By Ranil Senanayake –

The temperature of 111⁰F  sets the terrestrial thermal threshold or the limit of the sustainability of life, every increase in time spent beyond it will signify a decrease in the production of biomass and thereby the production of food. This is because all the food that we eat was made by a plant sometime along its production cycle.  It is the engine of photosynthesis powered by chlorophyll  that captures the energy of sunlight to drive all the ecosystems on this planet; But, this is also the achilles heel of life, the fact that chlorophyll cannot function if the chloroplasts and cellular membranes are destroyed by heat stress. The the point where the photosystem begins to break down.is termed  Critical Thermal Maximum. Depending on the plant species and its native climate, this limit ranges globally with a mean at about 43 C or 111 F. This temperature has already been experiened in localized areas during heat waves.  Thankfully, the periods of exposure have not been long.

Tragically, this reality has been pointed out many times, even at international for a on climate change, where at the COP21 in Paris in 2015 the  Sri Lanka Position Paper stated: 

“We are aware that the optimum operating temperature of chlorophyll is around 37 deg C. In a warming world where temperatures will soar well above that, food production will be severely impacted. We would request the IPCC to address responses to this phenomenon.”

Today, local temperature reading of 111°F (44°C) such as those recorded during recent severe regional heat waves  are becoming regular phenomena. Why is a heat wave so dangerous? Apart from the heat stress in human and animals, it will exceed the threshold for enzymatic activity. All of agriculture depends on the good growth of plants, all plants rely on their chlorophyll to grow and produce. As the Critical Thermal Maximum of 111°F is passed, their performance falls.  As  heat waves exceed this temperature  plant productivity is impacted and yields drop . The spring heat wave in the summer of 2015 in Australia demonstrated that phenonena with significantly reduced farmers’ yields.

he danger to agricultural production is further exasperated by the reliance on chemical farming with so-called ‘high yield ‘ crops of the so called ‘Green Revolution’. These crops have been bred by reducing the plant’s maintenance biomass (leaves and roots) in exchange for crop biomass (seeds or fruit). The reduction of the plant’s natural defences being made possible by the use of chemical fertilizers and toxins . But in a high temperature situation when chlorophyll is functioning sub-optimally such reductions in leaf volume will bring serious crop losses. Such a plant has a low potential for protection and maintenance, these functions being taken over by management, fuels and chemicals. It is selected to produce edible grain at the expense of non-edible tissue and responds excellently to high inputs of fertilizers. All the components that go to form this high-yield agriculture are also dependent on energy for their organization. In this case the source of energy is from fossil fuels, i.e. oil and coal. 

What are the ways out?  One would be to look for plants that have a wide heat stress tolerance to provide the genetic material that will become essential to developing heat resistant varieties of crops. Unfortnately there is no time to develop resistant variesties using concentional means. We will now need to look at importing heat resistant genes from across species boundaries to develop the crops to face the rising heat.

another will be to design future agroecosystems that can use heat reducing mechanisms of ecosystems to respond to temperature raises. This is where we need to consider the agricultural landscapes for a climate compromised world.  

The agricultural landscapes of today are changing to accommodate the wide acre monoculture farms, that depend on large machines and  featureless landscapes. This direction od agricultural development will also place productivity at risk at the 111F periods as there is no landscape feature to break the lamilar flow and there are no features that provide natural cooling in any way.

By removing trees, hedges and other liviing features of an agricultural landscape , you remove the engines of natural cooling to the ambient environment.

A single mature tree provides a powerful cooling effect equal to 20 to 30 kilowatts of cooling power. Trees provide essential shade, reducing ground-level temperatures by up to  59 15°C in rural areas. A complex labdscape breaks up hot air lamilar flow and disrupts heat, reinforcing the fact that, ecosystem services such as evaporative cooling have a great value in desigining the agricuktural landscapes of tomorrow. 

In the face of the reality of a 111F future

Investment in the productive capacity of land to increase its output of ecosystem services must become a critical economic goal.