I hope I am not implying anything. That's such a wishy washy term. I'm stating it.
Bunch of pimps who came along too late to work for Marlboro... "I do know that we've reached the point where defending our right to emit carbon on the scale we're doing it is several steps down the moral ladder from defending tobacco companies as innocent of causing cancer."
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Purty picture. Where is the MWP?
Message 22490203
Lots of this stuff in that PDF I linked you to; you can overlay the graphs...
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"using fake scientific studies, to fool people, in exchange for money"
Well, at least selectively massaging data...
Next, and slightly more troubling, we have some rather misleading and selective recollection regarding Jim Hansen's testimony to congress in 1988. "Dr. Hansen overestimated [global warming] by 300 percent" (p247). Hansen's testimony did indeed lead to a big increase in awareness of global warming as a issue, but not because he exaggerated the problem by 300%. In a paper published soon after that testimony, Hansen et al, 1988 presented three model simulations for different scenarios for the growth in trace gases and other forcings (see figure). Scenario A had exponentially increasing CO2, Scenario B had a more modest Business-as-usual assumption, and Scenario C had no further increases in CO2 after the year 2000. Both scenarios B and C assumed a large volcanic eruption in 1995. Rightly, the authors did not assume that they knew what path the carbon dioxide emissions would take, and so presented a spectrum of results. The scenario that ended up being closest to the real path of forcings growth was scenario B, with the difference that Mt. Pinatubo erupted in 1991, not 1995. The temperature change for the decade under this scenario was very close to the actual 0.11 C/decade observed (as can be seen in the figure). So given a good estimate of the forcings, the model did a reasonable job. In fact in his testimony, Hansen ONLY showed results from scenario B, and stated clearly that it was the most probable scenario. The '300 percent' error claim comes from noted climate skeptic Patrick Michaels who in testimony in congress in 1998 deleted the bottom two curves in order to give the impression that the models were unreliable. realclimate.org
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One record does not a global Medieval warm period make. 'Global' is the key word there. It turns out that many of the so-called 'MWP's seen in seperate records actually occur at different times, and so would not show up in the global mean. I recommend reading the Bradley et al (2003) Science Perspective dealing with this matter. - gavin
See also our discussion of "Hockey Stick myth #2", and the section "Was there a "Little Ice Age" and a "Medieval Warm Period" in chapter 2 of the 2001 IPCC report which specifically discussed the Keigwin (1996) record you mention and its likely reflection, at least in part, of changes in the North Atlantic Oscillation in past centuries. Changes in the NAO appear to play a prominent role in the spatial pattern of climate change in past centuries (see e.g. the review paper: Schmidt, G.A., D.T. Shindell, R.L. Miller, M.E. Mann, and D. Rind 2004. General circulation modelling of Holocene climate variability. Quaternary Sci. Rev., 23, 2167-2181, doi:10.1016. ). Regional influences due to changes in the NAO and the El Nino/Southern Oscillation in past centuries complicate the relationship between regional and truly hemispheric or global temperature estimates. For precisely this reason, the numerous proxy and model-based estimates of the variations in the average temperature of the Northern Hemisphere (not just just the Mann et al reconstruction, as implied by your comment) show far more modest temperature changes than those typically interpreted from specific proxy records from any one region. -mike
realclimate.org
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The "Medieval Warm Period"
NOAA...
Medieval Warm Period - 9th to 14th Centuries
Norse seafaring and colonization around the North Atlantic at the end of the 9th century was generalized as proof that the global climate then was warmer than today. In the early days of paleoclimatology, the sparsely distributed paleoenvironmental records were interpreted to indicate that there was a "Medieval Warm Period" where temperatures were warmer than today. This "Medieval Warm Period" or "Medieval Optimum," was generally believed to extend from the 9th to 13th centuries, prior to the onset of the so-called "Little Ice Age."
In contrast, the evidence for a global (or at least northern hemisphere) "Little Ice Age" from the 15th to 19th centuries as a period when the Earth was generally cooler than in the mid 20th century has more or less stood the test of time as paleoclimatic records have become numerous. The idea of a global or hemispheric "Medieval Warm Period" that was warmer than today however, has turned out to be incorrect.
For larger viewing version of graph, please click here or on image.
There are not enough records available to reconstruct global or even hemispheric mean temperature prior to about 600 years ago with a high degree of confidence. What records that do exist show that there was no multi-century periods when global or hemispheric temperatures were the same or warmer than in the 20th century. For example, Mann et al. (1999) generated a 1,000 year Northern Hemisphere temperature reconstruction (shown above) using data from multiple ice cores and tree ring records. This reconstruction suggests that the 1998 annual average temperature was more than two standard deviations warmer than any annual average temperature value since AD 1,000 (shown in yellow). (For complete scientific reference of this study, please click here. Link to Mann 1999 FTP Data.)
In summary, it appears that the 20th century, and in particular the late 20th century, is likely the warmest the Earth has seen in at least 1200 years. To learn more about the so-called "Medieval Warm Period", please read this review published in Climatic Change, written by M.K. Hughes and H.F. Diaz. (For complete review reference click here.)
ncdc.noaa.gov
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Oh, look; it's Willie and Sallie again :>)
In essence, the authors have revisited a question posed earlier in a paper by Willie Soon and Sallie Baliunas (2003: see our previous discussion here), investigating whether or not evidence from past proxy records of temperature support the existence of past intervals of warmth with the widespread global scale of 20th century warming. The Soon and Baliunas (2003) paper was heavily criticized in the scientific literature (e.g. Mann et al, 2003) for failing to distinguish between proxy evidence of temperature and drought or precipitation, and for not accounting for whether temperature anomalies in different regions were contemporaneous or not.
Osborn and Briffa, by contrast, have carefully taken these issues into account. They make use only of those proxy records which demonstrate a statistically significant relationship with modern instrumental temperature records, and which were dated accurately enough that records from different locations could be compared against each other in a chronologically consistent manner. They then standardize the records and look for evidence of simultaneous relative departures that point in the same direction (i.e. "warm" or "cold") using appropriate pre-set thresholds for defining a significant event (they try both one and two standard deviations). There is an important distinction between this careful statistical approach, and the selective cherry picking that is often used by contrarian commentators to misrepresent the available evidence. For example, it is possible to find evidence of significant warmth or significant coldness over literally any century-long interval in at least one of the 14 records used by Osborn and Briffa (see Figure 1 in the article). However, this alone tells us very little. What is of interest, instead, is whether centuries-long intervals can be found over which warm events or cold events tend to cluster.
Osborn and Briffa use Monte Carlo simulations to test the null hypothesis that a given number of simultaneous "warm" or "cold" events should simultaneously emerge among 14 such independent records from chance alone. Where they are able to reject this null hypothesis, they conclude that there is evidence of large-scale warmth or coldness, and they quantify its spatial extent. They also establish that their results are robust with respect to the elimination of any single record, and that the main conclusions are independent of the particular base period (e.g. whether they use the full interval AD 800-1995, or only the modern interval of 1856-1995 which overlaps with the instrumental record). While some of the caveats of some past studies are applicable in this study too (for example, the authors only use 14 proxy sites), the authors do attempt to address them. For example, they show that the modern instrumental record averaged only over their 14 sites captures the full Northern Hemisphere mean temperature variations remarkably well over the available (approximately 150 years) interval. The authors also examine the difference between the number of significant warm and cold events over time, and this tells a similar story.
realclimate.org
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In particular, no one knows whether this is unusual or merely something that happens periodically for natural reasons.
This is incorrect. The natural causes of past climate variations are increasingly well-understood, and they cannot explain the recent global warming. As discussed elsewhere on this site, modeling studies indicate that the modest cooling of hemispheric or global mean temperatures during the 15th-19th centuries (relative to the warmer temperatures of the 11th-14th centuries) appears to have been associated with a combination of lowered solar irradiance and a particularly intense period of explosive volcanic activity. When these same models are forced with only natural radiative forcing during the 20th century [see e.g. Crowley (2000)] they actually exhibit a modest cooling trend. In other words, the same natural forcings that appear responsible for the modest large-scale cooling of the "Little Ice Age" should have lead to a cooling trend during the 20th century (some warming during the early 20th century arises from a modest apparent increase in solar irradiance at that time, but the increase in volcanism during the late 20th century leads to a net negative 20th century trend in natural radiative forcing). In short, given natural forcing factors alone, we should have basically remained in the "Little Ice Age". The only way to explain the upturn in temperatures during the 20th century, as shown by Crowley (2000) and many others, is indeed through the additional impact of anthropogenic (i.e., human) factors, on top of the natural factors.
Most global warming alarms are based on computer simulations that are largely speculative and depend on a multitude of debatable assumptions.
This is not correct. Concern about global warming is not based primarily on models, but rather on an understanding of the basic physics of the greenhouse effect and on observed data. We know from data that we have caused the CO2 concentration in the atmosphere to rise sharply during the past century: it is now much higher than any time during the past 650,000 years (which is as far back as reliable ice core data exist). And we know that this rise in CO2-concentration changes the radiation balance of the planet and leads to a warming of global surface temperature. This is scientifically undisputed and well-established physics, which has been known since in the year 1896 the Swedish Nobel prize winner Svante Arrhenius calculated the climatic effect of a rise in CO2.
Since there is a continued increase in emissions of (in particular) CO2, continued greenhouse warming is highly likely to continue. The models serve merely to quantify these basic facts more accurately, calculate the regional climate response, and compute effects (such as the expected increase in ocean heat content or sea level) which can be tested against observed data from the real world.
The editorial then returns to the issue of paleoclimate reconstructions and the so-called "Hockey Stick", repeating literally each of RealClimate's documented "Hockey Stick" myths:
Then there's the famous "hockey stick" data from American geoscientist Michael Mann. Prior to publication of Mr. Mann's data in 1998, all climate scientists accepted that the Earth had undergone large temperature variations within recorded human history.
The actual prevailing view of the paleoclimate research community that emerged during the early 1990s, when long-term proxy data became more widely available and it was possible to synthesize them into estimates of large-scale temperature changes in past centuries, was that the average temperature over the Northern Hemisphere varied by significantly less than 1 degree C in previous centuries (i.e., the variations in past centuries were small compared to the observed 20th century warming). This conclusion was common to numerous studies from the early and mid 1990s that preceeded Mann et al (1998). The Mann et al (1998) estimates of Northern Hemisphere average temperature change were, in fact, quite similar to those from these previous studies (e.g. Bradley and Jones, 1993; Overpeck et al, 1997), but simply extended the estimates a bit further back (from AD 1500 to AD 1400). In reality, the primary contribution of Mann et al (1998) was that it reconstructed the actual spatial patterns of past temperature variations, allowing insights into the complex patterns of cooling and warming in past centuries. In fact, regional temperatures changes (e.g. in Europe) appear to have been significantly larger, and quite different, from those for the Northern Hemisphere on the whole. Neglecting the significance of the large regional differences in past temperature changes is another classic pitfall in the arguments put forward by many climate change contrarians (see Myth #2 here).
The WSJ editorial continues,
This included a Medieval warm period when the Vikings farmed Greenland and a "little ice age" more recently when the Thames River often froze solid.
The sentence, first of all, perpetuates two well-known fallacies regarding the so-called "Medieval Warm Period" and "Little Ice Age". See the RealClimate discussions of the Little Ice Age and Medieval Warm Period for explanations of why both the Viking colonization of Greenland and the freezing of the River Thames actually tells us relatively little about past climate change.
The actual large-scale climate changes during these intervals were complicated, and not easily summarized by simple labels and cherry-picked anecdotes. Climate changes in past centuries were significant in some parts of the world, but they were often opposite (e.g. warm vs. cold) in different regions at any given time, in sharp contrast with the global synchrony of 20th century warming.
The WSJ then continue with a statement that is problematic on several levels,
Seen in that perspective, the slight warming believed to have occurred in the past century could well be no more than a natural rebound, especially since most of that warming occurred before 1940.
Firstly, the overall warming of the globe of nearly 1 degree C since 1900 is hardly "slight". That warming is about 1/5 of the total warming of the globe from the depths of the last Major Ice Age (about 20,000 years ago) to present.
Secondly, the argument that the climate should have naturally "rebounded" with warming during the 20th century defies the actual peer-reviewed scientific studies which, as discussed earlier, suggest that the climate should have actually cooled during the 20th century, not warmed, if natural factors were primarily at play. Anthropogenic greenhouse gases are required to explain the observed warming. Also, it is incorrect that most of the warming occurred before 1940; in contrast, the warming since 1970 is larger than that up to 1940.
The WSJ proceeds with the claim that key scientific findings that are common to numerous independent studies (specifically that late 20th century hemispheric warmth is anomalous in the context of past centuries) can somehow be pinned on one particular research group or even individual (see Hockey Stick Myth #1 here):
Enter Mr. Mann, who suggested that both the history books and other historical temperature data were wrong. His temperature graph for the past millennium was essentially flat until the 20th century, when a sharp upward spike occurs -- i.e., it looks like a hockey stick. The graph was embraced by the global warming lobby as proof that we are in a crisis, and that radical solutions are called for.
This is patently incorrect.
The WSJ then echoes the final of the "Hockey Stick" myths discussed on RealClimate (see Myth #4 here), claiming that the "Hockey Stick" has now been discredited:
But then, in 2003, Canadian mathematician Stephen McIntyre and economist Ross McKitrick published a critique calling Mr. Mann's work riddled with "collation errors, unjustifiable truncations or extrapolation of source data, obsolete data, geographical location errors, incorrect calculations of principal components, and other quality control defects."
In fact, these claims have been demonstrated to be incorrect by an independent group of scientists at the National Center for Atmospheric Research (NCAR) . These authors have shown that the 'alternative' reconstruction promoted by McIntyre and McKitrick (which disagrees not only with the Mann et al reconstruction, but nearly a dozen independent reconstructions that agreee with the Mann et al reconstruction within statistical uncertainties) is the result of censoring of key data from the original Mann et al (1998) dataset. Unlike the original reconstruction of Mann et al (1998), the reconstruction that McIntyre and McKitrick produced using the censored data set fails standard statistical tests for validity, and, in the words of the NCAR group, is "shown to be without statistical and climatological merit".
Correct for those errors, they showed, and the Medieval warm period returns.
This is just bizarre. The claimed reconstruction of McIntyre and McKitrick, in fact, indicates anomalous warmth during the 15th century. This period doesn't fall even remotely within the interval commonly referred to as the "Medieval Warm Period" Instead, it actually falls within the heart of the "Little Ice Age" itself! The irony of contrarian supporters of the claims of McIntyre and McKitrick is that, if their reconstruction were valid (which it is not), it would actually argue for unusual warmth during the heart of the "Little Ice Age".
realclimate.org
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Were the Vikings who grew grains in Greenland a thousand years ago sucessful? Should have stuck to fishing.
Greenland Used to be Green ...
Greenland used to be a lovely hospitable island when the Vikings settled it. It was not until the Little Ice Age that it got so cold and it was clearly not the frozen wasteland it is today.
A bit of urban myth here, just try to correct the record and mention how a regional anecdote is not evidence of global anything.
Answer:
Firstly, Greenland is just a part of a single region and as such can not be assumed to represent any kind of global climate shift. See the article on the Medieval Warm Period for a global perspective on this time period. In short, the available proxy evidence indicates that globally this period was not particularily pronounced though certainly some regions may have experienced greater warming than others.
Secondly, a quick reality check shows that Greenland's ice cap is hundreds of thousands of years old and covers 95% of that island, so just how different could it have been only 1000 years ago?
Greenland was called Greenland by Erik the Red (was he red??) who was in exile and wanted to attract people to a new colony. He believed that you should give a land a good name so that people want to go there! It very likely was a bit warmer when he landed for the first time than it was when the last settlers starved due to a number of factors, climate change a likely major one. But it was never lush and their existence was always harsh and meager, especially due to the Viking's disdain for other peoples and other ways of living. They attempted to live a European lifestyle in an arctic climate side by side with the Inuit who easily out survived them. For heaven's sake, these people starved surrounded by oceans and yet never ate fish! (Note: this is not a european thing and is in fact a bit of a mystery to this day).
Instead of hunting whales in kayaks, they farmed cattle, goats and sheep despite having to keep them in a barn 24-7 for 5 months out of the year! It was a constant challenge to get enough fodder for the winter and starvation of the animals was frequent, emaciation routine. The pressures of grazing pasture and growing fodder for the winter led to over production of pastures, erosion and the need to go further and further afield to sustain the animals. Deforestation for pastures and firewood was unsustainable leading, after a couple of centuries, to having to cut and burn precious sod for fuel and housing construction.
When finally confronted with a few severe winters, they, along with the little remaining livestock, simply starved. Much as you can not judge a book by its cover, you can't determine the climate of Greenland from its name.
illconsidered.blogspot.com |
