The issue I'm referring to is something I've dealt with only sporadically on this blog, but nevertheless of the greatest interest and importance: global warming, aka climate change. In two earlier posts (see here and here), I discussed the dangers, both economic and social, of over-reacting to what appeared to be a very legitimate, but also little understood, threat. Despite my serious misgivings about some of the more extreme measures being contemplated to stave off the effects of climate change, it was never my intention to "debunk" the science itself, as many of these effects seemed all too evident. I was never a climate change "denier" so much as a skeptic regarding some of the more drastic "remedies" being proposed, which seemed far more dangerous than anything we could expect from the disease itself.
However! Just the other day, I came across a report from NASA that stopped me cold. For anyone who's been following the g.w. debate, the title says it all: NASA Study Finds Earth’s Ocean Abyss Has Not Warmed. Why is this finding important? Because of something called "the hiatus," i.e., the period from roughly 1998 to present, in which the steady rise of global temperatures, so strongly evident during so much of the 20th century, appears to have leveled off. The overall picture is neatly summarized in the follow graph, courtesy of Wikipedia:
Here's another, more close-up view, from the 1970's on:
And here's an even closer look, from the website climate depot, illustrating how global warming, overall, appears to have stalled completely ever since a dramatic peak in 1998:
What makes the hiatus especially puzzling is its apparent indifference to the rise in CO2 emissions, which has continued unabated:
While climate scientists have come up with a variety of explanations for the hiatus, including their own versions of denial, the most convincing explanation by far has focused on the oceans.
The most likely explanation for the lack of significant warming at the Earth’s surface in the past decade or so is that natural climate cycles—a series of La Niña events and a negative phase of the lesser-known Pacific Decadal Oscillation—caused shifts in ocean circulation patterns that moved some excess heat into the deep ocean. . .
. . . scientists estimate the ocean absorbs more than 90 percent of the excess heat trapped in the atmosphere by greenhouse gases. When analyzing temperature patterns at different depths of the ocean, scientists observed that deep ocean temperatures—measured more than a half-mile down from the surface—began to rise significantly around 2000, while shallower waters warmed more slowly.While this sort of explanation first struck me as a bit of a fudge, I saw no reason to reject it, especially since the science appeared sound. But now, with actual measurements replacing estimates, everything has changed. According to the NASA report,
The cold waters of Earth’s deep ocean have not warmed measurably since 2005, according to a new NASA study, leaving unsolved the mystery of why global warming appears to have slowed in recent years. [my emphasis]
Scientists at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, analyzed satellite and direct ocean temperature data from 2005 to 2013 and found the ocean abyss below 1.24 miles (1,995 meters) has not warmed measurably. . . .
In the 21st century, greenhouse gases have continued to accumulate in the atmosphere, just as they did in the 20th century, but global average surface air temperatures have stopped rising in tandem with the gases. [my emphasis] The temperature of the top half of the world's oceans -- above the 1.24-mile mark -- is still climbing, but not fast enough to account for the stalled air temperatures.
Many processes on land, air and sea have been invoked to explain what is happening to the "missing" heat. One of the most prominent ideas is that the bottom half of the ocean is taking up the slack, but supporting evidence is slim. This latest study is the first to test the idea using satellite observations, as well as direct temperature measurements of the upper ocean. Scientists have been taking the temperature of the top half of the ocean directly since 2005, using a network of 3,000 floating temperature probes called the Argo array.
"The deep parts of the ocean are harder to measure," said JPL's William Llovel, lead author of the study published Sunday in the journal Nature Climate Change. "The combination of satellite and direct temperature data gives us a glimpse of how much sea level rise is due to deep warming. The answer is -- not much."
NB: From the above, it's clear that the NASA scientists, unlike the many skeptics, accept the hiatus as real, characterizing this rather dramatic anomaly as a "mystery."
So does this mean NASA, and other influential government organizations, will change their minds about climate change? Not likely.
Study coauthor Josh Willis of JPL said these findings do not throw suspicion on climate change itself. "The sea level is still rising," Willis noted. "We're just trying to understand the nitty-gritty details."Hmmm. I thought the issue was determining the cause of global warming, not its effects. If g.w. is in fact causing sea levels to rise, that tells us nothing about what is causing g.w. itself.
And while we're on the topic of sea level rise, let's examine yet another graph:
According to this display, sea levels have been rising steadily since some time around 1885. Interesting. Because according to one of the graphs we've just seen,
[Added 10-17-14: Here's a graphic comparison put together by "MARodger," one of the commenters on the RealClimate blog. It's a combination of data from two different sources: Jevrejeva et al. (2008) and BEST land temperatures:
As you can see, this one covers a much larger time-span, though of course the earlier data is not as reliable as the latter. According to Mr. Rodger, this comparison demonstrates my error, based on the less complete graphs, in assuming that sea level rise (in blue) preceded global warming (in red). What I see in Rodger's graph is very interesting, but also somewhat confusing. The first rise of any kind appears around 1750, in red (temperature). It peaks around 1770 and then dips pretty sharply downward until 1793. This is followed by a rise in blue (sea level), beginning a bit later. It's possible the sea level rise was a delayed reaction to the temperature rise, but that doesn't account for the following temperature dip, which is followed by another temperature dip from 1795 through 1810. No comparable dip can be seen in the sea level data. Moreover, since the Industrial Revolution didn't begin until around 1760 it would be difficult to attribute the initial temperature rise to CO2 emissions.
From 1810 onward, however, we see a pronounced rise in the temperature data that continues almost unabated until almost 2000. And this is, in fact, followed by a somewhat similar rise in sea level, beginning around 1870, which, if the former were causing the latter, would represent a delay of about 60 years. There is also a second rise in temperature, beginning around 1840 that should also be considered. If that caused the sea level rise it would shorten the delay to ca. 30 years.
So. From this broader perspective we do seem some evidence consistent with a possible influence of global warming on sea level, since in this case the former can be seen as having preceded the latter. What remains confusing is the relation of these trends to CO2 emission, since 1810 represents a very early phase indeed of the Industrial Revolution and 1840 is also still pretty early.
Here's a graph representing fossil fuel emissions, originating with the Carbon Dioxide Information Analysis Center:
In any case, I must admit that the situation with respect to sea level rise is more interesting and complex than I had initially assumed. So thank you, Mr. Rodger.]
Statistical correlation is one of the most useful tools known to science. It can be very misleading however, and is all too frequently abused, even by experienced scientists. Properly understood, a correlation can point us to a relationship that could, potentially, be meaningful. However, as is well known, correlation in itself does not imply causation. The problem was neatly encapsulated by the individual who first promoted correlation as a scientific tool, Karl Pearson:
All causation as we have defined it is correlation, but the converse is not necessarily true, i.e. where we find correlation we cannot always predict causation. In a mixed African population of Kaffirs and Europeans, the former may be more subject to smallpox, yet it would be useless to assert darkness of skin (and not absence of vaccination) as a cause. [Pearson, The Grammar of Science, footnote to the second edition of 1900.]When scientists began paying attention to the relationship between atmospheric warming and the production of greenhouse gases, there appeared to be a very strong correlation between the two, as illustrated in the following graph:
However, as just noted, the presence of a correlation between any two datasets does not, in itself, tell us one represents the cause of the other. To determine cause we need to look more deeply into the evidence, applying logic, critical thinking and above all, simple common sense.
Now. If we look critically at the various graphs what we see is a relationship between warming and greenhouse gas emission that does indeed seem to be correlated -- some of the time. But certainly not all of the time. In the graph just above, for example, I see a complete lack of correlation until roughly 1975. Greenhouse gases have been emitted into the atmosphere in ever-increasing numbers since the beginning of the Industrial Revolution, so why is it that the correlation begins only three quarters of the way into the 20th century?
The anomaly has been explained as the result of a major increase in the use of fossil fuels since 1975, and that may be the case. However, if global warming and CO2 emission were causally connected, the correlation should be evident throughout. Thus, if higher rates of CO2 emission led to higher temperatures, then lower rates should have led to lower temperatures. The anomaly is most evident between the years 1930 and 1945, when temperature spiked dramatically while CO2 production continued to increase at the same slow but steady rate as before.
The key issue: it's not only that correlation does not imply causation, but also, in the above-quoted words of Karl Pearson: "All causation . . . is correlation." In other words, if one thing is truly the cause of another, correlation will be evident at all points, not just certain selected ones.
Which returns us to the hiatus. Here, once again, is the telltale graph:
And here again we see a rather dramatic example of non-correlation. It is indeed very hard to understand why warming would remain essentially flat over a period of almost 18 years while CO2 emissions continued to soar, given the almost universal conviction among climate scientists that the latter is the cause of the former. The "mystery" has now been compounded by the recent NASA findings, which all but rule out the hypothesis, taken for granted by so many, that the expected warming trend was somehow transported from the atmosphere to the depths of the sea.
The NASA paper is, of course, only one study out of many and could be flawed. Given the importance of the issue at hand, I would hope our government would make it a priority to conduct followup research as soon as possible, to make sure these results can be replicated. If they are, indeed, accurate, there will no longer be any valid reason to doubt the reality of the "mysterious" hiatus. And thus no longer any logical reason to hold onto the almost universally accepted conviction that "the science" supports human induced global warming.
While it is undeniably true that our atmosphere, if not our oceans, is heating up -- as illustrated by the above graph things are definitely warmer than they were at the beginning of the 20th century -- it seems highly unlikely that greenhouse gas emissions could be the cause. If that were true, then the steady increase in fossil fuel emissions over the last 18 years or so would almost certainly have resulted in a concomitant increase in temperatures. Temperatures have varied considerably during the history of our planet, so what looks to have been a temporary period of rapid increase may not be so mysterious after all, but simply the work of Mother Nature.
It looks to me as though we can also rule out a causal relation between global warming and sea level rise as well, since the beginnings of the latter predate the earliest evidence of the former. Sea levels have been rising steadily since at least the late 19th century and probably well prior to that period, and will no doubt continue to rise well into the 21st. This is certainly a major concern, to which we will definitely need to adapt. But cutting down on the burning of fossil fuels will, in all likelihood, not make a difference. [Added 10-17-14: But see the segment I've interpolated above, which displays a more comprehensive graph, suggesting a broader and more complex view of this issue.]
Climate scientists may be especially knowledgeable when it comes to collecting data and creating hypothetical models, but they are no more capable than the rest of us when it comes to applying simple logic and common sense to the models they produce.
There are a great many very real challenges ahead of us in the remainder of this century and considerable resources will need to be expended in order to deal with them. I see no point, therefore, in diverting vast amounts of money and resource in a quixotic attempt to reverse global warming by seriously undermining one of the most precious resources we have: fossil fuels. Even if the burning of fossil fuels were in fact the cause of global warming, any effort to seriously cut down on their use would almost certainly lead to consequences in the near future far worse than anything we could expect from climate change even over the next hundred years. And by then fossil fuels will have run out in any case. In fact the increasing scarcity of fossil fuels is the real challenge we face. For more of my thoughts on such matters I refer you to the blog posts I linked to at the outset of this post.
Before concluding I must make it clear that I am not a conservative, nor a Republican, nor a libertarian, nor am I connected in any way with the oil industry or any other purveyor of fossil fuels. I have absolutely no skin at all in this game, either monetary or ideological. As anyone reading very far in this blog will soon realize, my sentiments are definitely on the left side of the political spectrum, so I don't see myself having anything in common with the usual set of "deniers" whose motives do in fact seem primarily ideological. I'm not at all comfortable in siding with these folks, who in my opinion, are doing serious damage to our democracy and even common decency, respect for others, etc. But in this case I have no choice but to side with them -- because as far as I can tell, despite their questionable motives, they are right, and my fellow liberals -- most of them -- are wrong. And not only wrong but, very possibly, disastrously so.
[Added at 3:30 PM, Oct. 11: Here's a link to a well written, comprehensive and balanced discussion of the hiatus, as published at the website of the journal Nature: Climate Change: The Case of the Missing Heat.
Judging from the many serious responses to this challenge by recognized climatologists, the hiatus is not simply a myth, as has sometimes been alleged, but a very real anomaly that must be accounted for if global warming is to be attributed to the release of greenhouse gases.
Given all the many, and very different, explanations for the hiatus "mystery," one wonders whether it's any longer necessary for a hypothesis to be falsifiable. One wonders also what evidence could possibly falsify this theory in the minds of its adherents, since finding "good reasons" for just about any anomaly seems to have become a favorite sport.]