Testing ice sheet models and modelled estimates of Earth's climate sensitivity using Miocene palaeoclimate data

Lead Research Organisation: CARDIFF UNIVERSITY
Department Name: School of Earth and Ocean Sciences

Abstract

Climate models use computational techniques to mimic real physical and chemical processes in the climate system in order to predict future climate change. Such models have been used to quantify how sensitive Earth's climate is to atmospheric carbon dioxide levels. Knowing this 'climate sensitivity' is essential for politicians to set goals for future CO2 emissions that will keep Earth's climate within 'safe' limits. Until recently, the estimates for this climate sensitivity have been based on models that look only at the short-term (e.g., years-decades) effects of increasing CO2 and rising temperatures. They do not include other longer-term effects, such as melting ice sheets or changing global vegetation cover. An example of such a feedback is the melting of the Greenland ice-sheet, which in addition to causing rising sea levels will also cause further regional warming. The problem with ignoring such components of the climate system is that there are large uncertainties regarding the timescales on which they operate. Recently there have therefore been suggestions from the academic community that estimates of Earth's sensitivity to atmospheric CO2 levels should include all feedbacks within the climate system: both those that operate fast and those that operate more slowly. This more comprehensive view of the relationship between Earth's climate and pCO2 is termed 'Earth System Sensitivity'. The best way to estimate Earth System Sensitivity is to use intervals in the geological past when we know that CO2 and temperature were different to today. However, thus far this approach has led to very different estimates, largely due to uncertainties in the levels of atmospheric pCO2 reconstructed for these intervals. In the first part of the proposed work we will generate new pCO2 records using a relatively new method of estimating pCO2 (using the ratio of boron isotopes within marine planktonic microfossils) that has recently been refined. We will also use several methods for reconstructing temperatures from the same interval in the past, so that we can calculate Earth System Sensitivity. The second part of the proposed work is to use data to test a computational ice sheet model. Ice sheets are dynamically complex, and sophisticated models are required in order to predict their response to changing climate and therefore their effect on global sea level. The models need to be tested if we are to have confidence in their predictions. The long timescales involved with ice sheet dynamics means that we cannot test ice sheet models with real-time observational data. The best way to test ice sheet models is to use them to predict ice sheet changes for a period in the geological past where we have good records of Earth's temperature gradients, and compare the model results with well-constrained records of ice sheet growth for the same interval. In the proposed work we will use the Middle Miocene Climate Transition to test an ice sheet model. We know that CO2 decreased, climate cooled, and the Antarctic ice sheet expanded at this time (~14 million years ago). In this work we will obtain new, accurate records of pCO2 and temperature to drive our models. The models will then predict ice sheet changes, which we can compare to an existing record of ice sheet growth across the climate transition. If the model and the data are in good agreement then our confidence in the ice sheet model will be increased. If the model and the data are not in good agreement, then this work could lead to the identification of certain parameters within the model that may need to be adjusted. This may then lead to improved future predictions of ice sheet, and hence sea level change.

Publications

10 25 50
 
Description This research studied the links between atmospheric CO2, global climate, and ice sheet growth and decay through the Miocene. We have generated a quantitative record of atmospheric CO2 through the Neogene. We have modelled the relationship between ice sheet size and global climate. We have better quantified the relationship between changes in global climate and atmospheric CO2 during the Miocene.

We have also studied the links between the cryosphere and the carbon cycle through the mid-Pleistocene Transition, and found evidence for important carbon cycle feedbacks in the middle Miocene.
Exploitation Route Both the data and the modelling results will be of use to a wide range of researchers. In particular the data will be of use to those studying the sensitivity of the Antarctic ice sheet to environmental change.
Sectors Environment

 
Description The findings have been used by academics in various research fields - e.g., geochemistry, modelling, palaeoclimate. The results have also been communicated to the public in a variety of outreach events.
Sector Environment
Impact Types Societal

 
Description 2 interviews: BBC Radio 4 Today Program, and BBC Radio Wales Morning Program 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Interviewed in the news, BBC Radio 4 Today Program. Also interviewed on BBC Radio 4 Good Morning Wales Program. Discussed the link between CO2 and climate change.
Year(s) Of Engagement Activity 2016
 
Description Activity at National Museum Wales 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Schools
Results and Impact Activity introduced school students to geology and palaeoclimate. Many questions were sparked and climate change in general was discussed.

Increased knowledge and interest in climate change
Year(s) Of Engagement Activity 2013,2014
 
Description Daniell Lecture at Kings College London 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Schools
Results and Impact Recorded talk about how paleoclimate research helps us understand the climate system. Followed by live Q&A: questions about the research, how to pursue careers in STEM etc.
Year(s) Of Engagement Activity 2020
URL https://www.kcl.ac.uk/events/daniell-lecture-2020
 
Description Talk at Hay Literary Festival 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Audience described how their opinion of climate change changed.
Year(s) Of Engagement Activity 2015
URL https://www.hayfestival.com/p-9763-caroline-lear-and-rhoda-ballinger.aspx
 
Description Talk to Geologists Association 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Third sector organisations
Results and Impact I gave a talk about my research, including climate change and sea level predictions. This was for an audience where there are some "climate sceptics". There was a lot of interest, and I had a request for my slides afterwards.
Year(s) Of Engagement Activity 2017
URL https://geologistsassociation.org.uk/conferences2017.html
 
Description Visit by academics to schools (within Wales) 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact Activity prompted students to work together to answer scientific questions. It sparked discussion on the scientific method and climate change in general.

Students were introduced to field of palaeoclimate research, sparking a new interest for them.
Year(s) Of Engagement Activity 2013,2014