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Paleoclimate

Is Antarctic climate changing?

25 Aug 2006 by eric

Is the Antarctic ice sheet getting bigger or smaller? Is it warming or cooling?

As we’ve reported in earlier posts (here and here), getting accurate answers to these questions is non-trivial, because the available instrumental data remain sparse and generally date back only a few decades, at best. While modern satellite-based techniques such as laser altimetery and gravity anomaly measurements provide important information on very recent changes, to get at the longer term we must rely on less direct methods. In the last 5 years or so, an effort has been under way, much of it under the banner “International Trans Antarctic Scientific Expedition” (ITASE), to do this by collecting many dozens of ice cores from across the Antarctic continent. Two papers out this month represent the first major compilations of results from these efforts. The first, in Science on August 11th, provides a new estimates of Antarctic snowfall changes over the last 50 years. The second, in Geophysical Research Letters (August 30th) provides the first statistical reconstruction of Antarctic temperature change, extending about 200 years into the past.
[Read more…] about Is Antarctic climate changing?

Filed Under: Arctic and Antarctic, Climate modelling, Climate Science, Paleoclimate

The missing piece at the Wegman hearing

19 Jul 2006 by group

It’s not often that blogs come up in congressional hearings, but RealClimate was mentioned yesterday in the Energy and Commerce hearings on the ‘Hockey Stick’ affair. Of course, it was only to accuse us of being part of tight-knit social network of climate scientists, but still, the public recognition is nice.

There is much that could be said about the hearings (and no doubt will be) and many of the participants (Tom Karl, Tom Crowley, Hans von Storch, Gerry North) did a good job in articulating the big picture on climate change independently of the ‘hockey stick’ study as we’ve highlighted before. But it seems to us that there was a missing element in the discussions. That element was the direct implication of the critique that was the principal focus of Wegman’s testimony and that was mentioned periodically throughout the day. [Read more…] about The missing piece at the Wegman hearing

Filed Under: Climate Science, Paleoclimate

Medieval warmth and English wine

12 Jul 2006 by Gavin

Never let it be said that we at RealClimate don’t work for our readers. Since a commenter mentioned the medieval vineyards in England, I’ve been engaged on a quixotic quest to discover the truth about the oft-cited, but seldom thought through, claim that the existence of said vineyards a thousand years ago implies that a ‘Medieval Warm Period‘ was obviously warmer than the current climate (and by implication that human-caused global warming is not occuring). This claim comes up pretty frequently, and examples come from many of the usual suspects e.g. Singer (2005), and Baliunas (in 2003). The basic idea is that i) vineyards are a good proxy for temperature, ii) there were vineyards in England in medieval times, iii) everyone knows you don’t get English wine these days, iv) therefore England was warmer back then, and v) therefore increasing greenhouse gases have no radiative effect. I’ll examine each of these propositions in turn (but I’ll admit the logic of the last step escapes me). I’ll use two principle sources, the excellent (and cheap) “Winelands of Britain” by geologist Richard C. Selley and the website of the English Wine Producers. [Read more…] about Medieval warmth and English wine

Filed Under: Climate Science, Paleoclimate

National Academies Synthesis Report

22 Jun 2006 by group

The long-awaited NAS synthesis report on surface temperature reconstructions over the last few millennia is being released today. It’s a long (155 page) report and will take a while to digest, but we applaud the committee for having tried to master a dense thicket of publications and materials on the subject over a relatively short time.

It is probably expecting too much for one report might to put to rest all the outstanding issues in a still-developing field. And given the considerable length of the report, we have little doubt that keen contrarians will be able to mine the report for skeptical-sounding sentences and cherry-pick the findings. However, it is the big picture conclusions that have the most relevance for the lay public and policymakers, and it is re-assuring (and unsurprising) to see that the panel has found reason to support the key mainstream findings of past research, including points that we have highlighted previously:
[Read more…] about National Academies Synthesis Report

Filed Under: Climate Science, Extras, Paleoclimate, Reviews

How Red are my Proxies?

24 May 2006 by group

Guest commentary by David Ritson

Realclimate recently gave a detailed review of the issues surrounding the Von Storch et al. (2004) Science article that purported to show that the paleo-reconstructions of Mann et al. were invalid. Part of the review centered on a comment of Wahl, Amman and myself and the response to it by Von Storch et al that appeared on April 27 in Science. The response admitted that our critique of their original results was correct but then opened up a new area of debate. As in their original 2004 article von Storch et al had used a coupled climate model (AOGCM) to simulate the temperatures of the last two thousand years. They had then generated pseudo-proxies by adding noise at selected spatial locations to the AOGCM generated temperature histories. The added noise was purportedly designed to represent non-climatic effects such as disease or insect infestation. This simulated ‘noisy’ world then can be used as a test-bed for the reconstruction methodology. A given analysis procedure is validated if it successfully recovers the original AOGCM noise free results and could be rejected if it fails to recover the original results. Of course such testing only makes sense if the simulated test world has characteristics similar to the real-world. [Read more…] about How Red are my Proxies?

Filed Under: Climate Science, Paleoclimate

A Mistake with Repercussions

27 Apr 2006 by group

Today, Science published an important comment pointing out that there were serious errors in a climate research article that it published in October 2004. The article concerned (Von Storch et al. 2004) was no ordinary paper: it has gone through a most unusual career. Not only did it make many newspaper headlines [New Research Questions Uniqueness of Recent Warming, Past Climate Change Questioned etc.] when it first appeared, it also was raised in the US Senate as a reason for the US not to join the global climate protection efforts. It furthermore formed a part of the basis for the highly controversial enquiry by a Congressional committee into the work of scientists, which elicited sharp protests last year by the AAAS, the National Academy, the EGU and other organisations. It now turns out that the main results of the paper were simply wrong.
[Read more…] about A Mistake with Repercussions

Filed Under: Climate modelling, Climate Science, Paleoclimate

How much future sea level rise? More evidence from models and ice sheet observations.

26 Mar 2006 by eric

Lots of press has been devoted to four papers in this week’s Science, on the topic of ice sheets and sea level.

We’ve already discussed the new evidence that Greenland’s glaciers are speeding up. What is new this week is an effort to evaluate the impact of future warming on Greenland by looking at what happened to it last time it got very warm — namely during the Last InterGlacial (LIG) period, about 125,000 years ago. The same group of authors looked at this in two ways, using NCAR’s Community Climate System model (CCSM) coupled to a state-of-the-art 3-D ice sheet model.
[Read more…] about How much future sea level rise? More evidence from models and ice sheet observations.

Filed Under: Arctic and Antarctic, Climate modelling, Paleoclimate

Climate sensitivity: Plus ça change…

24 Mar 2006 by Gavin

Almost 30 years ago, Jule Charney made the first modern estimate of the range of climate sensitivity to a doubling of CO2. He took the average from two climate models (2ºC from Suki Manabe at GFDL, 4ºC from Jim Hansen at GISS) to get a mean of 3ºC, added half a degree on either side for the error and produced the canonical 1.5-4.5ºC range which survived unscathed even up to the IPCC TAR (2001) report. Admittedly, this was not the most sophisticated calculation ever, but individual analyses based on various approaches have not generally been able to improve substantially on this rough estimate, and indeed, have often suggested that quite high numbers (>6ºC) were difficult to completely rule out. However, a new paper in GRL this week by Annan and Hargreaves combines a number of these independent estimates to come up with the strong statement that the most likely value is about 2.9ºC with a 95% probability that the value is less than 4.5ºC. [Read more…] about Climate sensitivity: Plus ça change…

Filed Under: Climate modelling, Climate Science, Paleoclimate

Art and climate

8 Mar 2006 by Gavin

Washington_Crossing_the_Delaware As anecdotal evidence of past climate change goes, some of the most pleasant to contemplate involve paintings of supposedly typical events that involve the weather. Given the flourishing of secular themes in European art from the Renaissance on, most of this art comes from the 16th to 19th centuries. As readers here will know, this coincides (in the public mind at least) with the so-called ‘Little Ice Age’ and somewhat inevitably this canon of work has been combed over with a fine tooth comb for evidence of particularly cold conditions.

The image that brought this issue to mind was seeing ‘Washington crossing the Delaware’ at the Met the other day and seeing the iceberg-like ice it was imagined (75 years after the event) that the rebels had had to row through in 1776. The first thing I noticed was that the ice is completely wrong for a river (which is just one of the errors associated with this picture apparently). River ice is almost always of the ‘pancake’ variety (as this photo from the Hudson river shows), and doesn’t form ‘growlers’. However, the confusion of artistic license with climatology appears to be a bit of a theme in other oft-cited works as well…. [Read more…] about Art and climate

Filed Under: Climate Science, Paleoclimate, Reporting on climate

Sir Nicholas Shackleton

21 Feb 2006 by Ray Bradley

With the recent death of Sir Nicholas Shackleton, paleoclimatology lost one of its brightest pioneers. Over the last ~40 years, Nick made numerous far-reaching contributions to our understanding of how climates varied in the past, and through those studies, he identified factors that are critically important for climate variability in the future. His career neatly encompasses the birth of the new science of paleoceanography to its synthesis into the even newer science of ‘Earth Systems’; he made major contributions to these evolving fields throughout his life, and his insightful papers are required reading for students of paleoclimatology.
[Read more…] about Sir Nicholas Shackleton

Filed Under: Climate Science, Oceans, Paleoclimate

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