The Effects of Climate Change on Agriculture

Outline

1. Introduction: What is global warming?

2. Are we getting warmer?

3. Historical perspective: How has climate change affected agriculture in the past?

4. How do predict effects on agriculture?

5. How will global warming negatively affect agriculture?

6. Are there benefits to global warming?

7. Conclusions

What is global warming?• Global warming is an increase in the Earth’s average surface temperature.

• Infrared radiation (IR) released from the earth’s surface after it is warmed may be reabsorbed by atmospheric gases known as greenhouse gases.

• The absorption of IR by these gases causes heat to be radiated back to the earth. This results in warming known as the greenhouse effect.

• Humans, have caused a significant increase in greenhouse gas concentrations, especially CO2,largely through the use of fossil fuels.

• It is commonly accepted that this large increase in greenhouse gas emissions has led to a very rapid period of global warming over the later portion of the 20 th century.

• On the basis of this rapid increase in temperature and also climate simulations it has been predicted that temperatures could rise significantly increasing the frequency of severe weather events.

Are we getting warm?• The hypothesis that the earth’s climate remained stable for 1000 years

during the pre-industrial era after which it rapidly increased is known as the “hockey-stick” model.

• The main paper in support of this model has been demonstrated to have used faulty methodology and other errors. This conclusion has also been reached by the US House of Representatives in 2006.See for example: Holland, David. 2007. Bias and concealment in the IPCC process: The “hockey-

stick” affair and its implications. Energy & Environment 18, 951- 983.

McKitrick, Ross. What is the “Hockey-stick” debate about? APEC Study Group, Australia. April, 2003.

• Conclusion: The ``hockey-stick model`` greatly underestimates periods of significant climate change in the past (i.e. before a large increase in CO2).

Historical perspective

• During 800 – 1200 AD, during the Medieval Warm Period (MWP), Iceland and Greenland were settled by the Vikings. However, cooling weather causing poor harvests resulted in the virtual extermination of Viking settlements by1492.

• Between 1150 – 1460 AD Europe experienced a general cooling period known as the “Little Ice-Age”. The climate was especially cool during 1560 – 1850. There were frequent crop failures and intermittent starvation during this period1.

• The Mayan civilization in the southern Yucatan entered a period of collapse between 800 – 1000 AD. This period was marked by increased warfare, human sacrifice, and migration. It is thought that this was caused by increased solar activity causing recurrent drought1.

1. Feynman, Joan. 2007. Has solar variability caused climate change that affected human culture? Advances in Space Research 40, 1173.

How do predict effects on agriculture?

• Similar models are used to forecast changes in climates as are used to predict the impact of climate change on crops.

• This requires increasing understanding physiological responses of crops to changing weather and climate, particularly drought and heat.

• Crop prediction methods2:

1. Statitistical-past associations between crop production and climate (may not be valid in an altered climate).

2. Dynamic methods-attempt to represent the physiology of crops and allow for the testing of adaption strategies.

• Typically (see ref 3 for eg.) simulation models of climate change are used to predict changes in temperature, precipitation and solar radiation. These climate predictions are used in crop modeling programs.

• Limitations: Dependant on accuracy of multiple models; difficult to model advances in human crop/farming technology; assume micronutrients not limiting3; do not account for pests, weeds, etc3.

2. Slingo, J.M. et al. 2005. Introduction: Food crops in a changing climate. Phil. Trans. R. Soc. 360, 1983 – 1989.

3. Tubiello, F.N. et al. 2000.US national assessment technical report: Effects of climate change on US crop production.

Predicted Impacts of Climate Change on Agriculture

• Some crops may benefit from elevated CO2.4

• Warming: accelerates plant development, reduces grain-fill, and nutrient use efficiency. It also increases water consumption. 4

• Warmer winters may affect plant-insect interactions and increase the rate of winter survival of insect pests4.

• Warming climates may increase the impact of heat stress in crops grown in already dry areas, particularly in the developing world where inadequate infrastructure is unable to adapt.

• Example: 81% of wheat consumed in the developing world is produced within that same country and many poor families must depend on their own farms for food security5.

• Environmental change can lead to large population migrations which often trigger violent conflicts6.

4. Fuhrer, J. 2003. Agroecosystem responses to elevated concentrations of CO2, ozone and global climate change. Agriculture, Ecosystems and Environment 97, 1-20.

5. Ortiz, R. Et al. 2008. Climate change: Can wheat beat the heat? Agriculture, Ecosystems and Environment 126, 46-58.

6. Reuveny, R. 2008. Ecomigration and violent conflict: Case studies and public policy implications. Human Ecology 36, 1-13.

Are there benefits to global warming?

• There are many regions of the US predicted to have wheat yield increases under various climate change projections (Tubiello et al.) .

• In North America, by 2050 (assumed doubling of CO2) from 55oN to 65oN. Similar expansions are predicted for northern Eurasia (Ortiz et al.).

Final Comments/ Perspectives:

• 1. Climate change (both warming and cooling) has had profound impact on agriculture and human cultures in the past.

• 2. Assuming the globe is and will continue to get warmer, what should policy considerations be?

– 2a. Increase research on drought resistant crop.

– 2b. Development of water conserving agriculture practices

– 2c. Diversification of production systems to reduce vulnerability to climate change.

– 2d. Biofuels: Is the use of agriculture resources for the production of biofuels a responsible or sustainable idea?

[cf: Searchinger, T et al. 2008. Use of US croplands for biofuels increases greenhouse gases through emissions from land-use change. Science 319, 1238 – 1240.]