Jesse

http://www.portal.telegraph.co.uk/ne...06/ixhome.html

The article suggest that, although this would not affect the evidence for global warming itself, it might call into question the idea that recent warming is mainly due to human activity. Any thoughts on this from people who know more about this issue than I?

Also, here's the press release on this study, which goes into a little more detail:

http://cfa-www.harvard.edu/press/pr0310.html

repoman

I am beginning to think that the whole global warming issue is one that is so complex that it can be used by both environmentalists and industrys flaks unscrupulously. (edit to say that the news article looks to be good science, but it may be abused by some who make blanket statements and aren't interested in science) Also, there are many more important environmental issues that don't have the level of uncertainty of global warming.

I'm just dreading that bastard Rush Limbaugh telling all his selfish listeners to go drive their SUVs because global warming is Mother Nature at work!

What about deforestation, species extinction, toxin accumulation in the arctic lands and waters as well in the third world dumping grounds, overcrowding, depletion of mineral deposits -- and many other tangible effects we have on this planet.

But getting back directly to global warming and the effects that the greenhouse gases that we human continue to pump have on the climate -- there are many variables. I think that the biggest one is whether the ocean can buffer all of the excess CO2 in the atmosphere via carbonic acid and then carbonate precipitates. But this is very touchy depending on the temperature and other factors and can actually accelerate global warming.

But I hope Rush doesn't hear about the carbonic acid buffering in the ocean, maybe he'll tell his listeners to drink soda to save the environment

ps418

The Medieval Warm Period (MWP), ~800-1200CE, and the following Little Ice Age (LIA) , ~1300-1800, are well-established, global climatic 'events.' The MWP allowed Vikings to reach Greenland, while the following LIA may have brought their colony to an end. The general timing and scale of the MWP are indeed quite similar to the 20th century warming trend, although there may have been more climatic variability during the MWP. Global mean temp was maybe 1C greater than today at the peak, although this magnitude of temp change is pushing the limits of the resolution of available paleotemperature proxies.

Esper et al, 2002. Low-Frequency Signals in Long Tree-Ring Chronologies for Reconstructing Past Temperature Variability. Science 295, pp. 2250-2253.

Keigwin, 1996. The Little Ice Age and Medieval Warm Period in the Sargasso Sea. Science 274, pp. 1503-1508.

Patrick

SULPHUR

The average mean temperatures in australia have shown a greater than expected rise allowing for natural temperature variations As far back as1994 this was predicted using cray computer modelling
Information can be obtained from the aust. weather bureau. melbourne.au

Claudia

What I have read in the article proposed is that 20th century was probably cooler than MWP. Fine, I suppose that they are serious and that it is true. But nowhere in this article do they try to look specifically at the last 10 years ot the century which are specifically the warmer. May be thay have worked correctly and separated them in their studies, but when I work I usually avoid to compare peak statistics (maxima) to averages ("the century was cooler"). I hope that the impression to have done so in this paper is due to a poor press rephrasing.

SULPHUR

I agree that there was a period in the middle ages from 9-14 century that was warmer and was followed by a mini ice age. However the warming in the last century has shown discrepencies which show other factors are involved. If all gas emissions where stopped at this moment it would take to 2050 to slow the greenhouse effect

Arbogast

It seems to me we dont really know enough about the weather to do more than speculate on these matters.

Internal combustion engines are useful machines, but they are nasty regardless of global warming/cooling.

All you have to do is check out the air in your local metropolis, then check out the air out in the countryside.

A clean world is a nice world.

nermal

What discrepencies are those exactly? It's my understanding we don't know enough about what changes the climate is undergoing to point to discrepencies, or specific causes. These things are modeled, not measured per se, and the models continue to fall short of any predictive value as yet.

Ed

SULPHUR

What are we putting into atmosphere.I live in tasmania and there is a bloody great hole inthe ozone layer which is gradually getting smaller because of the ban on CFC so my children wont get skin cancer by age ten.I take it you saw the picture of the smoke layer over india and SE asia which nust have an effect on climate .Contact any majjor weather bureau and ask about the research being done. I was lucky to spend two weeks in melbourne observing the amount of work being done and the concern about the unusual conditons which have been created

nermal

Sorry, thought the thread was about global warming only. I certainly wouldn't claim CFC's aren't bad.
All very good. Lots of smoke, lots of research. But enormous smoke causing events aren't new. I was asking about unusual conditions you said exist now that didn't exist before. That's all. I read your original post to indicate discrepencies in the climate which didn't exist in the MWP, and I was wondering what they were.

Ed