View Single Post
sylas
#34
Nov14-09, 05:57 PM
Sci Advisor
sylas's Avatar
P: 1,750
Quote Quote by Andre View Post
Well there is little doubt that somebody is going to claim that glacier growth is caused by global warming as it happened some 9000 years ago.

abstract here
It's more than merely a claim. It's a well supported conclusion backed up with multiple lines of research and many research papers.

Is anyone seriously doubting that there can be major regional differences in response to globally changing temperatures? Either now or in the past? And given this, is there anyone actually disputing that some glaciers may be advancing in the present due to changes arising in the present global warming episode?

NONE of the sources cited in this thread -- including the discussion paper, or the papers on the western Himalaya by Fowler and Archer, and by Shroder's group -- is disputing the observation that there is a significant worldwide trend of retreat in glaciers. They are looking at exceptions to the trend. Inferences and hypothesis about dynamics will also differ between scientists. Research on these anomalous glaciers that are advancing is critically useful for understanding better the complexities of glacier dynamics and their interaction with climate.

The links Andre is giving are to a recent publication and to an associated news report which is relevant to this whole discussion.
Glaciers are in a continuous state of change, and respond to changes in climate in sometimes quite complicated ways. There can be time delays in response; there are responses to temperature and to precipitation, and sudden surges or moves as melt water lubricates the base of a glacier and changes how much friction there is for movement. The paper is mostly on changes 6000 years ago, with some comparison also to 9000 years ago. The reference of the newspaper story title is about a few anomalous glaciers in central Asia which did advance in the early Holocene when global temperatures were increasing and most glaciers were retreating.
.. Although there is evidence for large pre-LGM and LGM advances in the southern Himalayas and Tibet (eastern zone), evidence for a large early Holocene (∼9 ka) advance distinguishes it from the rest of Central Asia...
-- Rupper et al (2009) p338
In the modern era, there are all kinds of quite drastic changes going on. Scientists investigating changes in glaciers can benefit from studying also the changes that have occurred in the past. An extract from the news report explains this plainly:
The story of these seemingly anomalous glaciers underscores the important distinction between the terms “climate change” and “global warming.”

“Even when average temperatures are clearly rising regionally or globally, what happens in any given location depends on the exact dynamics of that place,” Rupper said.

The findings come from a framework Rupper developed as an alternative to the notion that glaciers form and melt in direct proportion to temperature.
-- Thaindian news Aug 28, 2009.
Global change and regional change

This paper is particularly relevant to the point which is being made in the previous references: that there are strong regional differences in a time of globally changing climate. The previous papers in this thread have explained and measured such differences. For example, from the abstract of Fowler and Archer (2006) (see msg #15):
The observed downward trend in summer temperature and runoff is consistent with the observed thickening and expansion of Karakoram glaciers, in contrast to widespread decay and retreat in the eastern Himalayas. This suggests that the western Himalayas are showing a different response to global warming than other parts of the globe.
-- Fowler et al (2006), abstract
The Earth periodically experiences times of strong global change, such as the start of the Holocene some 9000 years ago, or the current global warming trend. This research is helping to explore the changes at such times in more detail, and particularly to consider differences in different regions. To help it read more easily as a summary, I have removed the references. Here are the opening paragraphs of Rupper et al (2009):
In modern climate dynamics a central concept is that climate variability tends to be expressed in spatial patterns on a regional scale. Well-known examples of this are the El Nino-Southern Oscillation, the Pacific Decadal Oscillation, and the Arctic Oscillation. In past climates too, there are strong indications that climate changes occur in patterns, and no reason to suspect that they do not. Proper characterization and interpretation of past climate variability therefore requires a dense network of paleoclimate proxy records.

Glaciers are a particularly attractive paleoclimate proxy record for two reasons. First, geomorphic evidence of glacier advances is widespread across much of the Northern Hemisphere land masses. Second, glaciers are excellent recorders of properties of the atmosphere, retreating and advancing directly in response to changes in accumulation and ablation. Reconstructions of past glacier variability are some of the most useful records of paleoclimate. In fact, in many parts of the world, the glacier history is the primary descriptor of the climate history beyond the instrumental record, particularly where glacier deposits are widespread and confidently dated. This is true, for example, in the Pacific coast of the United States, South America, New Zealand, the European Alps, and Asia. Therefore, reconciling the glacier histories with the climatic variations that caused them is essential.

The glacier history of Central Asia provides a promising opportunity to distinguish between global and regional climate change. ...
-- Rupper et al (2009) p337
And from the conclusion:
The consistency between all GCMs reinforces confidence that the model results are a robust response of the climate to the changes in insolation forcing. In the case for Central Asia, spatial patterns in climate occur in response to a relatively uniform increase in solar insolation at the top of the atmosphere. The patterns in glacier advances across Central Asia are a result of the spatial variability in the climate response. This suggests that spatial patterns in climate and glaciers should be expected even in cases where there is a uniform change in forcing (e.g., increasing CO2).
-- Rupper et al (2009) p345
Summer Rupper has also been in the news recently, for a letter to Utah legislators on policy responses to climate change issues.
"We have no specific political agenda to support but agree that whatever action is taken, it should be informed by the best available scientific evidence," the scientists said. "We encourage our legislators not to manipulate the scientific evidence to suit any political agenda."
[...]
Summer Rupper, a BYU climate scientist, led the letter-writing effort. ...
-- extract from BYU scientists take lawmakers to task on climate change issues, The Salt Lake Tribune, 7 July 2009
The letter that was sent is here: Open letter to the Utah Public Utilities and Technology Interim Committee, Governor, U.S. Senators and Congressmen.

Cheers -- sylas