My trip to New Zealand

Post By: Rachael Shuttleworth

What drives glacial – interglacial CO2 level changes is what is known as the “holy grail” of palaoceanography. Though the question as to whether these changes are caused by biologically or circulation dominated process is still hotly debated. To better quantify and enhance our understanding of the processes and mechanisms which control CO2 on these timescales we must look to the past for answers. This is the focus of my PhD @thefosterlab and we are initially targeting cores taken from variety of latitudes in the southern Pacific Ocean, ranging from subtropical to polar waters. These cores are stored at NIWA in Wellington, New Zealand – someone had to do the tough job of collecting the samples...

In order to get the data we want, a lot of preparatory work on the samples has to be undertaken. Firstly we must sample to core itself, taking slices of mud at specific depths which correspond to the time periods of interest.

These cores are then put into an oven overnight to dry out.

These dried samples are then washed over a 63micrometer serve to remove the very fine mud particles. They are then put back into the oven to dry again.

The information that we want is stored in foraminifera within these sediments, and so the next step is to pick these micro fossils out one by one.

These samples are now prepped and will be sent back to @thefosterlab based at the National Oceanography Centre, Southampton where analysis on their isotopes will be undertaken. Many of these cores already have carbon, oxygen and nitrogen isotope records which can tell us about temperature, age, ice volume, and productivity. For my PhD I will focus on obtaining a boron isotope record which will tell us about the change in flux of CO2 into the oceans from the present day back to the last glacial maximum. By comparing this with dust flux and productivity records I hope to better quantify the role that relaxation of micronutrient (such as iron) limitation due to enhanced dust deposition played during the last glaciation. This will provide further insight into how much biology played a part in driving glacial-interglacial CO2 change, as well as the potential carbon storage via this mechanism of iron fertilisation.

Its still early days for my PhD, and I now have my first sample set.  Next stop – the lab!

Future relevant climate sensitivity (part deux)

A paper out this week by Friedrich et al. (2016) is the latest in what seems like a series this year determining climate sensitivity using the palaeoclimate record (see here).  This is a very powerful approach but has its difficulties many of which are discussed in our previous post and here.  The Friedrich et al (2016) study used a new empirical estimate of Surface Air Temperature (SAT) based on a compilation of Sea Surface Temperatures (as did Snyder recently) and a complete assessment of the processes “forcing” climate change over the last ~800 thousand years (e.g. CO2, land-ice albedo, and dust) to identify that climate sensitivity changed as a function of climate state: they found it was ~1.8 K per CO2 doubling when the Earth was substantially colder than today and ~5K per doubling when the Earth was only a little bit colder than the pre-industrial.  We @theFosterlab were just involved in a review on this subject (here) and a summary of the literature from that paper is shown below.  

Friedrich et al. go further than other studies and apply the palaeo-sensitivity to predict our warm future (see figure below).  They correct for the fact that over the next 100 years the climate isn’t in equilibrium with its forcing and show that the high “warmer-paleo” sensitivity yields temperature in 2100 AD, given a business as usual RCP8.5 emissions scenario, that could be as high as 6 K (5-7 K) compared to 5 K (3 -6 K) from the CMIP5 models (see figure below). 

The accuracy of such a paleo-sensitivity approach to predict the future climate is: (i) very dependent the accuracy of the temperature record used to determine sensitivity in the past (and others limitations, see; (ii) but is reliant on the assumption that the sensitivity estimated from climates slightly warmer and substantially cooler than today is applicable to Earth temperatures up to 5 K warmer.

I think it’s a great finding of this paper that climate sensitivity is state dependent over the Pleistocene glacial cycles, but this also means it’s probably an over simplification to assume that a similar state dependency doesn’t characterise the system when temperatures are substantially higher than the pre-industrial (see top figure). 

We attempted to investigate this in this paper in 2015 using boron isotope based CO2 data from the Pliocene.  We didn’t examine the data for a state dependency within the Pliocene (see here for why) but determined that the average climate sensitivity in the Pliocene was ~3.7 K per CO2 doubling (with an uncertainty of 2-6 K).  This overlaps with what Friedrich et al. determine as “warm-paleo” sensitivity.  However, my feeling is that, given the current uncertainties in determining climate sensitivity in the past, rather than indicating the Earth system is more sensitive than the future, studies like that of Friedrich et al. (2016) and our own ( are very important validators of our understanding of the behaviour of the climate system encapsulated by the CMIP5 models.  These are very different ways to understand the climate system yet they give the same results – this is very powerful and is a great illustration of the utility of palaeoclimate research.  As a community we now need to work hard to reduce the inherent uncertainties and get the most out of the rock record of past climate changes.

Future Relevant Earth System Sensitivity

A recent paper by Carolyn Snyder published in Nature this week presented a record of global average surface temperature (GAST) reconstructed from a compilation of sea surface temperature records.  This is a great approach and the GAST record, and the techniques used, will be very valuable in efforts to use the geological past to understand how the climate system works.

However, towards the end of the abstract, and the focus of the press release, was a statement about Earth System Sensitivity (the temperature change in response to CO2 change – subtly different to equilibrium climate sensitivity – see here for detail).  Earth system sensitivity, unlike equilibrium climate sensitivity, includes the action of all climate feedbacks (except those relating to the carbon cycle) and is very dependent on the background climate state.  Synder calculated that ESS was around 9 oC per CO2 doubling over the last 800 thousand years.  As discussed here, this is not a relevant measure of how our future climate system will behave because the high ESS during the cold Pleistocene was driven in part by the changes in surface albedo caused by the waxing and waning of the continental ice sheets of North America and Europe – ice sheets that are no longer present on the Earth so are not able to act as a feedback in the future.  ESS for the future is therefore much lower than what Synder calculates.  In a paper last year we @thefosterlab used new Pliocene CO2 data from the boron isotope proxy to show that a future relevant ESS is more likely in the range 2.2 to 5.2 oC per CO2 doubling (which is in good agreement with modelling studies; Lunt et al. 2010).  This suggests that estimates of equilibrium climate sensitivity from the IPCC (1.5 to 4.5 oC per CO2 doubling) do adequately describe the long-term (1000 year) response of the future climate system to CO2 change because the northern hemisphere ice sheets are currently at close to their minimum extent.

The figure above is from Martinez-Boti et al. (2015) showing the Sensitivity Parameter for the Pleistocene (red) and Pliocene (blue) for two different temperature records - mean surface air temperature (left) and sea surface temperature (right).  The Sensitivity Parameter describes the temperature change for a given change in climate forcing.  Panels (a) and (c) show the sensitivity parameter due to CO2 change only.  ESS = this sensitivty parameter multiplied by 3.7 (the radiative forcing from a doubling of CO2).  ECS is approximately the senstivity parameter in panels e and g multipled by 3.7 (because here we also take into account the radiative effect of the ice sheets).  As in the Synder paper we also found a high ESS for the Pleistocene because of the large ice sheets present (ca. 2 x 3.7 = 7.4 oC per CO2 doubling).  The Pliocene however lacked large ice sheets and ESS is about equal to ECS, which both fall in the IPCC range (ca. 1 x 3.7 = 3.7 oC per CO2 doubling).

2016: the first year of 400 ppm? The Foster Lab interviewed on BBC Radio Weather Show

A paper published this week by Richard Betts of the UK Met Office predicted that 2016 will be the first year CO2 will be >400 ppm at the Mauna Loa observatory all year round.  Given the 2-3 ppm yearly increase this signals that CO2 is likely to remain >400 ppm for our lifetime.  This was featured by the BBC website that also included reference to the work fo the Foster Lab and one of our earlier blog posts.  On Wednesday this week Gavin was also interviewed for the Paul Hudson Weather Show about the last time CO2 was 400 ppm.  The show was broadcast this morning at 6am (18/6/16) on BBC Radio Humberside and will be broadcast on BBC Radio Lincolnshire on monday (20/6/16).  You can also listen to the entire show here:

or fast forward to 32 mins to hear Gavin!

The question is now not if we are heading for a Pliocene-like future, but how long will it take to get there...


Ancient marine sediments provide clues to future climate change

Fossil planktonic foraminifera (33-50 million years old) from Tanzania by Paul Pearson, Cardiff University is licensed under a Creative Commons Attribution 4.0 International License

Fossil planktonic foraminifera (33-50 million years old) from Tanzania by Paul Pearson, Cardiff University is licensed under a Creative Commons Attribution 4.0 International License

A paper led by the fosterlab’s Dr. Eleni Anagnostou and featuring Prof. Gavin Foster is published today in Nature (here). It represents the latest in our efforts to use the geological record to provide information about how the Earth’s climate system operates when significantly warmer than today (e.g. see here).  It was work funded as part of the “descent into the icehouse” project that involved researchers from a number of UK universities, and is part of the NERC life and planet theme.

Here is the press release from the University of Southampton.  And here is a short video that discusses the wider project:

Our principle finding in this new paper is that atmospheric CO2 was around 1400 ppm during the warmest part of the Eocene and approximately halved through the Eocene.  We determined this by using boron isotopes.

Last year Dr. Gordon Inglis from Bristol who is also involved in this work published this paper that better demonstrated that: (a) the early Eocene (~53 million years ago) was warm (the best estimates, here, are at +14 oC compared to the pre-industrial); (b) there was around 8 oC of cooling for the high latitude surface ocean and around 2 oC of low latitude cooling through the Eocene (from ~53 to ~34 million years ago).

We know from earlier work that some of the warmth of the Early Eocene was caused by changes in the position of the continents, vegetation change, and the lack of any ice sheets on the South or North poles.  This leaves around 9 oC of the early Eocene warmth to be explained.  CO2 is a potent greenhouse gas (see here for example; ) and when its concentration is doubled in the atmosphere ( the Earth should warm by 1.5 to 4.5 oC.  Levels of CO2 of 1400 ppm is ~5 times the pre-industrial concentration of atmospheric CO2. This means, if the Earth’s climate system really behaves like we think, the early Eocene should be between 4 and 11 oC warmer than the pre-industrial (when CO2 was 280 ppm).  The 9 oC warmth of the early Eocene is thus entirely explained by the enhanced greenhouse effect due to the higher CO2 at the time. This finding also supports our earlier work that suggests the sensitivity of the climate system to forcing from CO2 doesn’t depend hugely on climate state. 

We also know from previous work that surface temperature in high latitude regions tend to change more than the global mean, and low latitude regions tend to exhibit a more muted change than the mean.  Given the nature of this “polar amplification”, we further demonstrated in this new paper that the CO2 drop through the Eocene (from 53 to 34 million years ago) was sufficient to drive the observed (2 oC low latitude and 8 oC high latitude) cooling in sea surface temperature.

These two findings (that CO2 drove much of the warmth of the Eocene, and its decline drove much of the cooling through the Eocene) confirm that not only are the IPCC estimates of climate sensitivity consistent with the geological record, but that CO2 change was a major player in driving the switch between the Cretaceous/early Cenozoic greenhouse climate state to the late Cenozoic ice house climate we currently find ourselves.   The next question of course, and one we are working on, is why did CO2 decline through the Eocene? A recent paper in Science by MacKenzie et al. suggest it’s all about volcanoes and their emissions of CO2. Whatever the cause, its only with CO2 records like we present here we will be able to provide a deeper understanding of the role of CO2 in natural and anthropogenic climate change.

The Earth in a bottle - CO2 games on my kitchen bench

UPDATE 02/09/2016: it has come to my attention (thanks Katharine Hayhoe) that the experiment below was first performed by Mrs. Eunice Foote and reported to the American Association of Science in 1856! here is the report (thanks Gavin Schmidt for the link).  She even foretold the future "An atmospheric of [carbonic acid gas - CO2] would give our earth a high temperature...".

John Tyndall was perhaps the first scientist to recognise the radiative properties of CO2 in 1859. In recent years the study of the role of CO2 and global warming has moved beyond the physics of CO2 and more frequently we hear discussions of record breaking temperatures or equilibrium climate sensitivity in state of the art computer models.  I think it’s quite refreshing though to go back to basics and remember that the theory of global warming is: 1. Over 150 years old; 2. rooted in simple physics (CO2 present in the atmosphere  absorbs long-wave radiation that it later releases warming the air a bit). 

There are quite a few experiments that you can do at home to demonstrate this underlying physics (e.g. here). Over the last couple of weeks I’ve been gathering the necessary equipment to do one of these simple experiments and this weekend I thought I’d give it go.

Here is a picture of my “experimental set-up” on my kitchen bench

It consisted of two Infrared heat lamps (200W), two plastic drinks bottles, to silicone rubber stoppers, two digital fridge thermometers (with some play-doh to seal the hole in the stoppers),  and the all-important CO2 in a can.   

I filled one of the bottles with CO2 (the one on the left in the picture of above) and turned on the lamps.   Entirely consistent with our understanding of the physical properties of CO2, the extra CO2 in this bottle absorbed more of the infrared radiation from the lamp and subsequently released it warming the bottle more than the one with just air in it.

It doesn’t take someone with a Nobel prize to draw parallels between what is happening in this bottle and what is currently happening to the Earth! So remember: the theory of global warming is quite simple and the question should not be “are we warming?” but “how hot is it going to get?”

Decent into the Icehouse Teaser Trailer

Heres a short video introducing a recent project from The Foster Lab that is shortly coming to an end.  Tune in soon to find out more and take a look at some of our recent publictions for some of the latest results:

Lunt, D.J., Farnsworth, A., Loptson, C., Foster, G.L., Markwick, P., O'Brien, C.L., Pancost, R.D., Robinson, S.A., Wrobel, N. (2015) Palaeogeographic controls on climate and proxy interpretation Climate of the Past Discussion 11, 5683-5725,  doi:10.5194/cpd-11-5683-2015

Inglis, Gordon N., Farnsworth, Alexander, Lunt, Daniel, Foster, Gavin L., Hollis, Christopher J., Pagani, Mark, Jardine, Phillip E., Pearson, Paul N., Markwick, Paul, Galsworthy, Amanda M. J., Raynham, Lauren, Taylor, Kyle. W. R. and Pancost, Richard D. (2015) Descent toward the Icehouse: Eocene sea surface cooling inferred from GDGT distributions. Paleoceanography, Early View (doi:10.1002/2014PA002723). click here for data.


Is this the last year below 400 ppm?

The average CO2 value for October 2015 was 398.29 ppm.  Ralph Keeling (and he should know) thinks this month (November) may be the last time that CO2 will be below 400 ppm again in his life time (or for that matter, anyone’s lifetime).  His post here discusses why he thinks this is.

CO2 compilation from ice core (in red; Bereiter et al., 2015, GRL, doi: 10.1002/2014GL061957) and boron isotopes in blue (Hoenisch et al., 2009, Science,  doi: 10.1126/science.1171477 and Martinez-Boti et al., 2015, Nature, doi:10.1038/nature14145)

CO2 compilation from ice core (in red; Bereiter et al., 2015, GRL, doi: 10.1002/2014GL061957) and boron isotopes in blue (Hoenisch et al., 2009, Science,  doi: 10.1126/science.1171477 and Martinez-Boti et al., 2015, Nature, doi:10.1038/nature14145)

400 ppm is of course only a symbolic threshold but as the guys at Mountain Beltway suggest it should give us reason to pause and contemplate what a momentous change it is in terms of the planet.  Something we do in thefosterlab is reconstruct CO2 in the geological past using the boron isotope proxy and this allows a little bit more perspective on this issue.  The image above is a plot compiling the state of the art when it comes to CO2 over the last 3 million years or so, including some data for the Pliocene (2.6 to 5.3 Million years ago that we published this year in Nature).  What is clear is that the last time CO2 was 400 ppm was around 2.5 to 3 million years ago.  The world was a different place back then – global temperatures around 3 C warmer than the pre-industrial and sea-levels were around 20 m higher (due to retreat/collapse of the West Antarctic and Greenland ice sheets).  With global temperatures likely to top 1 C above pre-industrial levels this year and CO2 now likely to stay above 400 pppm it appears we are well on the way to a Pliocene-like future.