Like with pretty much all of jQuery, scollLeft() is a function, not a variable, easily indicated by the parenthesis, so giving it a value means nothing.
It took only a few seconds to look at the documentation to see that scollLeft takes a value, so yes, you can scroll left, by giving it the value you want it to be at. And given that, it should work with animate() (read the animate documentation to be sure).
curPos = Number($(window).scrollLeft());
$(window).scrollLeft(curPost + 30);
I'm not sure what format scollLeft returns, so if its not a number, you'll have to do a substring or something similar to get what you want.