The first episode of the BBC’s three Part series on the “Future of Food” made claims about the impact of global warming, that are the opposite made by Ian Pilmer in his book “Heaven and Earth” (or a short video here)
Will Global Warming cause food shortages?
Alagiah interviews a Masai chief, whose 700 head of cattle have declined to 30 due to the prolonged drought in Kenya caused by Climate Change. He also interviews IPCC chief Dr. Rajendra Pachauri who claims that each one degree rise in temperatures in India will lead to at 10% to 20% in temperatures, and that a we could see falls in food production in Africa of up to 50%. Alagiah also mentions recent food riots as being a result of rising prices cause by climate change.
Pilmer claims that the warm periods (such as the Medieval Warm period and the Roman Period) had were times of plenty. Southern Italy had rain all the year round in the 2nd century AD (now only winter rain). North Africa, Central America and Central Asia were warmer and wetter. (p.59) This was a time of population increase, with crop failures and famine becoming a rarity.(p.60). A simliar story for the MWP, where England and China (p.68) flourished. It was warm enough for a Viking colony to establish on Greenland, growing crops.
He also claims that the benefit of the current (more modest) warming is that the increased CO2 may lead to increased crop yields, although this could be offset by pollution (P.197)
Will Warming lead to more volatile climate?
On the BBC, we were shown pictures of flooding, and the destruction of crops, such as strawberries. A bit a warming has meant more volatility in weather. This can only increase.
Pilmer claims that it is the cooler, drier periods that have the more volatile climate. This lead to population decreases in the dark ages and at the end of the MWP. Plague did much to reduce the population in these periods.
Who to believe?
The BBC only gives short examples, and concentrates on current, localised, examples. Pilmer gives the long-term sweep of history, with lots of examples. Although Pilmer may have lots of errors (see here and here), these critics do not contradict the the implication of Pilmer that a little warming would be of net benefit to both humankind and other living things. For instance the late 20th century warming may have increased the number of species on mountain tops in the European Alps (p.195)
It is easier to give localised examples to give totally the wrong picture e.g. the droughts being caused by local deforestation elsewhere – or appearance of more extreme weather patterns due to looking for variations. It is like watching cricket. In any season, no end of records and novel facts to be recorded in every season, because there is an endless number of statistics to be collated. However, over the long period, general trends are observed, and the claimed theories contradict the data more difficult to maintain.