Compared to the 1990 version, zone boundaries in this edition of the map have shifted in many areas. The new map is generally one 5-degree Fahrenheit half-zone warmer than the previous map throughout much of the United States. This is mostly a result of using temperature data from a longer and more recent time period; the new map uses data measured at weather stations during the 30-year period 1976-2005. In contrast, the 1990 map was based on temperature data from only a 13-year period of 1974-1986.Here's a Comparison between 1990 and 2012 USDA hardiness zone maps, showing where the zones have changed.
Moderate climate change will likely increase yields of North American rain fed agriculture, but with smaller increases and more spatial variability than in earlier estimates. Most studies project likely climate-related yield increases of 5-20 percent over the first decades of the century, with the overall positive effects of climate persisting through much or all of the 21st century.posted by notme at 12:55 PM on May 27, 2012 [3 favorites]
- Food production is projected to benefit from a warmer climate, but there probably will be strong regional effects, with some areas in North America suffering significant loss of comparative advantage to other regions.
- The U.S. Great Plains/Canadian Prairies are expected to be particularly vulnerable.
- Crops that are currently near climate thresholds (e.g., wine grapes in California) are likely to suffer decreases in yields, quality, or both.
- Climate change is expected to improve growing conditions for some crops that are limited by length of growing season and temperature. (e.g. fruit production in the Great Lakes region and eastern Canada).
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Sure, it may be warmer on average in Northern Canada, so it may be possible to grow more or better crops there some years. But improved farm yields aren't possible if every year is different. If the seasonal changes in temperature, the amount of rainfall, and the amount of sunshine can't be predicted, you're not going to be able to have successful agriculture.
Similarly, climate change increases the frequency of extreme weather events. Those are also very bad for agriculture.
So while you might find some isolated instances of temporarily improved conditions, it will be hard to take advantage of them and I don't think you'll find consistently improved conditions anywhere.
posted by alms at 12:23 PM on May 27, 2012 [4 favorites]