What Does the Future Hold?
You would think that climate zone maps would represent only the highest standards of objectivity. Instead, the process of updating the 1990 USDA Hardiness Zone Map has taken on a political component as the White House has apparently stifled any update that would support those who claim we are experiencing global warming. The controversy has not stopped other organizations from issuing updates that show a marked northward movement in the hardiness zones. Hopefully, the recent Intergovernmental Panel on Climate Change report statement that, "Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global mean sea level," will lead the debate in a more positive direction and the adoption of an update to the USDA Hardiness Zone Map that does reflect the current warming trend. It should be noted that the USDA's Agricultural Research Service (ARS) has initiated a project to revise the 1990 USDA Hardiness Zone Map using data from 1971 - 2000 and to issue a new version in 2008 (see the commentary in freerepublic.com).
As a gardener in Central Florida, I'm confused and concerned. Are the recent changes in the weather in this state reliable predictors of a long term warming trend? If you look at the chart below from the National Climatic Data Center, which shows a marked warming trend since 1980
or the most recent hardiness zone map from the National Arbor Day Foundation where Zone 10 is shown moving North into Central Florida:
there is a clear implication that we are in for warmer weather for the next few years. But how long will it last? Can we start planting Plumeria in the front yards of Central Florida with little worry of frost or even leaf drop due to cold weather? As a resident of the Tampa Bay area can I assume we will be in Zone 10 for at least the next decade or even 25 years?
The chart above would favor a "yes" answer. We are definitely experiencing a pronounced upward spike in temperature patterns and it is unlikely we will see a dramatic drop any time soon. But what if you take an even longer term view? Instead of going back to 1880 as with the chart above, what if we go back a thousand years? It would appear that the answer is the same - yes we are in a period of global warming and it may be just the beginning of an era of above average temperatures.
What to do? I'm not really sure . But I do know that any decisions about which plants will thrive in my yard pale in comparison to the question of whether global warming has lead to the prolonged drought in Australia, the recent devastating hurricanes that have tore through Florida and the rest of the Gulf Coast, and the disappearance of active coral reefs around the globe. I may be able to plant a Plumeria in my front yard and not worry about it being killed by frost, but that may be "cold comfort" if the tree is soon blown away in a hurricane.