Posts Tagged‘carbon dioxide’

Dry Ice Screaming.

Dry ice is a very interesting substance, both from a scientific and “it’s just plain cool” point of view. Many are familiar with the billowing clouds of smoke it can produce when placed in water, seemingly a staple of anything that needs to be made to look spooky. Others will know it for its culinary applications, able to cool things down far more rapidly than any fridge or freezer. However whats less understood is the mechanisms of how dry ice actually works which is what can produce some rather interesting effects like those shown below.

Dry ice is the solid form of carbon dioxide which, thanks to its useful properties, has found many everyday applications. It’s also quite easy to manufacture as carbon dioxide is a byproduct of many other processes. This gas is then trapped and pressurized, changing it into a liquid form. Then the pressure is released, causing some of the liquid to boil off which rapidly cools down the remaining liquid. This then forms a kind of carbon dioxide snow which can then be compressed into blocks or small pellets. Industrial applications often use the large blocks whilst the pellets are used in more everyday applications.

The video above demonstrates a property of dry ice that’s not completely obvious if you don’t know what to look for. Carbon dioxide doesn’t have a liquid state at atmospheric pressures which means that it transitions directly from a solid to a gas, bypassing the liquid phase. This process is called sublimation and means that the entire surface of dry ice is constantly emitting carbon dioxide gas. When you put something on top of it, like a large metal part shown above, the gas has to squeeze past the surface in order to escape. This is akin to pulling the ends of a balloon apart to make that loud screeching noise which is why this part appears to “scream”.

There are many other videos of people producing similar effects with dry ice and other metal objects like spoons and pennies. One interesting thing I noted from some of the other ones that the screaming effect would often stop after a short period of time. I believe this is due to the metal’s temperature approaching that of the dry ice which means that the dry ice no longer sublimates. The part in the video above is likely carrying quite a bit of heat which is why the screaming continues on for so long.

Quite fascinating, if I do say so myself.

Dry Ice on Mars (and Earth).

Mars doesn’t have much of an atmosphere and the little it does have is rather hostile to life, being composed almost entirely of carbon dioxide with only small percentages of other gasses detectable. Due to the freezing temperatures that grip it constantly -60°C in summer and -125°C in winter a lot of this carbon dioxide ends up in its solid form, usually buried in the permafrost. Last year NASA even confirmed that Mars experiences dry snow a phenomena where frozen carbon dioxide falls to the surface in the form of snow not unlike the water based version we have on Earth. These are all mightily cool in their own regard but there was one particular interaction that came to my attention recently that’s just so much cooler because I realized I had first seen it for myself in my backyard.

I had heard about these gullies before and had always wondered how the heck they formed. It’s not like Mars is a completely dead planet, we’ve caught crazy things like avalanches happening on it, but things that look like they require surface water (or some other liquid) in order to create them are usually out of the question (at least for new features anyway). They’re even reminiscent of the sailing stones in Death Valley, although we’ve probably solved that mystery, but the lack of something at the end of them was the thing that was really puzzling.

Where I saw this in my backyard was a chance encounter with a couple blocks of dry ice that came with a delivery of frozen meals. They weren’t as big as the blocks in the movie above, although you can get them pretty easily if you know where to look, but of course the science nerd in my wife and I couldn’t resist playing with them in the kid pool we had set up. The result wasn’t exactly surprising since we’ve all seen this kind of stuff before but it was rather interesting to see the same principles at work on Earth just as they are on Mars.

The effect isn’t nearly as dramatic but you can definitely see the same carbon dioxide cushion at work which makes the block appear to glide on the surface rather than bobbing in it like water ice does. Another cool thing (which I didn’t show in the video) is when it’s placed just below the surface that same cushion will actually propel it straight to the bottom where it will pin itself and bubble like crazy until it’s all melted away.

I’d recommend doing this for yourself as it’s one thing to see it in a video and a completely different thing altogether to play around with it. Of course there’s a whole host of other things you can do, some which I’d probably not recommend (anything that involves a pressure vessel contains a certain amount of danger), but just watching it interact with other things is pretty satisfying.

Howard, Plimer and The Folly of Climate Change Skepticism.

I’ll admit that for quite a long time I too was skeptical about the whole climate change movement. I attribute this to being ignorant of most of the science around the matter basing my opinion off “facts” I had heard over the course of my lifetime without bothering to look them up. The rise of my inner skeptic changed that however, taking an axe to many of my beliefs and forcing me to verify everything before I dared say that it was true. Today there is zero doubt in my mind that climate change is happening, it is affecting us in serious ways and, most importantly, we are to blame for it.

I will forgive anyone who dismisses me out of hand as just another blogger ranting about something, that’s fair enough. Realistically you have no reason to believe me at all, what with my qualifications placing me as far away from being an authority on this matter as most of the public. However I will make the point that my view closely echoes that of the greater scientific community which includes many people far more qualified than myself (and indeed most others who comment on this subject) in matters of climate change. It’s a common misconception that the science is still out on whether or not we’re the cause of the recent changes in our climate, but the truth is anything but that. 

Taking the figures presented here into consideration you can see why there’s a lot of confusion on this matter. Among the general public the acceptance of anthropogenic climate change is around 50~60%, a majority but enough to cause confusion amongst the uninformed. When you select for scientists (which includes people who’s area of expertise is not climatology) that number jumps up to around 70~80%. As we further select for climatologists we see that number soar to 90% with those who are actively publishing on the subject bringing the number to a staggering 97%. If 97% of all doctors told you that asbestos caused cancer you’d sure as hell believe them, so it still boggles me as to why people think otherwise.

It’s not helped when public figures jump on the climate change skepticism bandwagon either. Today as I was driving into work I caught whiff of a story that former prime minister of Australia, John Howard, was supporting a book that promotes kids questioning climate change:

Professor Plimer launched the book, a follow up to his book Heaven and Earth, at the Sydney Mining Club.

The new work includes 101 questions which it says students can use to challenge their teachers on climate science.

Mr Howard helped launch the book and last night said the “progressive left” had a “grip on the commanding heights of education instruction in this country”.

The book, How to get Expelled From School, comes to us courtesy of Ian Plimer. He’s a well published geologist and a director of 4 mining companies. He’s gone on the offensive against creationism in the past so you’d think that I’d be one of his supporters. Unfortunately, whilst Plimer does agree that climate change is occurring, he does not believe that humans are to blame for it. His stance is that the current scientific community ignores the geological evidence that says the current period of warming is a natural occurrence and that natural sources of carbon dioxide contribute far more than humans ever could.

These stances are, to say the least, unscientific.

One of Plimer’s main arguments was that volcanoes, including undersea ones which have been “drastically underrepresented” in current studies, contribute far more carbon dioxide than humans ever do. The reality is quite the opposite with human contributions to global carbon dioxide being on the order of 130 times greater than that of all volcanoes, including those ones under the sea. This has been confirmed several times over by independent bodies so the idea that humans are somehow producing less carbon than natural sources has no basis in reality and is little more than conjecture on the part of Plimer.

Indeed Plimer’s previous publication on the matter of climate change,  Heaven and Earth — Global Warming: The Missing Science, was met with heavy criticism from the scientific community. Like many climate change skeptics Plimer fell prey to the idea that the climate change movement is somehow a conspiracy, usually of the form of transferring wealth away from the rich west in order to prop up the third world. To say he has a vested interest in spreading such ideas is putting it lightly, as a director of 4 mining companies sowing seeds of disinformation about his industry’s impact on the world ensures his businesses can continue as they always have. I could go on, but there’s already a substantial amount of information about the error of Plimer’s ways out there, enough for anyone to conclude that he’s not to be trusted on this subject.

In the end it comes down to who you trust more, a lone geologist with a vested interest in denying humans are responsible for climate change or the greater scientific community? Just because someone has a rational approach to some subjects does necessarily mean they’ll apply that same rationality to others, especially when there’s money on the line. Howard’s support of Plimer’s views is disappointing but it shows that there’s little wiggle room for dissent when you’re stuck on the right. It’s a shame really as even Tony Abbott has finally come around and I would’ve thought he’d be the tough nut to crack.