This is the second blog of a four-blog series. The first one reviewed why our perception of “climate change’ is so narrowly focused on greenhouse gas emissions. This second blog provides an overview why we should also consider the biosphere’s role in regulating the climate, and how our climates are impacted by our land use management decisions. Future blogs will review these from a reductionist/holistic lens, and suggest approaches to manage climate change more holistically.
Over geological times, the biosphere has regulated the global climate by drastically altering the atmosphere’s gas composition. Microbes and plants, fungi and animals worked together and reduced the atmosphere’s concentration of CO2 from 8000 parts per million (ppm) to as low as 100ppm. With fossil fuel emissions, the concentration of CO2 has risen from its pre-industrial level of 280ppm to 420ppm and is continuing to increase exponentially. Changes in greenhouse gases will warm the Earth by 2-6°C within this century – a dramatic shift in global ecosystems.
Within this dramatic warming of the globe, it is easy to not see the forest for the trees. Nature continues to have a vital role in regulating our climate, and humans now have a fundamental responsibility in ensuring that nature can continue to do its thing. Before intervening in the Earth’s system further, I advocate that must recognize the biosphere’s role in regulating the climate. In fact, 95% of the heat dynamics of planet Earth are not driven by greenhouse gases but by water – half of which may depend on the biosphere! Water interacts with the climate as clouds that cover almost half of the Earth’s surface, water droplets and haze determine whether sun radiation is reflected back into space or transformed into heat. When water transitions from a liquid into vapour, water absorbs massive amounts of heat that is then released once the vapour condenses back into a droplet. This “latent heat flow” cools the near-surface wherever vegetation transpires water. Water vapour also makes up 70% of the atmosphere’s greenhouse effect.
Uncertainly in the water cycle was often used by climate deniers to undermine the IPCC’s efforts to mainstream the Greenhouse effect. This is not my intention. But we have to recognize that climate is more than just greenhouse effect, more than carbon dioxide. We have to recognize climate in its entirety – greenhouse and the biosphere. My perception is that mainstream media really under-emphasizes the biosphere’s role in the climate crisis. Political advocates sometimes propose “false climate solutions” that sequester carbon at the expense of the biosphere’s ability to self-regulate the climate – something I find deeply worrying. So what is this “local climate impact” from our landuse? What are the methods that we can use to describe these?
Biosphere climate self regulation
In recent years, much is being written about the biosphere’s role of the local climate. Educators like Walter Jehne offer online videos (e.g. [1]. Academics papers (e.g. [2],[3],[4],[5],[6] and media articles are emerging (e.g. Judith Schwartz in The Guardian[7]). My summary here only provides a brief context. Three major dynamics of the biosphere include watershed runoff, cloud formation and rainfall dynamics, and heat & energy dynamics:
- River runoff is partly tied to rainfall and snow melt, and partly to the water retention within the soils and wetlands of a watershed. Forest soil absorbs water and release it slowly into the groundwater; if the surface is covered by asphalt and degraded agricultural soil then water runs off rapidly at the surface. Drainage and wetlands are other buffers that slow down water runoff. Together, landscape management determines whether a region stays hydrated and moist, or whether water drains in a flash flood and the region then dries out. This has impacts on wildfire risk, irrigation requirements of crops, the biosphere at large, and even rainfall formation.
- Vegetation triggers cloud formation and rainfall. Above forests, plants “create” clouds by transpiring water and also by exuding organic particles where micro droplets then form. Also, plants transpire water vapour that is required for condensation. Two islands that have exactly the same mountains and are in view of each other, one with intact forest and one that is deforested, may have totally different rainfall readings – just because of this vegetation effect.
- Heat islands originate where surfaces have low moisture and high heat absorption. The best-known heat islands are our cities – everyone can sense the urban heat island effect when driving from the countryside into town. But the same effect exists in rural areas: if a beaver wetland is drained, or if a field is fallow, it is easy to observe changes in temperature (it’s much hotter), updrafts, cloud patterns, and wind patterns.
All of these changes to our local climate are triggered by changes of our land use. Birds and glider plane pilots know these effects well and rely on local updrafts, e.g. above fallow fields. With some awareness, every one of us can sense how these activities modify our local climate: Have you walked from an asphalt parking lot into an area of natural vegetation on a warm summer day? You will perceive a pleasant drop in temperature. Or, on a sunny day above a fallow field that catches the heat of the sun, you may notice birds circling in its thermal updraft. While the neighbouring wetland stays cool and foggy. Every single large tree cools the ground like 10 residential air-conditioning units running all day – cities with trees are cool, we know that. Direct climate impacts are everywhere and happen at all scales:
- when I walk from the hot asphalt of a street into our garden or from a forest into a fallow field,
- when an entire landscape is drained, and natural vegetation is turned into annual crop fields such that cloud formation and wind patterns shift;
- when a region desertifies after landscapes are degraded, or
- when the biosphere of an entire continent was changed, as happened in Australia when British colonizers discontinued 50,000 years of aboriginal land management and settlers brought British’s temperate-zone agricultural practices into a brittle landscape [8],[9].
From local climate to continental scale of biosphere’s climate regulation
We now understand that “local climate effects” can change the climate of very large regions [17],[18]. Soil degradation from intensive agriculture has already shifted the terrestrial water cycle globally and dried out large patches of land [Levia et al., 2020]. Human history offers a bounty of examples where land use activities have shifted the climate of entire regions.
Australia. For good reason, Australia brought forth some of the most innovative Regeneration educators: on this continent, the direct climate regulation of the biosphere was most powerful, and dramatic was its destruction with European settlement. Early settlers described the continent as fertile and lush. In 1788, the British Crown annexed the Australian continent in 1788 and organized resource extraction, logging and plough-based farming. The colonizers repeated the settlement strategy that had proven successful in the robust temperate climates of North America: Clearing large stretches of land, engineering drainage, and establishing large farms with prisoners as workers. Within only a hundred years, the ecology and climate of the entire continent was transformed. With British farming methods that were developed in temperate zones, the brittle continent quickly lost its fertility. Australia’s water cycle broke down, the continent’s fragile ecology collapsed, soils eroded, and entire landscapes desertified [19].
California’s drying central valley was once a beaver wetland [20],[21],[22]. Its lush swamp grasses fostered indigenous traditions of basket making [23], which seems unlikely in today’s vegetation [24]. With the removal of keystone species, broad engineered drainage, and frequent ploughing, the former wetland is now desertifying and farmers rely on regular irrigation. California’s land cover change has deep implications for the entire region’s climate: today, sunshine heats up the dry valley and creates a large heat dome with updrafts. In the same valley, wetlands had once pulled the cool and moist coastal airflow downward. Indigenous people kept biomass low with controlled burning [25],[26]. Today’s heat dome can block or re-direct the coastal winds that once carried rainfall toward the Rocky Mountains. With today’s land use, moist airflow is often blocked from the valley as it is pushed upward, eventually exploding in massive downpours. Furthermore, humans removed large Redwood forests of the Coastal mountain ranges. These large trees once “harvested” fog with their needles such that it dripped down and moistened the soil, enabling the decomposition of biomass by microbes. With trees removed, biomass now accumulates. Together, human land use change in California has created conditions that foster wildfire, prolonged droughts, cause flash floods, and intensified storms. The region has lost its resilience toward the upcoming threats of global warming that will further exasperate this situation.
We can find similar stories around the world: Much of the US prairies were once lush green and home to 40 billion bison, plus mammoths, pronghorns, and countless deer. Grasses were regularly mowed by huge herbivore herds, and fertilized with their moist dung that also provided moisture for germination.
West Asia (the Middle East) was once fertile – it’s drying is mostly driven by human land use, soil erosion, and human disruption of the water cycle.
Direct climate impacts cannot be fully isolated from ongoing changes in natural forcing, or greenhouse-gas driven global warming [34]. Typical for complex systems, these three drivers of climate change all interact with each other in a non-predictable way. A good example is the drying of the Sahara: For several million years, the Sahara’s climate has swung back and forth between lush grasslands and sandy desert. What brought on the ice ages also drives this oscillation: the Earth circles around the sun in a slight wobble, enough to shift our global climate. So about 10,000 years ago, the Sahara was lush grassland and inhabited by large herds and pack predators – similar to the Serengeti today [35]. The ecological balance of grassland, with ruminant herds moved by pack predators and human pastoralists, stabilized the region’s climate by keeping a biosphere that actively maintained its cool [36]. Eventually, humans also interfered with the natural balance, e.g. by hunting herbivores or exterminating predators. With lesser predation, ruminants changed their grazing behaviour and quickly overgrazed the land. Some scientists now believe that human hunting had triggered the ecosystem collapse of the Sahara thousands of years earlier than its natural grassland ecology would have – yet we may never find final proof.
In short, weather has changed in the US [27],[28], India [29], [30], China [31], the tropics [32], and almost all grasslands. Not because of global warming, but because we have significantly modified our landscapes, our water cycle, our biosphere’s ability to self-regulate its climate. Almost every part of this earth is now experiencing direct climate change, in cities and in rural areas.
Scientific methodology
All of these dynamics are incorporated into large global climate models that were designed to analyze the greenhouse effect. However, the resolution of these models is still very coarse – one “computation unit” or gridcell is between 150km to 250km long and wide. Most “local” climate dynamics happen below this cell resolution of global climate models and cannot be simulated dynamically. Instead, scientists “hard-wire” models such that they behave realistically at given land use, using parameterization techniques. So changes of land use on regional climate remain simulated fairly poorly – and it was never the intention to use global climate models for such analysis. Models had been designed with the aim of meeting the mandate of UN organizations: demonstrating GHG warming.
To simulate and understand regional climate impacts of human land use change, climate scientists have been developing another family of “Regional climate models” [10]. These resolve the complex interplay between natural systems, landscapes that are impacted by human management, and global warming [11],[12]. As data availability improve and regional climate models become more sophisticated, we are starting to understand the role of the biosphere in climate regulation [13],[14] and the scale of humankind’s direct impact on our climate [15],[16]. And we are beginning to realize how humankind’s activities have directly changed the climate of entire continents.
Activities that directly impact the local climate are “any activities that modify how energy and water vapour flows between land and the atmosphere” (IPCC Special Report on Climate Change and Land, Ch 2, Summary for Policy Makers). Scientists study these local climate effects, as driven by asphalt and concrete, forests and wetland, agricultural fields and watershed drainage, and soil water retention.
Few examples of biosphere regeneration exist to date, and studies that quantify climate impacts of these regeneration events are even fewer. An exception is the Chinese Loess plateau, which was reforested from a highly desertified state in the world’s largest ecological restoration programs ever implemented. By combining real-time remotely sensed land use/land cover data and vegetation characteristics between 2001 and 2010 and a coupled land-atmosphere model, scientists showed that “vegetation restoration has exerted strong influences on regional climate” [33]. Rainfall changed by 1mm/day and near-surface temperatures by 1-2°C, a considerable improvement in this dry zone.
Outlook
Over recent decades, climate research was focused on the greenhouse effect. As a consequence, we may have underestimated or overlooked how our actions directly change the climate by modifying our biosphere. Our landuse, watershed management and land development have changed the climate – locally, regionally, and even globally.
Yet, it remains very difficult or maybe impossible to exactly quantify and predict these direct climate changes. Research remains limited by the higher complexity of its dynamics. Emerging methods elucidate the relevance of these changes in specific regions, but still fail to provide generic tools at reasonable costs. Due to the inherent complexity of our biosphere and its multitude of climate feedback loops, we may never be able to fully understand how the biological and physical world interact on our planet. Is this remaining uncertainty a reason to ignore the role of the biosphere in our global climate? I personally believe that we’d be well advised to consider all of our options (and potential feedback effects) when addressing climate change.
Media and the general public are well-advised to remind politicians that climate change is more than greenhouse gases. We should also consider land use management as a central aspect of climate change policies. Today, it remains an afterthought.
How can I learn more?
- Walter Jehne educates about direct human climate impacts (e.g. here).
- John Liu talks about large-scale ecosystem regeneration for healing our climate (e.g. here)
- Zach Weiss offers an excellent video on ecosystem regeneration through water restoration (here).
- Kiss The Ground educates about soil health and also has an excellent movie (link).
- Didi Pershouse educates about soil health & watershed functions (here).
- Allan Savory summarizes the role of regenerative grazing in our fight against desertification (here).
- Diana Rogers’ movie “Sacred Cow” and its companion book explain the role of integrated animal-crop agriculture (link).
References
[1] https://www.youtube.com/watch?v=Te6D3y3EyGg
[2] Van der Ent RJ, Savenije HH, Schaefli B, Steele‐Dunne SC. Origin and fate of atmospheric moisture over continents. Water Resources Research. 2010 Sep;46(9).
[3] Ellison D, Morris CE, Locatelli B, Sheil D, Cohen J, Murdiyarso D, Gutierrez V, Van Noordwijk M, Creed IF, Pokorny J, Gaveau D. Trees, forests and water: Cool insights for a hot world. Global Environmental Change. 2017 Mar 1;43:51-61.
[4] Bonan GB. Forests and climate change: forcings, feedbacks, and the climate benefits of forests. science. 2008 Jun 13;320(5882):1444-9.
[5] Mahmood R, Pielke Sr RA, Hubbard KG, Niyogi D, Dirmeyer PA, McAlpine C, Carleton AM, Hale R, Gameda S, Beltrán‐Przekurat A, Baker B. Land cover changes and their biogeophysical effects on climate. International Journal of Climatology. 2014 Mar;34(4):929-53.
[6] Pielke RA, Mahmood R, McAlpine C. Land’s complex role in climate change. Phys. Today. 2016 Nov 1;69(11):40.
[7] https://www.theguardian.com/commentisfree/2017/apr/03/climate-change-water-fossil-fuel
[8] Hallam S. The biggest estate on earth: how Aborigines made Australia. Australian Aboriginal Studies. 2011 Sep 22;2011(2):123-7.
[9] Melissa Nursey-Bray, R. Palmer, T. F. Smith & P. Rist (2019) Old ways for new days: Australian Indigenous peoples and climate change, Local Environment, 24:5, 473-486, DOI: 10.1080/13549839.2019.1590325
[10] Rummukainen M. State‐of‐the‐art with regional climate models. Wiley Interdisciplinary Reviews: Climate Change. 2010 Jan;1(1):82-96.
[11] Feser F, Rockel B, von Storch H, Winterfeldt J, Zahn M. Regional climate models add value to global model data: a review and selected examples. Bulletin of the American Meteorological Society. 2011 Sep;92(9):1181-92.
[12] Christensen, J. H., Kanikicharla, K. K., Aldrian, E., An, S. I., Albuquerque Cavalcanti, I. F., de Castro, M., Dong, W., Goswami, P., Hall, A., Kanyanga, J. K., Kitoh, A., Kossin, J., Lau, N. C., Renwick, J., Stephenson, D. B., Xie, S. P., Zhou, T., Abraham, L., Ambrizzi, T., … Zou, L. (2013). Climate phenomena and their relevance for future regional climate change. In Climate Change 2013 the Physical Science Basis: Working Group I Contribution to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (Vol. 9781107057999, pp. 1217-1308). Cambridge University Press. https://doi.org/10.1017/CBO9781107415324.028
[13] Van der Ent RJ, Savenije HH, Schaefli B, Steele‐Dunne SC. Origin and fate of atmospheric moisture over continents. Water Resources Research. 2010 Sep;46(9).
[14] Ellison D, Morris CE, Locatelli B, Sheil D, Cohen J, Murdiyarso D, Gutierrez V, Van Noordwijk M, Creed IF, Pokorny J, Gaveau D. Trees, forests and water: Cool insights for a hot world. Global Environmental Change. 2017 Mar 1;43:51-61.
[15] Bonan GB. Forests and climate change: forcings, feedbacks, and the climate benefits of forests. science. 2008 Jun 13;320(5882):1444-9.
[16] Mahmood R, Pielke Sr RA, Hubbard KG, Niyogi D, Dirmeyer PA, McAlpine C, Carleton AM, Hale R, Gameda S, Beltrán‐Przekurat A, Baker B. Land cover changes and their biogeophysical effects on climate. International Journal of Climatology. 2014 Mar;34(4):929-53.
[17] Findell KL, Berg A, Gentine P, Krasting JP, Lintner BR, Malyshev S, Santanello JA, Shevliakova E. The impact of anthropogenic land use and land cover change on regional climate extremes. Nature communications. 2017 Oct 20;8(1):1-0.
[18] Sy S, Quesada B. Anthropogenic land cover change impact on climate extremes during the 21st century. Environmental Research Letters. 2020 Feb 18;15(3):034002.
[19] Dawson CR. (2011) ‘Field Guide to 1788’: The Biggest Estate on Earth: How Aborigines Made Australia. Swamphen: a Journal of Cultural Ecology (ASLEC-ANZ). 2013 Apr 8;2:96-106.
[20] Lanman CW, Lundquist K, Perryman H, Dolman B, Lanman RB, Pollock MM. (2013) The historical range of beaver (Castor canadensis) in coastal California: an updated review of the evidence. California Fish and Game. 2013 Sep 1; 99(4):193-221.
[21] Goldfarb, Ben (2018) – Eager – the surprising, secret life of beavers and why they matter. Chelsea Green Publishing
[22] Outwater A. (2008) Water: a natural history. Basic Books; 2008 Aug 6.
[23] Chavez Y. (2019) Basket Weaving in Coastal Southern California: A Social History of Survivance. In: Arts 2019 Sep (Vol. 8, No. 3, p. 94). Multidisciplinary Digital Publishing Institute.
[24] https://indiancountrytoday.com/archive/reviving-the-ancient-art-of-basket-weaving-in-california
[25] Kimmerer RW, Lake FK. The role of indigenous burning in land management. Journal of Forestry. 2001 Nov 1;99(11):36-41.
[26] Cuthrell RQ. Archaeobotanical evidence for indigenous burning practices and foodways at CA-SMA-113. California Archaeology. 2013 Dec 1;5(2):265-90.
[27] Alter RE, Douglas HC, Winter JM, Eltahir EA. Twentieth century regional climate change during the summer in the Central United States attributed to agricultural intensification. Geophysical Research Letters. 2018 Feb 16;45(3):1586-94.
[28] Mahmood R, Pielke RA, McAlpine CA. Climate-relevant land use and land cover change policies. Bulletin of the American Meteorological Society. 2016 Feb 1;97(2):195-202.
[29] Lodh A. Reassessment of land–atmosphere interactions over India during summer monsoon using state-of-the-art regional climate models. Theoretical and Applied Climatology. 2020 Nov;142(3):1649-73.
[30] Nayak S, Mandal M. Impact of land use and land cover changes on temperature trends over India. Land Use Policy. 2019 Dec 1;89:104238.
[31] Dong N, Liu Z, Luo M, Fang C, Lin H. The effects of anthropogenic land use changes on climate in China driven by global socioeconomic and emission scenarios. Earth’s Future. 2019 Jul;7(7):784-804.
[32] Salazar A, Baldi G, Hirota M, Syktus J, McAlpine C. Land use and land cover change impacts on the regional climate of non-Amazonian South America: A review. Global and Planetary Change. 2015 May 1;128:103-19.
[33] Cao Q, Wu J, Yu D, Wang W. The biophysical effects of the vegetation restoration program on regional climate metrics in the Loess Plateau, China. Agricultural and Forest Meteorology. 2019 Apr 15;268:169-80.
[34] Pielke RA, Mahmood R, McAlpine C. Land’s complex role in climate change. Phys. Today. 2016 Nov 1;69(11):40.
[35] Castañeda IS, Mulitza S, Schefuß E, dos Santos RA, Damsté JS, Schouten S. Wet phases in the Sahara/Sahel region and human migration patterns in North Africa. Proceedings of the National Academy of Sciences. 2009 Dec 1;106(48):20159-63.
[36] Brierley C, Manning K, Maslin M. (2018) Pastoralism may have delayed the end of the green Sahara. Nature communications. 2018 Oct 1;9(1):1-9.
Recent Comments