Ok all you Inconvenient Truth groupies out there answer me this - is this the first time the earth has heated up?

If you take the above Reconstructed Temperature graph as gospel then the answer is undoubtedly yes - (Reconstructed means that the data has come from analysis of tree rings and ice core samples). But if you take another graph of the first 1million years of earth's existence then you will notice that heating and cooling looks quite similar to the ebb and flow of our tides.

So while the USDA Zones have all been changed in accordance with the increased earth temperatures we may see that they actually revert back within the next few decades.