Over the past 30 years, researchers have used satellite images, among other techniques, to accurately measure the extent of Arctic sea ice. The graph below plots the the area of the Arctic sea covered by sea ice in September, the month when Arctic sea ice is at its minimum. In September 2007, the Northwest Passage was opened for the first time in recorded history. Shown below is a graph of the September minimum sea ice coverage from 1979 to 2010.

Question: What is the rate of decline of summer minimum Arctic sea ice coverage from 1979 to 2010?

Open up the Arctic Ice Cover Measuring tool. Beginning in 1979, grab the slider bar on the right and slowly scroll through to 2010. Then, use your mouse to click and fill in the area of the Polar Ice Cap.

While you are filling in the area, pay attention to the area check at the bottom right to see how close you came to the actual area of Arctic Sea Ice cover. Select "Show Graph" to see your measurement on a plot. Repeat this process for at least four other years between 1979 and 2010.

Once you have taken your final measurement, select "View Graph" and take note of the slope of the line of best fit drawn on the plot. Your plot should resemble the image above.