ECMWF have many public datasets (for example the ERA-interim global reanalysis dataset and a few CAMS datsets) that can be accessed programatically. There are API:s for a bunch of languages but not for R.
Maybe something for the rOpenSci community? The Python API seems well worked through, so maybe somebody here with Python knowledge that could port that to R?
The CAMS datasets have a bit restrictive terms today, but I heard they will get less restrictive sometime soon.