The biggest health impact and risk of global climate change is
on food security.
Yet climate models don't include all the adverse effects of climate change on agriculture. Even so we can discern a world food security disaster at already committed (locked in) future global climate change.
The best assessment we have is the 2010 National Research Council Climate Stabilization Targets Food chapter 5.
The climate crop models relied on for the crop yield impact assessemnts do not yet capture most of the known adverse effects on crops.
"The expected impacts (from climate crop models) are useful as a measure of the likely direction and magnitude of average yield changes, but fall short of a complete risk analysis, which would, for instance, estimate the chance of exceeding critical thresholds.
A list of adverse impacts not captured by the models from NRC (page 161):
Other adverse effects not captured are:
The models also do not consider the combined adverse additive and synergistic effects.
On the other hand the models assume a large benefit from elevated CO2 - the CO2 fertilization effect. How ever this does not apply to all crops (not C4 crops maize, sugar cane, millet, and sorghum ), does not apply to low latitudes, is highly uncertain and gets overwhelmed with adverse impacts of rising temperatures.
"For C3 crops, the negative effects of warming are often balanced (in the model results) by positive CO2 effects up to 2-3°C local warming in temperate regions, after which negative warming effects dominate. Because temperate land areas will warm faster than the global average this corresponds to roughly 1.25-2°C in global average temperature. For C4 crops, even modest amounts of warming are detrimental in major growing regions given the small response to CO2." (NRC 2010 p.160)
All studies show that with rising temperatures all crops in all regions under all situations are declined below today's yields at some point below a global average warming of 3C.
If we exclude the questionable high CO2 benefit for mid-high latitude wheat, all crops in all regions are declined below the baseline from 2.5C.
It makes most sense to take the point where a crop is tipped into decline by climate change as the most significant definition of decline. In this case all crops all regions are tipped into declining yields from a 1.5C warming.
The IPCC AR4 (126.96.36.199.) says that world net food productivity is threatened at a global warming of 1.5C.
The assessments refer to "all crops" while in fact only a few cereal crops have been assessed, most crops, including many crucial to African populations, have not been.
Figure 1: Adapted from NRC/IPCC (2007) chart of global average temperature increase impacts relevant to food security
(from pre-industrial era)
According to the Intergovernmental Panel on Climate Change, or IPCC (2007), with less than a 1.0ºC increase in global average temperature, localized small holders and subsistence farmers, especially those in low-latitude developing nations, will suffer declining crop yields. (It is interesting — and frightening — to note that in these regions, subsistence farming contributes practically all food produced.)
It has been assumed by past IPCC assessments based on highly deficient climate crop models that the temperate northern hemisphere will actually benefit from global warming as a result of longer growing seasons and CO2 fertilization (excluding the many adverse effects) and only the Global South would loose out on food. On this basis it has been concluded there would be no losses of food because the Global South would buy more from the Global North's assumed increased food surplus.
For labour intensive agriculture climate change health damage and crop damage will interact negatively to reduce crop losses further.
The extreme weather events because of their very nature are not captured by the climate crop models, making the model results that are relied for assessing food security unrealistically optimistic, particularity for the Global North and so dangerously misleading for world food security.
If we take the point where crop yields are tipped into decline by climate change as the definition for "decline" our assessment has a better basis in science and gives realistic results.
Below is an IPCC (2007) graphic on extreme weather events, found under "Five Reasons for Concern." Extreme weather events (one of the IPCC's five reasons for concern) will have the single greatest impact on both agriculture and human health.
Figure 4: IPCC (2007) Extreme Weather Events Reason for Concern
The most recent publication on climate change and food security is from the National Research Council (NRC), 2010. In Stabilization Targets for Atmospheric Greenhouse Gas Concentrations, research on food security and climate change is synthesized and explored.
Even in the most highly mechanized agricultural systems, food production is very dependent on weather. Concern about the potential impacts of climate change on food production, and associated effects on food prices and hunger, have existed since the earliest days of climate change research. Although there is still much to learn, several important findings have emerged from over three decades of research....
[S]tudies often do not estimate impacts without adaptation, making it difficult to gauge assumptions. The costs of adaptation are also not considered in these studies, or reflected in price changes.... [M]ost assessments have not adequately quantified sources of uncertainty. Although different climate scenarios are often tested, processes related to crop yield changes and economic adjustments are often implicitly assumed to be perfectly known. An additional source of uncertainty is potential competition with bio-energy crops for suitable land, which could limit the ability of croplands to expand in temperate regions as simulated by most trade models.
— National Research Council, 2010
The National Research Council's chapter 5 on Food Production, Prices, and Hunger also explains:
Food insecurity is the single greatest danger of climate change to vulnerable human populations and indeed to all humanity. That is because there are multiple adverse impacts of global warming and climate disruption on agriculture — and all of these impacts will increase as the global temperature increases.
Healthcare professionals are well positioned to keep reminding the global community about the importance of integrated risk assessment when modelling the impacts of climate change on food security.