Climate 'warmest for millennium' (BBC News)

[Up2Late]

(I'm sure the Global Warming deniers will still say 1,200 Years back is still not enough, but I guess just add this study to the mounting pile of evidence)

Thursday, 9 February 2006, 19:25 GMT

Climate 'warmest for millennium'

By Paul Rincon
BBC News science reporter

In the late 20th Century, the northern hemisphere experienced its most widespread warmth for 1,200 years, according to the journal Science.

The findings support evidence pointing to unprecedented recent warming of the climate linked to greenhouse emissions. University of East Anglia researchers measured changes in fossil shells, tree rings, ice cores and other past temperature records or "proxies".

They also looked at people's diaries from the last 750 years. Timothy Osborn and Keith Briffa of UEA analysed instrument measurements of temperature from 1856 onwards to establish the geographic extent of recent warming.

Then they compared this data with evidence dating back as far as AD 800. The analysis confirmed periods of significant warmth in the Northern Hemisphere from AD 890 - 1170 (the so-called "Medieval Warm Period") and for much colder periods from 1580 - 1850 (the "Little Ice Age").

(more at link above)

<http://news.bbc.co.uk/2/hi/science/nature/4698652.stm>

[burrowowl]

1. If we send this article to

Bu$h will it do any good?

[hatrack]

2. Nahh, it'll just spur the Raptards to even greater heights of stupidity.

:eyes:

[xchrom]

3. this stuff is about to bite wall street on the ass.

SUPPOSEDLY wall street doesn't like instability.

well, they are going to see some serious instability real soon -- because of their short sightedness and greed.

[Blue_Forney05]

4. Yeah could you imagine the ocean level actually flooding Wall St. and New

York on a consisistent basis. Geez. When are these yo-yos going to wake up and smell the coffee? I live in Pa and even I am concerned about Global Warming. I can not imagine the effects it would have on people near rivers, on the coasline areas, and in deserts.

[dysfunctional press]

15. at least it's not going to be boring-

:popcorn:
interesting times ahead...

[RedEarth]

5. World is warmer than it has been for 1200 years

GLOBAL warming in the past century has been greater than any other shift in the world's climate over the past 1200 years, researchers have reported.

The analysis of data from tree rings, shell fossils, ice cores and temperature measurements from 14 locations on three continents shows that the current warming trend is the most extensive change - warm or cold - since the time of the Vikings.

Reporting their findings in the journal Science, Timothy Osborn and Keith Briffa, climatologists at the University of East Anglia, home to the leading British climate research centre, stop short of blaming the 20th-century warming on industrial emissions or other human factors.

But they say the geographic extent of the warming is more widespread and more pronounced than the one that turned Greenland green 1000 years ago.
Their analyses of tree ring and other climate "proxies" from Europe, Asia and North America show two other pronounced climate shifts during the same period: the Medieval Warm Period from 890 to 1170, and the Little Ice Age, which gripped the northern hemisphere from 1580 to 1850.

http://smh.com.au/news/world/world-is-warmer-than-it-has-been-for-1200-years/2006/02/10/1139542403065.html

[benburch]

6. Bush still has his head up his ass...

And it is just as warm there as it ever was...

[babylonsister]

7. Can I LOL and go EWWWW simultaneously? nt

[babylonsister]

8. But I thought global warming wasn't

real?! :sarcasm:

[Neshanic]

9. No rain since October 18th. Fires are going on in AZ now.

[phusion]

10. What part of AZ are you in?

It's really bad here in Albuquerque...No good rain for about 4 months. The mountain snowpack is WAY down...It's going to be a really bad fire season.

[Viking12]

11. A more in-depth look at the study

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).

This is not to say that all estimates agree in their details. Indeed, there is a fair scatter among the various published estimates. Some of these differences are believed to reflect differences in seasonality and spatial emphasis. Past summer, extratropical temperature changes appear, for example, to have have differed significantly from annual temperature changes over the entire (tropical and extratropical) Northern Hemisphere, and tropical Pacific Sea Surface Temperatures appear to have varied oppositely with temperatures in the extratropical regions of the globe. See for example the review paper by Jones and Mann (2004), in particular the discussion and references in section 5.3 therein. Some differences appear to be related to the particular method used to "calibrate" the proxy data against modern instrumental records. While the various methods can be tested with climate model simulations , it would arguably be more satisfying if inferences could be obtained in a manner which bypasses the difficult issue of calibration entirely, and also eliminates any need to establish the precise seasonality of information reflected by the various available proxy records.

This is what Osborn and Briffa have done in their article "The Spatial Extent of 20th Century Warmth in the Context of the Past 1200 Years", which appears in the Feb 10 issue of the journal Science. The article uses a rigorous statistical methodology to re-examine the question of whether late 20th century warmth is anomalous in the context of the past 1200 years. This is done in a manner that does not require the explicit calibration of the proxy records. 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.

http://www.realclimate.org/index.php?p=253

[xchrom]

12. thank you for the site -- i don't understand half of it

but i've bookmarked it -- and will visit from time to time -- to get as much info as i can from it.

[Viking12]

13. You're welcome!

It really is a great site and the climate scientists that run it do their best to discuss issues in layman's terms but in many cases it's impossible to simplify complex scientific discussions. Take a look around RealClimate and you'll see some easy to undertsand debunking of "popular" contrarian tropes.

[benburch]

14. I would be interested in your comments on a theory of mine...

I believe that the Greenland glacier will melt quicker than anybody expects because of industrial soot trapped in the ice.

Same effect as a dirty snowdrift; The ice melts and percolates down to the bottom and runs off leaving the rime of dirt on the top that has a very low albedo. This accelerates the melting and further darkens the glacier.

Do you know if this effect has been accounted for in current models?

[Viking12]

16. Soot is certainly a contributor, but not the dominant factor

The erosive capacity of water is probably more significant.

Here's a couple papers from the Proceedings of the National Academy of Sciences that discuss surface melt, soot and albedo:

Surface Melt-Induced Acceleration of Greenland Ice-Sheet Flow
H. Jay Zwally,1* Waleed Abdalati,2 Tom Herring,3 Kristine Larson,4 Jack Saba,5 Konrad Steffen6

Ice flow at a location in the equilibrium zone of the west-central Greenland Ice Sheet accelerates above the midwinter average rate during periods of summer melting. The near coincidence of the ice acceleration with the duration of surface melting, followed by deceleration after the melting ceases, indicates that glacial sliding is enhanced by rapid migration of surface meltwater to the ice-bedrock interface. Interannual variations in the ice acceleration are correlated with variations in the intensity of the surface melting, with larger increases accompanying higher amounts of summer melting. The indicated coupling between surface melting and ice-sheet flow provides a mechanism for rapid, large-scale, dynamic responses of ice sheets to climate warming.

http://www.sciencemag.org/cgi/content/abstract/297/5579/218

Soot climate forcing via snow and ice albedos
James Hansen * , and Larissa Nazarenko *

*National Aeronautics and Space Administration Goddard Institute for Space Studies and Columbia University Earth Institute, 2880 Broadway, New York, NY 10025

Contributed by James Hansen, November 4, 2003


Plausible estimates for the effect of soot on snow and ice albedos (1.5% in the Arctic and 3% in Northern Hemisphere land areas) yield a climate forcing of +0.3 W/m2 in the Northern Hemisphere. The "efficacy" of this forcing is 2, i.e., for a given forcing it is twice as effective as CO2 in altering global surface air temperature. This indirect soot forcing may have contributed to global warming of the past century, including the trend toward early springs in the Northern Hemisphere, thinning Arctic sea ice, and melting land ice and permafrost. If, as we suggest, melting ice and sea level rise define the level of dangerous anthropogenic interference with the climate system, then reducing soot emissions, thus restoring snow albedos to pristine high values, would have the double benefit of reducing global warming and raising the global temperature level at which dangerous anthropogenic interference occurs. However, soot contributions to climate change do not alter the conclusion that anthropogenic greenhouse gases have been the main cause of recent global warming and will be the predominant climate forcing in the future.



http://www.pnas.org/cgi/content/abstract/101/2/423

[benburch]

17. Thank you!

It is good to have my naive hypothesis validated, and good also to see that I wasn't the first to think of it.

[Up2Late]

18. That raises an interesting question, if you think back to the late 19th...

...to mid 20th Century London, England, they say that the soot from all the Coal burning was so bad that much of the "fog" was actually air-borne coal soot, and when it rained, the rain was almost black, and you would end up filthy if you ventured outside.

I wonder how much of that ended up in the Greenland Ice sheet? maybe it will melt out in sooty layers?