If you question the numbers, ask the plants

The 2012 Plant Hardiness Zone Map unveiled by the US Department of Agriculture this week shows average annual extreme minimum temperatures based on data from 1976-2005.This version is modified to use the same colour code as 1990. See the end of the entry for original image and link to USDA interactive map. Credit: US Department of Agriculture/Friend of the Earth

The 2012 Plant Hardiness Zone Map unveiled by the US Department of Agriculture this week shows average annual extreme minimum temperatures based on data from 1976-2005.This version is modified to use the same colour code as 1990. See the end of the entry for original image and link to USDA interactive map. Credit: US Department of Agriculture/Friend of the Earth

You may have heard of dandelion clocks, but have you ever thought of looking at plants to check the temperature? It may not give you a precise reading, but changes in where plants can live in the US and when they grow in China have clearly demonstrated global warming this month. They reinforce the recently reported worldwide average surface temperature for 2011, providing a real world example of the climate change shown in scientists’ graphs.

Much of the US was one 5°F (2.8°C) half-zone colder in the 1990 Plant Hardiness Zone Map compared to the latest version. Credit: US Department of Agriculture

Much of the US was one 5°F (2.8°C) half-zone colder in the 1990 Plant Hardiness Zone Map compared to the latest version. Credit: US Department of Agriculture

On Wednesday, the US Department of Agriculture (USDA) unveiled its latest map of planting zones, which has been redrawn to reflect warming seen since the last version was published in 1990. The Plant Hardiness Zone Map shows zones representing average annual extreme minimum temperatures. The old map was based on temperatures from 1974-1986, but updating it to include temperatures from 1976-2005 has shifted many zone boundaries. Though that’s in part due to new technology and better weather data, across much of the US the map is one 5°F (2.8°C) half-zone warmer.

And while the USDA says that the map is “not a good instrument” to assess climate change, David Wolfe, professor of plant and soil ecology in Cornell University’s Department of Horticulture says it’s being too cautious. “At a time when the ‘normal’ climate has become a moving target, this revision of the hardiness zone map gives us a clear picture of the ‘new normal,’ and will be an essential tool for gardeners, farmers, and natural resource managers as they begin to cope with rapid climate change,” he told Associated Press reporter Seth Borenstein.

Earlier springs, later autumns

The cycles in China during the 1960s (blue line) and a 1998-2007 (red line). Dashed lines indicate temperature thresholds for the 24 solar terms, which have risen during this period, making spring events happen earlier and autumn events later. Credit: Science China Press

The cycles in China during the 1960s (blue line) and a 1998-2007 (red line). Dashed lines indicate temperature thresholds for the 24 solar terms, which have risen during this period, making spring events happen earlier and autumn events later. Credit: Science China Press

Meanwhile, Chinese researchers described a similarly notable shift in phases in the seasonal cycle of crop growth in their country between 1960 and 2008. Historically the phases have been linked to 24 ancient solar terms timed by the position of the stars, like “Waking of Insects”, “White Dew”, and “Grain Rain”, and have been used to to plan agricultural activity. In a research paper in the January issue of the Chinese Science Bulletin Qian Cheng from the Chinese Academy of Sciences in Beijing and colleagues tracked the changes in the climate conditions each term is traditionally supposed to represent.

Qian’s team found that over this period the timings of springtime events have advanced by 6-15 days and Autumn events are now 5-6 days later. From 1998-2007 there were less than half as many days of conditions relating to the coldest terms as during the 1960s, and almost twice as many of the warmest phases. “The implication of the present study for agriculture is that under the climate change of earlier timings of the Waking of Insects, Pure Brightness, Grain Full, and Grain in Ear almost everywhere in China, agricultural activities need to be brought forward by several days,” the researchers write.

The US National Oceanic and Atmospheric Administration says that 2011 tied with 1997 as the 11th warmest year since records began in 1880, and was the warmest La Niña year. Credit: NOAA

The US National Oceanic and Atmospheric Administration says that 2011 tied with 1997 as the 11th warmest year since records began in 1880, and was the warmest La Niña year. Credit: NOAA

Thanks to the cool phase of a global climate cycle, the warming underlying these happenings took a pause last year. This month NASA ranked 2011 as the 11th warmest year on record, and the US National Oceanographic and Atmospheric Administration (NOAA) ranked it as the 9th warmest. After 2010 had been the warmest year in these organisations’ records the world was visited by La Niña, the colder sister of, and part of the same climate pattern as, the warming El Niño. It was the warmest La Niña yet, however, half a degree Celsius higher than the average temperature for the 20th century.

Despite this, I still heard British politician Nigel Lawson, who served as chancellor under Margaret Thatcher, arguing that the 2011 data show that there’s been no warming this century on the radio this week. This is a common argument used by those who argue that the climate isn’t warming, that works because they’re looking at short time periods, as the graph below shows.

It's possible to see cooling trends in the record of global temperatures if you focus on short time periods, but the record as a whole reveals steady warming. Credit: Skeptical Science
It’s possible to see cooling trends in the record of global temperatures if you focus on short time periods, but the record as a whole reveals steady warming. Credit: Skeptical Science

It’s true that the temperature graphs used to show warming aren’t always easy to understand. But the temperature changes are having clear effects on the natural world, like where and when plants grow. These are effects that many of us experience directly – and provide a powerful demonstration of global warming beyond what tables and charts can achieve.

This is the 2012 Plant Hardiness Zone Map from the US Department of Agriculture with revised half zone colour coding. Credit: US Department of Agriculture
This is the 2012 Plant Hardiness Zone Map from the US Department of Agriculture with revised half zone colour coding. Credit: US Department of Agriculture

For the full interactive Plant Hardiness Zone map visit: http://planthardiness.ars.usda.gov/PHZMWeb/

8 Responses to “If you question the numbers, ask the plants”

  1. climatebites Says:

    Great map and post. This one has “broken through” with people who don’t usually talk about climate, because everybody who gardens, even a bit, has to pay attention to hardiness zones.

    I heard it over dinner last night.

    • andyextance Says:

      Thanks Tom. Were they scientist friends, or people who otherwise wouldn’t be talking about climate? The trend bit at the end was inspired by your “dog-walking” post.

  2. climatebites Says:

    P.S. I’ve posted your headline as a new bite at climatebites.org. — with credit and a link back to here of course. nice one!

  3. GDConklin Says:

    real skeptics don’t question warming, we question the cause of warming. the plants will tell you to buy 3 more SUVs and crank up the CO2 because 390 pmm is just a teaser for them (plants “eat” CO2, at 1200 ppm they’re very happy). the rate of warming since the last ice age is very stable and not “accelerating” and certainly not linked in any major way to CO2. real skeptics will tell you that humans impact on the climate/temperature is real, and it’s small enough that it defies quantifiable measurement. anyone who claims they can determine the temperature to +/- .001 degrees C is very full of him/herself. even more so if they claim they can predict that temp 10, 20, 50, 10 years in the future. calm down, the end of the world will be televised!

    • andyextance Says:

      Hi GDConklin,

      Thanks for the comment. The most interesting part, I think, is where you question the cause of the temperature rises. Can I ask why you do?

      Otherwise, I’m a bit confused. First you say that you don’t question the warming, then you say “the rate of warming since the last ice age is very stable and not accelerating”. You say you question the link between CO2 and temperature – and then you comment on a post about how where plants can grow has already changed due to TEMPERATURE change by talking how they respond to CO2. You talk about how plants are happy at up to 1200 ppm CO2 – but the Earth hasn’t seen this level in at least 800,000 years! See the video below (the end is most relevant):

      You talk about determining temperature to +/- .001°C – but you’ll note the data in NASA’s Global Annual Mean Surface Air Temperature Change table are 10 times less precise than that:

      http://data.giss.nasa.gov/gistemp/graphs_v3/Fig.A2.txt

      And no-one is predicting the end of the world – just a harder life that could be avoided.

      Finally, can I ask that if you post here with claims like this again, you include links to sources that back up your points? I’m not against debate, but it must have a grounding in fact.

  4. Tony William Powell Says:

    Hi,

    A great post there.

    I run a UK based Phenology blog which I hope may be of some interest to you. Of course, as you would clearly realise, plants are only one of the climate change indicators and the deeper you look, evidence of change can be found in all manner of things.

    Kind Regards

    Tony Powell

  5. Warming brings home the value of a meal « Simple Climate Says:

    […] warming world has already noticeably changed plant growing conditions, for example shifting the regions they are suited to grow in the US. In January, the US Department […]


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