Add line to ci.plot

Question

I've made a confidence interval plot to a simple linear regression problem using ci.plot from the HH library

observations2 <- subset(observations, year > 1994 & year < 2049)
model.seaice <- lm(seaice ~ NHtemp, data=observations2)
ci.plot(model.seaice, conf.level=0.95)

And it works really well. However, I want to add to the plot. Firstly, I'd like to join the points so I can easily follow their order in time. I tried:

plot(observations2[,'NHtemp'], observations2[,'seaice'], add="TRUE", type="b")

but it doesn't like it:

Warning messages:
1: In plot.window(...) : "add" is not a graphical parameter
2: In plot.xy(xy, type, ...) : "add" is not a graphical parameter
3: In axis(side = side, at = at, labels = labels, ...) : 

...etc

Any ideas how to add features to a ci.plot?

UPDATE

I've ended up just running with:

model.seaice <- lm(seaice ~ NHtemp, data=observations2)
plot(observations2[,'NHtemp'],observations2[,'seaice'],type="l",
 + xlab=expression(paste(Delta, ~degree~C)), 
 + ylab=expression(min.~~sea~~ice~~(italic(millions~~sqr.~~km))),
 + main="Temperature anomaly and minimum sea ice extent")
 + points(observations2[,'NHtemp'],observations2[,'seaice'],pch=21,
 + col=topo.colors(dim(observations2)[1]),bg=topo.colors(dim(observations2)[1]))
newdata = data.frame(NHtemp=seq(0,2,0.1))
conf.vals <- predict(model.seaice, newdata, interval="prediction")
lines(newdata[,'NHtemp'],conf.vals[,'fit'],col="red")
lines(newdata[,'NHtemp'],conf.vals[,'lwr'],col="red",lty=2)
lines(newdata[,'NHtemp'],conf.vals[,'upr'],col="red",lty=2)

The figure looks like this (note the dashed lines are the prediction interval rather than the conf. int. which is what I now realise I actually wanted):

What I still can't do is show a legend of the colormap (in Matlab this would be the command: colorbar). The idea is to highlight the slight hysteresis in the data. The color progresses from blue to pink as the years progress from 1995 to 2048.

Anyone know how to show the colorbar?

SOME DATA

As requested here is a subset of the data to play with:

observations2 <- structure(list(year = c(1995, 1996, 1997, 1998, 1999, 2000, 2001, 
2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009), NHtemp = c(0.314632441576551, 
0.186366426772796, 0.476974553197026, 0.60389558449144, 0.808296103505494, 
0.960909839541133, 0.755078064632368, 0.698608832025563, 0.795763098867946, 
0.929551971074, 0.978281142325487, 1.11821925610747, 1.23718650073483, 
1.19223388599054, 0.966671466003422), SHtemp = c(0.210929776358558, 
0.139817106972881, 0.21783040846463, 0.43431186700407, 0.370475749149358, 
0.255331083239238, 0.385363664392244, 0.403967011006417, 0.473766310099707, 
0.440515909854607, 0.69104778063082, 0.716519830684257, 0.678544576020567, 
0.590446589601271, 0.430452631622458), global = c(0.262781108967546, 
0.163091766872832, 0.347402480830821, 0.519103725747748, 0.589385926327418, 
0.608120461390177, 0.570220864512299, 0.551287921515984, 0.634764704483819, 
0.685033940464296, 0.834664461478146, 0.917369543395855, 0.957865538377691, 
0.891340237795898, 0.698562048812933), seaice = c(-0.79633165604255, 
-0.0484464471858699, -0.821451994832936, -0.761853932432746, 
-1.21404527404276, -1.80462439656434, -2.33021932073994, -1.62220305218969, 
-1.75453917196037, -2.32457807586636, -2.58044546640576, -2.93648428237656, 
-2.24364361423478, -2.63830194428149, -2.53740259589355)), .Names = c("year", 
"NHtemp", "SHtemp", "global", "seaice"), row.names = 137:151, class = "data.frame")

Answer 1

In addition to the problems mentioned above, the plotting of ci.plot is done in the Lattice framework (since its help page says a "trellis"-object is returned.) There are three major plotting paradigms in R and the plot command given with a numeric vector as its first argument gets you the base-graphics paradigm and this does not integrate easily with the Lattice paradigm.

You could try adding type="b" to the original plot arguments, but I cannot guarantee that will be satisfying, since doing it to the example on the help pages did not seem particularly informative. I did get the effect I was expecting ... which is not an effect I generally seek, but I think is what you asked for.