## Class on January 25 2018

Rob led a Google Spreadsheets work assignment for students to perform during class time.

Skills included:
• accessing on-line water level data
• selecting water level data
• exporting Comma-Separated Values (CSV) data
• basic plotting
• trend-line fitting
• detrending data
• plot histogram of residuals
• calculate standard deviation

Rob motivated students to gain some initial experience with accessing online data sources and analyzing them with popular tools for analysis through the following tasks:

Task 1: Get Newport Sea Level Data

Go to https://tidesandcurrents.noaa.gov/waterlevels.html?id=8452660

Sea Level for Newport

Change date range From: Jan 29, 2000 To: Jan 30, 2017
Choose Meters for units
Change the Datum to MSL (Mean Sea Level)
Click on the Plot button

An error is returned:

Error: Range Limit Exceeded: The size limit for data retrieval for this product is 31 days

Choose the Month interval and request the whole monthly range (June 1, 1938 to today’s date)
Export the data to CSV format (comma separated values)
Save the file on a local hard drive (consider creating a project folder for all week 1 analyses)

Task 2: Analyze the Newport Sea Level Data

Go to google.com and choose the Google Apps Icon in the upper-right.
Choose the Sheets app that comes up as an option:

Choose File-Open and then Upload (drag your CSV file onto the drop location provided)
Insert a new column B between what initially is the first two columns in the CSV file
In cell B, add a formula for a decimal representation of the year:  (=A2+C2/12â€¬)
Replicate a relative formula in column B for all rows with data in the spreadsheet
Select column A (from the column header), hold Command key (or CNTL), and select column G (the MSL data)
Once selected, Insert a Chart with the data.
Investigate the Chart Types tab (select a Scatter chart)
Choose the Customization tab and scroll down to the bottom to add a Trendline of type Linear
Choose the Use equation option for the Label options under the Trendline options
Insert the Chart into the spreadsheet

RESULTS:

Note the equation. As of January 30, 2017, the cumulative trend line equation  for Oct 1930 through Jan 2017: y = 2.737E-3 * x - 4.919

Evaluate the trend line: Since the units are in meters and the slope of the trend line is 2.737E-3, the trend has been an increase in MSL by .002737 meters (2.737 mm) per year from 1938 to 2017.

Investigate based on instincts to see if instincts are good or not. My instinct suggests sea level rise has been faster of late. Redoing the chart with just Feb 2007 through today the last ten years, provides a new equation:

Feb 2007 through Jan 2017: y = 3.37E-3 * x - 6.18

which does have more slope (a 3.37 mm increase per year).

3. Now repeat the process for Providence MSL data:

Go to https://tidesandcurrents.noaa.gov/waterlevels.html?id=8454000

Note the equation. With monthly data from Jun 1938 to Jan 2017, the cumulative trend line equation is y = 2.254E-3 * x - 4.482

Insert the Chart

Evaluate the trend line: Since the units are in meters and the slope of the trend line is 2.254E-3, the trend has been an increase in MSL by .002254 meters (2.254 mm) per year from 1938 to 2017.

Investigate based on instincts to see if instincts are good or not. My instinct suggests sea level rise has been faster of late. Redoing the chart with just Jan 31, 2007 through today the last ten years, provides a new equation:

y = 2.114E-3 * x - 4.183

which has less slope (instinct fails me here)!

4. Repeat the process for Juneau, Alaska MSL data:

https://tidesandcurrents.noaa.gov/waterlevels.html?id=9452210

Note the equation. With monthly data from Jun 1936 to Jan 2017, the cumulative trend line equation is y = -0.013E-3 * x + 26.312

(decrease of .013 mm/year)

Redoing the chart with just Feb 2007 through Jan 2017 the last ten years, provides a new equation:

y = -9.622E-3 * x + 19.327

(decrease of 9.622 mm/year)

So sea level seems to be decreasing faster of late.

AH HAs: Seems sea level change over time is affected by global sea level changes but is also affected by local changes to land mass elevation. As glaciers have melted since the last ice age, land has been rebounding upwards since when it was pushed down from when it was under the weight. But, land is also connected so there are levers created whereby other land can fall from the uplift of connected land.

Also, the data used is a monthly value for each month. Sea level varies by tides and other factors on a cyclical basis that is not necessarily tied to monthly values - so it is important to see how the Monthly values have been determined.