Global Warming (statistics)

Could anybody help me(Crying)
I have statistical data about temperature from 1940 (for exact place). How can I use them to accept or reject the hypothesis about global warming?
I can calculate mean and standard deviation...
What should I take as the population? What is for the sample? (Thinking)

Thanks and I'm really appreciated for any hints

1. Write down your null and alternate hypothesis.
2. From the problem, figure out the appropriate test statistic
3. Figure out the rejection region
4. Carry out your test and determine whether you should reject the null hypothesis in favour of the null hypothesis or fail to reject it.

Thank you.