Extra space added in table with multi-rows and columns

Question

I am working with a table with multi-rows and headers. The problem is when I run it, extra space is added both between rows and at the end of the last column.

\documentclass{article}         
\usepackage{geometry}                       
\geometry{a4paper}                              

\usepackage{array}
\usepackage{ragged2e}
\newcolumntype{P}[1]{>{\RaggedRight\hspace{0pt}}p{#1}}
\newcolumntype{R}[1]{>{\raggedleft\arraybackslash}p{#1}}
\newcolumntype{C}[1]{>{\centering\arraybackslash}p{#1}}
\newcommand{\head}[1]{\textsf{\textbf{#1}}}

\usepackage{tabulary}

\usepackage{booktabs}
\usepackage{multirow}               % Allows rows in tables to be combined.


\usepackage{tabulary}

\begin{document}
\begin{table*}
\caption{Summary of studies examining MENA or OPEC oil export revenues under climate policies}
    \begin{tabular}{@{}C{2.0cm}C{2.0cm}P{2.0cm}P{3.0cm}C{1.0cm}C{1.0cm}@{}}
\toprule
\ \head{Study} & \head{Time horizon} & \multicolumn{1}{c}{\head{Climate policies}} & \head{\centering {Uncertainties tested}} & \multicolumn{2}{c}{\head{Impact on oil export revenue}} \\
\midrule
\ \multirow{4}{2.0cm}{ABC} & \multirow{4}{2.0cm}{Results: 2025, 2050; Model: 2100} & \multirow{4}{2.0cm}{550 ppm \& 650 ppm GHG stabilization} & \multicolumn{3}{c}{\head{Middle East \& Turkey region versus the Baseline}} \\
\ & & & & 2025 & 2050 \\
\ & & & 550 ppm & -10\% & -20\% \\
\ & & & 650 ppm & -25\% & -35\% \\  
\midrule
\ \multirow{2}{2.0cm}{CEF} & \multirow{2}{2.0cm}{2030} & \multirow{2}{2.0cm}{Global carbon taxes} & \multicolumn{3}{c}{\head{OPEC wealth versus no carbon tax}} \\
\ & & & Carbon tax (\$50/TC -- \$2500/TC) & -3\% & -63\% \\

    \bottomrule
\end{tabular}
\end{table*}

\end{document}

Answer 1

You don't need the \␣ commands (backslash + space) at the beginning of each line. If you remove them, your table displays as I think you intended.

This gets rid of the vertical space, but upon closer look at the table, I'm not actually very sure how you want the table to be structured. Is "Middle East ... Baseline" a header? Or the contents of a cell? Or perhaps the header in a sort of sub-table?

I also removed the duplicate \usepackage{tabulary} you had, and commented out the other call to tabulary, since it doesn't seem to have any impact on the output. I removed the \centering on the cell reading "Untested certainties" as well (since it doesn't change the output, and you can specify that that column should be centered in the table definition).

\documentclass{article}         
\usepackage{geometry}                       
\geometry{a4paper}                              

\usepackage{array}
\usepackage{ragged2e}
\newcolumntype{P}[1]{>{\RaggedRight\hspace{0pt}}p{#1}}
\newcolumntype{R}[1]{>{\raggedleft\arraybackslash}p{#1}}
\newcolumntype{C}[1]{>{\centering\arraybackslash}p{#1}}
\newcommand{\head}[1]{\textsf{\textbf{#1}}}

% \usepackage{tabulary}

\usepackage{booktabs}
\usepackage{multirow}               % Allows rows in tables to be combined.

\begin{document}
  \begin{table*}
  \caption{Summary of studies examining MENA or OPEC oil export revenues under climate policies}
    \begin{tabular}{@{}C{2.0cm}C{2.0cm}P{2.0cm}P{3.0cm}C{1.0cm}C{1.0cm}@{}}
    \toprule
    \head{Study} & \head{Time horizon} & \multicolumn{1}{c}{\head{Climate policies}} & \head{Uncertainties tested} & \multicolumn{2}{c}{\head{Impact on oil export revenue}} \\
    \midrule
    \multirow{4}{2.0cm}{ABC} & \multirow{4}{2.0cm}{Results: 2025, 2050; Model: 2100} & \multirow{4}{2.0cm}{550 ppm \& 650 ppm GHG stabilization} & \multicolumn{3}{c}{\head{Middle East \& Turke\newline region versus the Baseline}} \\
    & & & & 2025 & 2050 \\
    & & & 550 ppm & -10\% & -20\% \\
    & & & 650 ppm & -25\% & -35\% \\  
    \midrule
    \multirow{2}{2.0cm}{CEF} & \multirow{2}{2.0cm}{2030} & \multirow{2}{2.0cm}{Global carbon taxes} & \multicolumn{3}{c}{\head{OPEC wealth versus no carbon tax}} \\
    & & & Carbon tax (\$50/TC -- \$2500/TC) & -3\% & -63\% \\
    \bottomrule
    \end{tabular}
  \end{table*}

\end{document}