Tree rings may underestimate climate response to volcanic eruptions: study

February 5, 2012, Pennsylvania State University

Some climate cooling caused by past volcanic eruptions may not be evident in tree-ring reconstructions of temperature change because large enough temperature drops lead to greatly shortened or even absent growing seasons, according to climate researchers, who compared tree-ring temperature reconstructions with model simulations of past temperature changes.

"We know these tree rings capture most temperature changes quite well," said Michael Mann, professor of meteorology and and director of the Penn State Center. "But the problem appears to be in their response to the intense short-term cooling that occurs following a very large . Explosive volcanic eruptions place particulates called aerosols into the stratosphere, reflecting back some fraction of incoming sunlight and cooling the planet for several years following the eruption."

are used as proxies for climate because trees create unique rings each year that often reflect the that influenced the growing season that year. For reconstructing , tree-ring researchers seek trees growing at the extremes of their growth range. Inferring temperature changes required going to locations either at the tree line caused by elevation or at the boreal tree line, the northern most place where the trees will grow.

For these trees, growth is almost entirely controlled by temperature, rather than precipitation, or sunlight, yielding a good proxy record of surface temperature changes.

"The problem is that these trees are so close to the threshold for growth, that if the temperature drops just a couple of degrees, there is little or no growth and a loss of sensitivity to any further cooling. In extreme cases, there may be no growth ring at all," said Mann. "If no ring was formed in a given year, that creates a further complication, introducing an error in the chronology established by counting rings back in time."

The researchers compared temperature reconstructions from actual tree-ring data with temperature estimates from climate models driven with past volcanic eruptions.

Comparing the model-simulated temperatures to the Northern Hemisphere temperatures reconstructed from tree-ring thickness, Mann, working with Jose D. Fuentes, professor of meteorology, Penn State, and Scott Rutherford, associate professor of environmental science, Roger Williams University, found the overall level of agreement to be quite good.

However, they report in the current issue of Nature Geoscience that "there is one glaring inconsistency; the response to the three largest tropical eruptions -- AD 1258/1259, 1452/1453 and the 1809+1815 double pulse of eruptions -- is sharply reduced in the reconstruction."

Following the 1258 eruption, the climate predict a drop of 3.5 degrees Fahrenheit, but the tree ring-based reconstruction shows only about a 1 degree Fahrenheit dip and the dip occurs several years too late. The other large eruptions showed the same type of discrepancy.

Using a theoretical model of tree-growth driven by the simulated , the team determined that the cooling response recorded by the trees after a volcanic eruption was limited by biological growth effects. Any temperature drop exceeding roughly 1 degree Fahrenheit would lead to minimal tree growth and an inability of trees to record any further cooling. When growth is minimal enough, it is likely that a ring will not be detectable for that year.

The potential absence of rings in the first one to three years following eruption further degrades the temperature reconstruction. Because tree-ring information is averaged across many locations to obtain a representative estimate of northern hemisphere temperature, tree-ring records with and without missing rings for a given year are merged, leading to a smearing and reduced and delayed apparent cooling.

The researchers also noted that aerosol particles forced into the air by volcanoes block some direct sunlight causing cooling and they produce more indirect, scattered light at the surface. Trees like indirect sunlight and grow better under those conditions. However, this effect is small compared to that of lower temperatures and shorter .

By accounting for these various effects in the tree growth model, the researchers were able to reproduce the reduced and smeared cooling seen in the actual tree-ring reconstruction, including the near absence -- and delay -- of cooling following the massive 1258 eruption.

"Scientists look at the past response of the climate to natural factors like volcanoes to better understand how sensitive Earth's climate might be to the human impact of increasing greenhouse gas concentrations," said Mann. "Our findings suggest that past studies using tree-ring data to infer this sensitivity have likely underestimated it."

Explore further: Seeing the wood for the trees: New study shows sheep in tree-ring records

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not rated yet Feb 05, 2012
Could varved clays, seasonal bands in lake bed deposits, not be used to explore the years where volcanic particles are present in the atmosphere and the amount of biological activity in those years.
1.6 / 5 (7) Feb 05, 2012
When you're working to promote a lie, it can be helpful to have support among "collegaues". The "researchers" pushing that the Little Ice Age began four centuries before it did were stymied by the existence of disagreeing information. Such as that tree tings did not show such temperature drops. So they cobbled together the fiction that tree rings do not accurately reflect temperature. Then the present that as a "separate" "discovery" and use it to maintain the claim for the early beginning of the Little Ice Age.
1 / 5 (4) Feb 05, 2012
Extremely ironic, though. This will likely by defended by the anti-climate change forces who play with words to say the unnatural heating of the air is actually, "the earth warming up after the cooling". BUt, another favorite point for the "skeptics" is the supposed "deception" by climate scientists. But the root of that incident was the realization that tree rings are not necessarily so reliable in revealing past temperatures. Before the '70's, tree rings did mirror temperatures, but, after the middle of that decade, they diverged, and climatologists' emails recommended playing down tree ring reliability, just as thess "researchers" are saying. Yet the anti-climate change "nay-sayers" denounced them!
2 / 5 (8) Feb 05, 2012
Tree rings stopped working in 1960. And never had worked before 1550. That data was deleted by dishonest fraudsters.

Which means tree rings never worked as a proxy for temperature.

Climate Frauds just kept lying about it.

5 / 5 (1) Feb 06, 2012
Vendicar Decarian, one possible explanation is that he never claimed that they show good correlation for only ten years. He said 1550, not 1950, giving a time span of 1550-1960--about four hundred years.
2.7 / 5 (7) Feb 06, 2012
When you're working to promote a lie, it can be helpful to have support among "collegaues". The "researchers" pushing that the Little Ice Age began four centuries before it did were stymied by the existence of disagreeing information. Such as that tree tings did not show such temperature drops. So they cobbled together the fiction that tree rings do not accurately reflect temperature. Then the present that as a "separate" "discovery" and use it to maintain the claim for the early beginning of the Little Ice Age.

I so love conspiracy theorists. This article is talking about a few years discrepancy, in 3 different massive volcanic events. A few years doesn't wipe out 400 years of data.

Can you hear everyone laughing at you? You might need to remove your tinfoil hat to hear it.
3 / 5 (6) Feb 06, 2012
Wow.. According to denialist Parker Tard, tree rings correlate with temperatures for a period shorter than the calibration time of the data.

What a moron....

Are you a child or do you just act like one on physorg?
1 / 5 (3) Feb 06, 2012
Lets say you claim trees are a proxy for temperature. And you claim they match the temperature record from 1850 (when modern thermometers came into being in enough places) all the way to the present.

And then it turns out you lied. The proxies went down starting in 1950 when supposed temperatures went up.

That means the proxies either never work and 1850 to 1950 were a fluke or they underestimate temperature 30% of the time.

If the latter is true then there could be 300 years in the last 1000 that were warmer than today.

But NOOOOOOOO. Mann and his cohorts claim today was the warmest period in the last 1000 using bogus proxies.
1 / 5 (3) Feb 06, 2012
The climate audit article shows that inconvenient data was deleted post-1950 and pre-1550 to hide the decline.

A proxy that does not match thermometers after 1950 is not a good proxy. A proxy that does no match other proxies before 1550 is not a good proxy.

Scientists who hide data that proves their proxy a failure are frauds.
1 / 5 (3) Feb 07, 2012
Where did Climate Audit get the data to show this if it was deleted as you have dishonestly claimed?

Read about it here:


1 / 5 (3) Feb 07, 2012
That is why tree rings are supplemented by isotopic ratio's, sea shell growth rates, borehole temperature measurements, sediment deposition rates, written historical records, etc. etc. etc.

Funny you should say that Vendicam ....

"A paper published this week in the journal Climate of the Past analyzes an "unprecedentally large network of temperature...proxy records" [a total of 120] and concludes that warming of the 20th century was "within the range of natural variability over the last 12 centuries."

Only two of the eight types of temperature proxies analyzed indicate 20th century warming exceeded that of the Medieval Warming Period."
1 / 5 (3) Feb 07, 2012
"However, our results show the rate of warming from the 19th to the 20th century is clearly the largest between any two consecutive centuries in the past 1200 yr."

Well Duh. The Little Ice Age was the coldest period in 10,000 years.

Go from the coldest period in this interglacial to the 5th warmest period after the Holocene Optimum, Minoan Warming, Roman Optimum and MWP and it might appear a large jump.

"Temperatures in Greenland were about 1.5 C warmer 1000 years ago than now.

It was perhaps 2.5 C warmer 4000 years ago.

The period around 1875, at the lowest point of the Little Ice Age, marked the coldest point in the last 10,000 years."


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