Climate change and agriculture

The ancient Greeks knew about the climate change and agriculture connection. They observed that when swamps were drained, the local climate became drier and affected the growth of crops.

So how come we forgot what the ancients had figured out?

Modern intensive agriculture alters landscapes from vegetation-covered soils that act as a sponge holding onto rainfall into high tech input-output systems of irrigation booms and combine harvesters.

This land conversion does exactly what the Greeks observed only on a vast scale. Only this does not alter a northern European climate where moisture laded low-pressure cells roll off the Atlantic all year around. But in drier or warmer regions it alters the soil microclimate at scale can be very damaging.

Stand by a wheat field in Western Australia and you will feel the hot summer wind — it is as if you can actually watch the soil dry out.

Then there is this problem...

when vegetation is cleared for agriculture carbon in the soil declines significantly eventually reaching a new equilibrium under the agricultural management practice — improved round cover, crop residue management and minimum tillage can help restore soil carbon but usually not to pre-clearing levels

Loss of soil carbon is inevitable following conversion of natural vegetation to to arable production. This reduces the soil sponge effect even further. Rain is less likely to percolate into the soil and any moisture that does get in more easily evaporates.

The net effect of loss of cover and soil carbon is lower infiltration and water soil holding capacity and so much faster wetting and drying cycles after rain — often enough to change local climate.

The extreme of this is desertification a process that the UN estimates affects some 6-12 million km2 across the globe especially in sub-Saharan Africa where the social and economic consequences are acute.

dryand grazing in western NSW, Australia

Now for the conventional connection between climate change and agriculture 

At a time when we need production from every hectare of agricultural land the obvious climate change and agriculture link is compounding the risk of food crisis and undermining of food security.

Climate change effects include many that impact on agriculture directly, especially changes to the frequency, intensity and extent of 

  • drought 
  • flood
  • extreme weather
  • heatwaves
  • early or late frosts

There can also be shifts in the onset and duration of seasons and within seasons subtle shifts rainfall and temperature patterns.

In Kenya subsistence farmers rely on two rainy seasons. Under current climate change the short rains are shortening or failing more often. Traditional agricultural practices are not effective in these conditions. farmers are either still planting in the traditional way and finding their crops fail or searching for alternatives.

Drought has always been a problem for farmers. They usually tough it out and recover in the wet years. This works so long as the drought duration is within the economic buffering of the farming system [when this article was being prepared Australian farmers were again seeking government subsidies in the form of low interest loans to cover the latest of a series of droughts].  

The global atmospheric circulation models that we use to predict these climate change effects suggest that many parts of the world will be drier, wetter, hotter or colder than recent times with many places having a higher likelihood of extreme weather events. Not many places will escape changes.

The attention should be on areas where the predicted changes will tip the balance for agricultural production. Agricultural systems that are already marginal are obvious candidates [for example, some dryland grazing systems, shifting agriculture, some rain-fed broad-acre farming]

But equally vulnerable are the high-production systems of intensive agriculture and industrial agriculture for these are like racehorses, fit but fragile.

Pragmatology 

It is hard to be pragmatic when it comes to agriculture. We all need to eat and, when done well, there is money in farming. This combination of demand and opportunity is potent. It means there will always be farms and garners.

No matter that there is a clear climate change and agriculture connection that will make farming more risky in many areas. The risk will be always be worth it for the commercial farmer who will tough it out for the rewards of the years of plenty.

But the risk is much more acute for the subsistence farmer who needs at least some production every year in order to eat. This type of farming needs help.

The smart play is to design more nimble farming systems that can cope with a changing climate. And these systems will focus more on soil than on the crop.

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› climate change and agriculture


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swampland in the Okavango delta, Botswana


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