Arctic Ice Extent Understated Because of "Sensor Drift" 823
dtjohnson writes "The National Snow and Ice Data
Center (NSIDC) has been at the forefront of predicting doom in the arctic as ice melts due to global warming. In May, 2008 they went so far as to predict that the North Pole would be ice-free during
the 2008 'melt season,' leading to a lively Slashdot discussion. Today, however, they say that they have been the victims of 'sensor drift' that led
to an underestimation of Arctic ice extent by as much as 500,000 square
kilometers. The problem was discovered after they received
emails from puzzled readers, asking why obviously sea-ice-covered
regions were showing up as ice-free, open ocean. It turns
out that the NSIDC relies on an older, less-reliable method of tracking
sea ice extent called SSM/I that does not agree with a newer method called AMSR-E. So why doesn't NSIDC use the newer AMSR-E data? 'We do not use AMSR-E data in our analysis because it
is not consistent with our historical data.' Turns out that the AMSR-E data only goes back to 2002, which is probably not long enough for the NSIDC to make sweeping conclusions about melting. The AMSR-E data is updated daily and is available to the public. Thus far, sea ice
extent in 2009 is tracking ahead of 2005, 2006, 2007, and 2008, so
the predictions of an ice-free north pole might be premature."
Re:alternative solutions (Score:5, Informative)
Both the AMSR_E and SSM/I data are satellite derived products.
http://www.ncdc.noaa.gov/oa/satellite/ssmi/ssmiproducts.html
http://www.aqua.nasa.gov/about/instrument_amsr.php
Re:Oh gosh. (Score:2, Informative)
Looking at the new graph it's still pretty obvious that the trend is "downwards", there was about 2 million square kilometers less ice in September 2007 than in September 2003.
http://www.ijis.iarc.uaf.edu/en/home/seaice_extent.htm [uaf.edu]
But yeah, the deniers will be all over this.
Re:How can people expect... (Score:5, Informative)
Re:Oh gosh. (Score:5, Informative)
Good, but.. (Score:3, Informative)
still plenty of data from other sources, NASA in this case showing a trend of ice melting... http://earthobservatory.nasa.gov/Newsroom/view.php?old=2006101923416 [nasa.gov]
Re:We only use data that support our hypothesis (Score:4, Informative)
Look who's talking. BadAnalogyGuy, the reason why scientists sometimes prefer inaccurate but precise and historically consistent data over data sources which are more accurate but have not been around for long is that they are interested in trends, not absolute values.
Re:Oh gosh. (Score:2, Informative)
Typical spin job (Score:5, Informative)
In May, 2008 they went so far as to predict that the North Pole would be ice-free during the 2008 'melt season,'
Er, no, they said it was possible and later quote "a 59% chance of a new record minimum this year". How the media chose to report this is another matter... Oh yes, note the date: May 2008.
Today, however, they say that they have been the victims of 'sensor drift' that led to an underestimation of Arctic ice extent by as much as 500,000 square kilometers.
And if you read TFA, the sensor drift started in January 2009, was spotted within a few weeks and only affected their daily images which are effectively "live" and hence haven't gone through QA.
So how exactly does an error which occurred in Jan/Feb 09, was almost immediately spotted and declared affect a (misreported) prediction made last May?
<irony>Meanwhile, I'm sure the little fairies are hard at work ensuring that the geological era's worth of sequestered CO2 we're in the process of releasing back into the atmosphere magically changes its physical properties. After all, it is made from special carbon that God put there in 4004BC for us to burn, unlike that nasty communist CO2 that exhibits the greenhouse effect in godless laboratories.</irony>
Re:Not sure what to believe anymore... (Score:3, Informative)
Not sure what to believe anymore...
The fun thing about science is you don't have to "believe" anything. Science is all about facts that you can reproduce for yourself. Therefore take a glass of water and put an ice cube in it. Mark the water level on the glass with a felt pen. Then wait for the ice cube to melt. Notice that the water level has not changed...
Melting ice from the north pole will not alter the sea level at all. Now the south pole is a different matter because there is actual land underneath the ice, so that ice - if it melted, would run off into the sea. However Antarctica contains around 22 million cubic kilometers of water stored in its ice (13.7 M sq km area x 1.6 km avg ice depth). Now considering that the area of the earth's oceans is around 361 M km, this ice is around 22/361 x 100 = 6% of the current volume of water in the oceans. Considering that the average depth of the oceans is around 3800 meters, increasing the water by 6% would add around 234 meters to sea level - assuming the oceans stuck to exactly same shorelines, which they wouldn't - so the sea level increase would actually be much less than 234m.
Fortunately, the average annual temperature in Antactica is still around -50C, with steamy summers being around -30C. Therefore THAT polar ice is in no danger of melting soon, even if the average temperature on Earth increases by a couple degrees (which is, after all, what the big fuss is about).
So don't expect to cash in on that "beachfront" desert property in Arizona just yet. Although it's smart and it makes sense for us to pollute as little as possible, the "global warming" preachers are absolutely full of shit - just like anyone else that tells you the world is about to end.
Re:Oh gosh. (Score:4, Informative)
No, I've heard lots about Global Warming. As you can see by the threading, I was replying to parent (comment 26915303) - now GGP - which stated 'Looking at the new graph it's still pretty obvious that the trend is "downwards", there was about 2 million square kilometers less ice in September 2007 than in September 2003.'
There is evidence to back up global warming. Of course there is. But saying that there is less ice in 2007 than there was in 2003 constitutes a downward trend is like saying climate has had a downward temperature trend here because we've had a colder winter this year here than in the last five years. It just isn't enough to constitute a 'trend'.
Re:Rocket science? (Score:5, Informative)
So, to be clear, this issue has arisen over the last 4-6 weeks. The records for the last decade, clearly showing a significant trend towards less sea-ice, are unaffected.
Re:Rocket science? (Score:1, Informative)
and choose data to make people afraid so they do what they want.
mmmmh... like use the car less, lobby for better public transportation, pushing for cleaner ways to produce energy, consume less, consume better, ask for better recycling programmes, etc. etc. all things which are indeed evil and damaging. Bad environmentalists bad.
Comment removed (Score:2, Informative)
Re:Typical spin job (Score:3, Informative)
To be perfectly accurate (unlike the measurements :)), from the article (linked to in the summary):
Re:Rocket science? (Score:1, Informative)
Or even from trauma from having "their guy" loose an election....
What guy? They (McCain/Obama) both supported global warming.
Re:Rocket science? (Score:5, Informative)
Such as the immunization and the possible link to autism, lets say it creates a 1% increase in autism how ever it saves 25% from death, the benefits out weigh the risks and the parents who avoid this are poor judges on risk assessment.
Arrgh!
Speaking of fear mongering, it has been repeatedly shown [sciencedaily.com] that there is absolutely no link between autism and vaccines.
Please, can't this FUD just die already? It's already caused deaths in the UK from a loss of herd immunity!
the "drift" was only for Jan/Feb 2009 (Score:5, Informative)
You might want to read TFA. The sensor drift only started in Jan 2009, and it was spotted within a few weeks.
Re:Not consistent? (Score:3, Informative)
It was saying that it isn't man made change.
Re:Rocket science? (Score:5, Informative)
To quote TFA:
Re:We only use data that support our hypothesis (Score:3, Informative)
That was the original assumption behind Carbon dating, however, we now know that the first assumption, at least, is not completely accurate. We know that the amount of atmospheric carbon has fluctuated throughout history. That is why scientists now use "Calibrated Carbon dates", which take these fluctuations into account. Dates up to about 6000 years ago have been calibrated using tree rings, and there are other techniques that have been used to calibrate dates back as far as 13,000 years. If anything the typical result has been that we have learned things were older than previously thought. It is now believed that an old (uncalibrated) radio carbon date of 9000BC actually corresponds to a "real" (calibrated) date of 11000BC.
As far as your other assumption, well, if that turns out to be false, we have much bigger problems than radio dating.
Of course, there have been other problems with radio carbon dating in the past as well. One big problem historically was that a fairly large sample was needed to get an accurate date, so scientists would measure ages of small things like seeds indirectly by measuring the carbon in e.g. a large piece of charcoal that was found at the same site. Obviously this was prone to problems, because that charcoal could have come from a forest fire thousands of years earlier. However, with "modern" techniques (i.e. as of the 1980's), indirect measurement is no longer really an issue, because scientists can accurately measure the carbon ratios even in very small samples using mass spectrometry.
Re:It wasn't going to be ice free 2012 (Score:1, Informative)
Re:Rocket science? (Score:4, Informative)
RealClimate, and their FAQs as well, are accessible to a motivated person (it's easier if you've got some sort of grasp of science and "how she is spoke", of course.)
Many workers in the field have published books for the general reader; again, RC has some good pointers. Finally, the IPCC assessment reports [www.ipcc.ch] are reasonably accessible (the summaries in particular.)
Now, you could say that getting into this level of research is a non-trivial thing to do, and you'd be right. There's jargon and shorthands for concepts and acronyms that mean little to the outsider. Climate is also, fundamentally, a very complicated phenomena; work in the field covers a multitude of specialist disciplines, an understanding of statistical methods, chemistry, biology, emergent phenomena, atmospheric physics, paleoclimatology (ice and sediment cores and the like), and so on and so forth. Fair enough, if you don't want to put that amount of effort in, you get to *take their word for it*.
Re:Oh gosh. (Score:1, Informative)
"Unfortunately, now that the old data have been shown to be badly flawed"
This is false - there was a BRIEF inconsistency in the data due to drift for only a few weeks. Let's not throw out the baby with the bathwater...
Re:Rocket science? (Score:4, Informative)
At the heart of the issue is usually the measurements themselves. Bias should never be part of a measurement, but failure to completely understand the system being measured often is. Since many measurement systems today are not direct measurements but indirect, and many are "remote sensing", it is often a failure to understand both the system being measured AND the proxy for the desired measurement that causes failure.
For example, several years ago it was determined that the satellite-based sensing of ocean surface temperature was off by several degrees, because the atmospheric effects on the IR radiation being used to measure the temperature weren't being correctly corrected. It is no surprise to hear that any proxy measurement has been found to be off with a biased error.
What? Bias? Well, "biased error" is the technical term for an error in measurement that is wrong in a consistent manner. For example, a thermometer that has been miscalibrated so that it always reads high. But please do not mention this possibility of measurement error to anyone involved in global warming research. They are right, everyone else is wrong.
Don't EVER ask why they assume that CO2, a gas that is soluble in water to a great extent, cannot diffuse out of air bubbles in ice that have been trapped for millenia. It is the measurement of CO2 in those bubbles that global warming scientists use to tell us what the level of CO2 was ten thousand years ago -- even though there is no recorded measurement from then, and only the proxy of "trapped bubbles" to rely on.
Many people have strong feelings that disaster is about to occur. Perhaps this comes from childhood recollections of maternal warnings about running with scissors or touching hot stoves.
Today's strong feelings of disaster are prompted by catastrophe-based science and the scientists who are paid to find solutions to catastrophes. Scientists who warn us that a stray comet could obliterate life on this planet don't get paid to deal with comets that don't come anywhere near us. Scientists who predict gloom and doom from global warming don't get paid if they report that there really isn't a problem. I am repeatedly fascinated by global warming scientists who dismiss studies that contradict their cries of alarm as the product of people who are being paid to say there is no problem. Why would the only scientists who lack ethics be the ones on one side of an issue? (The state of Oregon just created a group to deal with global warming issues. Do you think that the head of this group is someone who doesn't toe the line regarding the causes and results of global warming? He's getting paid, so why aren't his ethics questioned?)
Re:Rocket science? (Score:4, Informative)
Nonsense. The data from this particular survey are in dispute, and people here are conflating this to all of climate science. That the earth is warming, and that globally, ice is melting at an alarming rate, is not even disputed by the oil industry any more.
If the atmosphere heats up, physics predicts that the ground will heat up as well, and that ice will melt.
You're correct that the system is more complex than that, because, for example, melting ice can trigger other mechanisms that are too complex to model, currently. This doesn't refute the very basic fact that adding global heat to the atmosphere tends to melt ice.
I'd also point out that we know all of this because we've studied it scientifically, just the same way that we know that CO2 tends to heat the atmosphere, and ice tends to melt with warmer air.
Re:Not consistent? (Score:3, Informative)
I did see an argument over whether it is man-made
It's interesting to note that this specific problem with the data descibed in TFA does not touch on the issue of whether the global warming is man-made or not; indeed, it only shows that GW is happening slower than we thought it is.
Re:Rocket science? (Score:4, Informative)
For example, several years ago it was determined that the satellite-based sensing of ocean surface temperature was off by several degrees, because the atmospheric effects on the IR radiation being used to measure the temperature weren't being correctly corrected. It is no surprise to hear that any proxy measurement has been found to be off with a biased error.
What? Bias? Well, "biased error" is the technical term for an error in measurement that is wrong in a consistent manner. For example, a thermometer that has been miscalibrated so that it always reads high.
But please do not mention this possibility of measurement error to anyone involved in global warming research. They are right, everyone else is wrong.
I am unaware of the experiment and controversy surrounding it, have a link to a peer reviewed journal article?
Really, even if a bias is discovered later in an experiment and if that bias can be estimated, whether the added error is constant or variable, corrections to the old data can be made and the corrected data would be accurate. This assumes the supposed error is actually an error and not some global warming denier's fantasy. One correctable error does not mean that all of the data from the experiment is useless, and the same conclusion from the experiment can still hold.
Even if the data from an experiment has uncorrectable errors and the data is faulty, GW deniers have one experiment discredited, and only have a whole truck load more valid experiments showing Global Warming to discredit. GW deniers still have still shown no credible alternate to explain the trends in the world's climate. Thus, GW deniers are just that, in denial, they are not advocating their own hypothesis by using accepted scientific practices and existing data.
Don't EVER ask why they assume that CO2, a gas that is soluble in water to a great extent, cannot diffuse out of air bubbles in ice that have been trapped for millenia. It is the measurement of CO2 in those bubbles that global warming scientists use to tell us what the level of CO2 was ten thousand years ago -- even though there is no recorded measurement from then, and only the proxy of "trapped bubbles" to rely on.
Water, in its solid crystalline form, ice, has no capability to hold CO2 in solution, only liquid water can hold CO2 in solution. It would seem to follow that when trapped in a gas bubble in ice, CO2 does not diffuse because water ice is not permeable to CO2 at any of the temperatures or pressures that the ice has been at since it formed.
Many people have strong feelings that disaster is about to occur. Perhaps this comes from childhood recollections of maternal warnings about running with scissors or touching hot stoves.
Today's strong feelings of disaster are prompted by catastrophe-based science and the scientists who are paid to find solutions to catastrophes. Scientists who warn us that a stray comet could obliterate life on this planet don't get paid to deal with comets that don't come anywhere near us. Scientists who predict gloom and doom from global warming don't get paid if they report that there really isn't a problem. I am repeatedly fascinated by global warming scientists who dismiss studies that contradict their cries of alarm as the product of people who are being paid to say there is no problem. Why would the only scientists who lack ethics be the ones on one side of an issue? (The state of Oregon just created a group to deal with global warming issues. Do you think that the head of this group is someone who doesn't toe the line regarding the causes and results of global warming? He's getting paid, so why aren't his ethics questioned?)
I'm not sure how to respond, I am nearly certain that over many the years as corporations like Phillip Morris, Exxon, and alike sponsored anti-GW groups, that at least some research was done at least one sound and valid published study should still be available. No