Saturday, March 24, 2007

Convenient Myths

I promised you guys last time I'd get to debunking some of the arguments against Global Warming, but I figured I'd go a step further and also debunk some of the bad arguments made in favor of it (oddly enough, I couldn't find nearly as many of these). Onto the myths!

Note: This post was so long I decided to get into the habit of using a "fold" to hide the bulk of it. Don't want to overload everyone's browser unnecessarily.

The Myth: The Earth goes through warming and cooling cycles, causing ice ages and warm periods. It's simply been warming since the last ice age.

The Truth: It is true that the Earth goes through cycles, but there are a couple of problems here. The first of these is the linear assumption, which is where people assume that since it was at point A in the past and point B now, it followed a linear path between them and will continue on it. In truth, the cycles are anything but linear. Let's take a look at what they actually look like:



Okay, first of all there's a lot of random variance at any time, but ignore that for now and look at the overall pattern. It's pretty cyclical alright, but it's not like a simple sine wave or saw blade. Rather, we see a pattern of a sharp rise in temperature of around 10°C taking place in a span of around 10,000 years followed by a gradual cooling over the next 100,000 years or so.

Now, let's look at our recent history on the far right side of the graph. We see that we've just come off of a spike which has stayed strangely level afterwards. (The timescale of the graph is too much to attribute this leveling to human activities.) What we would expect to happen next judging from the long-term cycles is that the temperature would plunge back down into another ice age.

There's another variant to this myth, however, that relates to a more recent cooling period: the "Little Ice Age," which took place within the last millenium. See the following image:
During the Medieval Warm Period you can see on this graph, Greenland was actually temperate enough that colonies were set up there, but they had to be abandoned in the later years. We're now approaching those temperatures again in the recent century. Does this mean we're due for a melting of it? Time will tell... (well, hopefully not)

But anyways, onto the claim they're making. They say that the present warming is simply the Earth correcting itself after that Little Ice Age. But wait, as seen on the previous image, which way should the Earth be correcting itself next? That's right, it should be going downwards. Looking at historical trends, we don't see as much of short-term (on the scale of a few centuries) cycles as we do just random fluctuations, so we don't really have any reason to assume that from a short-term trend we're due to come back up.

In fact, if you want to be really pessimistic, you could argue that the escape from the Little Ice Age occured in the middle of the world's industrialization, and it's possible that this is what caused us to come back to a peak, and possibly rise some more. But that's just speculation.

There's one other problem here, with the Medieval Warm Period itself. It's hard to accurately gauge temperatures that far back in time, and when we can, it's often only in a few places in the world. The best evidence we have shows that outside of Europe, it was indeed probable that many areas experienced the warm period, but it's not conclusive. In fact, Antarctic Ice Core samples showed an additional cold period from 1000-1100 AD.

But there's another big problem with using the Medieval Warm Period to extrapolate anything about cycles in the Earth's climate: It was also the time of an extremely hyperactive phase of solar activity known as the Medieval Maximum. The relationship between the sun's activity and the temperature on Earth is well-accepted, especially by Global Warming skeptics who try to use it to explain the rise now. You know what they fail to point out? We're at the same temperature as in the Medieval Warm Period now, but the sun is not in a hyperactive phase (at least, nowhere near how it was back then).

The Myth: Temperature causes the CO2 levels, rather than CO2 causing the temperature levels.

The Truth: While it is true that temperature plays a role in changing the CO2 levels in the atmosphere (higher temperatures decrease the solubility of gasses in liquids, so CO2 is released from the oceans. The opposite happens as temperatures decrease, though not as quickly), it's also true that CO2 plays a role in affecting global temperatures. This latter process happens through the greenhouse effect, where CO2 in the atmosphere allows more heat to enter than to leave. Just because A can cause B doesn't mean B can't cause A as well.

In fact, the truth is even more frightening: Once the temperature starts to move up for some reason, it will cause more CO2 to be released from the oceans, which will cause the temperature to increase even more, which will cause even more CO2 to be released, and so on. With this in mind, it's easy to see why the upward spikes on the first chart were so sharp. The reason the downward trends weren't so sharp was because the process of the oceans reabsorbing CO2 in low temperatures is much slower than the process by which it releases it in high temperatures (only the interface between the atmosphere and water allows reabsorbtion, so it takes a long time for the water to get back up to its saturation point).

Now, there are a few big things we don't know: Why did the spikes stop? It's possible the oceans ran out of CO2 to contribute to the atmosphere, so the temperature leveled out. But then there's the problem of what caused the decline (this might also cover what caused the stop in the spike). And there's also the problem of what started the spike in the first place.

While these questions are intriguing, they're not necessarily relevant. In the current situation, the critical factors are that: 1. We're releasing huge amounts of CO2 into the atmosphere (no dispute here), 2. CO2 in the atmosphere plays a role to warm the Earth, and 3. This warming can cause a cascading effect resulting in sharp spikes in temperature. What caused the warming that brought us out of the ice ages isn't relevant here; the important factor is what might cause warming today.

I'll make one final note on this subject: It appears that the warming trends hit a maximum of around 2°C higher than our current average. This might imply we don't have to worry about unlimited warming, but we still do have those 2 degrees to worry about. And, as I mentioned a bit earlier, even a rise of half a degree could drastically change the face of Greenland, which is one of the biggest threats to us.

The Myth: Thermal expansion of water in the oceans could cause as much sea level rise as glacial melting, if not more.

The Truth: Water's a peculiar material in many ways. Part of its peculiarity is how its density changes with temperature and phase. Unlike most substances, its solid form is actually less dense than its liquid form (that's why ice floats in water). Additionally, for a region between 0°C and 4°C, water's density actually increases with temperature, in contrast to the general trend of most substances to decrease their density with temperature. This point is actually very important here, as the average temperature of the water in the oceans is 3.5°C - where an increase in temperature would cause it to contract.

Now, things are actually a bit more complicated. The surface temperature of water is around 10°C, and this is the water which gets warmed up first. This means that we'd actually start to see some expansion in this region. However, although the water in this region would expand, the thermal expansion coefficient is still pretty small at the temperature, so we won't likely see the predicted 5 meters of rise which was calculated using the expansion coefficient at 20°C. Instead, according to one model I've looked at, we could expect the next rise of a degree Celsius to only contribute a few centimeters. This degree could, however, cause significant glacial melting, and this would contribute a lot more than thermal expansion.

The Myth: Water vapor is the more important greenhouse gas, not CO2.

The Truth: Some estimates give the following proportions for how much different gases contribute to the greenhouse effect:

  • Water vapor: 36-70%
  • CO2: 9-26%
  • Methane: 4-9%
  • Ozone: 3-7%

So, in an average scenario, we have CO2 contributing about a third as much as water vapor, and methane about a third as much as CO2. Let's throw in some more numbers to make a probably-not-at-all-accurate estimate:

  • CO2 levels have increased by 31% in the last 250 years.
  • Methane levels have increased by 149% in the last 250 years.
  • So, if we assume a linear relationship, the greenhouse strength has increased by about 17% * 31% + 6.5% * 149% = 15%
  • The total effect of the greenhouse gases is to raise the atmospheric temperature by around 14°C.
  • If we again assume a linear relation, we get an increase caused by man of about 15% * 14°C = 2°C.

That's big. Let's go back to the chart of recent temperature cycles:The rise at the end of the Little Ice Age was around .6°C. Given that our rough estimate was 2°C, mankind causing a .6°C rise in this timeframe is well within reason. As for water vapor being the main greenhouse gas... does it matter? Raising the CO2 and methane levels alone is easily sufficient to cause significant change.

(Note though that there's far from a scientific consensus that that rise in temperature was actually caused by human activity; more so than other claims of global warming. I'm just pointing out its plausibility here, so don't take my word on faith.)

Now, that was just using a really simple model. Climate scientists have of course come up with better models. One model which a lot of them favor actually shows that the presence of water vapor in the atmosphere actually amplifies the effect of increased CO2 and methane. Another model that a lot of the Global Warming dissenters favor argues that instead the water vapor will dampen the effects of increased CO2. To me, both models seem like they're favored by the applicable groups of people mostly because they predict the same thing as the hypothesis they already favor. If both of their models have good points, the true answer probably lies somewhere in the middle. And as I showed above, estimates in the middle are still pretty damn bad.

The Myth: The "Hockey Stick Graph," which was used to show the sharp spike in Global Warming recently, is critically flawed and has been debunked.

The Truth: The graph of course has its share of statistical errors, as you'd expect from any chart of scientific data, particularly when delving this far into the past and then trying to average the entire planet's temperature. This does not equate, however, to it being "critically flawed." Let's take a look at the (in)famous graph:


The first big complaint about this graph is that it doesn't show the Medieval Warm Period at all. However, I'd like you to take a look at a part of the graph most people ignore: The error bars, which in this case are the shaded grey regions. A shift up in the early second millenium by a half a degree would account for the Medieval Warm Period and would be within statistical error. Also, it appears the before the 20th century, the temperature did appear to be on a slow decline, and it's possible that the very slightly warm temperatures at the left side of the chart in fact were the Medieval Warm Period.

Aside from this, there were a lot of criticisms of the statistics used to create this graph, and alternate models proposed. I'm not going to go into the actual criticisms here, as that's likely far out of the scope of my average reader's expertise, but I'll just point out a couple of things. First of all, remember that Global Warming is a politically controversial subject, and even a flawless paper that supports it is going to be criticized. The presence of a criticism doesn't imply the presence of flaws.

Secondly, there was a big independant review of the report performed by the National Research Council at the prompting of the US Congress over the last few years which published their results in 2006. Specifically, they summarized their results as:

  • Large-scale surface temperature reconstructions yield a generally consistent picture of temperature trends during the preceding millennium, including relatively warm conditions centered around A.D. 1000 (identified by some as the “Medieval Warm Period”) and a relatively cold period (or “Little Ice Age”) centered around 1700. The existence and extent of a Little Ice Age from roughly 1500 to 1850 is supported by a wide variety of evidence including ice cores, tree rings, borehole temperatures, glacier length records, and historical documents. Evidence for regional warmth during medieval times can be found in a diverse but more limited set of records including ice cores, tree rings, marine sediments, and historical sources from Europe and Asia, but the exact timing and duration of warm periods may have varied from region to region, and the magnitude and geographic extent of the warmth are uncertain.
  • It can be said with a high level of confidence that global mean surface temperature was higher during the last few decades of the 20th century than during any comparable period during the preceding four centuries. This statement is justified by the consistency of the evidence from a wide variety of geographically diverse proxies.
  • Less confidence can be placed in large-scale surface temperature reconstructions for the period from A.D. 900 to 1600. Presently available proxy evidence indicates that temperatures at many, but not all, individual locations were higher during the past 25 years than during any period of comparable length since A.D. 900. The uncertainties associated with reconstructing hemispheric mean or global mean temperatures from these data increase substantially backward in time through this period and are not yet fully quantified.
...

The basic conclusion of Mann et al. (1998, 1999) was that the late 20th century warmth in the Northern Hemisphere was unprecedented during at least the last 1,000 years. This conclusion has subsequently been supported by an array of evidence that includes both additional large-scale surface temperature reconstructions and pronounced changes in a variety of local proxy indicators, such as melting on icecaps and the retreat of glaciers around the world, which in many cases appear to be unprecedented during at least the last 2,000 years. Not all individual proxy records indicate that the recent warmth is unprecedented, although a larger fraction of geographically diverse sites experienced exceptional warmth during the late 20th century than during any other extended period from A.D. 900 onward.

Based on the analyses presented in the original papers by Mann et al. and this newer supporting evidence, the committee fi nds it plausible that the Northern Hemisphere was warmer during the last few decades of the 20th century than during any comparable period over the preceding millennium. The substantial uncertainties currently present in the quantitative assessment of large-scale surface temperature changes prior to about A.D. 1600 lower our confi dence in this conclusion compared to the high level of confidence we place in the Little Ice Age cooling and 20th century warming. Even less confidence can be placed in the original conclusions by Mann et al. (1999) that “the 1990s are likely the warmest decade, and 1998 the warmest year, in at least a millennium” because the uncertainties inherent in temperature reconstructions for individual years and decades are larger than those for longer time periods, and because not all of the available proxies record temperature information on such short timescales.


Scientist-to-Lay translation: Yes, there are statistical uncertainties. However, they are not significant enough to change the conclusion. It's hot in here and it's not just me.

I'll remind you that this came out from a committee commissioned by the Republican-controlled congress of the time under the (ongoing) censorship of scientists who espoused views or came up with results the administration doesn't like. Despite all that, the report was in favor of the validity of the Hockey Stick Graph. Must be some strong science if it can make it through those barriers.

Oh yeah, there was also one other review done. This one (known as the Wegner Report) was performed at the instigation of Representative Joe Barton, an outspoken Global Warming "skeptic" (don't worry, we're doing our best to steal that word back from them). The report also wasn't subject to peer review, and it didn't even result in changing the shape of the graph after fixing supposed errors. Compare: (The "Hockey Stick Graph" on the left, the graphs the Wegner Report came up with on the right)

(Source: NY Times)

Is it just me, or is the spike even more profound on the new graphs? And they had the gall to use this as evidence against Global Warming?

The Myth: Scientists were going just as crazy back in the 1970's about Global Cooling. And now they think it's Global Warming. Why should we believe them?

The Truth: There was speculation about Global Cooling back in the 1970's (though it wasn't called that back then. The term was invited by Global Warming "skeptics" who wanted to make it look like a comparable theory was proposed back then), but it was only by a few scientists and never got close to the amount of research that's been done on Warming. It never gained the consensus of scientific support that Warming did, so it's unfair to imply that the mass of "Scientists" believed in it.

In fact, since there was so little actual "hysteria" about it, let's go over every scientific paper published on Cooling:

Rasool and Schneider (1971) - Examined the possible effects of greenhouse gases and particulate pollution (such as from aerosols) on the climate. They found that greenhouse gases would result in warming the Earth and particulate pollution in cooling it, and guessed the latter to be more likely. They estimated that sustained effects of particulate polluntants could decrease the temperature of Earth by up to 3.5°C, and if this went on for long enough, it could cause Earth to drop into another ice age. Note that they didn't actually predict this would happen, they just proposed it as a possible future scenario. Nowadays, most scientists are indeed predicting that the Earth is going to warm up.

National Academy of Sciences Report (1975) - Often claimed to show fear of Global Cooling. In fact, all it said was that it's possible for the climate to change, they didn't know in which way it might, and so we should research it more. No big fears there.

Okay, we have one actual paper which shows any support at all for the hypothesis of Global Cooling. That's it. Some hysteria, eh?

Oh yeah, I'd be remiss if I didn't mention that this is just a fallacious appeal to "Science was wrong before."

The Myth: This is the end of the post.

The Truth: Well, it may be all I'm putting up now, but I'm nowhere near closing the book on this subject. Feel free to argue in the comments, and if there's anything worthwhile that comes up, I'll add it in here (or edit one of the above sections). Particularly, I know that my conclusion about thermal expansion is contrary to what TheBrummell heard. If you've heard of some better model which does show significant expansion, I'd be interested in seeing it.

2 comments:

Berlzebub said...

Info,

Something you may want to cover is one I've heard. "Only a small percentage of scientists actually believe in Global Warming."

Is there any hard data on how many Global Warming dissenters their are in the scientific fields. Specifically, in climatology, meteorology, etc. I think it would make a greater impact with those fields, than say a neurosurgeon who believes in ID. *tongue in cheek*

I realize that the truth doesn't care how many people believe it, but if some light could be shed on the possible massaging of numbers... Well, you know how that goes.

-Berlzebub

Infophile said...

Okay, it took a bit of time to do proper scouring on the numbers, and unfortunately I can't find any hard numbers. This isn't that surprising, seeing as scientists are rarely officially polled on their opinions. the rough numbers seem to break down to (among climate scientists):

Virtually all agree that there's been a rise of 1 degree F in the last 200 years.

Of the 928 papers published in the ten years from 93-03, not one expressed disagreement with the premise that Global Warming is happening now and is caused by humans.

The really controversial aspect is in what will happen in the future, and climate scientists are really divided over whether we will see no effect, see some small problems, some large problems, or even see some benefit. No good studies have been done on how many scientists fall into each of these camps, so I can't give you any numbers here.