Error bars are automatically offset. they look correct just the error bar for any point should be located at the point before it

scatter(t,d40avg)
hold on
%plot(t,trend40)
errorbar(d40avg,d40std)

hold off

Answer 1

[Daniel Pollard]

The scatter plot is

plot(t, d40avg).

The Error bar plot is

plot(d40avg, d40std).

At first glance it may look like the error bars are higher than you want, but actually they're further to the right. Instead, use

plot(t, d40avg, d40std)

to plot your error bars.

[Liam Williams]

Thank you very much, your quick reply was very helpful.