\documentclass[10pt]{article}

\usepackage{fullpage}
\usepackage{setspace}
\usepackage{parskip}
\usepackage{titlesec}
\usepackage[section]{placeins}
\usepackage{xcolor}
\usepackage{breakcites}
\usepackage{lineno}
\usepackage{hyphenat}





\PassOptionsToPackage{hyphens}{url}
\usepackage[colorlinks = true,
            linkcolor = blue,
            urlcolor  = blue,
            citecolor = blue,
            anchorcolor = blue]{hyperref}
\usepackage{etoolbox}
\makeatletter
\patchcmd\@combinedblfloats{\box\@outputbox}{\unvbox\@outputbox}{}{%
  \errmessage{\noexpand\@combinedblfloats could not be patched}%
}%
\makeatother


\usepackage{natbib}




\renewenvironment{abstract}
  {{\bfseries\noindent{\abstractname}\par\nobreak}\footnotesize}
  {\bigskip}

\titlespacing{\section}{0pt}{*3}{*1}
\titlespacing{\subsection}{0pt}{*2}{*0.5}
\titlespacing{\subsubsection}{0pt}{*1.5}{0pt}


\usepackage{authblk}


\usepackage{graphicx}
\usepackage[space]{grffile}
\usepackage{latexsym}
\usepackage{textcomp}
\usepackage{longtable}
\usepackage{tabulary}
\usepackage{booktabs,array,multirow}
\usepackage{amsfonts,amsmath,amssymb}
\providecommand\citet{\cite}
\providecommand\citep{\cite}
\providecommand\citealt{\cite}
% You can conditionalize code for latexml or normal latex using this.
\newif\iflatexml\latexmlfalse
\providecommand{\tightlist}{\setlength{\itemsep}{0pt}\setlength{\parskip}{0pt}}%

\AtBeginDocument{\DeclareGraphicsExtensions{.pdf,.PDF,.eps,.EPS,.png,.PNG,.tif,.TIF,.jpg,.JPG,.jpeg,.JPEG}}

\usepackage[utf8]{inputenc}
\usepackage[english]{babel}



\usepackage{float}








\begin{document}

\title{LGM paleoclimate constraints inform cloud parameterizations and
equilibrium climate sensitivity in CESM2}



\author[1]{Jiang Zhu}%
\author[2]{Bette L Otto-Bliesner}%
\author[2]{Esther C. Brady}%
\author[3]{Christopher Poulsen}%
\author[4]{Jonah K Shaw}%
\author[5]{Jennifer E Kay}%
\affil[1]{National Center for Atmospheric Research}%
\affil[2]{National Center for Atmospheric Research (UCAR)}%
\affil[3]{University of Michigan-Ann Arbor}%
\affil[4]{University of Colorado, Boulder}%
\affil[5]{University of Colorado Boulder}%


\vspace{-1em}



  
  \date{May 21, 2024}


\begingroup
\let\center\flushleft
\let\endcenter\endflushleft
\maketitle
\endgroup





\selectlanguage{english}
\begin{abstract}
The Community Earth System Model version 2 (CESM2) simulates a high
equilibrium climate sensitivity (ECS \textgreater{} 5 degC) and a Last
Glacial Maximum (LGM) that is substantially colder than proxy
temperatures. In this study, we use the LGM global temperature from
geological proxies as a benchmark to examine the role of cloud
parameterizations in simulating the LGM cooling in CESM2. Through
substituting different versions of cloud schemes in the atmosphere
model, we attribute the excessive LGM cooling to the new schemes of
cloud microphysics and ice nucleation. Further exploration suggests that
removing an inappropriate limiter on cloud ice number (NoNimax) and
decreasing the time-step size (substepping) in cloud microphysics
largely eliminate the excessive LGM cooling. NoNimax produces a more
physically consistent treatment of mixed-phase clouds, which leads to
more cloud ice content and a weaker shortwave cloud feedback over
mid-to-high latitudes and the Southern Hemisphere subtropics.
Microphysical substepping further weakens the shortwave cloud feedback.
Based on NoNimax and microphysical substepping, we have developed a
paleoclimate-calibrated CESM2 (PaleoCalibr), which simulates well the
observed 20th century warming and spatial characteristics of key cloud
and climate variables. PaleoCalibr has a lower ECS (\textasciitilde{}4
degC) and a 20\% weaker aerosol-cloud interaction than CESM2.
PaleoCalibr represents a physically and numerically better treatment of
cloud microphysics and, we believe, is a more appropriate tool than
CESM2 in climate change studies, especially when a large climate forcing
is involved. Our study highlights the unique value of paleoclimate
constraints in informing the cloud parameterizations and ultimately the
future climate projection.%
\end{abstract}%



\sloppy




\selectlanguage{english}
\FloatBarrier
\end{document}

