Anthropogenic climate change and the nature of Earth System science

April 2, 2014
Fray

Core teddyFrazer Bird on:

Oldfield, F., Steffen, W. 2014. Anthropogenic climate change and the nature of Earth System Science. The Anthropocene Review,1, 70-75.

This paper is a very interesting read for anyone working in the field of palaeoecology. It briefly discusses some of the key criticism of earth systems science research and demonstrates how a good understanding of our past is critical to our future projections.

 “Nature of the Science”

Often Earth System Science is described as being “fuzzy”. It doesn’t always fit the model Popperian approach to science whereby refutable hypothesis are defined and tested. The authors point out however that this is somewhat an unfair criticism. The Earth system is complex, non-linear and often there are no cause-consequence relationships. The scientific method involved is much more complex and often we are trying to understand phenomena that occur over immense timescales. To demonstrate this a little further the authors use the example of freshwater acidification.

“By choosing a variety of field-based case studies with or without key characteristics, each of which was a putative cause of acidification, it proved possible to isolate past variables such as land-use change or catchment afforestation and thereby home in on the only remaining hypothesis not rejected by the evidence, namely the dissemination of industrially generated SO2.”

Rather than testing and refuting or accepting whether industrial generated S02 was causing acidification, cumulative research showed it to be the universal variable across multiple examples. Often when we make inferences about environmental change we have multiple working hypotheses which stand until more and more evidence arises to support one over the others.

 “Toward Projective science”

Projecting the future consequences of climate change is of vital importance for society and critical to policy and mitigation strategies. Climate models are really the only tools at our disposal in trying to understand future scenarios. However models alone cannot provide us with all the answers, the paper demonstrates that the only evidence we ever have is from the past.

“All the evidence we have regarding environmental change comes from the past, whether of the previous few seconds as changes are logged continuously, or of the more remote past revealed through the study of environmental archives.”

If we want to refine our models and have better projections in the future then these tools must have the ability to capture the empirical evidence we have from the past. Future projections are based on data-model comparisons; this is an interactive relationship that is ever refined as each side gains in knowledge and skills.

 

The Anthropocene Review – reviewed

March 26, 2014
WDG

AnthropoceneReviewThe Anthropocene Review is a new journal focusing on the impact of humans on planet Earth through time; information on the latest publications can be found on the associated blog.

Given that much of the research we are interested in relates human-environment interactions in the past we decided to take a closer look at the range of articles being covered by this journal. Our thoughts on seven articles published in the first issue of The Anthropocene Review will appear in a series of blog posts soon. To get started here are a list of the papers we will be covering:

Full Anthropocene Review table of contents here.

 

 

 

American tour: Biogeography meeting & Ecuador field work

February 26, 2013
Fray

PCRG COMPLETE AGAIN

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I am glad to say that after almost two months out of the office running around with 8 bags of equipment, Frazer and I have finished our tour of the Americas. As the work has been so diverse, we would like to split our comments and impressions into two different posts, we hope you enjoy them!

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The Mighty Midge

May 11, 2012
Fray

Fossil chironomid from the Andes

CHIRONOMIDAE AS A PALAEO-ECOLOGICAL TOOL
Chironomidae is a family of two-winged flies more commonly referred to as non biting midges. This diverse group of insects have been known for a long time to be sensitive environmental indicators. Early research in the field showed that the trophic status of lakes could be classified according to the characteristic chironomid assemblages found within them (Thienemann, 1922). Furthermore the head capsules of the larvae are well preserved within the sedimentary record. As a result palaeolimnological researchers became increasingly interested in the potential for using Chironomids to track the trophic development of a lake through time by examining the changing assemblages within the accumulated sediments. With geographically close lakes displaying significantly different midge faunas the potential for the insects being used as climatic indicators was dismissed and the following hypothesis became established: Chironomid assemblage composition reflects in-lake variables, e.g. lake depth, pH, dissolved oxygen, trophic status and substrate. However work by Walker and Matthews (1989) demonstrated that temperature was by far the most significant variable in controlling the broad scale distribution and abundance of midge fauna.

Walker and Matthews realised the potential for the non biting midge to be used as a palaeoclimatic indicator from two initial observations. Firstly within the fossil records, as climate began warming following the deglaciation of the northern hemisphere, the relative abundance of taxa associated with cold oligotrophic lakes (Heterotrissocladius) abruptly declined. Secondly they noticed the best analogues for late glacial assemblages were found in modern day arctic and alpine settings. Overall Walker and Matthews concluded that the northern limit of temperate taxon was controlled by cold summer air and/or water temperatures. The southern limit of Arctic species was instead driven by cold oxygenated refugia in the profundal zone of deep, temperate lakes. These temperatures were significant with respect to the insect’s life cycles as many species require critical temperature thresholds to complete pupation and emergence stages.

Since the pioneering work of Walker and Matthews (1989) and others the debate linking Chironomids to temperature has raged. Debate has centred upon what controls chironomid distribution and  how suitable, if at all, the insects are in the context of palaeoecological studies. Recently Velle et al. (2010) discussed some key factors which must be considered when working on chironomid based temperature resonstructions.

Below I present some of the debate around the midge-environment-temperature debate; focusing on both midge distribution and identification and the potential of this proxy as a indicator of past environmental and climatic change.

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Thinking about proxies

January 31, 2012
Fray

COMMENT ON DISCUSSION OF PROXIES IN HUNTLEY (2012)
All areas of research have strengths and limitations which are readily acknowledged by the scientists involved. The reconstruction of past climates (palaeoclimates) from biological indicators contained within the fossil record (proxies) presents some specific challenges; for example key limitations might be gaps in a sedimentary sequence or post-depositional degradation of samples. Understanding and interpreting data sets in the face of these challenges require the researcher to develop a wide range of skills. Huntley (2012) focuses upon the uncertainties within palaeoclimate reconstruction which he considers to be “frequently overlooked” (p. 2) by scientists making climate reconstructions from proxy records. Specifically Huntley urges researchers to consider carefully:

  • What a given proxy is actually capable of reconstructing, i.e. what climate variables controls its distribution?
  • What other variables might be influencing the proxy, i.e. could there be multiple influences, might these vary through time?
  • What is the spatial relevance of the proxy, i.e. macro versus micro scale?
  • Can multiple proxies be compared, either within or between sites?

In other words: which and how many climatic variables can be reconstructed form any one aspect of the fossil record?

Below I review and comment on some key arguments made by Huntley (2012) related to the use of proxies in reconstructing palaeoclimates.

REFERENCE
Huntley, B. (2012) Reconstructing palaeoclimates from biological proxies: Some often overlooked sources of uncertainty. Quaternary Science Reviews 31: 1-16.

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