Eemian interglacial period poor analog for current Arctic warming

Warm climate -- cold Arctic? The Eemian is a poor analogue for current climate change

by phys.org, June 14, 2012

The Eemian interglacial period that began some 125,000 years ago is often used as a model for contemporary climate change. In the international journal Geophysical Research Letters, scientists from Mainz, Kiel and Potsdam, Germany, now present evidence that the Eemian differed in essential details from modern climatic conditions.

To address the question about how climate may develop in the future, earth scientists direct their attention to the past. They look for epochs with similar conditions to today. The major identified climatic processes are then simulated with numerical models to further test possible reactions of the Earths' system. An epoch which is often regarded suitable for such an undertaking is the Eemian warm period, which began around 125,000 years ago following the Saalian ice age.

For about 10,000 years, average temperatures on Earth in the Eemian were rather enhanced – probably several degrees above today's level. This seems to be well documented in both ice cores as well as terrestrial records from land vegetation. Substantial parts of the Greenland ice had melted, and global sea level was higher than today. "Therefore, the Eemian time is suited apparently so well as a basis for the topical issue of climate change", says Dr Henning Bauch, who works for the Academy of the Sciences and the Literature Mainz (AdW Mainz) at GEOMAR | Helmholtz Centre for Ocean Research Kiel.

However, in a study which appears in the recent issue of the international journal Geophysical Research Letters Dr Bauch, Dr Evgeniya Kandiano of GEOMAR as well as Dr Jan Helmke of the Institute for Advanced Sustainability Studies in Potsdam now show that the Eemian warm period differed from the present day situation in one critical aspect – the development in the Arctic Ocean.

In our current warm period, also called Holocene, oceanic and atmospheric circulation delivers large amounts of heat northward into the high latitudes. The most well known heat conveyer is the Gulf Stream and its northern prolongation called the North Atlantic Drift. The currents provide not only the pleasant temperatures in Northern Europe, they also reach as far as the Arctic. Studies in the last years have shown that the oceanic heat transport to the Arctic has even increased, while the summer sea ice cover in the Arctic Ocean seems to be decreasing continuously. It has long been assumed that such conditions also prevailed 125,000 years ago. Accordingly, the Arctic should have been by and large ice-free in the Eemian summers.

Dr Bauch's group examined sediment cores from the seabed in which information about the climate history of the past 500,000 years is stored. These come from the Atlantic to the west of Ireland and from the central Nordic Seas to the east of the island of Jan Mayen. The sediments contain minute calcite tests of dead microorganisms (foraminifers). "The type of species assemblage in the respective layers as well as the isotopic composition of the calcitic tests give us information about temperature and other properties of the water in which they lived at that time", explains Dr Bauch.

The samples from the Atlantic delivered the higher-than-Holocene temperature signals so typical for the Eemian. The tests from the Nordic Seas, however, tell quite another story. "The found foraminifers of Eemian time indicate comparatively cold conditions." The isotope investigations of the tests, in combination with previous studies of the group, "indicate major contrasts between the ocean surfaces of these two regions ", according to Dr Bauch. "Obviously, the warm Atlantic surface current was weaker in the high latitude during the Eemian than today." His explanation: "The Saalian glaciation which preceded the Eemian was of much bigger extent in Northern Europe than during the Weichselian, the ice age period before our present warm interval. Therefore, more fresh water from the melting Saalian ice sheets poured into the Nordic Seas, and for a longer period of time. This situation had three consequences: The oceanic circulation in the north was reduced, and winter sea ice was more likely to form because of lower salinity. At the same time, this situation led to a kind of 'overheating' in the North Atlantic due to a continuing transfer of ocean heat from the south."

On the one hand, the study introduces new views on the Eemian climate. On the other hand, the new results have consequences for climatology in general: "Obviously, some decisive processes in the Eemian ran off differently, like the transfer of ocean warmth towards the Arctic. Models should take this into consideration if they want to forecast the future climate development on the basis of past analogues like the Eemian ", says Dr. Bauch.

http://phys.org/news/2012-06-climate-cold-arctic-eemian.html

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MORE MUST READ TIDBITS: Kevin Trenberth on ocean heat content, changing trade winds, mechanism for heat to be carried down deeper in the ocean

Global warming is here to stay, whichever way you look at it

by Kevin Trenberth, University Corporation for Atmospheric Research, The Conversation, May 22, 2013

Has global warming stalled? This question is increasingly being asked because the local weather seems cool and wet, or because the global mean temperature is not increasing at its earlier rate or the long-term rate expected from climate model projections.

The answer depends a lot on what one means by “global warming.” For some it is equated to the “global mean temperature.” That keeps going up but also has ups and downs from year to year. More on that shortly.

Why should it go up? Well, because the planet is warming as a result of human activities. With increasing carbon dioxide and other heat-trapping greenhouse gases in the atmosphere, there is an imbalance in energy flows in and out of the top of the atmosphere: the greenhouse gases increasingly trap more radiation and hence create warming. “Warming” really means heating, and this can exhibit itself in many ways.

Rising surface temperatures are just one manifestation. Melting Arctic sea ice is another. So is melting of glaciers and other land ice that contribute to rising sea levels. Increasing the water cycle and invigorating storms is yet another. But most (more than 90%) of the energy imbalance goes into the ocean, and several analyses have now shown this. But even there, how much warms the upper layers of the ocean, as opposed to how much penetrates deeper into the ocean where it may not have much immediate influence, is a key issue.

The ups and downs of global temperature

My colleagues and I have just published a new analysis showing that in the past decade about 30% of the heat has been dumped at levels below 700 meters, where most previous analyses stop.

The first point is that this is fairly new; it is not there throughout the record. The cause of the shift is a particular change in winds, especially in the Pacific Ocean where the subtropical trade winds have become noticeably stronger, changing ocean currents and providing a mechanism for heat to be carried down into the ocean. This is associated with weather patterns in the Pacific, which are in turn related to the La Niña phase of the El Niño phenomenon.

The second point is that we have found distinctive variations in global warming with El Niño. A mini global warming, in the sense of a global temperature increase, occurs in the latter stages of an El Niño event, as heat comes out of the ocean and warms the atmosphere. The ocean’s temperature is also affected by volcanic eruptions, which also affect the perceptions of global warming.

Normal weather also interferes by generating clouds that reflect the sunshine, and there are fluctuations in the global energy imbalance from month to month. But these average out over a year or so.

Another prominent source of natural variability in the Earth’s energy imbalance is changes in the sun itself, seen most clearly as the sunspot cycle. From 2005 to 2010 the sun went into a quiet phase and the warming energy imbalance is estimated to have dropped by about 10 to 15%.

Some of the penetration of heat into the depths of the ocean is reversible, as it comes back in the next El Niño [whenever that is -- no signs of one for the rest of this year]. But a lot is not; instead it contributes to the overall warming of the deep ocean. This means less short-term warming at the surface, but at the expense of greater long-term warming, and faster sea level rise. So this has consequences.

Global warming is here to stay

Coming back to the global temperature record, one thing is clear. The past decade is by far the warmest on record. Human-induced global warming really kicked in during the 1970s, and warming has been pretty steady since then.

While the overall warming is about 0.16 °C per decade, there are three 10-year periods where there was a hiatus in warming, as the graph above shows, from 1977 to 1986, from 1987 to 1996, and from 2001 to 2012. But at each end of these periods there were big jumps. We find exactly the same sort of flat periods in climate model projections, lasting easily up to 15 years in length.

Focusing on the wiggles and ignoring the bigger picture of unabated warming is foolhardy, but an approach promoted by climate change deniers. Global sea level keeps marching up at a rate of more than 30 cm per century since 1992 (when global measurements via altimetry on satellites were made possible), and that is perhaps a better indicator that global warming continues unabated. Sea level rise comes from both the melting of land ice, thus adding more water to the ocean, plus the warming and thus expanding ocean itself.

Global warming is manifested in a number of ways, and there is a continuing radiative imbalance at the top of atmosphere. The current hiatus in surface warming is temporary, and global warming has not gone away.

Kevin Trenberth does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations.


This article was originally published at The Conversation. Read the original article.

http://theconversation.com/global-warming-is-here-to-stay-whichever-way-you-look-at-it-14532

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"Strengthening of ocean heat uptake efficiency associated with the recent climate hiatus," by Masahiro Watanabe et al., GRL (2013); doi:10.1002/grl.50541

Geophysical Research Letters,  DOI: 10.1002/grl.50541

Strengthening of ocean heat uptake efficiency associated with the recent climate hiatus^†

1. Masahiro Watanabe^1,*, 
2. Youichi Kamae²,
3. Masakazu Yoshimori¹, 
4. Akira Oka¹, 
5. Makiko Sato^3,4, 
6. Masayoshi Ishii⁵, 
7. Takashi Mochizuki⁶, and
8. Masahide Kimoto¹

Abstract

The rate of increase of global-mean surface air temperature (SAT_g) has apparently slowed during the last decade. We investigated the extent to which state-of-the-art general circulation models (GCMs) can capture this hiatus period by using multi-model ensembles of historical climate simulations. While the SAT_g linear trend for the last decade is not captured by their ensemble means regardless of differences in model generation and external forcing, it is barely represented by an 11-member ensemble of a GCM, suggesting an internal origin of the hiatus associated with active heat uptake by the oceans. Besides, we found opposite changes in ocean heat uptake efficiency (κ), weakening in models and strengthening in nature, which explain why the models tend to overestimate the SAT_g trend. The weakening of κ commonly found in GCMs seems to be an inevitable response of the climate system to global warming, suggesting the recovery from hiatus in coming decades.

http://0-onlinelibrary.wiley.com.library.hct.ac.ae/doi/10.1002/grl.50541/abstract

Open-access pdf file:  http://0-onlinelibrary.wiley.com.library.hct.ac.ae/doi/10.1002/grl.50541/pdf

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Sea Surface Temperatures Reach Highest Level in 150 Years on Northeast Continental Shelf

enlarge image The four subregions of the Northeast Shelf Large Marine Ecosystem, which extends from Cape Hatteras, N.C. to the Gulf of Maine. MAB is the Mid-Atlantic Bight, SNE is Southern New England, GB is Georges Bank, and GOM is the Gulf of Maine. Credit: NOAA

by Shelley Dawicki, Research Communications, Northeast Fisheries Science Center, NOAA, April 13, 2013

Sea surface temperatures in the Northeast Shelf Large Marine Ecosystem during 2012 were the highest recorded in 150 years, according to the latest Ecosystem Advisory issued by NOAA’s Northeast Fisheries Science Center (NEFSC). These high sea surface temperatures (SSTs) are the latest in a trend of above average temperature seen during the spring and summer seasons, and part of a pattern of elevated temperatures occurring in the Northwest Atlantic, but not seen elsewhere in the ocean basin over the past century.

The advisory reports on conditions in the second half of 2012.

Sea surface temperature for the Northeast Shelf Ecosystem reached a record high of 14 °C (57.2 °F) in 2012, exceeding the previous record high in 1951. Average SST has typically been lower than 12.4 °C (54.3 °F) over the past three decades.

Sea surface temperature in the region is based on both contemporary satellite remote-sensing data and long-term ship-board measurements, with historical SST conditions based on ship-board measurements dating back to 1854. The temperature increase in 2012 was the highest jump in temperature seen in the time series and one of only five times temperature has changed by more than 1 °C (1.8 °F).

The Northeast Shelf’s warm water thermal habitat was also at a record high level during 2012, while cold water habitat was at a record low level. Early winter mixing of the water column went to extreme depths, which will impact the spring 2013 plankton bloom. Mixing redistributes nutrients and affects stratification of the water column as the bloom develops.

Temperature is also affecting distributions of fish and shellfish on the Northeast Shelf. The advisory provides data on changes in distribution, or shifts in the center of the population, of seven key fishery species over time. The four southern species -- black sea bass, summer flounder, longfin squid and butterfish -- all showed a northeastward or upshelf shift. American lobster has shifted upshelf over time but at a slower rate than the southern species. Atlantic cod and haddock have shifted downshelf.”

“Many factors are involved in these shifts, including temperature, population size, and the distributions of both prey and predators,” said Jon Hare, a scientist in the NEFSC’s Oceanography Branch. A number of recent studies have documented changing distributions of fish and shellfish, further supporting NEFSC work reported in 2009 that found about half of the 36 fish stocks studied in the Northwest Atlantic Ocean, many of them commercially valuable species, have been shifting northward over the past four decades.

The Northeast U.S. Continental Shelf Large Marine Ecosystem (LME) extends from the Gulf of Maine to Cape Hatteras, North Carolina. The NEFSC has monitored this ecosystem with comprehensive sampling programs since 1977. Prior to 1977, this ecosystem was monitored by the NEFSC through a series of separate, coordinated programs dating back decades.

Warming conditions on the Northeast Shelf in the spring of 2012 continued into September, with the most consistent warming conditions seen in the Gulf of Maine and on Georges Bank. Temperatures cooled by October and were below average in the Middle Atlantic Bight in November, perhaps due to Superstorm Sandy, but had returned to above average conditions by December.

“Changes in ocean temperatures and the timing and strength of spring and fall plankton blooms could affect the biological clocks of many marine species, which spawn at specific times of the year based on environmental cues like water temperature,” Kevin Friedland, a scientist in the NEFSC Ecosystem Assessment Program, said. He noted that the contrast between years with, and without, a fall bloom is emerging as an important driver of the shelf’s ecology. “The size of the spring plankton bloom was so large that the annual chlorophyll concentration remained high in 2012 despite low fall activity. These changes will have a profound impact throughout the ecosystem.”

Michael Fogarty, who heads the Ecosystem Assessment Program, says the abundance of fish and shellfish is controlled by a complex set of factors, and that increasing temperatures in the ecosystem make it essential to monitor the distribution of many species, some of them migratory and others not.

"It isn’t always easy to understand the big picture when you are looking at one specific part of it at one specific point in time,“ Fogarty said, a comparison similar to not seeing the forest when looking at a single tree in it. “We now have information on the ecosystem from a variety of sources collected over a long period of time, and are adding more data to clarify specific details. The data clearly show a relationship between all of these factors.”

“What these latest findings mean for the Northeast Shelf ecosystem and its marine life is unknown,” Fogarty said. “What is known is that the ecosystem is changing, and we need to continue monitoring and adapting to these changes.”

Ecosystem advisories have been issued twice a year by the NEFSC’s Ecosystem Assessment Program since 2006 as a way to routinely summarize overall conditions in the region. The reports show the effects of changing coastal and ocean temperatures on fisheries from Cape Hatteras to the Canadian border. The advisories provide a snapshot of the ecosystem for the fishery management councils and also a broad range of stakeholders from fishermen to researchers.

The Spring 2013 Ecosystem Advisory, covering the fall of 2012 with supporting information, is available online at: 

http://www.nefsc.noaa.gov/ecosys/advisory/current/advisory.html.

http://www.nefsc.noaa.gov/press_release/2013/SciSpot/SS1304/

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