Focus

Past climate sensitivity

Focus
July 2011 Volume 4 No 7 pp413-492

(Image credited to: Richard Barclay)

Understanding the amplitude of climate variability in the past, as well as the causes and mechanisms responsible for this variability is important in its own right. Yet it also helps us get a better idea of the range of possible Earth system responses to human-induced greenhouse gas emissions. In this web focus we explore the links between past climate and carbon cycle perturbations, along with the ability of state-of-the-art climate models to capture these links.

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Editorial

Climate past and future p413

doi:10.1038/ngeo1206

Earth's climate is changing rapidly. A closer look at the planet's distant past can help determine its sensitivity to changes in atmospheric greenhouse gas concentrations.

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Commentaries

Built for stability pp414 - 416

Paul Valdes

doi:10.1038/ngeo1200

State-of-the-art climate models are largely untested against actual occurrences of abrupt change. It is a huge leap of faith to assume that simulations of the coming century with these models will provide reliable warning of sudden, catastrophic events.

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Where are you heading Earth? pp416 - 417

Richard E. Zeebe

doi:10.1038/ngeo1196

Accurate prediction of Earth's future warming hinges on our understanding of climate sensitivity. Palaeoclimatology will help solve the problem if the feedbacks included in palaeoclimate sensitivity are properly identified and reconstructions of past atmospheric CO2 can be improved.

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Convergent Cenozoic CO2 history pp418 - 420

David J. Beerling & Dana L. Royer

doi:10.1038/ngeo1186

Reconstructions of atmospheric carbon dioxide concentrations over the past 65 million years are heading towards consensus. It is time for systematic testing of the proxies, against measurements and against each other.

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Article

Slow release of fossil carbon during the Palaeocene—Eocene Thermal Maximum pp481 - 485

Ying Cui, Lee R. Kump, Andy J. Ridgwell, Adam J. Charles, Christopher K. Junium, Aaron F. Diefendorf, Katherine H. Freeman, Nathan M. Urban & Ian C. Harding

doi:10.1038/ngeo1179

A brief period of warming 55.9 Myr ago has been attributed to the release of massive amounts of carbon. Geochemical and model data suggest the peak rate of carbon emission during this interval was relatively slow, and significantly lower than present-day levels of carbon emissions to the atmosphere.

Abstract | Full text | PDF (630KB)

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From the archives

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News & Views

Palaeoclimate: Global warmth with little extra CO2

Birgit Schneider & Ralph Schneider

doi:10.1038/ngeo736

Most climate models consider only short-term processes such as cloud and sea-ice formation when assessing Earth's sensitivity to greenhouse-gas forcing. Mounting evidence indicates that the response could be stronger if boundary conditions change drastically.

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Article

Earth system sensitivity inferred from Pliocene modelling and data

Daniel J. Lunt, Alan M. Haywood, Gavin A. Schmidt, Ulrich Salzmann, Paul J. Valdes & Harry J. Dowsett

doi:10.1038/ngeo706

The equilibrium response of global temperatures to an increase in atmospheric carbon dioxide concentrations is difficult to quantify. Simulations and proxy data of the mid-Pliocene warm climate suggest that the response is 30 to 50% higher than traditionally calculated when slowly adjusting components of the Earth system, such as ice sheets and vegetation, are included in the estimate.

Abstract | Full text | PDF (2,207KB)

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Letter

High Earth-system climate sensitivity determined from Pliocene carbon dioxide concentrations

Mark Pagani, Zhonghui Liu, Jonathan LaRiviere & Ana Christina Ravelo

doi:10.1038/ngeo724

Earth-system climate sensitivity includes the effects of long-term feedbacks such as changes in continental ice-sheet extent and terrestrial ecosystems. A reconstruction of atmospheric carbon dioxide levels 4.5 million years ago suggests that Earth-system climate sensitivity is significantly higher than that estimated from global climate models, which includes only fast feedback mechanisms such as changes in clouds and sea ice.

First Paragraph | Full text | PDF (623KB)

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Article

Climate sensitivity to the carbon cycle modulated by past and future changes in ocean chemistry

Philip Goodwin, Richard G. Williams, Andy Ridgwell & Michael J. Follows

doi:10.1038/ngeo416

The carbon cycle plays a central role in climate change. An analytical framework shows that the influence of atmospheric carbon dioxide concentrations on climate is more sensitive to carbon perturbations now than it has been over much of the preceding 400 million years.

Abstract | Full text | PDF (880KB)

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News & Views

Palaeoclimate: Enigmatic Earth

David J. Beerling

doi:10.1038/ngeo582

Global warming 55 million years ago was accompanied by a massive injection of carbon into the ocean–atmosphere system, but the resulting climatic warming was much greater than expected from the modelled rise in atmospheric carbon dioxide alone.

Full text | PDF (170KB)

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Letter

Carbon dioxide forcing alone insufficient to explain Palaeocene—Eocene Thermal Maximum warming

Richard E. Zeebe, James C. Zachos & Gerald R. Dickens

doi:10.1038/ngeo578

About 55 million years ago global surface temperatures increased by 5–9 °C within a few thousand years, following a pulse of carbon released to the atmosphere. Analysis of existing data with a carbon cycle model indicates that this carbon pulse was too small to cause the full amount of warming at accepted values for climate sensitivity.

First paragraph | Full text | PDF (711KB)

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Review

The equilibrium sensitivity of the Earth's temperature to radiation changes

Reto Knutti & Gabriele C. Hegerl

doi:10.1038/ngeo337

The quest to determine climate sensitivity has been going on for decades, with disturbingly little progress in narrowing the large uncertainty range. But fascinating new insights have been gained that will provide useful information for policy makers, even though the upper limit of climate sensitivity will probably remain uncertain for the near future.

Abstract | Full text | PDF (554KB)

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Letter

Close mass balance of long-term carbon fluxes from ice-core CO2 and ocean chemistry records

Richard E. Zeebe & Ken Caldeira

doi:10.1038/ngeo185

On geological timescales, carbon dioxide enters the atmosphere through volcanism and organic matter oxidation and is removed through mineral weathering and carbonate burial. An analysis of ice-core CO2 records and marine carbonate chemistry indicates a tight coupling between these processes during the past 610,000 years, which suggests that a weathering feedback driven by atmospheric CO2 leads to a mass balance between CO2 sources and sinks on long timescales.

First paragraph | Full text | PDF (335KB)

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Article

Influence of high-latitude vegetation feedbacks on late Palaeozoic glacial cycles

Daniel E. Horton, Christopher J. Poulsen & David Pollard

doi:10.1038/ngeo922

Ice ages during the Palaeozoic era are marked by glacial–interglacial cycles thought to be driven by variations in the Earth's orbit. Numerical simulations suggest that the response of vegetation to the varying insolation may be an important factor in the associated climate response.

Abstract | Full text | PDF (3,499KB)

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Letter

Atmospheric carbon dioxide linked with Mesozoic and early Cenozoic climate change

Benjamin J. Fletcher, Stuart J. Brentnall, Clive W. Anderson, Robert A. Berner & David J. Beerling

doi:10.1038/ngeo.2007.29

Carbon isotopes of fossil plants and model simulations suggest that atmospheric carbon dioxide levels were variable during the period 200 to 60 million years ago. The large decreases in the partial pressure of CO2 coincide with glaciations, providing evidence against climate-CO2 decoupling during the Mesozoic.

Abstract | Full text | PDF (434KB)

Antarctic temperature and global sea level closely coupled over the past five glacial cycles

E. J. Rohling, K. Grant, M. Bolshaw, A. P. Roberts, M. Siddall, Ch. Hemleben & M. Kucera

doi:10.1038/ngeo557

Sea level has varied by over one hundred metres across glacial–interglacial cycles over the past 520,000 years. An extended sea-level reconstruction shows a strong coupling between these sea-level changes and Antarctic surface temperatures over the past five glacial cycles.

Abstract | Full text | PDF (4,921KB)

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