We will investigate trends in the temperature and CO₂ data sets. Clearly the CO₂ data shows a long-term trend, although a seasonal variation can also be seen. The long-term trend in temperature record is less obvious. All function calls and plotting requested below should be done in your main script assign1.m. You will write a function getstats.m that will return a running mean and a measure of seasonal variability of CO₂. The function should take as input the CO₂ record, and window length IN THAT ORDER, and return as output the running mean and seasonal variability IN THAT ORDER. Details:

1. Figure will contain 3 subplots. Plot the CO₂ data vs. time using green symbols in the top subplot.

2. Use your running mean function from the week 8 lab to calculate a running annual mean (i.e., a running yearly average) for the CO₂ data (your mean will be over a period that is slightly longer or shorter than a year - why?). Plot your running mean on top of the original data using a black line.

3. We can estimate the seasonal variability in CO₂ measurements within each year by a variabilty of methods. Two good choices would be to use either the standard deviation or the peak-to-peak variations CO₂ in a year. This is easy to do now that you have your running mean function. Modify the running mean function to return both the running mean and your choice of measure (peak-to-peak or standard deviation) of seasonal "variability". Rename your modi?ed function getstats.m

4. Plot your seasonal variability in CO₂ versus time in the second subplot. Label your plot clearly. (You can include more than one way of estimating seasonal variability if you like.) Calculate the mean seasonal CO₂ variability for the 1960-2008 period. Hint: The MATLAB function isnan is helpful.

5. Now, use your annual running mean to calculate the annual change (e.g., from January to January of successive years) in CO₂ concentration. (Hint: logical indexing into ?elds of your structure co₂ is useful.) Plot your results in the third subplot. Calculate the average annual change for the 1960-2010 period.

6. Answer the following questions using your results:

(a) For every year that you have an estimate of the annual change in CO₂, is CO₂ increasing? How did you decide this?