pygmt continues to provide annoying errors about GMT_COMPATIBILITY. These can arise in many circumstances (such as in jupyter notebooks), but here is the easiest one:
In [1]: import pygmt
In [2]: exit
pygmt-session [ERROR]: GMT_COMPATIBILITY: Expects values from 6 to 6; reset to 6.
> gmt --version
6.0.0
> brew info gmt
gmt: stable 6.0.0 (bottled), HEAD
Tools for manipulating and plotting geographic and Cartesian data
https://www.generic-mapping-tools.org/
/usr/local/Cellar/gmt/6.0.0_5 (1,584 files, 150.6MB) *
OS: macos
pygmt: v0.1 (installed via pypi)
gmt: installed by brew (v. 6.0.0_5)
python: 3.7.7