Thursday, July 2, 2009

The Changing Hardiness Zones of the US

From the Baltimore Sun's B'More Green blog comes news (via the Sun's Garden Variety blog) that the US Department of Agriculture is planning to revise its map of plant hardiness zones across the country by this fall. But the Arbor Day Foundation has already updated changes in hardiness zones from 1990 to 2006, which they show in their interactive map:

us hardiness zones

This shows the changes in zone classification over that time period:



Some isolated areas of the interior West and Midwest have actually warmed enough to move up two zones, while a few areas in the Southwest have actually gone down a zone. But you can infer from the streaked pattern that most areas, especially in the eastern two-thirds of the country, have warmed by the equivalent of about half a zone. That actually strikes me as a bit extreme; zones are classified by average annual low temperature, as per the scale on the left; so if I'm reading it right, a half-zone change would correspond to the average annual low being about 5 degrees F warmer in 2006 than it was in 1990. Is that really plausible? Average temperatures certainly haven't warmed by that much; but maybe the climate has changed in such a way that especially cold snaps are less common at the height of winter. I don't know.

28 comments:

Matt Osborne said...

An interesting map either way.

bruce said...

This map is solid proof that global warming is a lot worse than we thought. As you pointed out, this map indicates a pretty big climate change and alot bigger than people were estimating. To all the Republican global warming deniers, what do you say to this map? Well, you would probably say "let's build nuclear plants." But that is no answer because we are running out of uranium. It's time for action.

bruce said...

Interesting, there are a few places (like south eastern California) where small areas have actually gotten a lower hardiness zone between 1990 and 2006. One wonders if it really has gotten colder there on average, or if the map is a bit arbitrary.

Chachy said...

I wouldn't call this map "solid proof" of anything; I'm still not convinced it's accurate, since an apparent average increase of annual low temperatures of 5F across most of the country between 1990 and 2006 doesn't seemplausible. Though I'm open to explanations...

Of course, it's my view that we've had solid proof of nascent effects of global warming for years now.

bruce said...

Well maybe the change is not 5F, but global warming has resulted in less weather extremes and more moderate weather over all?

Anonymous said...

It's the opposite - more droughts, more floods, more heat waves. But less extreme cold; I'd just be surprise dif it was that much less in just 16 years (how could you even establish new norms based on such a short timeframe?).

Andrew said...

This map is not solid proof of anything more than 20 years of additional data points.

Lets dig a little deeper. Wikipedia notes:

"The USDA first issued its standardized hardiness zone map in 1960, and revised it in 1965. A new map was issued in 1990, based on U.S. and Canadian data from 1974 through 1986 (and 1971-1984 for Mexico). While the 1990-issue map utilized approximately double the number of stations, it also divided the temperature zones into five-degree a/b zones for greater accuracy. This revised map showed many areas to be suddenly colder than the 1960 map, due largely to a number of severely colder winters in the central and eastern U.S. in the 1974-1986 data-gathering period as opposed to the mid-20th century data-sampling period used in the 1960 map. In 2003, a preliminary draft of a new USDA map was produced by the American Horticultural Society (AHS), compiled by Meteorological Evaluation Services Co., Inc. of Amityville, NY, using temperature data collected from July 1986 to March 2002. This was a period of warmer winters than the 1974-1986 period, especially in the eastern U.S.A., and thus the 2003 map placed many areas approximately a half-zone higher (warmer) than the 1990 map had. Many have noted that the map seemed to have drifted closer to the original 1960 map in its overall zone-delineations."

So the revision which is "proof" of global warming to some, turns out to be nothing more than a superseding of the cold 1970's data from the database. Way too much global warming "proof" seems to turn on the assertion, "well, it wasn't that way when I was young!". A human lifetime and human memory are not to be trusted as reliable measuring sticks of the world.

Chachy said...

So the 1990 map was slightly anonymously cold. I buy that.

However, this:

Way too much global warming "proof" seems to turn on the assertion, "well, it wasn't that way when I was young!". A human lifetime and human memory are not to be trusted as reliable measuring sticks of the world."

is a peculiar statement. The scientific concensus around global warming is not based on anecdote; it's about as empirically-based as anything can get. Whereas much anti-theory-of-global warming commentary, such as this pack of lies from George Will (see here for the debunking) tends to use selective data and arbitrary timeframes ("the world got colder from 1998-2002! it's all a hoax!") - essentially dressing up anecdotal arguments with a pseudo-scientific veneer.

bruce said...

Andrew, global warming deniers like you will pay one day for the damage that your denial of the facts and obstruction is causing the world. Global warming denial is akin to holocaust denial, except this time the Holocaust is going to happen once the world changes and whole populations are wiped out by GW, and you are denying that.

Andrew said...

bruce:

If AGW is true and will cause dire catastrophes, mere cuts of emissions to 50% of 2005 levels by 2050 are simply going to slow its pace of occurance, eventually, not stop or reverse it.

If AGW advocates really believed what they were selling, they'd be campaigning to end all fossil fuel carbon use worldwide within the next 5 years.

Since they are not, I think we are free to speculate that other motives are behind AGW advocates position, and to dispute the reality of the claims.

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