Browsing articles tagged with " Pliocene"

Past evidence confirms recent IPCC estimates of climate sensitivity

Feb 6, 2015   //   by Athena   //   Blog  //  Comments Off on Past evidence confirms recent IPCC estimates of climate sensitivity

Public Release: 

University of Southampton

New evidence showing the level of atmospheric CO2 millions of years ago supports recent climate change predications from the Intergovernmental Panel on Climate Change (IPCC).

A multinational research team, led by scientists at the University of Southampton, has analysed new records showing the CO2 content of the Earth’s atmosphere between 2.3 to 3.3 million years ago, over the Pliocene.

During the Pliocene, the Earth was around 2ºC warmer than it is today and atmospheric CO2 levels were around 350-400 parts per million (ppm), similar to the levels reached in recent years.

By studying the relationship between CO2 levels and climate change during a warmer period in Earth’s history, the scientists have been able to estimate how the climate will respond to increasing levels of carbon dioxide, a parameter known as ‘climate sensitivity’.

The findings, which have been published in Nature, also show how climate sensitivity can vary over the long term.

“Today the Earth is still adjusting to the recent rapid rise of CO2 caused by human activities, whereas the longer-term Pliocene records document the full response of CO2-related warming,” says Southampton’s Dr Gavin Foster, co-author of the study.

“Our estimates of climate sensitivity lie well within the range of 1.5 to 4.5ºC increase per CO2 doubling summarised in the latest IPCC report. This suggests that the research community has a sound understanding of what the climate will be like as we move toward a Pliocene-like warmer future caused by human greenhouse gas emissions.”

Lead author of the study, Dr Miguel Martínez-Botí, also from Southampton said: “Our new records also reveal an important change at around 2.8 million years ago, when levels rapidly dropped to values of about 280 ppm, similar to those seen before the industrial revolution. This caused a dramatic global cooling that initiated the ice-age cycles that have dominated Earth’s climate ever since.”

The research team also assessed whether climate sensitivity was different in warmer times, like the Pliocene, than in colder times, like the glacial cycles of the last 800,000 years.

Professor Eelco Rohling of The Australian National University in Canberra says: “We find that climate change in response to CO2 change in the warmer period was around half that of the colder period. We determine that this difference is driven by the growth and retreat of large continental ice sheets that are present in the cold ice-age climates; these ice sheets reflect a lot of sunlight and their growth consequently amplifies the impact of CO2 changes.”

Professor Richard Pancost from the University of Bristol Cabot Institute, added: “When we account for the influence of the ice sheets, we confirm that the Earth’s climate changed with a similar sensitivity to overall forcing during both warmer and colder climates.”

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Notes for editors

1. The paper Plio-Pleistocene climate sensitivity from a new high-resolution CO2 record by M.A. Martínez-Botí, G.L. Foster, T. B. Chalk, E.J. Rohling, P.F. Sexton, D.J. Lunt, R.D. Pancost, M.P.S. Badger, D.N. Schmidt is available from Media Relations on request. Please contact Steven Williams, Tel: 023 8059 2128, email: [email protected]

2. Ocean and Earth Sciences at the University of Southampton has a well-established reputation for outstanding research and teaching. Our unique waterfront campus at the National Oceanography Centre, Southampton attracts prominent researchers and educators from around the world, who join us to work within the areas of geochemistry, geology and geophysics, ocean biodiversity, geochemistry and ecosystems, physical oceanography, palaeoceanography and palaeoclimate, and coastal and shelf seas.

Through degree programmes in oceanography, marine biology, geology and geophysics, our students have access to ships, ocean technology and opportunities for fieldwork and scientific cruises not traditionally found in standard university environments. http://www.southampton.ac.uk/oes

3. Through world-leading research and enterprise activities, the University of Southampton connects with businesses to create real-world solutions to global issues. Through its educational offering, it works with partners around the world to offer relevant, flexible education, which trains students for jobs not even thought of. This connectivity is what sets Southampton apart from the rest; we make connections and change the world.

http://www.southampton.ac.uk/

http://www.southampton.ac.uk/weareconnected

#weareconnected

4. The National Oceanography Centre (NOC) is the UK’s leading institution for integrated coastal and deep ocean research. NOC operates the Royal Research Ships James Cook and Discovery and develops technology for coastal and deep ocean research. Working with its partners NOC provides long-term marine science capability including: sustained ocean observing, mapping and surveying, data management and scientific advice. NOC operates at two sites, Southampton and Liverpool, with the headquarters based in Southampton.

Among the resources that NOC provides on behalf of the UK are the British Oceanographic Data Centre (BODC), the Marine Autonomous and Robotic Systems (MARS) facility, the National Tide and Sea Level Facility (NTSLF), the Permanent Service for Mean Sea Level (PSMSL) and British Ocean Sediment Core Research Facility (BOSCORF). The National Oceanography Centre is wholly owned by the Natural Environment Research Council (NERC).

For further information contact:

Steven Williams, Media Relations, University of Southampton, Tel: 023 8059 2128, email: [email protected]

http://www.soton.ac.uk/mediacentre/

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Past and Future CO2 – Reconstructing atmospheric Carbon Dioxide

Mar 23, 2014   //   by Athena   //   Blog  //  Comments Off on Past and Future CO2 – Reconstructing atmospheric Carbon Dioxide

by Gavin Foster, Dana Royer and Dan Lunt

Figure 1: Compilation of available CO2 data for the last 450 million years. For data sources see text. Proxy records are colour coded and labelled in the relevant panel. Greenhouse gas emission scenarios (RCP – Representative Concentration Pathways) used in IPCC AR5 are shown in the right hand panel. Note the variable log scale for time. For the geological data a smoothed line has been fit to the data with an uncertainty accounting for uncertainty in age and CO2. The black line describes the most probable long-term CO2 with 68% confidence limits in red, and 95% confidence in pink.

Carbon dioxide (CO2) in the Earth’s atmosphere is a potent greenhouse gas, responsible for trapping longwave radiation and ensuring the habitability of our planet. Variations in its concentration are thought to be important for controlling the evolution of the Earth’s climate on geological timescales (hundreds of thousands to millions of years) and recent anthropogenic increases in atmospheric CO2 have played a major role in more recent global warming.  Read more here.

Reconstructing atmospheric CO2 in the past is a tricky business.  For the last 800 thousand years we have bubbles of ancient atmosphere trapped in ice that can be recovered from Antarctica.  Prior to this time we have to rely on more indirect methods also known as proxies.  Those available to us are discussed in detail in the latest IPCC report, and in particular in Table 5.A.2 in Chapter 5 “Information from Paleoclimate Archives”  and more briefly here.

In the Figure 1, we have plotted all the available pre-ice core CO2 reconstructions for the last 423 million years (a total of nearly 800 data points) and compared them to more recent records and projections for the future.  The palaeo-CO2 data can be found here, the ice core data here  & here , historical data here and the projections of CO2 for the future here.

For the ancient CO2 data there is an increased variability due to the existence of both real short term variability (e.g. orbitally driven change like the well-known glacial-interglacial cycles) and increased noise due to the uncertainty in CO2 reconstructed by these more indirect methods.  To account for this and to better reveal the long-term trends in the CO2 data we have fitted a smoothed curve, which has an uncertainty due to the uncertainty on the age and CO2 of each data point.  This smoothed curve can be found here (Phanerozoic-CO2).  This treatment reveals a number of interesting features:

  • Despite considerable variability, there has been a gradual long term decline in CO2 over the last 450 million years or so. On average this is around 13 ppm (parts per million) per million years.
  • Values similar to today (398.03 ppm for Feb 2014) were last seen during short intervals in the Pliocene some 3 to 5 million years ago, but the last time long-term mean CO2 was at this level was in the middle Miocene climatic optimum (~16 million years ago; see this blog piece by Paul Pearson for more discussion).
  • For much of the rest of the last 450 million years or so Earth generally had higher CO2 than today (with the exception of the Carboniferous-Permian ~300 million years ago where CO2 was once again similar to today).
  • Business as usual emission scenarios (RCP8.5 on the figures) indicate atmospheric CO2 will reach around 1000 ppm by around 2110 AD (less than 100 years’ time).  The last time CO2 was this high was during the early Eocene Climatic Optimum (EECO)– the warmest time period of the last 50 million years.  The planet was so warm during the period that it was completely ice free (sea-level +65 m or so relative to today) and the latest compilations put global temperatures +13 ± 2.6 oC warmer than today (Cabellero and Huber, 2013).  It is important to note though that around 5 oC of this warming was due to changes in continental configuration, vegetation and the loss of the continental ice sheets.
  • Business as usual emission scenarios (RCP8.5) indicate atmospheric CO2 will reach around 2000 ppm by around 2250 AD.  The last time long-term CO2 was at this level was 200 million years ago at the Triassic-Jurassic boundary when CO2 was elevated by the massive outpourings of lava (covering an area of 11 million km2) as the supercontinent Pangaea broke apart and the Southern Atlantic opened for the first time, Read more here.

Figure 2: Climate forcing by changing CO2 and solar output for the last 450 million years. CO2 data and projections are as outlined in Figure 1. Changing solar output calculated as described in Gough et al. (1981; Solar Physics, 74, 21-34) with CO2 forcing from Byrne and Goldblatt (2014; doi: 10.1002/2013GL058456). The red band is the 95% confidence interval around the smoothed line through the published CO2 data.

However, the evolution of climate over this time period is not only being forced by changing CO2.  As well as tectonics changing the position of the continents, and changes in vegetation and ice changing Earth’s albedo (its reflectiveness) through time (http://www.scotese.com/), models of stellar evolution predict that the output of our Sun has increased over its life time.  On relatively short geological timescales (e.g. the last 5 million years or so) this effect is not significant.  But over 400 million years the output of the sun has increased by around 4% (equivalent to ~12 W m-2 of climate forcing).  We calculated the climate forcing by CO2 (in W m-2) and the Sun for the last 400 million years (using doi: 10.1002/2013GL058456; see Figure 2).

What is revealed is that despite a dramatic change in solar output, the combined climate forcing by CO2 and the Sun has remained relatively constant (Figure 2).  This has been commented on before (here) and is likely due to the operation of a strong negative feedback process changing CO2 levels on geological timescales as a function of global temperature (silicate weathering – more here). However we see that with the latest treatment of the proxy data forcing has remained even more tightly constrained (within ± 5 W m-2) over the last 400 million years (Figure 2).  Given this longer term view of climate forcing, the scenarios for future fossil fuel use stand out as being even more extreme, and the business as usual scenario (RCP8.5) would amount to a climate forcing by CO2 that is largely unprecedented in the geological record (as far as we can tell).

Members of the Descent into the Icehouse project are working to improve our estimates of CO2 during the EECO.  It is important to note that winding the clock back to EECO CO2 levels in the coming century will not result in a simple return to the Eocene climate.  Understanding what drove the evolution of the Eocene climate however will aid our wider understanding of the Earth’s climate system and how it behaves in warm climate states.

 

 

When was CO2 last at 400 ppm? And what was the climate like?

May 13, 2013   //   by Athena   //   Blog, Earth System  //  Comments Off on When was CO2 last at 400 ppm? And what was the climate like?
Paul N. Pearson, School of Earth and Ocean Sciences, Cardiff University CF10 3AT, UK.
Email: [email protected]
 
Summary Atmospheric CO2 is approaching the 400 ppm mark for the first time in human history which begs the question: when was it last that high? A recent high profile suggestion is that CO2 was that high in the Pliocene epoch (approximately 2.6-5.3 million years ago) and this is now being repeated in the press and around the internet. Here I point out that this claim is based on a few extreme estimates, mostly from sites that systematically overestimate more recent CO2 levels, while the majority of published Pliocene CO2 values are in the 250-400 ppm range. The last time we have consistent evidence for pCO2 over 400 ppm is in the Early Oligocene epoch more than 26 million years ago. This post presents the key graphs and comments on some of the methods used to calculate past pCO2.
 
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