Current State of Our Knowledge on the Global Carbon Cycle

(Seminar course – RNR 696A-005, Spring 2017)

Meeting time and location: Friday 10am – ENR2 N375

Course overview

The concentration of CO2 in the atmosphere has been increasing at an unprecedented rate over the last few decades, largely due to fossil fuel use and land use change. We know from a global network of CO2 flask measurements that only half of these emissions remain in the atmosphere; therefore the ocean and terrestrial biosphere act as a global carbon sink, taking up carbon from the atmosphere. However, the exact location(s), magnitude and variability of the sink, the mechanisms driving it, and its future trajectory, remain uncertain because of the difficulty of measuring and modelling carbon fluxes and stocks at global scales.

In this graduate-level, discussion-based seminar series we will explore the current state of our knowledge on the global carbon cycle with a particular emphasis on the terrestrial biosphere and how human activity has altered its natural state. We will examine how the different components of the global annual carbon budget are calculated, including natural terrestrial and ocean fluxes and emissions from fossil fuels and land use and land cover change, as well as the uncertainties in the methods, observations and models involved. We will further review the literature on long-term trends in model projections in order to gain an understanding of the predicted interactions between the carbon cycle, human activity and climate.

In each class we will discuss what we have learned as a community over the past few decades, the remaining gaps in our understanding of the mechanisms, and what we can do to further enhance our knowledge in the future. Students will read one or two papers per week and will take turns to provide a summary of the paper followed by a discussion with the whole group.

Weekly outline

Click on the links below for the article pdf and discussion questions

PART 1: Carbon cycle processes

Week 1 (01/27/2017): IPCC Biogeochemical cycles chapter – importance of the contemporary global carbon cycle  pdf

Week 2 (02/03/2017): Photosynthesis – Rogers et al. (2017) “A roadmap for improving the representation of photosynthesis in Earth system models” pdf   discussion questions 

Week 3 (02/10/2017): C source vs C sink limitation – Fatichi et al. (2014) “Moving beyond photosynthesis: from carbon source to sink-driven vegetation modeling”  pdf   discussion questions 

Week 4 (02/17/2017): Allocation – Litton et al. (2007) “Carbon allocation in forest ecosystems”  pdf   discussion questions 

Week 5 (02/24/2017): Soil C decomposition/respiration – Davidson and Janssens (2006) “Temperature sensitivity of soil carbon decomposition and feedbacks to climate change”  pdf   discussion questions

PART 2: The contemporary global carbon budget

Week 6 (03/10/2017): Non-terrestrial components of the global C cycle – Le Quéré et al. (2016) “Global Carbon Budget 2016”  pdf   discussion questions

Spring Break

Week 7 (03/24/2017): Terrestrial components of the global C cycle – Le Quéré et al. (2016) “Global Carbon Budget 2016”  pdf   discussion questions

PART 3: Quantifying the global terrestrial carbon budget

Week 8 (03/31/2017): Top-down view of the global C cycle from atmospheric inversions – Peylin et al. (2013) “Global atmospheric carbon budget: results from an ensemble of atmospheric CO2 inversions”  pdf  discussion questions

Week 9 (04/07/2017): Bottom-up view of the global C cycle from land surface/terrestrial biosphere models (LSMs/TBMs and DGVMs) – Sitch et al. (2015) “Recent trends and drivers of regional sources and sinks of carbon dioxide”  pdf  discussion questions

PART 4: The future of the global terrestrial carbon sink

Week 10 (04/14/2017): The impact of elevated CO2 from site-based experiments – Norby and Zak (2011) “Ecological Lessons from Free-Air CO2 Enrichment (FACE) Experiments”   pdf  discussion questions

Week 11 (04/21/2017): Future projections of climate-carbon feedbacks – Friedlingstein et al. (2014) “Uncertainties in CMIP5 Climate Projections due to Carbon Cycle Feedbacks”  pdf

Week 12 (04/28/2017): Reconciling approaches to estimating the global C budget and climate/eCO2 feedbacks – Schimel et al. (2015) “Effect of increasing CO2 on the terrestrial carbon cycle”  pdf
Also see Dave Schimel’s FluxCourse ( chalk talk on this topic here.


Other useful papers:

Observations of C fluxes and stocks at global scales – Ciais et al. (2014) “Current systematic carbon-cycle observations and the need for implementing a policy-relevant carbon observing system”  pdf

Seminal papers on measuring the global C budget – Tans, Fung and Takahashi (1990) “Observational Constraints on the Global Atmospheric CO2 Budget”  pdf