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A Linkage Between the LIA and Gulf Stream?

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Michael Mann & Gavin Schmidt

The precise factors underlying the so-called “Little Ice Age” (LIA) have been intensely debated within the scientific community. One key metric in this debate is the spatial pattern of cooling which may provide a ‘fingerprint’ of the underlying climate change, whether that was externally forced (from solar or volcanic activity) or was part of an intrinsic mode of variability.

Surface temperatures in parts of Europe appear to have have averaged nearly 1°C below the 20th century mean during multidecadal intervals of the late 16th and late 17th century (and with even more extreme coolness for individual years), though most reconstructions indicate less than 0.5°C cooling relative to 20th century mean conditions for the Northern Hemisphere as a whole. There is much less data during these time intervals for the Southern Hemisphere, and that severely limits what conclusions can be drawn there. Just what combination of factors could explain this pattern of observations has remained somewhat enigmatic. A new ingredient in this debate comes with a recent paper in Nature by Lund et al.
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More on the Arctic

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By Michael Mann & Phil Jones (guest)

Svalbard, an Arctic island in the Northern North Atlantic, is predicted to warm considerably more than most of the rest of the earth in many model-based scenarios. See for example the figure to the right, which represents a relatively high-end IPCC Third Assessment Report scenario for the projected surface temperature difference between the period 2071 -2100 and 1961-1990. Svalbard is the island north of Norway at about 80N between 15-30E.

The enhanced warming in this region is related to the issue of polar amplification that we have discussed previously on RC. It also happens that the Svalbard meteorological station is the 2nd station in the World Meteorological Organization (WMO) meteorological station list. This means that it tends to get noticed. The Climatic Research Unit (CRU) of the University of East Anglia maintains one prominent version of the global surface temperature data set and as part of its routine quality control, CRU flags any unusual (anomalous warm or cold) new measurements that come in. Svalbard has now been flagged consistently over the past several months, but the values have been confirmed as accurate by the Norwegian Met Service, which operates the Svalbard station.
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A New Take on an Old Millennium

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The subject of reconstructions of temperature variations of the past millennium has been discussed many times before on this site (see e.g. here, here, here, and here). Despite the apparent controversy, the basic conclusion–that the global and hemispheric-scale warmth of the past few decades appears anomalous in a very long-term context–has stood up remarkably well in many independent studies (see Figure 1).

Temperatures over the Past 1000 Years
Figure 1. Reconstructions of Northern Hemisphere temperatures for the last 1000 years (various colored curves) compared with instrumental record (black curve).
 [source: Wikipedia] (click to enlarge)

This is not to say that all estimates agree in their details. Indeed, there is a fair scatter among the various published estimates. [Read more…] about A New Take on an Old Millennium

Groundhog Day

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Living in central Pennsylvania, it would seem remiss of me not to comment on Groundhog Day today. For those not familiar with the event, Groundhog Day, which takes place on February 2 every year, is the modern American version of an age-old tradition originating in Europe centuries ago. The modern Groundhog Day is celebrated in the United States in Punksutawney Pennsylvania (about 100 miles west of Penn State University, where I teach). According to legend, if the groundhog–who is named Punxsutawney Phil–sees his shadow, there will be six more weeks of winter weather. If he does not see his shadow, there will be an early spring. After Phil emerges from his burrow on February 2, he speaks to an event official in “Groundhogese”, and his prediction is then translated for the awaiting public. The event was popularized in the 1993 movie of the same name, starring Bill Murray.

Sadly, it appears that global warming may soon add Phil to the ranks of the unemployed. With the warming of 4-8ºC (7-14ºF) predicted over North America by the end of this century if we continue to increase greenhouse gas concentrations at current rates, the answer will become simple. Spring will come early every year. While this may seem like a pleasant outcome of climate change, it could in fact lead to serious problems for plants, animals, and entire ecosystems. Living things have adapted to the timing of the seasons over many thousands of years. Here, we are changing the timing of the seasons on timescales of decades. Plants and animals just don’t adapt well to changes on such short timescales. [Read more…] about Groundhog Day

The False Objectivity of “Balance”

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We here at RC continue to be disappointed with the tendency for some journalistic outlets to favor so-called “balance” over accuracy in their treatment of politically-controversial scientific issues such as global climate change. While giving equal coverage to two opposing sides may seem appropriate in political discourse, it is manifestly inappropriate in discussions of science, where objective truths exist. In the case of climate change, a clear consensus exists among mainstream researchers that human influences on climate are already detectable, and that potentially far more substantial changes are likely to take place in the future if we continue to burn fossil fuels at current rates. There are only a handful of “contrarian” climate scientists who continue to dispute that consensus. To give these contrarians equal time or space in public discourse on climate change out of a sense of need for journalistic “balance” is as indefensible as, say, granting the Flat Earth Society an equal say with NASA in the design of a new space satellite. It’s plainly inappropriate. But it stubbornly persists nonetheless. [Read more…] about The False Objectivity of “Balance”

Q & A: Global Warming

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There was an interesting piece that appeared in the October 12 edition of the Seattle Times, “Q&A: Global warming — a world of evidence”. This follows up on a previous article by journalist Sandi Doughton in the October 9 issue of the Times, “The Truth About Global Warming”.

In the Q&A, a group of University of Washington scientists, including atmospheric scientist and climate researcher J. Mike Wallace, weigh in with answers to questions fielded from the paper’s readers. Many of the questions, such as “Isn’t it true that scientists in the 1970s said the earth was cooling?” are quite similar to those we’ve addressed here at RealClimate (see “The Global Cooling Myth”). [Read more…] about Q & A: Global Warming

On Yet Another False Claim by McIntyre and McKitrick

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McIntyre and McKitrick (MM), in one of their many false claims regarding the Mann et al (MBH98) temperature reconstruction, assert that the “Hockey Stick” shape of the reconstruction is an artifact of the “non-centered” Principal Components Analysis (PCA) convention used by MBH98 in representing the North American International Tree Ring Data Bank (ITRDB) data series. We already demonstrated the falsehood of this assertion here by showing (a) that the hockey stick pattern emerges using either the MM (centered) or MBH98 (non-centered) PCA conventions, but was censored by MM through an inappropriate application of selection rules for determining the number of Principal Component (PC) to retain, (b) that use of the correct number of PC series (5) to be kept with the MM (centered) convention retains the characteristic “Hockey Stick” pattern as an important predictor, and yields essentially the same temperature reconstruction as MBH98, and finally [Read more…] about On Yet Another False Claim by McIntyre and McKitrick

Michael Crichton’s State of Confusion II: Return of the Science

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Our first post on Crichton’s new novel “State of Fear” hits most of the key points, though there are a few more errors in the book that we hope to expand upon in future posts.

But for those of you uninterested in buying and reading the book, you can actually find a similar-minded opinion piece by Crichton criticizing climate science (and everything from SETI and the “Drake Equation” to Carl Sagan in the process) here in the public domain.

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Climate Change Disinformation

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by Michael Mann and Gavin Schmidt
As highlighted in the introduction to the site, we seek to clarify the findings of scientists who study the earth’s climate, and have an informed view on the science of climate change. Additionally we will speak out where we feel that the public discourse surrounding the science is being detrimentally impacted by the shrill voices and disinformation campaigns of the “partisan think-tanks or other interested parties”.

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