Last week there was much buzz in the media about a new paper that used fossils from sediment and ice cores to reconstruct global temperatures for the last 11,000 years.

Typical of the headlines was this one from the Arizona Daily Star: “Study: Global heat spike unique in past 11,000 yrs.” The fuss was caused by this paper: “A Reconstruction of Regional and Global Temperature for the Past 11,300 Years” by Marcott et al., published in Science.

The paper’s graph causing all the stir is shown below:

The paper’s abstract contains this sentence: “Current global temperatures of the past decade have not yet exceeded peak interglacial values but are warmer than during ~75% of the Holocene temperature history.” That alone gives the lie to the graph and to the Star’s headline.

A critique of the paper may be found at WUWT here.

Essentially Marcott et al. used Michael Mann’s hockey stick trick to co-join two data sets of very different resolutions to come up with the spike, in other words they joined apples and oranges.

That procedure blurs out the Medieval Warm Period of about 1,000 years ago even though that period was as warm or warmer than current temperatures.

In the WUWT critiques, Robert Rhode, of the Berkeley Earth Surface Temperature Study, explains the problem:

“They rely on proxy data that is widely spaced in time (median sampling interval 120 years) and in many cases may also be subject to significant dating uncertainty. These effects will both tend to blur and obscure high frequency variability. They estimate…that only 50% of the variance is preserved at 1,000-year periods. This amount of variance suppression is roughly what you would expect if the underlying annual temperature time series had been smoothed with a 400-year moving average. In essence, their reconstruction appears to tell us about past changes in climate with a resolution of about 400 years. That is more than adequate for gathering insights about millennial scale changes during the last 10,000 years, but it will completely obscure any rapid fluctuations having durations less than a few hundred years…..one should be careful in comparing recent decades to early parts of their reconstruction, as one can easily fall into the trap of comparing a single year or decade to what is essentially an average of centuries….since their methodology suppresses most of the high frequency variability, one needs to be cautious when making comparisons between their reconstruction and relatively rapid events like the global warming of the last century.”

Another point from geologist Dr. Don Easterbrook:

“Eighty percent of the source data sites were marine, so temperatures from 80% of the data set used in this paper record ocean water temperatures, not atmospheric temperatures. Thus, they may reflect temperature changes from ocean upwelling, changes in ocean currents, or any one of a number of ocean variations not related to atmospheric climates. This in itself means that the Marcott et al. temperatures are not a reliable measure of changing atmospheric climate.”

Additional comments from Dr. Judith Curry, Georgia Tech: “There doesn’t seem to be anything really new here in terms of our understanding of the Holocene.  Mike’s Nature trick seems to be now a standard practice in paleo reconstructions.  I personally don’t see how this analysis says anything convincing about climate variability on the time scale of a century.”

Interestingly, buried in the supplementary material to their paper, Marcott et al. showed the results of running their data through a computer program which used different algorithms and assumptions. This exercise produced a quite different graph from the same data:

That graph is not nearly as scary looking as the one touted in the headlines. This just goes to show that the results depend on the assumptions and methods used in the computer program: Garbage in – Garbage out. Of course, that graph would not garner headlines.

 

 

 

 

 

WUWT update post: Marcott et al claim of ‘unprecedented’ warming compared to GISP ice core data.  This update from WUWT graphically shows that the current warmth is not unprecedented as claimed.  The first sentence of Marcott et al. says, “Surface temperature reconstructions of the past 1500 years suggest that recent warming is unprecedented in that time.”  This is clearly false.  Anthony Watts superimposes the Marcott data over an earlier study of Greenland ice core data  to get this graph:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 To put things in perspective, look at the following graph, a temperature reconstruction based on ice core data.  Unlike the Marcott paper, this reconstruction shows that current temperatures are among the coolest of the last 10,000 years.  Notice also the previous periods of rapid warming (red lines on the graph).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

UPDATE: April 2, 2013, Ross McKitrick explains how Marcott purposely changed the dates on proxy core to produce the uptick: http://opinion.financialpost.com/2013/04/01/were-not-screwed/

UPDATE: A simple test shows where Marcott goes wrong see here.  See a good explanation of the deception from Resilient Earth here.

Steve McIntyre deconstructs Marcott:

Marcott Mystery #1

No Uptick in Marcott Thesis

Marcott’s Zonal Reconstructions

How Marcottian Upticks Arise

The Marcott-Shakun Dating Service

Hiding the Decline: MD01-2421

 

See also:

20^th Century temperatures explained as natural recovery from Little Ice Age

More evidence that current warming is not unusual

There is an on-going controversy in studies of global sea level rise. The latest entry is a paper in the Proceedings of the National Academy of Sciences, which has become, unfortunately, a “pal-reviewed” journal rather than a peer-reviewed journal.

The paper in question is titled, “Climate related sea-level variations over the past two millennia.” One of the co-authors is Michael Mann of “hide the decline” fame and author of the now debunked hockey stick. (see full paper) These researchers used samples from just two sites is North Carolina to conclude: “A second increase in the rate of sea-level rise occurred around AD 1880–1920; in North Carolina the mean rate of rise was 2.1 mm/y in response to 20th century warming. This historical rate of rise was greater than any other persistent, century-scale trend during the past 2100y.” In other words, they say that the rate of sea level rise is accelerating.

The problem I see with this research is that there are only two sample sites and these sites are within an unstable geological environment: barrier islands/estuaries. The apparent sea level is subject to frequent change due to reconfiguration of the coast by storms and coastal currents. In fact, the two closest long-term tidal gauge records, Wilmington, N.C. and Hampton Roads, Va., show widely varying rates of sea level rise: 2.0 mm/yr and 4.5 mm/yr respectively. The sample size used by these researchers was too small and not representative of global sea level rise.

In another paper published in May, 2011, in the Journal of Coastal Research, the researchers analyzed the records of 57 U.S. tidal gauges and found that the rate of sea level rise was decreasing during the 20^th Century:

Our analyses do not indicate acceleration in sea level in U.S. tide gauge records during the 20th century. Instead, for each time period we consider, the records show small decelerations that are consistent with a number of earlier studies of worldwide-gauge records. The decelerations that we obtain are opposite in sign and one to two orders of magnitude less than the +0.07 to +0.28mm/y2

accelerations that are required to reach sea levels predicted for 2100 by Vermeer and Rahmsdorf

(2009), Jevrejeva, Moore, and Grinsted (2010), and Grinsted, Moore, and Jevrejeva (2010). Bindoff et al. (2007) note an increase in worldwide temperature from1906 to 2005 of 0.74uC. It is essential that investigations continue to address why this worldwide-temperature increase has not produced acceleration of global sea level over the past 100 years, and indeed why global sea level has possibly decelerated for at least the last 80 years.

An earlier study Holgate (2007), using data from worldwide coastal tidal gauge records, shows that the rate of sea level rise is decreasing. Specifically, the mean rate of global sea level rise was “larger in the early part of the last century (2.03 ± 0.35 mm/yr 1904-1953), in comparison with the latter part (1.45 ± 0.34 mm/yr 1954-2003).” (Citation: Holgate, S.J. 2007. On the decadal rates of sea level change during the twentieth century. Geophysical Research Letters 34: 10.1029/2006GL028492)

NASA satellite data show that sea level rise has been steady, not accelerating, and has in fact been decelerating since 2006.

For more background on sea level since the end of the last glacial epoch 15,000 years ago, see my post “Sea Level Rising?” That post presents graphs and shows that the rate of sea level rise is cyclical. It also gives more references.

It seems that both sample size and location matter when trying to determine what is happening with global sea level. And, it appears that researchers with an agenda can cherry-pick data to suit their needs.

See also:

Climate Data, Fact or Fiction

Sea Level Rise in the South Pacific: None