Paleoclimate

The NOAA Satellite and Information Service Paleoclimatology Branch has many links to Climate Reconstructions

Paleoclimatology is the study of past climate, for times prior to instrumental weather measurements. Paleoclimatologists use clues from natural “proxy” sources such as tree rings, ice cores, corals, and ocean and lake sediments to understand natural climate variability. NOAA Paleoclimatology operates the World Data Center for Paleoclimatology and the Applied Research Center for Paleoclimatology, with the goal to provide data and information scientists need to understand natural climate variability as well as future climate change.

The NOAA Paleoclimatology Program archives reconstructions of past climatic conditions derived from paleoclimate proxies, in addition to the Program’s large holdings of primary paleoclimatic proxy data. Included are reconstructions of past temperature, precipitation, vegetation, streamflow, sea surface temperature, and other climatic or climate-dependent conditions.

One of the favourite claims of skeptics, contrarians and denialists is to claim that the Medieval Warm Period was warmer than the twentieth century and recent twenty-first century temperatures. That may have been true of temperatures in the early part of the twentieth century but it is no longer –
it appears that the late 20th and early 21st centuries are likely the warmest period the Earth has seen in at least 1200 years.

Paleo Fig. 1 IPCC WG1 CH06 Radiative Forcings and Temperatures

Paleo Fig. 1 IPCC WG1 CH06 Radiative Forcings and Temperatures

IPCC AR4 WG1 Figure 6.13. Radiative forcings and simulated temperatures during the last 1.1 kyr. Global mean radiative forcing (W m–2) used to drive climate model simulations due to (a) volcanic activity, (b) solar irradiance variations and (c) all other forcings (which vary between models, but always include greenhouse gases, and, except for those with dotted lines after 1900, tropospheric sulphate aerosols). (d) Annual mean NH temperature (°C) simulated under the range of forcings shown in (a) to (c), compared with the concentration of overlapping NH temperature reconstructions (shown by grey shading, modified from Figure 6.10c to account for the 1500 to 1899 reference period used here). All forcings and temperatures are expressed as anomalies from their 1500 to 1899 means and then smoothed with a Gaussian-weighted filter to remove fluctuations on time scales less than 30 years; smoothed values are obtained up to both ends of each record by extending the records with the mean of the adjacent existing values. The individual series are identified in Table 6.2.


Paleo Fig. 2 IPCC WG1 CH06 Temperatures with and without anthropogenic forcings

Paleo Fig. 2 IPCC WG1 CH06 Temperatures with and without anthropogenic forcings

IPCC AR4 WG1 Figure 6.14. Simulated temperatures during the last 1 kyr with and without anthropogenic forcing, and also with weak or strong solar irradiance variations. Global mean radiative forcing (W m–2) used to drive climate model simulations due to (a) volcanic activity, (b) strong (blue) and weak (brown) solar irradiance variations, and (c) all other forcings, including greenhouse gases and tropospheric sulphate aerosols (the thin flat line after 1765 indicates the fixed anthropogenic forcing used in the ‘Nat’ simulations). (d) Annual mean NH temperature (°C) simulated by three climate models under the forcings shown in (a) to (c), compared with the concentration of overlapping NH temperature reconstructions (shown by grey shading, modified from Figure 6.10c to account for the 1500 to 1899 reference period used here). ‘All’ (thick lines) used anthropogenic and natural forcings; ‘Nat’ (thin lines) used only natural forcings. All forcings and temperatures are expressed as anomalies from their 1500 to 1899 means; the temperatures were then smoothed with a Gaussian-weighted filter to remove fluctuations on time scales less than 30 years. Note the different vertical scale used for the volcanic forcing compared with the other forcings. The individual series are identified in Table 6.3.


Climate-driven regime shifts in the biological communities of arctic lakes
PNAS (Proceeding of the National Academy of Sciences of the United States of America)

Communicated by David W. Schindler, University of Alberta, Edmonton, Canada, January 21, 2005 (received for review October 14, 2004)

Abstract

Fifty-five paleolimnological records from lakes in the circumpolar Arctic reveal widespread species changes and ecological reorganizations in algae and invertebrate communities since approximately anno Domini 1850. The remoteness of these sites, coupled with the ecological characteristics of taxa involved, indicate that changes are primarily driven by climate warming through lengthening of the summer growing season and related limnological changes. The widespread distribution and similar character of these changes indicate that the opportunity to study arctic ecosystems unaffected by human influences may have disappeared.
Our data show that many arctic freshwater ecosystems have experienced dramatic and unidirectional regime shifts within the last
[approx.] 150 years. For those sites where longer paleoecological records are available, recent changes in species composition appear unprecedented in the context of the last several centuries … or even millennia …
(Emphasis is mine)


2009-01-02
Science Magazine: Nanodiamonds in the Younger Dryas Boundary Sediment Layer

We report abundant nanodiamonds in sediments dating to 12.9 ± 0.1 thousand calendar years before the present at multiple locations across North America. Selected area electron diffraction patterns reveal two diamond allotropes in this boundary layer but not above or below that interval. Cubic diamonds form under high temperature-pressure regimes, and n-diamonds also require extraordinary conditions, well outside the range of Earth’s typical surficial processes but common to cosmic impacts. N-diamond concentrations range from ≈ 10 to 3700 parts per billion by weight, comparable to amounts found in known impact layers. These diamonds provide strong evidence for Earth’s collision with a rare swarm of carbonaceous chondrites or comets at the onset of the Younger Dryas cool interval, producing multiple airbursts and possible surface impacts, with severe repercussions for plants, animals, and humans in North America.

See also SciAm: Did a Comet Hit Earth 12,000 Years Ago?

Roughly 12,900 years ago, massive global cooling kicked in abruptly, along with the end of the line for some 35 different mammal species, including the mammoth, as well as the so-called Clovis culture of prehistoric North Americans. Various theories have been proposed for the die-off, ranging from abrupt climate change to overhunting once humans were let loose on the wilds of North America. But now nanodiamonds found in the sediments from this time period point to an alternative: a massive explosion or explosions by a fragmentary comet, similar to but even larger than the Tunguska event of 1908 in Siberia. …
The discovery lends support to a theory first advanced last year in that some type of cosmic impact or impacts—a fragmented comet bursting in the atmosphere or raining down on the oceans—set off the more than 1,300-year cooling period in the Northern Hemisphere known as the Younger Dryas for the abundance of an alpine flower’s pollen found during the interval.


2009-03-18
Andrill demonstrates climate warming affects Antarctic ice sheet stability
Obliquity-paced Pliocene West Antarctic ice sheet oscillations
– Nature 458, 322-328 (19 March 2009) | doi:10.1038/nature07867
Modelling West Antarctic ice sheet growth and collapse through the past five million years – Nature 458, 329-332 (19 March 2009) | doi:10.1038/nature07809

A five-nation scientific team has published new evidence that even a slight rise in atmospheric concentrations of carbon dioxide, one of the gases that drives global warming, affects the stability of the West Antarctic Ice Sheet (WAIS). The massive WAIS covers the continent on the Pacific side of the Transantarctic Mountains. Any substantial melting of the ice sheet would cause a rise in global sea levels.

The research, which was published in the March 19 issue of the journal Nature, is based on investigations by a 56-member team of scientists conducted on a 1,280-meter (4,100-foot)-long sedimentary rock core taken from beneath the sea floor under Antarctica’s Ross Ice Shelf during the first project of the ANDRILL (ANtarctic geological DRILLing) research program–the McMurdo Ice Shelf (MIS) Project.

Ross Powell,a professor of geology at Northern Illinois University, and Tim Naish, director of Victoria University of Wellington’s Antarctic Research Centre, served as co-chief scientists of the 2006-2007 ANDRILL project that retrieved the data and are lead authors in one of two companion studies published in Nature.

Naish said the new information gleaned from the core shows that changes in the tilt of Earth’s rotational axis has played a major role in ocean warming that has driven repeated cycles of growth and retreat of the WAIS for the period in Earth’s history between 3 million and 5 million years ago.

“It also appears that when atmospheric carbon dioxide concentrations reached 400 parts per million around four million years ago, the associated global warming amplified the effect of the Earth’s axial tilt on the stability of the ice sheet,” he said.

“Carbon dioxide concentration in the atmosphere is again approaching 400 parts per million,” Naish said. “Geological archives, such as the ANDRILL core, highlight the risk that a significant body of permanent Antarctic ice could be lost within the next century as Earth’s climate continues to warm. Based on ANDRILL data combined with computer models of ice sheet behavior, collapse of the entire WAIS is likely to occur on the order of 1,000 years, but recent studies show that melting has already begun.”

The second ANDRILL study in Nature–led by David Pollard of Pennsylvania State University and Rob DeConto from University of Massachusetts–reports results from a computer model of the ice sheets. The model shows that each time the WAIS collapsed, some of the margins of the East Antarctic Ice Sheet also melted, and the combined effect was a global sea level rise of 7 meters above present-day levels.

“It’s clear from our combined research using geological data and modeling that ocean temperatures play a key role,” DeConto said. “The most substantial melting of protective ice shelves comes from beneath the ice, where it is in contact with seawater. We now need more data to determine what is happening to the underside of contemporary ice shelves.”


2009-06-15
Sediment Yields Climate Record for Past Half-million Years

COLUMBUS, Ohio – Researchers here have used sediment from the deep ocean bottom to reconstruct a record of ancient climate that dates back more than the last half-million years.

The record, trapped within the top 20 meters (65.6 feet) of a 400-meter (1,312-foot) sediment core drilled in 2005 in the North Atlantic Ocean by the Integrated Ocean Drilling Program, gives new information about the four glacial cycles that occurred during that period. …

Harunur Rashid, a post-doctoral fellow at the Byrd Center, explained that experts have been trying to capture a longer climate record for this part of the ocean for nearly a half-century. “We’ve now generated a climate record from this core that has a very high temporal resolution, one that is decipherable at increments of 100 to 300 years,” he said. …

Rashid’s team was also able to score another first with their analysis of this sediment core – a record of the temperature at the sea surface in the North Atlantic. …


2009-08-13
Nature: Atlantic hurricanes and climate over the past 1,500 years , doi:10.1038/nature08219

Atlantic tropical cyclone activity, as measured by annual storm counts, reached anomalous levels over the past decade. The short nature of the historical record and potential issues with its reliability in earlier decades, however, has prompted an ongoing debate regarding the reality and significance of the recent rise. Here we place recent activity in a longer-term context by comparing two independent estimates of tropical cyclone activity over the past 1,500 years. The first estimate is based on a composite of regional sedimentary evidence of landfalling hurricanes, while the second estimate uses a previously published statistical model of Atlantic tropical cyclone activity driven by proxy reconstructions of past climate changes. Both approaches yield consistent evidence of a peak in Atlantic tropical cyclone activity during medieval times (around ad 1000) followed by a subsequent lull in activity. The statistical model indicates that the medieval peak, which rivals or even exceeds (within uncertainties) recent levels of activity, results from the reinforcing effects of La-Niña-like climate conditions and relative tropical Atlantic warmth.

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