function [volc,solaranom,aer,forcingcotwo] = extrapforcings(v1,s1,a1,f1);
% (C) Michael Mann, 2011.
%
% extrapolate forcings out to 2100
n1=length(v1); %  out to 2012
n2=n1+88; % to to 2100
%
% project no future volcanic forcing 
volc(1:n1)=v1;
volc(n1+1:n2)=0.0;
% use persistence (of decadal mean anomaly)to extend solar forcing
solaranom(1:n1)=s1;
solaranom(n1+1:n2)=mean(s1(n1-10:n1));
% assume exponential decay of aerosol forcing during 21st century
% with a tau=60 year decay constant
tau=60.0;
aer(1:n1)=a1;
for jj=n1+1:n2;
aer(jj)=aer(n1)*exp(-(jj-n1)/tau);
end
% use linear extrapolation of CO2 forcing based on trend over past decade
forcingcotwo(1:n1)=f1;
slope=0.1*(forcingcotwo(n1)-forcingcotwo(n1-9));
for jj=n1+1:n2;
forcingcotwo(jj)=f1(n1)+slope*(jj-n1);
end
% 
%
end
















      