Archives par mot-clé : Holocene

Less Ice In Arctic Ocean 6000-7000 Years Ago

by Geological Survey of Norway, October 20, 2008 in ScienceDaily


Recent mapping of a number of raised beach ridges on the north coast of Greenland suggests that the ice cover in the Arctic Ocean was greatly reduced some 6000-7000 years ago. The Arctic Ocean may have been periodically ice free.

”The climate in the northern regions has never been milder since the last Ice Age than it was about 6000-7000 years ago. We still don’t know whether the Arctic Ocean was completely ice free, but there was more open water in the area north of Greenland than there is today,” says Astrid Lyså, a geologist and researcher at the Geological Survey of Norway (NGU).

Scientists Document No Clear Warming Role For CO2 During The Last Deglaciation – Or The Last 10,000 Years

by K. Richard, April 4, 2019 in NoTricksZone


A new paper indicates the rise in CO2 concentration occurred well after the Northern Hemisphere’s ocean circulation changes drove the abrupt warming (~11,700 years ago) that ended the last ice age – a lag that effectively leaves no causal role for CO2 during deglaciation.

 

Nature Unbound III: Holocene climate variability (Part A)

by Javier, April 30, 2017 in ClimateEtc.


First in a two part series on Holocene climate variability.

Summary: Holocene climate is characterized by two initial millennia of fast warming followed by four millennia of higher temperatures and humidity, and a progressively accelerating cooling and drying for the past six millennia. These changes are driven by variations in the obliquity of the Earth’s axis. The four millennia of warmer temperatures are called the Holocene Climatic Optimum which was 1-2°C warmer than the Little Ice Age. This climatic optimum was when global glaciers reached their minimum extent. The Mid-Holocene Transition, caused by orbital variations, brought a change in climatic mode, from solar to oceanic dominated forcing. This transition displaced the climatic equator, ended the African Humid Period and increased El Niño activity.

 

 

Figure 36. Holocene temperature profile. A. Summer (July-August) Central England temperature reconstruction from multiple proxies and sources by H. H. Lamb.Crosses represent dating and temperature uncertainty. Black dots are centennial averages. Red dot is 1900-1965 average. Source: Lamb, H.H. 1977. Climate: Present, past and future. Volume 2. B. Greenland temperature reconstruction based on an average of uplift corrected δ18O isotopic data from Agassiz and Renland ice cores. This average has been corrected for changes in the δ18O of seawater and calibrated to borehole temperature records. Some historical periods are indicated. Source: B. Vinther et al., 2009.

New Paper: Widespread Collapse Of Ice Sheets ~5000 Years Ago Added 3-4 Meters To Rising Seas

by K. Richard, March 11, 2019 in NoTricksZone


During the Mid-Holocene, when CO2 concentrations were stable and low (270 ppm), Antarctica’s massive Ross Ice Shelf naturally collapsed, adding the meltwater equivalent of 3-4 meters to sea levels.

Because CO2 concentrations changed very modestly during the pre-industrial Holocene (approximately ~25 ppm in 10,000 years), climate models that are predicated on the assumption that CO2 concentration changes drive ocean temperatures, ice sheet melt, and sea level rise necessarily simulate a very stable Holocene climate.

In contrast, changes in ocean temperatures, ice sheet melt, and sea level rise rates were far more abrupt and variable during the Holocene than during the last 100 years.

Modern ocean changes are barely detectable in the context of natural variability

Image Source(s): Rosenthal et al., 2013Climate Audit

Novel hypothesis goes underground to predict future of Greenland ice sheet

by Penn State, February 2,  2019 in ScienceDaily


Paleoclimatic records indicate that most of Greenland was ice-free within the last 1.1 million years even though temperatures then were not much warmer than conditions today. To explain this, the researchers point to there being more heat beneath the ice sheet in the past than today.

Data show that when the Iceland hot spot — the heat source that feeds volcanoes on Iceland — passed under north-central Greenland 80 to 35 million years ago, it left molten rock deep underground but did not break through the upper mantle and crust to form volcanoes as it had in the west and east. The Earth’s climate then was too warm for Greenland to have an ice sheet, but once it cooled the ice sheet formed, growing and shrinking successive with ice ages.

The Discovery Of Tree Trunks Under Glaciers 600 Meters Atop Today’s Treeline Date To The Last ICE AGE

by K. Richard, December 24, 2018 in NoTricksZone


Between 60 and 40 thousand years ago, during the middle of the last glacial, atmospheric CO2 levels hovered around 200 ppm – half of today’s concentration.

Tree remains dated to this period have been discovered 600-700 meters atop the modern treeline in the Russian Altai mountains.  This suggests surface air temperatures were between 2°C and 3°C warmer than today during this glacial period.

Tree trunks dating to the Early Holocene (between 10.6 and 6.2 thousand years ago) have been found about 350 meters higher than the modern treeline edge.  This suggests summer temperatures were between 2°C and 2.5°C warmer than today during the Early Holocene, when CO2 concentrations ranged between about 250 and 270 ppm.

None of this paleoclimate treeline or temperature evidence correlates with a CO2-driven climate.

 

Paleoclimatological Context and Reference Level of the 2°C and 1.5°C Paris Agreement Long-Term Temperature Limits

by S. Lüning & F. Vahrenholt, December12, 2017 in FrontEarthSci


The Paris Agreement adopted in December 2015 during the COP21 conference stipulates that the increase in the global average temperature is to be kept well below 2°C above “pre-industrial levels” and that efforts are pursued to limit the temperature increase to 1.5°C above “pre-industrial levels.” In order to further increase public acceptance of these limits it is important to transparently place the target levels and their baselines in a paleoclimatic context of the past 150,000 years (Last Interglacial, LIG) and in particular of the last 10,000 years (Holocene; Present Interglacial, PIG). Intense paleoclimatological research of the past decade has firmed up that pre-industrial temperatures have been highly variable which needs to be reflected in the pre-industrial climate baseline definitions …

See also here

Higher sea surface temperature in the northern South China Sea during the natural warm periods of late Holocene than recent decades

by Hong Yan et al., November 2014, in ChineseSciBull


The large-scale syntheses of global mean temperatures in IPCC fourth report suggested that the Northern Hemisphere temperature in the second half of the 20th century was likely the highest in at least the past 1,300 years and the 1990s was likely the warmest decade. However, this remains debated and the controversy is centered on whether temperatures during the recent half century were higher than those during the Medieval Climate Anomaly (MCA, AD 800–1300) and the Roman Warm Period (RWP, BC 200–AD 400), the most recent two natural warm periods of the late Holocene. Here the high resolution sea surface temperatures (SSTs) of two time windows around AD 990 (±40) and AD 50 (±40), which located in the MCA and RWP respectively, were reconstructed by the Sr/Ca ratio and δ 18O of Tradacna gigas shells from the northern South China Sea. The results suggested that the mean SSTs around AD 990 (±40) and AD 50 (±40) were 28.1 °C and 28.7 °C, 0.8 °C and 1.4 °C higher than that during AD 1994–2005, respectively. These records, together with the tree ring, lake sediment and literature records from the eastern China and northwest China, imply that the temperatures in recent decades do not seem to exceed the natural changes in MCA, at least in eastern Asia from northwest China to northern SCS.

CNN: “Climate change endangers dozens of World Heritage sites”… Unmitigated horst schist

by David Middleton, October 19, 2018 in WUWT


Holocene Sea Level

I didn’t take the time to look up the dates of these World Heritage sites… But I’m going to guess they’re OLD.  Many of them probably date back to the Early to Mid-Holocene.  [My bad… That was a bad guess.  The Late Holocene (Meghalayan Age) begins in 4200 BP (2250 BC)]  Here’s a Holocene sea level reconstruction for the Arabian Gulf, with a recent reconstruction of global sea level since 1800 (Jevrejeva et al., 2014) and the satellite sea level trend from CU…

@UCSUSA “Union of Concerned Scientists” doesn’t understand what “unprecedented” means when used with the word “warming”

by Anthony Watts, August 30, 2018 in WUWT


Earth’s surface has undergone unprecedented warming over the last century, and especially in this century.

Every single year since 1977 has been warmer than the 20th century average, with 16 of the 17 warmest years on record occurring since 2001, and 2016 being the warmest year on recorded history. A study from 2016 found that without the emissions from burning coal and oil, there is very little likelihood that 13 out of the 15 warmest years on record would all have happened.

Source: https://www.ucsusa.org/global-warming/science-and-impacts/science/human-contribution-to-gw-faq.html


First a definition of the word “unprecedented”:

Note that “in this century” isn’t part of the definition. it says “never done or known before”

So in that spirit, here’s some other “unprecedented” warming in Earth’s history, via the Vostok Ice Core dataset:

Holocene Sea Level Trends

by P. Homewood, August 22, 2018 in NotaLotofPeopleKnowThat


There seems to be a general acceptance about overall sea level trends during the Holocene.

There was naturally a very rapid rise in sea levels at the end of the ice age, until 6000 years ago, since when the rise has been much more gradual. Some research puts the rate of rise in the last 2000 years at 0.07mm/yr, and this reflects the fact that ice caps left over from the ice age are still melting, rather than that the world is warmer than before.

However, the impression is often given that, until the 20thC, this rate of rise has been pretty steady. This is despite the fact some of the authors of the above studies have warned of the existence of significant short-term fluctuations in sea level such that the sea level curve might oscillate up and down about this ~1 kyr mean state. [The above graph is based around 1000 year averages].

 

HH Lamb looked carefully at many expert studies in his day, and wrote about the very significant fluctuations they found. The following excerpts come from “Climate, History and the Modern World”:

1) The most rapid phases [of sea level rise] were between 8000 and 5000 BC, and that the rise of general water level was effectively over by about 2000 BC, when it may have stood a metre or two higher than today.

2) …

….

https://commons.wikimedia.org/wiki/File:Holocene_Sea_Level.png

 

The Holocene Climate Optimum

by P. Homewood, August 19, 2018 in NotaLotofPeopleKnowThat


Booker commented the other day how one scientist claimed last week that we now have “the highest temperatures on Earth since the last ice age”. The BBC failed to even challenge this statement.

This certainly is not the first time I have heard claims (presented as fact) to this effect.

We have already seen concerted attempts to disappear the MWP, so it is time to reclaim the Holocene Optimum (so named for good reason), which is generally accepted to have run from about 9000 to 5000 years ago

Obviously we had no thermometers around in those days, so nobody knows what the average temperature of the Earth was then. There again, nobody really knows now either.

But there is plentiful evidence that many places were significantly warmer than now. I present some of this evidence below, though this is probably only skimming the surface: …

See also here

Evidence for the impact of the 8.2-kyBP climate event on Near Eastern early farmers

by M. Roffet-Salque et al., August 13, 2018


This study reveals that animal fats preserved in pottery vessels from the United Nations Educational, Scientific and Cultural Organization (UNESCO) World Heritage site of Çatalhöyük recorded the abrupt 8.2-thousand years B.P. climatic event in their hydrogen isotopic compositions. In addition, significant changes are observed in the archaeology and faunal assemblage of the site, showing how the early farming community at Çatalhöyük had to adapt to climate change. Significantly, this contribution shows that individual biomolecules preserved in ancient animal fats can be used to reconstruct paleoclimate records and thus, provides a powerful tool for the detection of climatic events at well-dated onsite terrestrial locations (i.e., at the very settlements where human populations lived).

How the Little Ice Age affected South American climate

by Fundação de Amparo à Pesquisa do Estado de São Paulo, July 24, 2018 in ScienceDaily


A new study published in Geophysical Research Journal shows that the so-called Little Ice Age — a period stretching from 1500 to 1850 in which mean temperatures in the northern hemisphere were considerably lower than at present — exerted effects on the climate of South America.

Based on an analysis of speleothems (cave formations) in the Brazilian states of Mato Grosso do Sul and Goiás, the study revealed that in the seventeenth and eighteenth centuries, the climate of southwestern Brazil was wetter than it is now, for example, while that of the country’s Northeast region was drier.

The same Brazilian cave records showed that the climate was drier in Brazil between 900 and 1100, during a period known as the Medieval Climate Anomaly (MCA), when the northern hemisphere’s climate was warmer than it is now.