Is Soil an Important Component of the Climate System?

The answer is a definitive YES.

A letter to Science (which was unfortunately not accepted) by Professor Dan Yaalon of the Institute of Earth Sciences of Hebrew University Givat Ram Cam is reproduced below with his permission. The letter was written in response to the Foley et al paper of earlier this year, which I commented on in the weblog. In the letter,

Professor Yaalon makes the very effective case that land management processes result in soil changes. This will necessarily alter land-atmosphere interactions, and thus climate. His 2000 Nature article (subscription required) is entitled “Down to earth – Why soil – and soil science – mattersâ€? provdes more information on his valuable perspective.

To the Editor of Science:

LAND USE IS ALWAYS ACCOMPANIED BY SOIL CHANGE

The global review by Foley, DeFries and others on consequences of land
use (22 July, p. 570, with ample online supporting material) is valuable, summarizes well the major current features and includes hints on developing future strategies. However for some reason it neglects to discuss the impact on soils due to changes in land use. Soils are a major factor in land use and the important link between climate and biogeochemical earth systems (1). Hence land use practices and land cover change are always accompanied by soil change. Not only the carbon and hydrologic cycle but equally the soil and sediment cycles have been and are being changed by human land use
practices over time. Is this not significant enough to review ? Why this slant on
biodiversity decrease and no mention of the possibly equally significant pedodiversity reduction and soil quality attributes change (2) ?

With nearly half of the earth land surface now drastically changed
to arable land and pastures (currently 12% and 25% respectively, with additional areas of managed forests), the respective surficial soils have changed their original nature and pedological properties, and some must now be differently classified (3). While largely turning more productive, some were degraded and certain soil varieties have become endangered or even extinct, like any other biota. This was surely worthwhile to draw attention to as consequence of changing land cover surfaces.

Pedology (soil science) is a relatively young branch of the earth
sciences (1, 4) and because combining both the bio-geo-chemical and physical aspects, soils developed into an exceptionally complicated system of ecosystem functions, including applied services for mankind, as the several recent articles in Science (11June 2004) so well demonstrated (5). Statistical evaluation of pedodiversity, partly analogous to biodiversity, is a growing topic in soils (3, 6). We must not neglect to consider soils appropriately in any global, regional or local context.

References

1. D.H. Yaalon, Nature 407, 391 (2000).

2. R. Amundson, Are soils endangered? In J. Schneiderman (ed.) The earth
around us; maintaining a livable planet, Freeman, New York
(p.144-153, 2000).

3. R. Amundson et al., Ecosystems 6, 470 (2003).

4. D.H. Yaalon and S. Berkowicz (eds.), History of Soil Science -
International Perspectives (Catena Cerlag, Reiskirchen, Germany, 1997)

5. Soils – The Final Frontier, Science 204, 1613 (2004) .

6. J.J. Ibanez et al., Geoderma 83, 171 (1998).

He stated in his e-mail of December 19, 2005 to me,

“This is in support of your brief review in SCIENCE (December 5) on Land Use and Climate Change. No doubt an important interaction which needs to considered, even though the definition of ‘climate change’ is only touched briefly in your discussion. As a soil scientist/pedologist I consider the interaction ‘land use and soil change’ equally relevant, and consider that humankind has transformed closer to half of the land surface rather than one-third and thus affected also the soils.

Strangely enough my response to a previous Science review (July 22) by Jon Foley et al. on Consequences of Land Use was not considered significant enough by the Editors of Science for publication (see [above]), even though Jon Foley agreed with me fully and regretted that soils were not mentioned. There is no doubt that the interacting trio of ‘Land Use – Soil Change – Climate Change’ have affected civilization in the past, present and future, and need to be appropriately evaluated.

Climate change, most frequently just connected with seasonal or intensity change of some the climatic parameters, has not been defined so far in detail and certainly needs more attention in this respect. When does the increase or decrease in temperature or precipitation count as ‘climate change’ ? Soils are greatly affected by climate and all the factors are strongly periodic or seasonal, but I consider or recognize climate change only when the direction of the soil forming processes has been changed. Slightly increased temperature or precipitation may only change the intensity of the already acting processes, not change their direction. Hence understanding changing soils, including the eolian processes of addition or removal, is important in all human affected ecosystems.â€?

Professor Yaalon’s provides a very valuable perspective in how we define climate. It also provides further substance to the need for us to treat climate as an integrated Earth system issue as articulated in the 2005 National Research Council report which expands the concept of climate as we have discussed numerous times on this weblog.

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