Effects of global warming on global water and food supply Nigel Arnell and Martin Parry Working Group II (Impacts and Adaptation) UN Intergovernmental Panel on Climate Change Royal Society of Medicine, 12 th November 2007

Climate change and health IPCC AR4 WG2 * * *

Climate change is happening IPCC AR4 2007

Future climate Change in climate depends on: - future emissions - sensitivity of climate to change

Future climate IPCC AR4 WG1: Change in rainfall white areas: lack of agreement between models

Implications for food and water How will climate change affect food production and hunger? How will climate change affect the availability of water resources?

How might climate change affect food production? change in weather, affecting crop growth change in occurrence of pests change in productivity due to the direct effects of increase in CO 2 concentrations change in availability of irrigation water change in frequency of damaging events change in global food markets

Weather and crop growth IPCC AR4

Change in Multiple Cropping Production Potential of Rain-fed Cereals Increase Decrease

Grain yields Percentage change in average crop yields. Effects of CO 2 are taken into account. Crops modelled are: wheat, maize and rice. Global production Parry et al. (2005)

Pests Overwintering range of potato leafhopper under two doubled CO 2 climate change scenarios. (Stinner et al., 1989) Range of expansion of soybean sudden death syndrome (Fusarium solani f.sp. glycines) in North America. (X.B. Yang).

CO 2 enrichment effect Crop productivity tends to increase as CO 2 concentrations increase - C3 crops (e.g.wheat) 10-20% - C4 crops (e.g.maize)0-10% BUT… effects may be offset by effects of higher temperatures, nutrient availability, water stress etc

Availability of irrigation water Scholze et al. (2006)Blue tendency to increase Redtendency to decrease

Extreme events: heat stress After a single hot day >30 o C, there is a large reduction in wheat grain yield Wheeler et al. cited in the Stern Review, 2006

Extreme events: lost production Tabasco State, Mexico, November 2007: “100% of crops lost” Reuters

How might this affect risk of hunger? change in the price of food change in incomes change in access to resources

Change in the price of food IPCC AR4 Impacts depend on how markets are assumed to operate

Food prices and risk of hunger Parry et al. (2004) Cereal prices Risk of hunger

Climate change and water resources Scholze et al. (2006)Blue tendency to increase Redtendency to decrease

Water scarcity 2055

Change in global water resources Millions of people with increase in water stress o C o C o C Impacts depend on change in climate and the state of the world

Consequences Reduced access to safe water Access is not just a problem of availability - property rights / power relations Now: 1 billion people lack access to safe drinking water 2.4 billion people lack adequate sanitation

Consequences Increased conflict over resources Increased exposure to floods Increased need for investment in water management

So what can we do? Mitigation: slow the rate of climate change No climate policy With policy targets Van Vuuren (2007) commitment

So what can we do? Adaptation is essential Alter resource base Alter exposureReduce vulnerability IMPACT change crops reservoirs more irrigation etc Reduce processing waste Increase irrigation efficiency etc Diversify Raise incomes Emergency support etc

Conclusions Climate change is happening, and will affect food and water supplies The consequences will vary with the amount of change, and with the vulnerability of the community Mitigation will not prevent impacts in the short-term – we need to start adapting now

Thank you