When Might We Be Able To Grow Oranges In Atlanta?

As temperatures rise, the areas in which specific crops will grow will shift. When will they shift enough for us to be able to grow oranges in Atlanta?

Hardiness Zone

To attempt to answer this, I first needed a metric for 'will a crop grow here?'. The one that I selected is the hardiness zone. To calculate it, I used a method similar to the one roughly described here:
  • take the minimum daily temperature for each year (Berkeley Earth for historical and CMIP5 for future)
  • get the average of those minimums for each decade
  • combine three decades into a group of climate normals
This yields the following result with RCP85 assumptions:

how will global warming affect crops?
RCP85 Hardiness Zones

Doing the same thing with RCP45 assumptions yields the following:

RCP45 Hardiness Zones
The rest of this post will use RCP85 assumptions. For reference:
  • RCP85 means roughly that we keep growing our overall emissions like we did for the first part of the 21st century
  • RCP45 means roughly that our overall emissions decline steadily after 2040

Oranges

Oranges can apparently grow in zones 9 to 11. Converting the above plot into that (red means can't grow):


This gives us a rough estimate of where oranges might be able to grow in each decade. Since temperature isn't all that matters, another criteria to add is precipitation. From the link above, oranges like 40 to 45 inches of water per year and can tolerate some deviation from that. Given that this is a really rough estimate, I went ahead and used 30 to 60 inches per year. Adding that to the previous run yields the following:



I don't know of any way to project how total available sunlight will vary going forward so I'm stopping at this point. According to this, though, the 2090 time frame is when it might be warm enough to grow oranges well in Atlanta. Recalling that '2090' here is the 30 year average preceding 2090, it actually might be fine in the 2060's. Maybe interesting to note is that it looks like it might get too hot to grow them in southern Florida in the next couple of decades.

Will It Ever Be Too Hot For Peaches In Georgia?

You can do this with other fruits once you have the hardiness zone projections. For example...it looks like peaches can grow in zones 4 to 8 and prefer 6 to 7. Doing the same thing I did above with hardiness zones for oranges (but not including precipitation) yields the following:


So it looks like sometime in the 2080-2090 timeframe, it might be too hot for peaches in Georgia. Of course we can probably genetically engineer different crops, use new farming techniques, etc., to get around this, but it was fun to look at.

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