Also, on the OP, I'm still a little curious as to how this whole thing became a big deal. I'm a bit in the dark, but here's
a nice quote I came across:
The best science we have argues the planet will continue to warm, melting icecaps, causing accelerated sea level rise. Between 1900 - 2007, global sea level rose at 1.7 mm per year (Bindoff et al., 2007). Between 1993 - 2012, sea level rise accelerated to 3.1 mm per year, a 75% increase over the 20th century rate. If this accelerated rate continues to 2100, global sea level rise will be 10.7", which is higher than the 8" rise North Carolina is being told to plan for.
I'm not all up-to-date on this whole sea level rising thing. Regardless of who's right or wrong is the difference between 8" and 10.7" really that large that it necessitates a different planning strategy? To the layman it seems a little silly of a thing to bicker about. I suppose its the principle of the thing though?
I suppose it does matter to engineers and planners. It also matters a lot to developers, since it directly affects the volume of coastal land they have to work with. Assuming that these numbers will end out affecting coastal building codes, it can be a big deal. Depending on the topology, the difference between a projected 1m worst case versus 15" can result in buildings having to be built a hundred feet or more back from the existing waterline. So yeah, it matters.
And of course, there's also the political angle and the whole "OMG! Global Warming!" versus "OMG! Global Warming Denial!". And let's face it, that's a **** of a lot more interesting and fun for most of us.
Having said that, I still have issues with the kinds of data in the quote you provided. IMO, it's still suffering from the same sorts of problems Kao spoke of. We have far more accurate measurements of (global) sea level change today than we did 50 years ago, or a century ago. So what's happening is that older measurements are going to tend to be extrapolated over time and area, versus recent data which is very precise. This is significant to something like global sea levels because it tends to soften out trends in the past, while making current ones very obvious. This creates exactly the sort of perception of radical change that said quote talks about.
To illustrate this, imagine you are riding in a car. Imagine also that your only perception of how fast you are going is based on information you are provided (no looking out windows in this case). The car is equipped with a speedometer and a computer which calculates average MPH for the trip. During the first hour of the trip, you are blindfolded and can't read any of the indicators. Then you are allowed to look at them (but nothing else). You note that the average speed for the trip reads 25MPH. Then you note that the current speed is 55MPH. Over the next 5 minutes, you watch these indicators and note that while the average measurement doesn't change, the speed keeps increasing and at the end of that 5 minutes, you are traveling 70MPH.
Would you conclude based on this information that the speed has increased steadily over time and will continue to increase until you crash? Or would you conclude that the speed at any 5 minute period of time varies, sometimes being faster and sometimes being slower? Obviously, the latter, right? You think that the current speed is an anomaly because you can see the exact speed at that time (and the odds of it staying the same as the average over the while trip is very close to zero). But it's your own perception and interpretation that is incorrect. In fact your speed has increased, then decreased, over and over the whole time. You just happened to first start watching the speedometer during a time when the car was traveling much faster than the average.
The point is that we can't say from looking at average increases over a long time during which we were not taking precise measurements what the actual pattern of that time period was. You *always* have to think about the methodology being used. We generate our historical data by taking the smallish bits that we know and then extrapolating across the whole that we don't know. This results in a smoothing of highs and lows just as an average MPH in a car will. You don't assume you traveled that speed the whole time, right? So why do that in this case? The odds of a relatively short period of any measurement we've taken matching an extrapolated average of the past is very very low. Certainly, if we then continue measuring in the present, we will see behavior which will appear to not match historical patterns. It's completely normal and (should be) expected. What's shocking to me is how many people who should know better appear willing to go along with (or even create) hysteria about this.
That's not to say that sea levels aren't rising at a faster rate. But it is to say that we should be skeptical of past data and doubly skeptical of comparing current data patterns to those in the past (which is exactly what you're doing when comparing relative rates of change as in this case). We should absolutely be cautious about making projections based on that sort of comparison. Because in the example I gave below, one might conclude that an hour later, their speed would be 200MPH or so. If they only looked at the data provided that is.