Thread: Greenland retained 99.7% of its ice mass in 20th Century!!!

Greenland retained 99.7% of its ice mass in 20th Century!!!


Naturally, the Real Clear Science headline actually read…


Greenland Lost 9 Trillion Tons of Ice in Century



Which sounds even more serious than the original headline…






One would think that the fact that 99.7% of Greenland’s ice sheet survived the 20th Century might just be more scientifically relevant than a 0.3% loss… But I guess that doesn’t make for a very dramatic headline.



Here’s the math…

First I converted 9 trillion tons to metric tonnes.
9,000,000,000,000 tons = 8,164,662,660,000 tonnes

Then I converted tonnes to gigatonnes.
8,164,662,660,000 tonnes = 8,165 gigatonnes
Then I converted gigatonnes of ice to cubic kilometers, assuming 1 Gt = 1 km³.
8,165 Gt ~ 8,165 km³
Note: This conversion is inexact because ice is slightly less dense than water. But it is close enough for this exercise.

Now that I roughly knew the volume of ice loss during the 20th century, I needed to know how much ice volume was still in place. I chose to rely on the USGS and their figure of 2,600,000 km³.
So now I could calculate the percentage of ice volume which survived the 20th century…

The ice volume at the onset of the 20th century should be…
2,600,000 km³ + 8,165 km³ = 2,608,165 km³
Converting to percentage surviving the 20th century…
2,600,000 km³ / 2,608,165 km³ = 0.997 = 99.7%

To put the math into perspective, I’m going to actually rely on the SkepScibots…
1 gigatonne of ice is big… Much bigger than an Olympic sized swimming pool.

So, throughout the 20th century, Greenland lost about 8,165 gigatonne ice cubes. 8,165 km³ equates to a 20 km x 20 km x 20 km cube of ice (3√ 8,165 = 20.136565). That would be one big@$$ cube of ice!


However, it’s not even a tiny nick when spread out over roughly 1.7 million square kilometers of ice surface. That works out a sheet of ice about 5 meters thick.

2,600,000 km³ / 1,700,000 km² = 1.53 km

The average thickness of the Greenland ice sheet is approximately 1.5 km (1,500 meters). 5 meters is obviously 0.3% of 1,500 meters.
Isopach map of Greenland ice sheet (Wikipedia). The “Lost Ice Cube” represents 8,165 cubic kilometers of ice.



From a thickness perspective, 5 meters looks like this…
Radar Cross Section of Greenland Ice Sheet (Source: Columbia University). Note that even with a vertical exaggeration of 75 x, 5 meters is insignificant.

The red line along the top of the cross section is approximately 5 meters thick. Here is an enlarged view…

While my math may not be exact, estimates of the volume of the Greenland ice sheet vary from 2.6 to 5.5 × 10⁶ km³. The difference between 2.6 and 5.5 million cubic kilometers of ice is quite a bit larger than 9,000 gigatonnes. For that matter, GRACE derived estimates of recent (2003-2011) ice mass balance vary widely as do the glacial isostatic adjustments…

For the analyzed period, the ice mass balance of Greenland and the corresponding GIA correction are, respectively, − 256 ± 21 Gt yr⁻¹ and − 3 ± 12 Gt yr⁻¹ (1%) for SM09, − 253 ± 23 Gt yr⁻¹ and − 6 ± 5 Gt yr⁻¹ (2%) for AW13, and − 189 ± 27 Gt yr⁻¹ and − 69 ± 19 Gt yr⁻¹(36%) for Wu10 (table 1). At the regional scale, the ice mass estimates are more dependent on the GIA correction, especially in NE Greenland where the Wu10-GIA correction is the largest portion of the signal measured by GRACE (table 1).
From Sutterley et al., 2014

With ~±10% margins of error in modern satellite measurements of glacial mass balance and GIA accounting for up to 1/3 of the reported ice mass loss, it is truly amazing that a 0.3% reduction in the Greenland ice sheet during the 20th century can be identified with such robustness [/Sarc].




http://wattsupwiththat.com/2015/12/3...-20th-century/