Daily Climate: As winter retreats northward across the nation, gardeners are cleaning tools and turning attention to spring planting. But climate change is adding a new wrinkle, and now a standard reference – the U.S. Department of Agriculture’s Plant Hardiness Zone Map – is about to make very clear how much rising temperatures have shifted planting zones northward. Hopefully the new map will clear up a lot of confusion about what’s happening to the climate. – Charlie Nardozzi, National …