Ice cores drilled in the Greenland ice sheet, recounting the history of the last great warming period more than 120,000 years ago, are giving scientists their clearest insight to a world that was warmer than today.
In a paper published today in the journal Nature, scientists have used a 2540 metre long Greenland ice core to reach back to the Eemian period 115-130 thousand years ago and reconstruct the Greenland temperature and ice sheet extent back through the last interglacial. This period is likely to be comparable in several ways to climatic conditions in the future, especially the mean global surface temperature, but without anthropogenic or human influence on the atmospheric composition.
The Eemian period is referred to as the last interglacial, when warm temperatures continued for several thousand years due mainly to the earth’s orbit allowing more energy to be received from the sun. The world today is considered to be in an interglacial period and that has lasted 11,000 years, and called the Holocene.
“The ice is an archive of past climate and analysis of the core is giving us pointers to the future when the world is likely to be warmer,” said CSIRO’s Dr Mauro Rubino, the Australian scientist working with the North Greenland Eemian ice core research project.
Dr Rubino said the Greenland ice sheet is presently losing mass more quickly than the Antarctic ice sheet. Of particular interest is the extent of the Greenland continental ice sheet at the time of the last interglacial and its contribution to global sea level.
Deciphering the ice core archive proved especially difficult for ice layers formed during the last interglacial because, being close to bedrock, the pressure and friction due to ice movement impacted and re-arranged the ice layering. These deep layers were “re-assembled” in their original formation using careful analysis, particularly of concentrations of trace gases that tie the dating to the more reliable Antarctic ice core records.
Using dating techniques and analysing the water stable isotopes, the scientists estimated the warmest Greenland surface temperatures during the interglacial period about 130,000 years ago were 8±4oC degrees warmer than the average of the past 1000 years.
At the same time, the thickness of the Greenland ice sheet decreased by 400±250 metres.
“The findings show a modest response of the Greenland ice sheet to the significant warming in the early Eemian and lead to the deduction that Antarctica must have contributed significantly to the six metre higher Eemian sea levels,” Dr Rubino said.
Additionally, ice core data at the drilling site reveal frequent melt of the ice sheet surface during the Eemian period.
“During the exceptional heat over Greenland in July 2012 melt layers formed at the site. With additional warming, surface melt might become more common in the future,” the authors said.
The paper is the culmination of several years work by organisations across more than 14 nations.
Dr Rubino said the research results provide new benchmarks for climate and ice sheet scenarios used by scientists in projecting future climate influences.
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An innovative global observing system based on drifting sensors cycling from the surface to the ocean mid-depths is being celebrated by scientists today after reaching a major milestone – one million incredibly valuable ocean observations.
From 10 drifting robotic sensors deployed by Australia in the Indian Ocean in late 1999, the international research program has been quietly building up a global array which is now enabling new insights into the ocean’s central influence on global climate and marine ecosystems.
The initial objective was to maintain a network of 3000 sensors, in ice-free open ocean areas, providing both real-time data and higher quality delayed mode data and analyses to underpin a new generation of ocean and climate services. The program is called Argo.
“We’re still about 50 years behind the space community and its mission to reach the moon,” says Argo co-Chair and CSIRO Wealth from Oceans Flagship scientist, Dr Susan Wijffels.
“The world’s deep ocean environment is as hostile as that in space, but because it holds so many clues to our climate future exploring it with the Argo observing network is a real turning point for science.
“In its short life the Argo data set has become an essential mainstay of climate and ocean researchers complementing information from earth observing satellites and uniquely providing subsurface information giving new insights into changes in the earth’s hydrological warming rates and opening the possibility of longer term climate forecasting,” Dr Wijffels said.
Although the one millionth profile of the upper ocean, measured from the surface to a depth of two kilometres, was achieved in early November, oceanographers around the world are today celebrating this critical benchmark in ocean monitoring which delivers data to a scientist’s desk within 24 hours of sampling.
Celebrations included a series of high-level international presentations by senior scientists involving Dr Wijffels, her Argo co-Chair Prof Dean Roemmich from Scripps Institution of Oceanography, oceanographer Dr Josh Willis from the NASA Jet Propulsion Laboratory, and Dr Jim Cummings from the US Naval Research Laboratory.
The Argo array has risen to now number more than 3500 sensors, the largest there has ever been. The average lifetime of the floats has improved in the past decade greatly increasing the efficiency of the operation.
Presently 28 countries contribute to the annual A$25M cost of operating the program. The US is the largest provider of sensors to the network, with Australia, led by CSIRO with the Integrated Marine Observing System and the Bureau of Meteorology, maintaining more than 300 profilers for deployment mainly in the Indian and Southern Oceans, and Tasman Sea.
The 1.5 metre tall robotic sensors cycle vertically every 10 days, sampling temperature and salinity. At the surface, the sensors despatches its data via satellite to national centres across the globe, where analysts then check it, package it and send it to synchronous assembly centres in France and the US. The sensor’s ascent and descent is regulated by a hydraulic pump, powered with lithium batteries. Their life expectancy is between 4-9 years, averaging more than 200 profiles per sensor as they drift with the currents and eddies.
Data are collected at the impressive rate of one profile approximately every four minutes, (360 profiles per day or 11000 per month) and on 4 November 2012 Argo passed the symbolic milestone of collecting its one millionth profile. To put this achievement in context, since the start of deep sea oceanography in the late 19th century, ships have collected just over half a million temperature and salinity profiles to a depth of 1km and only 200000 to 2km. At the present rate of data collection Argo will take only eight years to collect its next million profiles.
Dr Wijffels said almost 1200 scientific papers based on or incorporating Argo data have been generated since the start of the program. Prominent findings include:
- Analysis of ocean salinity patterns that suggests a substantial (16 to 24%) intensification of the global water cycle will occur in a future 2° to 3° warmer world.
- A more detailed view of the world’s largest ocean current, the Antarctic Circumpolar Current.
- An insight into changing bodies of water in the Southern Ocean and the way in which carbon dioxide is removed from the atmosphere.
- Isolating the effect of ocean warming and thermal expansion on the global energy and sea level budget.
Dr Wijffels said Argo data is now also being widely used in operational services for the community, including weather and climate prediction and ocean forecasting for environmental emergency response, shipping, defence, and safety at sea.
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Carbon dioxide emission reductions required to limit global warming to 2°C are becoming a receding goal based on new figures reported today in the latest Global Carbon Project (GCP) calculations published today in the advanced online edition of Nature Climate Change.
“A shift to a 2°C pathway requires an immediate, large, and sustained global mitigation effort,” GCP executive-director and CSIRO co-author of the paper, Dr Pep Canadell said.
Global CO2 emissions have increased by 58 per cent since 1990, rising 3 per cent in 2011, and 2.6 per cent in 2012. The most recent figure is estimated from a 3.3 per cent growth in global gross domestic product and a 0.7 per cent improvement in the carbon intensity of the economy.
Dr Canadell said the latest carbon dioxide emissions continue to track at the high end of a range of emission scenarios, expanding the gap between current trends and the course of mitigation needed to keep global warming below 2°C.
He said on-going international climate negotiations need to recognise and act upon the growing gap between the current pathway of global greenhouse emissions and the likely chance of holding the increase in global average temperature below 2°C above pre-industrial levels.
The research, led by Dr Glen Peters from CICERO, Norway, compared recent carbon dioxide emissions from fossil fuel combustion, cement production, and gas flaring with emission scenarios used to project climate change by the Intergovernmental Panel on Climate Change (IPCC).
“We need a sustained global CO2 mitigation rate of at least 3 per cent if global emissions are to peak before 2020 and follow an emission pathway that can keep the temperature increase below 2˚C,” Dr Peters said.
“Mitigation requires energy transition led by the largest emitters of China, the US, the European Union and India”.
He said that remaining below a 2°C rise above pre-industrial levels will require a commitment to technological, social and political innovations and an increasing need to rely on net negative emissions in future.
The Global Carbon Project, supported by CSIRO and the Australian Climate Change Science Program, generates annual emission summaries contributing to a process of informing policies and decisions on adaptation, mitigation, and their associated costs. The summaries are linked to long-term emission scenarios based on the degree of action taken to limit emissions.
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