SOILS, CARBON CYCLES, AND MASS TIMBER CONSTRUCTION

Independent Study, Spring 2019

• ATMOSPHERE •

The number one cause of climate change is excess carbon dioxide in the earth’s atmosphere, released by human activity.  This is an undisputed scientific consensus, but also a highly debated and contested issue in certain subsets of the popular literature.  The excess carbon in the atmosphere has accumulated there since the industrial revolution, and has been put there both directly and indirectly through human industrial activity.  It is “extremely likely” to be causing accellerated warming of polar areas, generally warmer global temperatures, and an overall increase in extreme weather (IPCC).  This assessment of the causal relationship between anthropogenic emissions and climate change was made by the International Panel on Climate Change in their 2014 synthesis report, representing a thorough analysis of the existing scientific research worldwide (IPCC). 

Greenhouse gasses function by trapping heat inside the atmosphere and increasing the overall temperature of the earth’s climate system.  Carbon dioxide in the upper atmosphere absorbs outbound infrared radiation released by the earth, reemitting some of it back into the global climate system (Schlesinger and Bernhardt, Cubasch et al).  The standard measurements that we use to track atmospheric CO2 concentrations in the northern hemisphere are taken at the Mauna Loa Observatory in Hawaii. With CO2 data beginning in 1958, the station has the longest record of direct measurements available and is located far from industrial centers that could skew the readings with local emissions (Graven et al, Mims).  Accurate long-term historical measurements are extracted from Antarctic and Greenlandic ice core samples, going back 400,000-800,00 years (Ahn, Luthi et al). Small bubbles of trapped air in the ice show a thoroughand precise record of past CO2 concentrations, but are limited by the depth of the ice sheet.  Older atmospheric carbon dioxide concentrations can be estimated through geologic data and modeling.  Our current atmospheric concentration of around 415 ppm has not been seen for an estimated two million years (Rubino, Cubasch et al).   

There is a very significant correlation between the fluctuations of atmospheric CO2 and measured global temperatures.  The Keeling curve, the measured CO2 concentrations from Mauna Loa over the last 50 years, matches modern temperature records extremely well.   Historical temperatures have been reconstructed via ice core analysis, by measuring the amount of heavier and lighter isotopes in water deposited on ice sheets.  When temperatures are warmer, more heavy isotopes are mobilized from the ocean into the atmosphere and fall as precipitation.  Snowfall on ice sheets accumulates over the years and stays in distinct layers, allowing both the trapped air bubbles and the isotopes to be analyzed from ice cores.  The temperature data are very synchronized with historical CO2 data, showing a significant relationship between the two (Cubasch et al, Schlesinger and Bernhardt).

The atmosphere has accumulated our carbon emissions because we live in a closed system.  Earth can be seen essentially as a closed terrarium or spaceship; carbon in different forms cycles through different parts of the planet, but is never added to the system.  When carbon is emitted as gas anywhere on earth’s surface, it generally ends up in the atmosphere. Plants and oceans also absorb carbon dioxide from the atmosphere, but not as fast as industrial emissions add to it.  This carbon circulation, known as the carbon cycle, is described in more detail Here.

 

References:

Ahn, Jinho; Brook, Edward J. (2014) Siple Dome ice reveals two modes of millennial CO2 change during the last ice age. Nature Communications. Vol. 5:3723. DOI:10.1038/ncomms4723

Cubasch U., Dai X., Ding Y., Griggs D.J., Hewitson B., Houghton J.T., Isaksen I., Karl T., McFarland M., Meleshko V.P., Mitchell J.B.F., Noguer M., Nyenzi B.S., Oppenheimer M., Penner J.E, Pollonais S., Stocker T., Trenberth K.E.  (2001) Technical Summary. In: Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change[Houghton, J.T., Y. Ding, D.J. Griggs, M. Noguer, P.J. van der Linden, X. Dai, K. Maskell, and C.A. Johnson (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp21.

IPCC -Intergovernmental Panel on Climate Change (2014) Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)]. IPCC, Geneva, Switzerland, 151 pp.  https://archive.ipcc.ch/report/ar5/syr/

Graven H. D., Keeling R. F., Piper S. C., Patra P. K., Stephens B. B., Wofsy S. C., Welp L. R., Sweeney C., Tans P. P., Kelley J. J., Daube B. C., Kort E. A., Santoni G. W., Bent J. D.  (2013) Enhanced Seasonal Exchange of CO2 by Northern Ecosystems Since 1960. Science  341: 6150, pp. 1085-1089 DOI: 10.1126/science.1239207

Mims, III Forrest M. (2012) Hawaii's Mauna Loa Observatory: Fifty Years of Monitoring the Atmosphere. Honolulu: University of Hawai'i Press, 2012.
Project MUSE., https://muse.jhu.edu/. 

Rubino, M., Etheridge, D. M.  (2019) Revised records of atmospheric trace gases CO2, CH4, N2O, and δ13C-CO2 over the last 2000 years from Law Dome. Earth System Science Data, Vol. 11.

Schlesinger W.H. and Bernhardt E.S. (2013) Biogeochemistry: An Analysis of Global Change, 3e. Academic Press.

Additional Resources:

NOAA carbon tracker CO2 visualization: video, visualization, carbon tracker site