Add average temperature line onto plot

The following code is used to plot a t2m plot and i want to add a horizontal average temperature line but not sure how

any ideas?

% combined_ERA_data_new

%% Load in the data 

data_1 = load('../data/ERA/ERA5_2_1979_1984.mat', 'data_to_save'); 
data_2 = load('../data/ERA/ERA5_2_1985_1990.mat', 'data_to_save');
data_3 = load('../data/ERA/ERA5_2_1991_2000.mat', 'data_to_save');
data_4 = load('../data/ERA/ERA5_2_2001_2010.mat', 'data_to_save');
data_5 = load('../data/ERA/ERA5_2_2011_2021.mat', 'data_to_save');

%% Combine data all

data_all = [data_1.data_to_save; data_2.data_to_save; data_3.data_to_save; data_4.data_to_save; data_5.data_to_save;];


%% Plot figure

disp('Plotting and saving a figure...');
% Make a figure
figure('units','normalized','outerposition',[0 0 1 1],'visible','on');
set(gcf,'color','w');

% Set axis font size
font_size = 12;
set(0, 'DefaultAxesFontSize', font_size);

% Plot
plot(data_all(:,1), data_all(:,2), '-r'); datetick('x')


%% Set plot details

ylabel ('T2M (degrees celcius)');
xlabel ('Time (years)');
title ('Reanalysis Dataset for T2M Data from 80.5N, to -58W, 1979-2021'); 
legend({'= T2M'},'Location','southwest');
ax = gca;
ax.FontSize = 14;

Answer 1

[Cris LaPierre]

Use the yline function.