Starting near the top of North America, Shen et al. (2005) derived and analyzed long-term (1901-2002) temporal trends in the agroclimate of Alberta, Canada, reporting that "an earlier last spring frost, a later first fall frost, and a longer frost-free period are obvious all over the province."  They also found that May-August precipitation in Alberta increased 14% from 1901 to 2002, and that annual precipitation exhibited a similar increasing trend, with most of the increase coming in the form of low-intensity events.  In addition, they note that "the area with sufficient corn heat units for corn production, calculated according to the 1973-2002 normal, has extended to the north by about 200-300 km, when compared with the 1913-32 normal, and by about 50-100 km, when compared with the 1943-72 normal."

These changes, in Shen et al.'s words, "imply that Alberta agriculture has benefited from the last century's climate change," and they note that "the potential exists to grow crops and raise livestock in more regions of Alberta than was possible in the past."  They also note that the increase in the length of the frost-free period "can greatly reduce the frost risks to crops and bring economic benefits to Alberta agricultural producers," and that the northward extension of the corn heat unit boundary that is sufficient for corn production "implies that Alberta farmers now have a larger variety of crops to choose from than were available previously."  Hence, they say "there is no hesitation for us to conclude that the warming climate and increased precipitation benefit agriculture in Alberta."

Also working in Canada, Bootsma et al. (2005) derived relationships between agroclimatic indices and average grain yields of corn, soybeans and barley obtained from field trials conducted in the eastern part of the country and used them to estimate the impacts of projected climate change scenarios on the yields of these commodities for the 2040-2069 period.  Based on a range of heat units projected by multiple climate model simulations, they determined that average yields achievable in field trials could increase by 40-115% for corn and by 21-50% for soybeans by 2040-2069, when "not including the direct effect of increased atmospheric CO2 concentrations."  Adding expected CO2 increases into the mix, along with gains in yield anticipated to be achieved through breeding and improved technology, these numbers rose to 114-186% for corn and 117-157% for soybeans.

Initial yields of barley, on the other hand, were predicted to decline, and by as much as 25% in areas with significant water deficits; but after reviewing the scientific literature on the subject, the Canadian researchers concluded that the direct effect of increased CO2 alone "would more than offset the yield reductions anticipated due to effects of rising temperature and changes in water deficit."  All things considered, they thus concluded that "barley yields would increase by an average of about 15% under this scenario."

In light of these impressive findings, Bootsma et al. predict there will be a "switch to high-energy and high-protein-content crops (corn and soybeans) that are better adapted to the warmer climate."  However, they say "there will likely still be a considerable area of land seeded to barley and other small grain cereals, as these are very desirable in rotation with potatoes."  Consequently, if climate-change predictions prove correct (even though based on totally false presumptions), Canada will be immensely blessed by the incredible stimulus the changed conditions will bring to the country's agricultural productivity.

Dropping down to the United States, Hicke and Lobell (2004) calculated cropland net primary production (NPP) in the central part of the country (South Dakota, Nebraska, Kansas, Missouri, Iowa, Minnesota, Wisconsin and Illinois), using U.S. Department of Agriculture information together with crop-specific parameters that convert agronomic data into carbon fluxes for the period 1972-2001.  This exercise revealed that total cropland area exhibited no temporal trend over the study period, but that "both NPP (flux per unit area) and P (spatially aggregated flux) increased during the study period (46 and 51%, respectively)."

In spite of the "twin evils" of rising air temperature and CO2 concentration that climate alarmists decry so mightily, these results indicate that agricultural productivity in the central United States increased, and dramatically so, over the last three decades of the 20th century.  Possible drivers of this increase, according to Hicke and Lobell, include "improved cultivars, better fertilizer and pest management, more favorable climate, shifts to productive crop types, and economic influences (Duvick and Cassman, 1999; Evans, 1997; Lobell and Asner, 2003)."  Consequently, it would appear that if either of the twin evils of the climate-alarmist crowd had a negative impact on crop productivity - which is highly unlikely, considering that Hicke and Lobell attribute part of the increase in NPP to a "more favorable climate" and that carbon dioxide is an effective aerial fertilizer that also increases plant water use efficiency - it was miniscule compared to the positive impacts of all of the other factors cited by Hicke and Lobell.  Based on these observations, therefore, we may expect to see more of the same in future decades, i.e., increased crop yields, even in the face of (and likely partly because of) continued increases in both the air's CO2 concentration and its temperature.

Moving all the way down to Argentina, for nine areas of contrasting environment within the Pampas region, which accounts for over 90% of the country's grain production, Magrin et al. (2005) evaluated changes in climate over the 20th century along with changes in the yields of the region's chief crops (soybean, wheat, maize and sunflower).  Then, after determining upward low-frequency trends in yield due to technological improvements in crop genetics and management techniques, as well as the aerial fertilization effect of the historical increase in the air's CO2 concentration, annual yield anomalies and concomitant climatic anomalies were used to develop relations describing the effects of precipitation, temperature and solar radiation on crop yields, so that the effects of long-term changes in these climatic parameters on Argentina's agriculture could be determined.

Although noting that "technological improvements account for most of the observed changes in crop yields during the second part of the 20th century, which totaled 110% for maize, 56% for wheat and 102% for sunflower, Magrin et al. report that due to changes in climate between the periods 1950-70 and 1970-99, yields increased by 38% in soybean, 18% in maize, 13% in wheat, and 12% in sunflower.  Consequently, 20th-century climate change, which is claimed by climate alarmists to have been unprecedented over the past two millennia and is often described by them as one of the greatest threats ever to be faced by humanity, has definitely not been a problem for agriculture in Argentina.  In fact, it has helped it.

Skipping across the Pacific Ocean, as well as back across the equator, Liu et al. (2004) made detailed calculations of the economic impact of predicted climate changes for the year 2050 (a mean countrywide temperature increase of 3.0°C and a mean precipitation increase of 3.9%) on agriculture in China via the methodology of Mendelsohn et al. (1994), based on agricultural, climate, social, economic and edaphic data for 1275 agricultural counties for the period 1985-1991.  In the mean, they found that "all of China would benefit from climate change in most scenarios."  In addition, they say "the effects of CO2 fertilization should be included, for some studies indicate that this may produce a significant increase in yield," an increase, we would add, that is well established and was not included in their analysis.  These findings are particularly important, for Liu et al. note that "China's agriculture has to feed more than one-fifth of the world's population, and, historically, China has been famine prone," reporting that "as recently as the late 1950s and early 1960s a great famine claimed about thirty million lives (Ashton et al., 1984; Cambridge History of China, 1987)."

On the other side of the world, Moonen et al. (2002) studied agriculturally-important data collected from 1878 to 1999 on the outskirts of Pisa, Italy.  Meteorological parameters routinely measured over this period were daily maximum, minimum and mean air temperature plus daily rainfall amount; while agrometeorological parameters included date of first autumn frost, date of last spring frost, length of growing season, number of frost days, lengths of dry spells, potential evapotranspiration, reference evapotranspiration, soil moisture surplus, theoretical irrigation requirement, number of days with soil moisture surplus, and number of days with soil moisture deficit.

With respect to temperature, they report that "extremely cold temperature events have decreased and extremely warm temperature events have remained unchanged."  They suggest that both of these observations may be attributed to the increase in cloud cover that would be expected to occur in a warming world, since more clouds would reduce midday heating and thereby offset much - if not all - of the impetus for global warming during the hottest part of the day.  At night, on the other hand, the increased cloud cover would enhance the atmosphere's greenhouse effect, thereby adding to the long-term warming trend.  Consequently, Moonen et al. say that "no negative effects can be expected on crop production from this point of view."  In fact, they find a real "silver lining" in the latter of these cloud feedback phenomena, reporting that "the number of frost days per year has decreased significantly resulting in a decrease in risk of crop damage."  Hence, they say the time of planting spring crops could be safely advanced by many days, noting that the length of the growing season increased by fully 47 days over the period of their study.

With respect to rainfall, Moonen et al. found a somewhat analogous situation. On an annual basis, extremely high rainfall events did not appear to have changed; but there was an increase in very low rainfall events.  The one exception to this rule on a seasonal basis was a decrease in high rainfall events in the spring, which might be expected to increase drought risk at that time of year.  However, when the maximum length of dry spells was assessed on a seasonal basis, the only significant change observed was a lengthening of this parameter in the autumn.  But autumn is the wettest season of the year in Pisa.  Hence, the authors concluded that "no increased drought risk is to be expected."

The bottom line with respect to water in agriculture, however, is the balance that exists between what is received via rainfall and what is lost via evapotranspiration, as this difference is what determines the soil moisture balance.  Hence, even though there was a downward trend in yearly rainfall at Pisa over the past 122 years (due to the decrease of high rainfall events in the spring), there was a nearly offsetting downward trend in evapotranspiration (possibly induced by enhanced daytime cloud cover), such that there were "no significant changes in soil water surplus or deficit on an annual basis."  In the autumn, however, the scientists noted a significant decrease in the number of surplus soil moisture days; but because autumn is the wettest season of the year, the scientists say "this indicates a reduced flooding risk in autumn, which could have positive effects on workability of the soil and imply a reduction of erosion."

Considering their several observations in total, Moonen et al. concluded that concomitant with the warming of the Northern Hemisphere over the past 122 years, "extreme events in Pisa have not changed in a way that is likely to negatively affect crop production."  More often than not, in fact, the changes that were demonstrated to have occurred seem to have had positive impacts on agriculture.  And as the authors state in concluding their study, "there is no doubt regarding the reality of the observed changes."

In a final study, Nicholson and Yin (2001) analyzed climatic and hydrologic conditions in equatorial East Africa from the late 1700s to close to the present, based on histories of the levels of ten major African lakes, while they used a water balance model to infer changes in rainfall associated with the different conditions, concentrating most heavily on Lake Victoria.  Their data revealed "two starkly contrasting climatic episodes."  The first, which began sometime prior to 1800 during the Little Ice Age, was one of "drought and desiccation throughout Africa."  This arid episode, which was most extreme during the 1820s and 30s, was accompanied by extremely low lake levels.  As the two researchers describe it, "Lake Naivash was reduced to a puddle ... Lake Chad was desiccated ... Lake Malawi was so low that local inhabitants traversed dry land where a deep lake now resides ... Lake Rukwa [was] completely desiccated ... Lake Chilwa, at its southern end, was very low and nearby Lake Chiuta almost dried up."  Throughout this unfortunate period, they say that "intense droughts were ubiquitous."  Some, in fact, were "long and severe enough to force the migration of peoples and create warfare among various tribes."

As the Little Ice Age's grip on the world began to loosen in the mid to latter part of the 1800s, however, things began to improve for most of the continent.  Nicholson and Yin report that "semi-arid regions of Mauritania and Mali experienced agricultural prosperity and abundant harvests; floods of the Niger and Senegal Rivers were continually high; and wheat was grown in and exported from the Niger Bend region."  Across the east-west extent of the northern Sahel, in fact, maps and geographical reports described "forests."

As the nineteenth century came to an end and the twentieth century began, there was a slight lowering of lake levels, but nothing like what had occurred a century earlier; and then, in the latter half of the twentieth century, things improved even more, with levels of some of the lakes actually rivaling high-stands characteristic of the years of transition to the Modern Warm Period.  Even in Africa, therefore, global warming has proven to be much better than global cooling for agriculture.

In conclusion, the results of the several studies we have reviewed in this Summary clearly demonstrate that the concomitant increases in air temperature and CO2 concentration experienced over the past century or more did not exert a significant negative influence on the agricultural enterprise.  In most cases, in fact, they actually contributed to the large increases in yield experienced over this period, even in the face of a temperature increase claimed by climate alarmists to have been unprecedented over the past two millennia and an atmospheric CO2 increase that may well have been unprecedented over the past several hundred millennia.  Yet these two atmospheric trends are claimed by the world's radical environmentalists to constitute the greatest threat facing the world today.

They could not be more wrong.  In light of the material presented here, and especially in our Subject Index under the heading Agriculture (Our Greatest Challenge), it is clear that we are going to need all of the extra atmospheric CO2 we can get in order to not have to usurp all remaining land and freshwater resources to produce the food that will be needed to feed our growing numbers in the years and decades ahead.

References
Ashton, B., Hill, K., Piazza, A. and Zeitz, R.  1984.  Famine in China, 1958-1961.  Population and Development Review 10: 613-615.

Bootsma, A., Gameda, S. and McKenney, D.W.  2005.  Potential impacts of climate change on corn, soybeans and barley yields in Atlantic Canada.  Canadian Journal of Plant Science 85: 345-357.

Cambridge History of China.  1987.  Volume 14.  Cambridge University Press, Cambridge, UK.

Duvick, D.N. and Cassman, K.G.  1999.  Post-green revolution trends in yield potential of temperate maize in the north-central United States.  Crop Science 39: 1622-1630.

Evans, L.T.  1997.  Adapting and improving crops: The endless task.  Philosophical Transactions of the Royal Society of London, Series B 352: 901-906.

Hicke, J.A. and Lobell, D.B.  2004.  Spatiotemporal patterns of cropland area and net primary production in the central United States estimated from USDA agricultural information.  Geophysical Research Letters 31: 10.1029/2004GL 020927.

Liu, H., Li, X., Fischer, G. and Sun, L.  2004.  Study on the impacts of climate change on China's agriculture.  Climatic Change 65: 125-148.

Lobell, D.B. and Asner, G.P.  2003.  Climate and management contributions to recent trends in US agricultural yields.  Science 299: 1032.

Magrin, G.O., Travasso, M.I. and Rodriguez, G.R.  2005.  Changes in climate and crop production during the 20th century in Argentina.  Climatic Change 72: 229-249.

Mendelsohn, R., Nordhaus, W.D. and Shaw, D.  1994.  The impact of global warming on agriculture: A Ricardian analysis.  American Economic Review 84: 753-771.

Moonen, A.C., Ercoli, L., Mariotti, M. and Masoni, A.  2002.  Climate change in Italy indicated by agrometeorological indices over 122 years.  Agricultural and Forest Meteorology 111: 13-27.

Nicholson, S.E. and Yin, X.  2001.  Rainfall conditions in equatorial East Africa during the Nineteenth Century as inferred from the record of Lake Victoria.  Climatic Change 48: 387-398.

Shen, S.S.P., Yin, H., Cannon, K., Howard, A., Chetner, S. and Karl, T.R.  2005.  Temporal and spatial changes of the agroclimate in Alberta, Canada, from 1901 to 2002.  Journal of Applied Meteorology 44: 1090-1105.