Climate Denial Crock of the Week

This figure shows the total change in accumulated mass of the Greenland ice sheet using two different methods.
Method 1 is based on monthly measurements of changes in gravity. Gravity changes as the amount of ice changes, and this can be detected by satellites (in this case the GRACE mission).
However the processing of the data from the satellites takes 2 to 3 months, and scientists at GEUS have therefore developed Method no 2: combining gravity measurements from GRACE with measurements of ice-reflection (“albedo”) it’s possible to get daily updates on the total mass change. The data on ice-reflection is retrieved from the MODIS satellite.
The grey line and grey area shows the average in the period 2003-2012 (with 95% confidence) using Method 1.
The blue dots represent the processed data sets from GRACE in 2013.
The red and blue lines uses method 2, as in the previous figure. The blue line (2013) is updated on a daily basis, based on the latest measurements of ice-reflectivity. The changes are shown in millimetres pr. month so it can be compared to Method 1.
When the lines are above zero, mass is lost. When below zero mass is accumulated.
Gravity data are from the NASA and German Aerospace Center (DLR) GRACE mission processed after Barletta et al. (2012).
The reflectivity-based mass change is based on the monthly relation between NASA MODIS MOD10A1 albedo data versus the same GRACE data (Colgan and others, in prep). The GRACE mass change is calculated using the difference of month i + 1 and month i – 1. The reflectivity-based mass change estimate is only valid from early April to September.
Albedo data processing are after Box et al. (2012).

During the last few days of the Dark Snow trip, Jason Box and I kicked around the idea of coming back in August if we did not get enough samples.  Fortunately, things worked out, that would have most likely been beyond our budget – but it would be awfully interesting to be up on the ice sheet now, as the melt season, which started slowly, seems to have gotten a second wind.  After tracking pretty closely with the record 2012 melt in the early season,  things turned cooler in late June, and fell off the pace.  In recent weeks, the melt has reasserted itself.
(above graph from Polarportal.dk)

Robert Scribbler:

A strong, late-season melt pulse continued over the Greenland ice sheet this weekend as melt covered a much greater portion of the ice sheet than is typical for this time of year. As of late July, the area of the Greenland ice sheet subject to melt had spiked to nearly 45%. Soon after, a second melt spike to around 38% followed. Over the past two weeks, melt area coverage has fluctuated between 5 and 25 percentage points above the seasonal average for this time of year, maintaining at or above the typical melt season maximum of around 25% for almost all of this time.

This late-season melt surge was driven by a switch in the polar Jet Stream. A trough which had dominated through much of summer, bringing near average temperatures and melt conditions, had eroded and by late July a broad ridge began to form. This high amplitude wave dredged warm air up from as far south as the south-eastern US, then dumped it on the west facing coast of Greenland. There, last week, a new record all time high temperature of 78.6 degrees (Fahrenheit) shattered Greenland’s previous highest temperature of 77.9 degrees.

And this record heat is beginning to have a very visible affect on the ice. Aqua satellite passes this weekend recorded a visible darkening of ice cover in the region most greatly impacted by high temperatures last week. The snow and ice cover there has taken on a sooty appearance with darker gray tendrils finding their way deep into the ice pack. At the same time, large melt lakes expanded over the region with some of these lakes measuring more than  three kilometers across.

In this first Modis shot we see a broad region of darkened, melt-pond speckled ice forming over a very large swath of Greenland’s western ice sheet:

For reference, Baffin Bay is toward the left of the image, the southern tip of Greenland, toward the bottom, and the far right frame of the image runs about down the center-line of the south Greenland ice spur. Note the swatch of dark ice that appears much like dirty snow running down western side of the ice sheet. This major melt region, at its widest, appears to dive as much as 100 miles into the ice sheet. Even at this level of resolution, we can see the large melt lakes speckling the inland border of this darkened region.

Zooming in to a region where melt appears to have penetrated deepest into the ice pack, we find even more dramatic features.

Over the past two decades, Greenland has shown a very disturbing and rapid melt response to human-caused warming. During the mid 1990s, Greenland began to show a net loss of ice mass. Through the 2000s, this melt rate accelerated, growing generally, but rapidly peaking in rather disturbing melt surges as warm weather conditions grew more extreme during certain years. By 2012, a very extreme melt year had occurred, resulting in ice sheet losses on the order of 700 cubic kilometers in just one year. These peak melt years appeared to re-cur at a rate of once every 2-5 years even as overall average melt from Greenland grew to a disturbing 500 cubic kilometers by the early 2010s.

Even worse, sensors deep within the ice sheet indicated that the ice sheet had become more mobile, increasing in velocity by about 2-3 percent each year since 2010.

Though 2013 does not appear to be a peak melt year, as weather conditions have favored less melt than in 2012, the continued softening of the Greenland ice sheet remains a very disturbing summer feature. This year’s west coast melt has been particularly dramatic, with the most recent shots shown above featuring some of the worst melts I have yet witnessed.