Week 6

Week 6 concerned the impact of climate change on human systems, looking at the built environment and urban heat islands, and food security.

Cities can be up to 9C above the surrounding countryside (I hadn’t realised the effect was this marked – on the UK weather forecasts they typically talk about temperatures being 2-3C higher.) If this is coupled with a heat wave the resulting high temperatures can lead to excess human deaths – an estimated 70,000 in Europe in 2003, for example. Deaths are caused by dehydration and hyperthermia – the body getting above its thermal comfort zone and being unable to cope. Where normally a person would cool at night, this becomes more difficult in a heat wave. Cooling people’s homes with air conditioning provides an apparent solution, but actually consumes more energy, adding to overall warming. To cool a whole city, you need to increase the amount of water on or just under the surface. You would have more evaporation and thus more cooling. This means having areas of vegetation, where the plants themselves transpire. It also means having porous surfaces where water can collect rather than running off and being drained rapidly away. Evaporation of this water would cool the surrounding area.

Atmospheric warming results in two main threats to food production: water supply and crop disease. Climate change is changing where water is. There is more rain in some areas, less in others. Both affect the stability of water supply and thus of food production. Glacier melt in the Himalayas will result in less water running into the lower lands around (India, etc) where a huge proportion of humanity lives. Much of India’s increase in food production in recent years has been dependent on water from underground aquifers, which will run out.

Crop disease, particularly from fungal pathogens, is being affected by climate change. Pathogens have been moving to higher latitudes at about 3km per year since 1960.

Increased production of food requires more efficient means of production. In industry, this has meant eliminating waste in its processes, lowering stock levels and using just-in-time deliveries. This makes for greater efficiency but at the cost of resilience. If you are reliant on a just-in-time delivery of raw materials and they don’t arrive, your entire process stops. There is an analogy with top athletes. They are trained to the peak of fitness for their sport, to the edge of resilience, but often tip over the edge into injury, which stops them competing at all. For farming, the edge of resilience is monoculture, highly efficient production – so long as things go right. But plant a flood-resistant crop and have a drought instead and you’ve no crop at all. Or plant one crop and have it devastated by a pest – same result.

Under climate change, what is required is resilience. If you are no longer so sure what the weather will be like, you have to plant a range of crops so that some them will do well even as others do badly. This by definition means less overall productivity. So to produce enough food, you need to farm over a larger area, cutting down forest or artificially irrigating vast areas.

Is that geo-engineering (week 4) or what?

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