Creating a linear model from a Time Series

I am trying to model the overall trend of the data set globtemp from the astsa R package with a polynomial: however, I am having problems creating the liner model.

library(astsa)
library(xts)
Loading required package: zoo

Attaching package: 'zoo'
The following objects are masked from 'package:base':

as.Date, as.Date.numeric
g.temp=as.matrix(globtemp)
plot(time~temperature, ylab="Temperature", main="Global Temperature Model")
Error in eval(predvars, data, env): object 'temperature' not found

Created on 2021-10-27 by the reprex package (v2.0.1)
localhost:14261/session/satin-urial_reprex_preview.html

The xts data should work with the plot function. Try this.

library(astsa)
library(xts)

plot(globtemp, ylab = "Temperature", main = 'Global Temperature Model')

That gives me the original plot. I am trying to remove the trend; therefore, I need to create a linear model of the data. So, it needs to be written in the form of x~y.