Holocene Climate Change Conference 2013

I attended the Holocene climate change conference on 04.04.13 – 05.04.13 at the Geological Society in Burlington House, London. The event was made possible by the following sponsors:

–          The Department Of Energy & Climate Change (governmental)

–          Quaternary Research Association (QRA)

–          MSG

–          The Scientific Committee On Antarctic Research (SCAR)

–          The Scientific Committee On Oceanic Research (SCOR)

The conference was organised and advised by the following committee:

–          Colin Summerhayes (Chair)

–          Nick McCave

–          Paul Valdes

–          Graeme Barker

–          Eric Wolff

–          Dan Charman

The conference was composed of a number of talks on a range of subjects; the sessions and keynote speakers for these are presented as follows:

  1. Ocean change

Ian Hall, Cardiff

Ulysses Ninnemann, Bergen

Anthony Long, Durham

2. Terrestrial change

Heinz Wanner, Bern

3. Polar change

Bo Vinther, Copenhagen

4. Modelling change

Paul Valdes, Bristol

5. Influence of climate on humans and humans on climate

Graeme Barker, Cambridge

The first thing that very quickly emerged from the conference was that the North Atlantic Oscillation (NAO) has a strong controlling influence on Holocene climate. In many of the studies it was hypothesised that shifts in Holocene climate or environment may be related to changes in the NAO oscillation from a positive to a negative state, or visa versa (talks that included this: Hall, Rogerson, Nieto-Morena, Long, Sanchez, Wanner, Ersek, Comas-Bru, Roland and Telesinski). I therefore feel that before moving on to discuss particular case studies, it is important to outline what the NAO is.

As the name suggests, the NAO is a predominantly atmospheric phenomenon within the North Atlantic region. The NAO phase (-/+ve) results as a consequence of variations in sea level atmospheric pressure between the Azores High and Icelandic low. The NAO phase has a controlling influence on the strength of the Westerly winds and therefore storm tracks across the North Atlantic. Prolonged positive NAO has been associated with a reduction in the strength of the Atlantic Meridional Overturning Circulation (AMOC)  (searching for either of these terms on Google will lead you to an array of sources).

I found it particularly interesting that the NAO was so often attributed to Holocene climatic change as there is no known cyclic recurrence of either positive or negative NAO phase and yet, some Holocene events (namely the 8.2 and Little Ice Age (LIA)) are associated specifically to ‘Holocene Bond events’ which have a recurrence interval of ~1470 years (Bond et al., 1997; 1999).  Clearly the 8.2kyr and LIA were ‘big names’ over the 2 day conference, but other climatic events were also discussed, for example Thomas Roland conducted a talk on his PhD thesis, which investigated the 4.2kyr event in Great Britain and Ireland using peatland records.

Events such as the 4.2kyr and 8.2kyr event are prevalent within the literature and are recorded in various parts of the World. However, the timing and magnitude of these events are notably different across regions. The general consensus of the climate community was that the 8.2kyr event was accepted as a globally expressed climate ‘event.’ While reviewing ocean circulation changes, Hall discussed Ellison et al’s work around the 8.2kyr event, who found that there was a reduction in AMOC during this centennial/millennial oscillation. Other events were deemed to have been less established as a global ‘event’ and perhaps were more spatially variable in terms of their expression in different regions. The Medieval Climate Anomaly (MCA) and LIA was described by Nieto-Morena, who suggested that these climatic ameliorations were potentially caused by a combination of solar irradiance and modulation of NAO in the Westernmost Mediterranean, which resulted in a weakening of the North Atlantic Deep Water (NADW) formation.

It is important to investigate these changes as they occur within the Holocene and arguably may occur again in the future, therefore the expression of these events in different locations should be investigated in order to develop a better understanding of potential causal mechanisms and to feedback to modellers in order to provide future climate change scenarios. This links well with the discussion provided by Paul Valdes (keynote for modelling change – session 4) who stated that good quality palaeoenvironmental data is key to improving models as these ultimately provide the palaeo’forcing’ data, palaeoclimate data and therefore palaeo-model information (produced in a diagram within the presentation).

Now, the majority of the modelling section went above my head. I’ve not really studied modelling and I find it immensely hard to comprehend how numbers can be attributed to little Cartesian squares which act for a set space of all the climatic components (eg oceans and atmosphere), so please comment or email me if I have completely got the wrong end of the stick! Valdes said that “palaeoclimate is not an analogue for the future.” Now, firstly, this sort of counteracts my basic understanding of uniformitarianism. However, I believe that what he was trying to tease out from that statement is that climate is dynamic and often in a state of flux, as indicated by palaeoclimatic events, such as the 8.2kyr event. Despite the Holocene being branded as ‘the stable climatic period’ by many, it has many influences and feedbacks which are able to alter the state of the system; this is particularly important when we consider the role of increasing CO2 concentrations in the atmosphere and the implications that this may have on the modelling components of climate both back through time and forward through time.

Paul by no means ignored the well debated issues with modelling. Recent news articles have highlighted problems in various models and rightly so…but he very rightly said:

“we learn the most where things are actually failing” and “successful things in science come from when things don’t work out.”

I cannot think of two better phrases to sum how I feel about Quaternary science. Skeptics will undoubtedly now jump in and scream that the science we produce is inherently wrong, but this is not true. This form of science has come a very long way, in a very, very short period of time and the public should respect that. There is trial and error in all science, for example the manufacturing of pharmaceuticals and this science is no different, except the science that we produce makes good press because it affects the people at present, and in truth, it scares society. As Tony Brown says:

“changes to the environment made by humans will alter their responses” and “humans respond not to climate per se but to changes in their environment.”

This is an important point to note. Humans are within the science that we study: they are directly involved. In previous times there were, perhaps, more obvious changes to the environment, such as draining peatbogs. Carbon emissions are exponential, but leads and lags in the climate system mean that we cannot (as a cluster of organisms on the Earth), at present, see the direct environmental responses caused by these emissions. The rate of emissions is by far exceeding the rate of climate system response and therefore at present, we are seeing only small changes to the climate – this makes it hard for society to understand the long term implications of emissions. Therefore, taking Tony’s ideologies, humans refute climate change as they cannot see the environmental implications of rising anthropogenic emissions. But I am digressing and this particular topic will, no doubt, continue to be argued until I am grey and old (and am hopefully lecturing a new generation of climate scientists).

Despite the conference admittedly glossing over the current debate on anthropogenic emissions having a controlling influence on future climate, there were discussions about what is happening with present day climate and environments. Hall provided an excellent overview of deep ocean circulation changes. His initial review, for example, looked at the work of Brydon et al. (2005). Their paper indicates that between 1957 and 2004 there was a ~30% decrease in AMOC. The implications for a slowing AMOC are a cooling climate as heat transfer to mainland UK, for example, decreases (eg. 8.2kyr event is associated with a weakened AMOC in many studies). Other present day research from Heinz Wanner (which, may I just add was fantastic) (in press) indicates the global warming (perhaps attributed to anthropogenic changes) seen in many records globally is not recorded in high resolution ice cores from Antarctica, and that Antarctica does not follow the same warming trend that is seen in other locations.

Wanner’s paper is in press and should be released in June, with (and he stated this a lot) the raw data available to play with on the NOAA raw data base after this point – I think everyone at the conference can all agree in that this will be the paper to read for that month. Other mentions in his talk included the role of volcanism. Volcanism is said to have a strong covariance with solar minima and that modellers have a job to do here! He snuck in that this relationship may have had an influence on the LIA (but I am sure that this is already the general consensus?!). Contrary to this data, Victoria Peck from BAS described West Antarctic ice sheet loss since the 1970’s as a consequence of ice shelf thinning and glacier flow changes due to circumpolar deep water upwelling (CDWU) whereby warm water causes melt from the base upwards. Reasons provided for the increase in CDWU include changes in the Westerlies in recent decades, with stronger more Southerly winds causing increased upwelling. It was admitted that we just don’t know the long term influence of increased CDWU, but it is generally acknowledged that this has a devastating effect on the total ice mass (Swart and Fyfe, 2012, was noted on the presentation as a paper to look up RE: predicted changes in Southern Westerlies).

However, Nieto-Morena’s study of the Westernmost Mediterranean over the last 2 Millennia concluded that anthropogenic contribution was evident. In addition, the summary stated that we know that humans have impacted the climate, but that is perhaps not the most pressing issue for future climate research. Summerhayes addressed this by describing the impact of humans as being the only real global ‘event’ and going on to state that it is evident by a marked uptick in temperatures in recent times. However, the key to future climate research improvements lies in gaining studies with better chronological control across a wider spatial extent (it had been mentioned that palaeoclimate and palaeoenvironmental studies are very Eurocentric and North Atlantic in origin) is key to studies. I believe that this means in the future, there will be an increasing reliance on tephrochronology and micro-tephras as isochronous marker horizons.

I was surprised that there was a lack of discussion on the hotly discussed ‘Anthropocene.’ I attended a conference at the Geological society a few years ago as a keeno fresher, just as the term was gaining momentum in the climate community. Within the conference, there was a fair acknowledgement of Walker et al’s (2012) formal subdivision of the Holocene paper (featured in JQS), but an ignorance of the notion of the Anthropocene. As a fresher at the talk (and I am sure I did not really understand the content fully then), I felt that it may be a fad, and I have sat on the fence as to whether I believe its existence. The abstract for Tony Brown’s talk stated:

“This research has important ramifications for our understanding….and for the current debate concerning the ‘Anthropocene’ as a postulated new human-dominated geological period.”

And debate it is. Brown failed to mention the word Anthropocene in the talk once, and this is not the first time that he has let me down in this sense. He gave a talk at Royal Holloway’s annual Gordon Maneley lecture recently, which would have been the perfect environment to really engage in a wide audience in a discussion on this proposed geological era of human influence. However, he barely gave it a mention at that talk, either. Therefore, I felt obliged to rather awkwardly ask the question:

“Forgive my naivety, but how does this talk [on deforestation, climatic sensitivity and the expansion of wetlands in North West Europe] relate to the Anthropocene, as it is mentioned in your abstract, but it hasn’t been mentioned in the talk?”

I hope I don’t come across as rude in asking this, but I feel if it is in the abstract, it should most certainly be written somewhere in the powerpoint and at the very least be mentioned. I was most disappointed by the reply, in all honesty. He responded by saying that sedimentological changes leave a mark on the geological landscape, shrugged and admitted that it was a dense answer. Really, I wanted to know if present day changes were seen in this site, but lacking confidence and doubting I had even asked an appropriate question meant that I didn’t push the issue… Tony, if you’re reading this, I would love to know a bit more about where your research sits in the Anthropocene argument and why?! Thanks!

Closing remarks included the use of the word “events.” It was argued by someone on the committee (I failed to take their name down in my notes – please comment if you know who it is!) that perhaps the use of the word “events” was too loose. He stated that events should only be termed events if they were abrupt and catastrophic, for example, the 8.2kyr and Heinrich (H) events whereby there was a collapse of the Laurentide Ice Sheet (LIS) and a release in ice rafted debris (IRD). He postulated that the 4.2kyr ‘event’ and MWP should simply be considered as a low or a high point within the natural variability and that perhaps some climate scientists are getting caught up in labelling small climatic deviations as ‘events.’

To a point, I feel he is right, particularly when the magnitude and timing of these events is actually investigated across a variety of locations, or compared to climatic deviations of say, the Pleistocene. Moreover, we can take Roland’s talk as an example of this: he found that 4.2kyr ‘event’ was not present in Northern Britain or Ireland peatlands, while ~130 other studies demonstrated a form of palaeoclimatic/environmental change (which have mainly been attributed to causal mechanisms including the NAO, THC and the role of westerlies). However, Roland concluded saying that more research was needed into the use of stable isotopes in sphagnum peatlands… this form of conclusion appeared recurrent: more research is needed to better confirm that the use of palaeoclimatic proxy indicators are measuring what they should be measuring. In terms of the δ18O signal derived from ice cores, Bo Vinther, from the Centre for Ice and Climate (CIC) in Copenhagen, stated it is clear this stable isotopes is a record of temperature as it matches the instrumental temperature record well for the past 200 years. For me, this talk was particularly interesting as it showed some of the continual flow analysis (CFA) work from Greenland records. When I visited the CIC, this was the lab where I spent the most time and it was nice to be able to relate to the instruments used in the study. The chemical changes (eg. Na, NH4 and dust conductivity) are used to show seasonal changes and SO4 peaks used to determine past volcanic eruptions. Errors are able to be determined by attributing a +/- ½ year error for every uncertain data point. Vinther said that the next step is to relate 10Be data (indicative of solar activity) to determine if the same signal for Na and SO4 is seen and should this be the case, it may be possible to extend the volcanic chronology back through time and that this data will be released in the not too distant future.

However, going back to the argument of ‘what is an event’… I was thinking that a climatic amelioration within a particular dataset is called an event often out of ease. If it deviates from what would be a ‘normal’ climatic trend for that region, then it is an event in the sense that it is a climatic oscillation which is (more than likely) of a large enough magnitude to impact the environment. This is in a similar view of what Lang argued. I feel that, as long as the paper explains the extent of the ‘event’ then there should be no issue with terming in an event (i.e. the 8.2kyr event is of global extent…or the 4.2kyr event witnessed within this study location). Perhaps there needs to be an investigation into the actual definition of an event? It seemed that there was considerable confusion between the classic Bond event in association with D-O cycles and the slightly different Holocene Bond event. This definition would link nicely with the call for a template in which to fit these climatic manifestations onto, by Nick McCave (…but, alas, I don’t think that he was volunteering to do this!).

In my personal conclusions of the conference I wrote a few pages in my (now almost filled) note pad:

–          It is easy to take the individual case studies presented in this conference as kosher, for example, Wanners talk was very compelling and convincing (RE: his in press paper to be released in June), but we must remember that these papers form a small proportion of an already vastly studied area of research (in some cases)

–          As a consequence of the above, it is important to (at least mentally) synthesise all this data without bias

–          The NAO plays a much bigger part in the climate system than I had anticipated (although I am sure the more experienced climatic scientists reading this already knew this), whereby it ultimately has an influence on oceanic components of the climate system, such as AMOC.

–          The climate system is complex (okay, so we all knew this already) and I think we are just scratching the surface. I have always had a particular interest in the 8.2kyr event and since carrying out my undergraduate, I am specifically interested in the expression of this event in the UK (much like Roland and his 4.2kyr study). However, this conference has opened my eyes more to the widespread variability in the expression of these climatic oscillations and makes me want to question some proxy records that have been used to interpret palaeoclimate and as Husum stated, the insufficient geographical coverage that is evident from many palaeoclimatic studies (although it was commented by someone at the conference that the lack of Southern hemispheric Holocene records comes from a lack of robust chronological control due to poor dating material found in these regions).

–          I didn’t feel confident asking this question at the time of the conference, but I am happy to ask it now from the comfort of my sofa and laptop. Pardos-Gene gave a talk on the climatic variability on the bottom water ventilation in the Westernmost Mediterranean during the Holocene… my question revolves around her positioning of the Younger Dryas (YD) (or Loch Lomond Stadial equivalent for the British Isles) at ~12.3-13kaBP (from the graphs with her palaeoclimatic/environmental proxies on). I understand the YD to be ~11.7-12.8kyr. So, is her timing incorrect? An issue with the dating perhaps? The YD was a globally extensive event and I’m pretty certain that the timing in Europe was no different to the timing in the Mediterranean. Could someone please clarify this?

–          I thoroughly enjoyed the conference. All of the speakers were fantastic, but I have to herald my particular praise to the following speakers for their enthusiastic contribution, their subject matter and presenting skills:

Ian Hall

Ulysses Ninnemann

Mike Rogerson

Antony Long

Heinz Wanner

Thomas Roland

Stephen Brooks

Bo Vinther

Victoria Peck

Paul Valdes

Please do comment, share, discuss or e-mail me with anything at all to do with the conference! (email and twitter is available in the ‘about me’ tab). I hope you enjoyed this short summary! 🙂

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