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Walter Jehne is an Australian soil microbiologist, with decades of experience teaching and advising governments, farmers, students and communities. Walter is the director of Healthy Soils Australia, and is also part of NGOs including Global Cooling Earth and Regenerate Earth.

I only came across Walter’s work recently, when I saw some of his lectures on YouTube (see here: one, two, three). And within the hour or two that it took me to watch those, he had managed to completely change the way I think about climate change.

Walter’s main message is that we need to regenerate what he calls the soil sponge.

Why is building soil so important?

It’s because so many of the problems we’re facing: extreme weather events from climate change, desertification, loss of biodiversity, water shortages, food shortages, reduced food nutrition and many others, can all be minimised – if not entirely eliminated – if we can re-build the living skin of the earth: the soil.

A particular point that Walter makes that shocked me was that carbon dioxide is only responsible for 4% of global heat dynamics. While the hydrological cycle (meaning, the way water moves between the atmosphere the ocean and the land) controls 95% of the heating or cooling of the planet. So even if we stopped burning fossil fuels completely tomorrow, it would barely make a dent in the overall temperature dynamics on earth. The only way we can really get the planet back to a stable climate is by building soil and letting the natural cooling processes that have been going on for billions of years, keep doing their work.

This episode is timely, because just a few days ago the United Nations announced that the years 2021 to 2030 will be named the Decade on Ecosystem Restoration. So clearly, Walter’s message has been reaching a lot of people, and now can hopefully reach even more.

As always, if you enjoy listening, please subscribe in whichever podcast app you use. And share the episode with anyone you know who might also like it.


03:07 Walter’s early career as a microbiologist

04:37 The origins of climate change science and the shift to focus on carbon dioxide at the expense of the water cycle.

07:02 Stockholm 1972, World Environment Summit: All elements that play a role in global heat dynamics were discussed. But scientists in the mid 80s said there were too many variables to model easily. And that it was necessary to simplify the message for politics and the public. This led to the focus on CO2, which governs only 4% of global heat dynamics. A very simplistic analysis of the big picture.

  • This was continued on through to the IPCC. So we’ve trapped ourselves in a tunnel of only looking at CO2
  • We can’t solve the problem with the climate with just CO2 reductions: there is 50 times more CO2 in oceans than in the atmosphere. So as we reduce atmospheric CO2, oceans will take centuries to re-equilibrate.
  • In 2005, talk moved to the reality of dangerous climate extremes (all based on hydrological effects).

11:04 Walter introduces pedogenesis as a major lever we can pull

  • The origins of life: in oceans first, moved on to land as symbiosis between lichen and fungi
  • Led to forests > massive drawdown of carbon > soil carbon sponge developed, which retained rainfall, maintained vegetation > vegetation cooled the planet
  • Every gram of water takes 590cal of heat from the earth’s surface into the atmosphere (evapotranspiration)
  • Now that we’ve degraded the sponge, we have degraded the earth’s carbon drawdown capacity and its hydrological cooling capacity
  • Even a minimal regeneration of this system can cool the planet back to safe levels
  • Large cultural change needed to get this narrative into people’s minds
  • The bulk density (mass/volume) of soil is low: 66% of soil is void for air and water to be held

18:03 342W/sq m of incident solar radiation hits the earth. For a stable climate, we need to emit the same amount. But at the moment, we are retaining 3W/sq m extra heat in the bio- and atmospheres. So we need to re-balance that 1% of extra energy.

  • natural transpiration heat flux from soil used to take away 80-90W/sq m of heat back into atmosphere. So if we can increase green transpiration by 4%, we can get that extra 3W/sq m heat to escape.
  • So how do we increase transpiration? Three ways: increase rate, area or longevity of transpiration. By building up the soil sponge, we increase area and longevity.
  • Greening cities: every sq m of soil helps
  • Nutrients from farmland come into cities: so you can either have pandemics from bad waste disposal, or you can increase productivity by making and using fertiliser, recycling nutrients: urban agriculture
  • Canberra is a good example of rejuvenating the landscape: the city is much cooler now than surrounding areas.
  • 5% of volumetric content of the air is made up of water; 50cm of water sitting above every sq cm of the earth’s surface: effectively rivers of water flowing above the land continually, but we don’t harvest it
  • Either the water stays as vapour, or as persistent humid hazes: water condenses onto haze micro nuclei such as dust or pollution > gets hot, with high humidity, but never rains.
  • Water in the air heats the air but also aridifies the land, because there’s no rain. So to make it rain, you need to coalesce 1 million haze droplets to make cloud droplet

30:43 Precipitation nuclei needed: ice, salt or bacteria from stomatal cavity in some trees

  • Forests don’t just need rain, they produce rain. But we ignore this information.
  • CO2 is not an effective lever to pull: it’s only 4% of heat dynamics and it has centuries-long lag. Can’t cool planet through just this paradigm
  • UN conference Sep 2019: innovative solutions for climate change
  • Economic efficiencies of building a soil sponge: so much more rational and efficient. No need for expemsive concrete culvits etc
  • In the last eight thousand years, humans created 5b ha of degraded land: desert and wasteland. Around 40% of the planet’s land surface.
  • safe, elegant solutions that have evolved over billions of years, and what created our climate in the first place. No need to re-invent the wheel. We know it works

37:25 Stable soil carbon as a way to reverse entropy: the energy in sugar is stored solar energy. So photosynthesis concentrates and stores that energy.

  • Plant matter can either end up as CO2 again (it becomes oxidised), or it can be bio-sequestered into stable soil carbon: the sponge, which can store the solar energy and has enormous positive multiplier effects

41:33 1958, Charles Keeling: CO2 in atmosphere is increasing in a zig-zag: winter emitted, summer/spring drawdown – but with a yearly net increase.

  • Of the total carbon released into atmosphere, only a portion comes from fossil fuel use. Also from aridifying land, which releases CO2 that had been trapped as plant matter, and also reduces the capacity of the land to drawdown that CO2

45:22 The best way for grasslands to prevent their carbon being oxidised is to have it eaten. Animals as bio-digesters that help sequester carbon.

49:31 measuring carbon in soil with satellites

  • soil sampling methods are useless – soil is so variable that proper results are almost impossible

58:05 We need a sense of urgency. We have less than a decade left. We know what we need to do to help cool the earth and reduce extreme weather events that result from disrupted hydrological processe