Cannabis Chronicles

As is our normal practice when reviewing or suggesting a book, we usually try to include a decent excerpt with a book review (or recommendation), and today is no exception. Since one of the interesting facets of Lester Brown’s book is the prediction of the effects that climate and social change will have on agriculture, the following passage makes a timely and worthwhile read for a blog devoted to Cannabis.

Farmers Facing Two New Challenges

As we exceed the earth’s natural capacities, we create new problems. For example, farmers are now facing two new challenges: rising temperatures and falling water tables.
Farmers currently on the land may face higher temperatures than any generation since agriculture began 11,000 years ago. They are also the first to face widespread aquifer depletion and the resulting loss of irrigation water.

The global average temperature has risen in each of the last three decades. The 16 warmest years since record keeping began in 1880 have all occurred since 1980. With the three warmest years on record—1998, 2001, and 2002—coming in the last five years, crops are facing heatstresses that are without precedent.¹.

Higher temperatures reduce crop yields through their effect on photosynthesis, moisture balance, and fertilization. As the temperature rises above 34 degrees Celsius (94 degrees Fahrenheit), photosynthesis slows, dropping to zero for many crops when it reaches 37 degrees Celsius (100 degrees Fahrenheit). When temperatures in the U.S. Corn Belt are 37 degrees or higher, corn plants suffer from thermal shock and dehydration. They are in effect on sick leave. Each such day shrinks the harvest. ²

In addition to decreasing photosynthesis and dehydrating plants, high temperatures also impede the fertilization needed for seed formation. Researchers at the International Rice Research Institute in the Philippines and at the U.S. Department of Agriculture have together developed a rule of thumb that each 1-degree-Celsius rise in temperature above the optimum during the growing season reduces grain yields by 10 percent. ³

These recent research findings indicate that if the temperature rises to the lower end of the range projected by the Intergovernmental Panel on Climate Change, grain harvests in tropical regions could be reduced by an average of 5 percent by 2020 and 11 percent by 2050. At the upper end of the range, harvests could drop 11 percent by 2020 and 46 percent by 2050. Avoiding these declines will be difficult unless scientists can develop crop strains that are not vulnerable to thermal stress. ⁴

Lester Brown

It’s especially important to note the details about high temperatures and plant growth. We’ve often compared corn to cannabis, the are both strong fast growing annuals who do best with lots of full sun and nice fertile soil. Although there is always some variance between different varieties and strains of a species, it’s been our general observation that 100 degrees Fahrenheit is where heat stress starts to become apparent to the eye with Cannabis too. When temperatures get that high, all facets of plant growth become more difficult to manage.

1. Goddard Institute for Space Studies, NASA Goddard Space Flight Center Earth Sciences Directorate, “Global Temperature Anomalies in .01 C,” at <www.giss.nasa.gov/data/update/gistemp/GLB.Ts.txt>, viewed 15 April 2003 [↩]
2. Effect of higher temperatures from John E. Sheehy, International Rice Research Institute, Philippines, e-mail to Janet
   Larsen, Earth Policy Institute, 2 October 2002. [↩]
3. Ibid. [↩]
4. U. Cubasch et al., “Projections of Future Climate Change,” in Intergovernmental Panel on Climate Change, Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change (New York: Cambridge University Press, 2001). [↩]