Global Warming, Illustrated

The shift of plant hardiness zones, 1990-2006, in the continental US is displayed by the Arbor Day Foundation.

PS: How the map was produced.

PPS: USA Today article explains more.

1. The 1990 map (Kramer, Marc Cathey) is based on 13 years of data.
2. Climatologists say a 30-year average is appropriate.
3. "Kramer's 2003 map rejected by the USDA was based on data from 1986 to 2002 and showed a significant march northward of boundaries for warm-weather plants. For example, plants that for decades had frozen and died in Nebraska suddenly were doing just fine."
4. Example by USA Today of the effect of the time-span:

"For example, the average annual low temperature for Columbia, S.C., based on the 1990 map (1974-1986) is 10 degrees. The 2003 draft map (1986-2002) is 16 degrees. The new map is based on data from 1976-2005. Using data from those years, the average is 13.5 degrees."

5. New USDA map using 30-year averages to be released Fall 2008 (but I can't find it).

6. SF Chronicle article about controversy

Although the USDA denies it, there is also lingering suspicion that the Bush administration's discomfort with the concept of global warming played a role in the rejection of the 2003 map. "The fact that the map shows warming put a big exclamation point out there," says Kramer. The draft map remained on the AHS Web site for several months until the USDA's Kaplan asked the organization to take it down or alter it: "We wanted them to make it clear this was not the official USDA map."

Three years later, the National Arbor Day Foundation released an updated version of the rejected map. "It's basically a duplicate," Kramer says. "They added some years to it, so it's not identical."

In the meantime, the USDA decided its next update should reflect 30 years of data. Oregon State University's PRISM Group is working on the new version. Kaplan says the result will allow users to zoom in on locales, or type in their ZIP codes and get back a zone. "Doing this at the GIS level, we can work at a much finer scale than ever before," she explains. "The zone borders will be much more refined." How soon will it be available? "The best I can tell you is the near future," says Kaplan. "The running joke," says AHS's Ellis, "is that it's not going to come out until we get a new president in office.

[AHS=American Horticulture Society]