Climate change beginning to impact global crop production

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The demand for world agriculture output will grow exponentially over coming decades due to world population growth and expanding world economies. At the same time, the agriculture sector will be impacted by changes in climate that will challenge the productivity of the world’s agriculture resources.

World population will continue to grow at a rapid rate. World population in 2010 was 6.9 billion people. By 2050 it is expected to grow to 9.3 billion people. This is a 35 percent increase in just 39 years or the addition of an average of 60 million people every year. For perspective this increase is equivalent to adding the population of the United States eight times to world population by 2050. The world’s agriculture resource base will be required to increase production to meet this increase.

In addition to population growth there has been an explosion of people moving out of poverty and into the middle class. This has occurred in several countries of the world but primarily in China and India that collectively make up over one-third of the world’s population. Rapid economic growth in these countries has resulted in increasing livings standards for a significant portion of their populations. As living standards increase, people’s diets change. Diets high in meat, which usually occurs as living standards improve, increase the demands on the agriculture sector because multiple pounds of feed are required to produce a pound of meat.

At the same time, millions of people in Africa and around the world remain in poverty. These people live in an environment of food insecurity where a weather event can quickly move them to a situation of food shortages. People in these regions are very sensitive to agricultural commodity price changes. They spend a much larger percentage of their incomes on food as compared to people in the developed world.

Climate change has begun to impact the agricultural landscape. The continuation of these changes due to rising greenhouse gases will challenge the agriculture sector to finds ways to maintain and improve productivity. Recent research has shown that climate change is already beginning to have a negative impact on global crop production levels. The research project, a collaborative effort by researchers at Stanford University, Columbia University and the National Bureau of Economic Research, examined the impact of climate change on the global production of maize, wheat, rice and soybeans from 1980 to 2008. These are the four largest commodity crops and represent roughly 75 percent of the calories that humans directly or indirectly consume. Access to the report can be found at Climate Trends and Global Crop Production since 1980.

The research is focused on temperature and precipitation changes over this period. A database of yield response models were developed to evaluate the impact of these climate trends on crop yields over the corresponding 1980 to 2008 time period. In addition, the positive yield impact of increased carbon dioxide levels was added to the analysis. Assessing the impact of past trends on agricultural crop yields will help project the impact of future trends on yields during coming decades. It will also help identify which agricultural regions will be impacted the most.

Temperature

Global average temperatures have risen by about 0.13 degrees Centigrade (.23 degrees Fahrenheit) per decade since 1950. It is expected to increase to about 0.2 degrees Centigrade (.35 degrees Fahrenheit) per decade over the next two to three decades. The temperature increase in agriculture areas is expected to be substantially higher.

In many agricultural locations, temperature trends increased and are more than twice the historic standard deviation, as shown in Figure 1. This includes Europe, Northern China, sub-Saharan Africa and Brazil. Sixty five percent of countries experienced temperature trends in crop production regions of at least one standard deviation for maize and rice. The corresponding percent of countries was 75 percent for wheat and 53 percent for soybeans. About a quarter of the countries experience trends of more than two standard deviations for each crop. By comparison, trends were evenly distributed about zero during the previous 20 year period (1960-1980).

Figure 1. Linear Trend in Temperature, 1980-2008, measured in standard deviations  1/  2/  3/

click image to zoom

1/  Linear trends for the growing season for the predominant crop in each grid cell.
2/  Trends are expressed as the ratio of the total trend for the 29 year period (1980-2008) divided by the historic standard deviation for the 1960-2000 period.
3/  Only cells with at least one percent of the area covered by either maize, wheat, rice or soybeans are shown.

Precipitation

Precipitation trends were less dramatic than temperature trends as shown in Figure 2. Modest increases or decreases in precipitation are evident in large parts of the world’s agricultural regions. Some parts of the world have experienced significant increases in precipitation while others have had significant decreases. However, when averaged, the effects of changes in growing season rainfall are near zero.

Figure 2. Linear Trend in Precipitation, 1980-2008, measured in standard deviations  1/  2/  3/

click image to zoom

1/  Linear trends for the growing season for the predominant crop in each grid cell.
2/  Trends are expressed as the ratio of the total trend for the 29 year period (1980-2008) divided by the historic standard deviation for the 1960-2000 period.
3/  Only cells with at least one percent of the area covered by either maize, wheat, rice or soybeans are shown.

Carbon Dioxide

Increased levels of carbon dioxide have a positive impact on plant growth. A plant takes in atmospheric carbon dioxide (CO2) during the photosynthesis process, utilizes the carbon (C) to build the plant, and releases the oxygen (O2) back into the atmosphere. For many crops, the photosynthetic pathway allows the plant to respond to elevated levels of atmospheric CO2. These are referred to as C3 plants and include wheat, rice, soybeans and most weeds. However, the photosynthetic pathway of C4 plants such as maize does not respond to elevated levels of CO2, so the impact on yield is likely much smaller. Atmospheric concentrations of carbon dioxide have increased by 47 parts per million (386 ppm less 339 ppm) over the 1980 to 2008 time period (Figure 3). Experiments of the impact of elevated levels of atmospheric CO2 indicated that the 47 ppm increase would increase the yields of C3 crops by approximately three percent.

Figure 3. World Atmospheric Carbon Dioxide (CO2) Levels

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Results

The affect of temperature and precipitation trends on the yields of maize, rice, wheat and soybeans is shown in Table 1. The impact on yields is greater for temperature than for precipitation. The greatest yield impact of temperature was on wheat followed by maize. When the three percent yield gain from elevated CO2 levels is added to wheat, soybeans and rice, the yield response for rice and soybeans become positive but remained negative for maize and wheat.

Table 1. Median Estimates of Global Impacts of Temperature and Precipitation Trends on Yields of Four Major Crops, 1980-2008.
Crop Global Production (1998-2002 avg. mil. metric tons) Global Yield Impact of Temperatures Trends Global Yield Impact of Precipitation Trends Subtotal Global Yield Impact of CO2 Trends Total
Maize 607 -3.1%
(-4.9%, -1.4%)
-0.7%
(-1.2%, 0.2%)
-3.8%
(-5.8%, -1.9%)
0.0% -3.8%
Rice 591 0.1
(-0.9, 1.2)
-0.2
(-1.0, 0.5)
-0.1
(-1.6, 1.4)
3.0 2.9
Wheat 586 -4.9
(-7.2, -2.8)
-0.6
(-1.3, 0.1)
-5.5
(-8.0, -3.3)
3.0 -2.5
Soybeans 168 -0.8
(-3.8, 1.9)
-0.9
(-1.5, -0.2)
-1.7
(-4.9, 1.2)
3.0 1.3

                           
Estimated changes in yields for maize, rice, wheat and soybeans for major producing countries are shown in Figure 4. The country with the largest impact was wheat production in Russia with an estimated negative yield impact of almost 15 percent. For the U.S., yield changes due to temperature and precipitation trends are negligible for maize, wheat and soybeans. This corresponds to the small temperature and precipitation trends shown in Figures 1 and 2. Yield impacts were smaller for rice than the other crops. The confidence intervals of the yield estimates were larger for soybeans than the other crops.

Figure 4. Estimated net impact of climate trends from 1980 to 2008 on crop yields for major producing countries and for global production. Values are expressed as percent of average yields. A = Maize, B = Rice, C = Wheat, D = Soybeans. *

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*  Gray bars show median estimate and error bars show 5 percent to 95 percent confidence internal from bootstrap resampling with 500 replicates. Red and blue dots show median estimate of impact for temperature trend and precipitation trend, respectively. Note, the sum of the temperature (red dots) and precipitation (blue dots) estimates equals the total estimate shown by the gray bars.

The researchers calculated the impact of the climate trends on global crop yields. Maize production would have been about six percent higher and wheat production about four percent higher had the climate trends since 1980 not existed. The effects on rice and soybeans were lower and not statistically significant. The researchers also calculated the impact of climate trends on global crop prices using price elasticities. The estimated changes in crop production excluding and including carbon dioxide fertilization resulted in commodity price increases of about 20 percent and about 5 percent respectively.

The analysis does not take into account the potentially mitigating impact of crop production climate adaptation strategies currently taking place such as where crops are grown and how crops are grow (seed varieties, planting dates, etc.)  Some adaptations strategies are already taking place in the U.S. Midwest.

However, it also does not take into account the negative impact of the increased occurrence of extreme weather events associated with global warming. An increase in the frequency of extreme weather events has been documented in the U.S. Midwest (Climate Change in Iowa).

Implications

To meet this expanding world demand, agriculture must become more adept at anticipating climate trends and finding ways of adapting to these changes. The research report shows that the impact of temperature on crop yields is a larger factor than the impact of precipitation. This would indicate that adaptation strategies should focus more on temperature changes than on precipitation changes.

The research report concluded that North America is the agricultural region least impacted by temperature and precipitation changes. The U.S. already accounts for about forty percent of the world’s production of corn and soybeans and a substantial portion of the world’s wheat. The U.S. share may increase if these patterns persist and the rest of the world is increasingly challenged by temperature increases. It will have significant implications for the world grain trade and the role of the U.S. in feeding the world.

Most of the increase in agricultural production over the last century is the result of yield increases rather than agricultural land area expansion. However, due to the world’s rapidly growing demand for food and the negative yield impact of climate change on food production, there will be great pressure to expand the world’s agricultural land area. Expanding the agricultural land area may significantly increase carbon dioxide emissions due to the release of carbon from converting native areas to farmland as discussed in Agricultural Research Combats Climate Change.

Increased investments in agricultural research in the U. S. and across the world is needed to meet the challenge of world food production. However, this must be combined with programs to substantially reduce greenhouse gas emissions. In the long run, agricultural research will not be able to compensate for the devastating effects of climate change on world agricultural production.

References

Dave Lobell, Wolfram Schlenker, Justin Costa-Roberts, Climate Trends and Global Crop Production since 1980.

Dave Lobell, Wolfram Schlenker, Justin Costa-Roberts, Climate Trends and Global Crop Production Since 1980, Program on Food Security and the Environment – Policy Brief.

Gene Takle, Climate Change in Iowa.

Don Hofstrand, Agricultural Research Combats Climate Change, AgMRC.


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masvaure artwell    
zimbabwe  |  January, 31, 2013 at 01:02 PM

the stuff is enlightening to say the least


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