The MWE below shows that the solution at How can I change the font family in pgfplots? does not cover all the cases. The digits in the plot itself and the subscript in math mode in the title need further attention.
\documentclass{standalone}
\usepackage{tikz,pgfplots}
\usepackage{pgfplotstable}
%deal with warning message in log
\pgfplotsset{compat=1.8}
\usepackage{helvet}
\usepackage[eulergreek]{sansmath}
\pgfplotsset{
tick label style = {font=\sansmath\sffamily},
every axis label = {font=\sansmath\sffamily},
legend style = {font=\sansmath\sffamily},
label style = {font=\sansmath\sffamily}
}
\pgfplotstableread[col sep=comma]{
name, footprint
Google search, 0.2
Movie download, 20
}\carbonfootprints
\begin{document}
\begin{tikzpicture}[font=\sffamily]
\begin{axis}[
xbar, xmin=0,
tick style={draw=none},
width=8cm, height=3cm,
title={Estimated carbon footprint, g CO${}_2$},
enlarge y limits=0.3,
ytick=data,
yticklabel style={align=right},
yticklabels={
2. Google search,
1. Movie download
},
nodes near coords,
nodes near coords align={horizontal},
]
\addplot [fill=red] table [x=footprint, y expr=\coordindex]
{\carbonfootprints};
\end{axis}
\end{tikzpicture}
\end{document}