Modern Warm Period its relative abundance was actually lower than the 2000-year mean." [Barron, J.A. and Bukry, D. 2007, Marine Micropaleontology 62: 115-139]
Read here. Peer reviewed research of oyster remains in Hudson River estuary continues to add to the overwhelmingevidence that Roman and Medieval warmings exceeded modern temperatures.
"The authors located fossil oyster beds within the area of the Hudson River estuary....Results of their analyses indicated that "oysters flourished during the mid-Holocene warm period," when "summertime temperatures were 2-4°C warmer than today." Thereafter, the oysters "disappeared with the onset of cooler climate at 4,000-5,000 cal. years BP," but "returned during warmer conditions of the late Holocene," which they specifically identified as the Roman and Medieval Warm Periods....They further report that their shell dates suggest a final "major demise at ~500-900 years BP," which timing they describe as being "consistent with the onset of the Little Ice Age." Because the oyster beds of Tappan Zee have not been reestablished during the Current Warm Period, we conclude that temperatures in this region today are not as warm as they were during the MWP (~ AD 600-1250)."
Read here. Another study that documents the Medieval Period being one of greater warmth than the recent modern warming. The Little Ice Age coolness is also well documented in this study. (click on image to enlarge)
"Working with a sediment core extracted from the central and deepest part of Lake Teletskoye in the northeastern part of the Altai Mountains in southern Siberia, the authors analyzed pollen and charcoal stratigraphy....This work revealed the existence of a period "at least since ca. AD 1020" when "climate conditions were similar to modern [our italics]." Then, "around AD 1200, climate became more humid with the temperatures probably higher than today [our italics]," and this period "lasted until AD 1410.""
(click on image to enlarge) Read here. Full map source here. Approximately 700 to 1,000 years before current times, bird populations swelled on an island off the coast of Greenland. Using a 3.5 meter sediment core from a lake, researchers determined from bird "leavings" that natural warming attracted more birds.
"Key to the study were biogeochemical data that, in the words of the authors, reflect "variations in seabird breeding colonies in the catchment which influence nutrient and cadmium supply to the lake." This work revealed sharp increases in the values of the parameters they measured between about 1100 and 700 years before present, indicative of the summer presence of significant numbers of seabirds during what they described as a "medieval warm period," which had been preceded by a several-hundred-year period of little to no (inferred) bird presence. Thereafter, their data pointed to another absence of birds during "a subsequent Little Ice Age," which they say was "the coldest period since the early Holocene in East Greenland.""
Read here. (map from Mapquest.com). Many of the peer-reviewed research studies on historical climate conditions reveal an extended Medieval Warming Period that had two distinct high warmth peaks. The second peak around the 1400-1550 AD period was not as warm as the first peak (1000-1300 AD) but still produced climate temperatures similar to modern day temperatures. This second MW peak shows up well in the research on a sediment core from Venezuela's Cariaco Basin. (click on image to enlarge)
"Working with a sediment core extracted in 1990 from the northeastern slope of the Cariaco Basin, the authors derived an 800-year Mg/Ca history of the planktic foraminifer Globigerina bulloides....What stands out most boldly of all, however, is the remarkable rise and fall of the region's SST that occurred between the Medieval Warm Period and the Little Ice Age, which we call the Little MWP....Compared to its "bigger brother," the Little MWP gets much less respect. Nevertheless, its prowess is indicated by the fact that Black et al. write that "on average, twentieth-century temperatures are not the warmest in the entire record," which prize must obviously go to the central portion of the Little MWP."
Read here. View full map source here and/or click on image to enlarge. From the Sargasso Sea, researchers worked with a combination of "biweekly hydrographic data, a long history of sediment trap collections to document the rain of particles from the sea surface to the seafloor, and exceptional deep sea cores of sediment" to reconstruct sea surface temperatures stretching back some 3,000 years. The empirical evidence confirms that the Bermuda sub-tropical area experienced warmer temperatures during both the Roman and Medieval warming periods versus modern temperatures. (click on image to enlarge)
"The core-top data indicate temperatures of nearly 23 degrees, very close to the average temperature at Station S over the past 50 years. However, during the Little Ice Age of about 300 years ago sea surface temperatures were at least a full degree lower than today, and there was an earlier cool event centered on 1,700 years ago. Events warmer than today occurred about 500 and 1,000 years ago, during the Medieval Warm Period, and it was even warmer than that prior to about 2,500 years ago."
"These results are exciting for a few reasons. First, events as young and as brief as the Little Ice Age and the Medieval Warm Period have never before been resolved in deep sea sediments from the open ocean. Because the Sargasso Sea has a rather uniform temperature and salinity distribution near the surface, it seems that these events must have had widespread climatic significance. The Sargasso Sea data indicate that the Medieval Warm Period may have actually been two events separated by 500 years, perhaps explaining why its timing and extent have been so controversial."