Blue ice: it is beautiful, but when it appears in the Antarctic sea it is also a symptom of dangerous global warming. Image from a post by Antonio Turiel titled coming to terms with nature" (in Spanish).
In a previous post titled "Blue ice" I reported some observations by Antonio Turiel on the color of Antarctic ice. In a post in his blog, "The Oil Crash", titled, "Coming to terms with nature" (in Spanish) Turiel tells of a colleague of his coming back from an Antarctic expedition. What made him worried about global warming, was not so much the increase in temperatures, but the color of the icebergs in the Antarctic sea. The icebergs had turned blue. Turiel reports the words of his colleague.
"You know, the worst is not that each year there is more free sea. 20 years ago, the icebergs were white. Now they are blue." I said, "yes," and we both remained silent.
I received several comments on this post over the mail and Turiel himself answered to some of them. With his permission, I am now reproducing an edited version of Turiel's mails in order to explain why old icebergs are blue and why this is relevant for climate. So, here is Turiel commenting on his post:
Something that I (deliberately) omitted in my story about blue ice is that my colleague is Russian, a former researcher in the Shirsov Institute (a well known oceanographic institution in the former Soviet Union). Soviet Russians had a wide knowledge about polar seas and they studied in great detail the physics of water formation in those areas, to the point that their studies on abyssal waters are still a reference in the field. Mikhail's voyage with a Spanish research vessel was, to some extent, a nostalgic travel as our ship was intended to meet at a given date his former ship and his former companions. To tell you the truth on Mikhail's return to my lab, when I was talking with him, I was unsure about the exact meaning of blue ice, but it seems that Russians know this very well...
..... surface melting creates crevasses which lead to water accumulate in the base of glaciers, lubricating and accelerating the ice tongue and that makes ice move faster towards the sea. This extra ice flux can cause an increase of the ice covered area of the seas nearby, especially in winter. But don't get confused about that: in such a case the sea is covered by a much thinner layer, but at the same time the ice cap has grown thinner. If you consider the total amount of ice in the ice caps you observe a net ice loss, as it is the case in Antarctica and everywhere.
Unfortunately we lost Cryosat-1 at launch, and Cryosat-2 has just started giving us data about ice thickness. Thus, we don't have a complete historical record and, in addition, we will need to calibrate these new remote sensing data during for many years to come. I'm personally involved in the calibration-validation of another ESA mission, SMOS, and I can confirm you that getting sensible data from new satellites is a lot of work that takes several years. So, we cannot rely on comfortable, large-scale measures of ice thickness to know what is exactly going on. Our only possible reliable evidence about ice thickness comes from repeated in situ measurements at selected locations, and all them indicate an increasing ice loss; but there is always of course a certain degree of uncertainty with these measurements.
Nevertheless, satellite gravimetry can give us good hints. Satellite missions such as Grace or GOCE allow us to measure small differences in the gravitational field of Earth. These measurements can be used to improve our knowledge of Earth's geoid or the average sea level, but also can be used to estimate very slow displacements of land masses and even of land ice (areas of active sea ice change too fast for those techniques to be of application). These measurements have been combined with new GNSS-R reflectometry techniques to evaluate discharge rates by glaciers; to my knowledge this has been done mostly for Greenland, with twenty of so large glaciers being monitored. I guess it is because it is the most accessible area of this kind from Europe and the United States. Pedro Elosegui is a known specialist who was for several decades in the US and now works at my lab. Quite recently Pedro gave us a presentation, compiling the state-of-the-art in the field, and the conclusion is that glacier discharge in Greenland seems to be accelerating, at least during the last decade.
Now, some comments from me. First of all, there is a persistent legend that says that Antarctic ice is "growing" and that this fact, somehow, disproves the whole concept of global warming. This is just a legend. Temperatures are increasing in Antarctica, as everywhere else on Earth. At most, it can be said that the area of the floating ice around Antarctica is constant or slightly growing. But the volume of the Antarctic ice shows a net loss, just as the volume of Arctic ice is decreasing, and Greenland's too. In other words, all the major ice sheets are losing mass because of global warming. Details on this point can be read here:
Allison, I., Alley, R., Fricker, H., Thomas, R., Warner, R. (2009). Ice sheet mass balance and sea level. Antarctic Science. 21(5), 413-426 (full text). In this paper, it is estimated that Anctartica loses something of the order of 100-200 Gigatons of ice every year. Some other estimates (http://www.skepticalscience.com/antarctica-gaining-ice.htm) report a loss of 300 Gigatons/year.
If Antarctica is losing ice, then the flow of icebergs from the ice sheet must increase. That means, in turn, that these icebergs must be older. Then, why the color blue? Well, Antarctic ice is compacted snow. Snow contains a lot of air in the form of small bubbles. As it is compacted under the pressure of an overlying ice mass, it loses more and more of these bubbles. The older the ice, the smaller the density of bubbles. Now, small bubbles scatter light just like the frosted glass of a shower panel. So new ice scatters light and it appears white. On the contrary, old ice is transparent and it takes the color blue because blue light penetrates to a higher depth than red light. In the end, older icebergs show up as blue icebergs. That is a confirmation of the fact that Antarctica is losing continental ice faster than it did 20 years ago.
So, as usual, the question of climate change is shrouded in legends of all kinds; the one about "Antarctica not warming" is just one of the many. But if you look at the science, there is no doubt that global warming is occurring faster than ever.
Antonio Turiel is a physicist working at the Institute of Marine Physics in Barcelona, Spain. In his blog, "the oil crash" (in Spanish) he discusses a wide variety of subjects, all related to Energy; from peak oil to climate change. A recent post of him on the "E-Cat" hoax is available in English on the EnergyBulletin.
h/t Euan Mearns for having started the discussion on blue ice.