When is Global Warming Significant?

[Astronuc]

Lamont's Broecker Warns Gases Could Alter Climate
Oceans' Circulation Could Collapse
Columbia University Record - VOL. 23, NO. 11 DECEMBER 5, 1997

On the eve of the international meeting on global warming that opened Dec. 1 in Kyoto, Japan, one of the world's leading climate experts warned of an underestimated threat posed by the buildup of greenhouse gases—an abrupt collapse of the oceans' prevailing circulation system that could send temperatures across Europe plummeting in a span of 10 years.

If that system shut down today, winter temperatures in the North Atlantic region would fall by 20 or more degrees Fahrenheit within 10 years. Dublin would acquire the climate of Spitsbergen, 600 miles north of the Arctic Circle.

"The consequences could be devastating," said Wallace S. Broecker, Newberry Professor of Earth and Environmental Sciences at Columbia's Lamont-Doherty Earth Observatory, and author of the new research, which appeared in the Nov. 28 issue of the magazine Science.

A complex of globally interconnected ocean currents, collectively known as the Conveyor, governs our climate by transporting heat and moisture around the planet. But the Conveyor is delicately balanced and vulnerable, and it has shut down or changed direction many times in Earth's history, Broecker reports. Each time the Conveyor has shifted gears, it has caused significant global temperature changes within decades, as well as large-scale wind shifts, dramatic fluctuations in atmospheric dust levels, glacial advances or retreats and other changes over many regions of the Earth, he said.

Some background -
Ocean Currents and Climate

Deep Water Circulation

Presumably some institutions (e.g. Columbia, USC, Scripps, etc) are measuring the variables such as temperature, salinity, flow, etc in order to determine if the Conveyor system is being undermined (?)

 

[Andre]

About ocean currents, the notion of a slowing conveyor belt is not that new. Another idea is the heat storage capacity of the oceans and the long delay caused by the deep circulation in which case the current warming of the ocean is all about natural cycles and nothing about human influence. But whatever the cause of warming is, there may or may not be some significant impact.

Incidentely, someone said:

Your bias is painfully obvious.

I assume that it is an 'ad hominem' to point out that this is an 'ad hominem'. So I'll limit myself to the observation that it appears to be difficult to see any significance of this statement to the current topic.

 

[Andre]

But then again, how much have the oceans warmed?

http://www.nodc.noaa.gov/OC5/PDF/PAPERS/grlheat05.pdf

During 1955–1998 world ocean heat content (0–3000 m) increased 14.5 10^22 J corresponding to a mean temperature increase of 0.037C.

That's a staggering ~0,1C per century. That way it takes another ten millenia (linear extrapolation) before global warming is getting significant.

I wonder why I'm debunking the 7-10 degrees warming-per-decade myth of the ice ages in the other thread.

 

[Soaring Crane]

If global temperature(s) continues to rise, does that mean that the troposphere will contain more water vapor?

 

[Andre]

I'm afraid that this question is off topic in this thread. But if you start another one we could analyse the different assessments of the role of water vapor on the climate.

 

[juju]

Hi,

A quote from:

http://www.unknowncountry.com/news/?id=4595

"Gulf Stream Scientists from Cambridge University have confirmed that the Gulf Stream is weakening, and this is likely to bring much colder temperatures to Europe within a few years. The weakening is significant: the Gulf Stream is flowing at a quarter of the strength that was present five years ago. This is happening because gigantic chimneys of cold water that were sinking from the surface to the sea bed off Greenland have disappeared."

Just saw this today and thought I'd pass it along.

juju

 

[Ivan Seeking]

Hi Juju,
Thanks for the link. Unfortunately [or perhaps fortunately] this is not a reliable source. I didn't see the original source listed - the Scientists from Cambridge or the paper.

 

[Ivan Seeking]

I want to stress that the motivation for this thread is to discuss the implications of GW, i.e. when is warming significant. This is not a debate about if its happening, or even why.

 

[Ivan Seeking]

After reviewing this thread I can see where there might have been a misunderstanding. So I will assume that the error is mine and hereby apologize to Monique. We had a bit of a spat about all of this, but I can see that we are seeking the middle ground. Thank you.

 

[Astronuc]

Part of the problem of determining when GW is significant is being able to determine that a particular problem can be causally associated with GW.

For instance, in my area, the weather has been wacky the last 15 years. We have had records in drought, temperature highs and low, rain, snow - but does any of have to do with GW?

We had a very dry period a couple of years ago and the crops in the area suffered. That was followed by a very wet fall and more precipitation in the winter. But how can one attribute it to GW.

We have had some flooding problems, but can that be ascribed to GW.

How does one determine that a weather system or a trend is the result of GW?

I suppose if Earth's winds became hurricane force on a regular basis, we might say that we have a problem, but then it would rather late.

Perhaps remedial steps should be taken now, regardless of the cause.

It takes seconds to cut down a tree, but 30-50 years to grow it back.

 

[Ivan Seeking]

Part of the problem of determining when GW is significant is being able to determine that a particular problem can be causally associated with GW.

Well, I am trying to look at this the other way around and ask: Are the observed changes consistent the predictions of the best models, or is this almost certainly a transient condition? Then if this is consistent with expectations, what should we expect next, how soon, and what should be or even can be done. I would also think that landmarks could identified. For example, if we see events x, y, and z, this suggests that certain actions should be taken. Here is a specific example. I talked with my sister yesterday. In the Sacramento area where she lives, they had yet another tornado warning. This is historically unusual by human standards, but it may or may not be in terms of climate cycles and the normal aberrations. So, is this a fluke, or is this expected rarely but always, or do GW models suggest that an increase in tornadic activity in the Sacramento valley is a reasonable to expect, even in the short term. If this is almost certainly a complete fluke, then no bid deal. But if this is expected based on GW models and given today's [this decade's] conditions, then it may be reasonable to promote public education about what to do if a tornado warning is issued.

 

[Andre]

Concerning modelling global warming, it might be a good idea to review how the idea of "global warming" has emerged. http://www.physicstoday.org/vol-56/iss-8/p30.html gives an excellent overview; it all boils down to the dramatic simultaneous changes in geologic proxies at the end of the last Ice age, known as the boundaries between "the Last Glacial Maximum", the "Bolling Allerod event", the "Younger Dryas" and the "Preboreal", with assumed temperature fluctuations of ~10 degrees C within less than a decade, both up and down. As long as this behavior is "not understood" it seems correct to have sincere considerations for climate changes.

it would be interesting to see if models could "retro-dict" what caused those dramatic palaeo climatic changes and how we would know when another dramatic decade would start yet again.

There is also the possibility that those decades are something completely different.

 

[russ_watters]

I tend to take a backwards-looking approach because it is most foolproof: take things like that 4 droughts in 13 years and compare it statistically to the previous 13 years, and the previous, and the previous, etc. Take a large enough sample over a long enough time and trends become clear.

There are, of course, three problems (at least) with this approach:

1. If its already happened, its too late to prevent it (though you can maybe keep it from getting worse).
2. This approach requires a lot of data over a long period of time and a good baseline for some such data does not exist.
3. It doesn't tell us anything about causality. But hey - at least we'll know what is happening, if not why.

 

[Ivan Seeking]

Hi,

A quote from:

http://www.unknowncountry.com/news/?id=4595
to the sea bed off Greenland have disappeared."

Just saw this today and thought I'd pass it along.

juju

Scientists now have evidence that changes are occurring in the Gulf Stream, the warm and powerful ocean current that tempers the western European climate... Cambridge University ocean physics professor Peter Wadhams points to changes in the waters of the Greenland Sea. Historically, large columns of very cold, dense water in the Greenland Sea, known as "chimneys," sink from the surface of the ocean to about 9,000 feet below to the seabed. As that water sinks, it interacts with the warm Gulf Stream current flowing from the south.

But Wadhams says the number of these "chimneys" has dropped from about a dozen to just two. [continued]

http://edition.cnn.com/2005/TECH/science/05/10/gulfstream/

 

[Andre]

It may be not that certain if that's significant of global warming. Let me give the opinion of a British specialist http://www.ukweatherworld.co.uk/forum/forums/thread-view.asp?tid=20974&posts=11 on this subject:

He's not said that the GS or that entire NADW has reduced by 75% just that one zone,(not the biggest) has reduced. I think this also goes back to findings from 2004.
No Scientific paper has been published on it, simply because the science is not good enough. These Columns are very variable at best and flucatuate on a seasonal basis.
The initial investigation to find 12 Columns was I believe back in the 70's or 80's and the 2 columns back in 90's or early this decade.
It's quite possible that the 12 Columns was a vast over estimate or that the 2 columns was an understatement as extra columns formed further North.

IMO the Times very belatedly picked this up, with a science editor who wanted a story that just does not exist.

THE GS is very strong if a bit straggly at the moment and I believe that NADW production is running very hard at the moment.

IF NAD Shut off were to occur it would be through overload of the NADW production not through Ice melt freshwater impact.

edit: NADW is North Atlantic Deep Water, GS = Gulf Stream

And then again. What is cause and what is effect? As somebody else remarked. Suppose that for some reason the down flow of the water is blocked, then the shear inertia of the Gulf Stream would continue to push water towards the area and if that relatively warm water can't go down it must continue northwards causing the warming of the pole.

So what is cause and what is effect?

 

[Ivan Seeking]

Andre, if the Earth is warming, be it a natural cycle or due to increased solar activity, or caused by humans, what effects do you think will be significant to humans, and how soon.

 

[Andre]

Well perhaps a change in the http://www.newmediastudio.org/DataDiscovery/Hurr_ED_Center/Easterly_Waves/Trade_Winds/Trade_Winds.html .

When global warming was to be due to increased solar output, you would perhaps expect a pretty even rate of warming simultaneously but this would increase the temperature difference between pole and equator, therefore you would expect perhaps a stronger hadley cell activity, consequently an increase of atmospheric interaction, with perhaps more severe weather.

If increased greenhouse gas forcing was to be the main cause, the cooling of the Earth would be slowing down. That would probably be most notable in areas with high extreme temperature differences like deserts, in the down draft areas of the hadley cells. The lesser cooling would counteract the downdrafts, so the hadley cell activity would weaken. Less downdraft also means less aridity and deserts could get some more precipitation.

But this is most speculative and a lot of secundary effects could spoil those neat hypotheses.

 

[Marijn]

If increased greenhouse gas forcing was to be the main cause, the cooling of the Earth would be slowing down. That would probably be most notable in areas with high extreme temperature differences like deserts, in the down draft areas of the hadley cells. The lesser cooling would counteract the downdrafts, so the hadley cell activity would weaken. Less downdraft also means less aridity and deserts could get some more precipitation.

Forgive me if i´m wrong but isn´t the current situation one of increasing aridity and growing deserts?

 

[Andre]

I would tend to have that impression too which could point to scenario one (stronger solar input - stronger hadley cells). However you will find that some global warming / IPCC are predicting more precipitation - (due to weakening hadley cells?)

 

[juju]

Hi,

Peter Wadhams interview

http://www.earthfiles.com/news/news.cfm?ID=910&category=Environment

juju

 

[Andre]

Hi,

Peter Wadhams interview

http://www.earthfiles.com/news/news.cfm?ID=910&category=Environment

juju

http://ocean.mit.edu/~giulio/publications/Boccaletti_et_al_GRL_2005.pdf

Boccaletti, et al (2005) The vertical structure of ocean heat transport. Geophys. Res. Lett., 32, L10603, doi:10.1029/2005GL022474, May 17

Abstract

"One of the most important contributions the ocean makes to Earth's climate
is through its poleward heat transport: about 1.5 PW or more than 30% of
that accomplished by the ocean-atmosphere system (Trenberth and Caron,
2001). Recently, concern has arisen over whether global warming could affect
this heat transport (Watson et al., 2001), for example, reducing high
latitude convection and triggering a collapse of the deep overturning
circulation (Rahmstorf, 1995). While the consequences of abrupt changes in
oceanic circulation should be of concern, we argue that the attention
devoted to deep circulations is disproportionate to their role in heat
transport. For this purpose, we introduce a heat function which identifies
the contribution to the heat transport by different components of the
oceanic circulation. A new view of the ocean emerges in which a shallow
surface intensified circulation dominates the poleward heat transport."... cont

 

[juju]

Hi,

This may not be significant globally, but to me and my friends it is sure a pointer.

Our local climate has not had a day in the last 10 years when the temperature did not get to freezing.

15 years ago we had at least two weeks every winter where the temperature did not get to freezing.

This is a warming locally, that may be related to a global warming trend.

I live in the mountains of southern Oregon at about 3400 ft altitude.

juju

 

[selfAdjoint]

Our local climate has not had a day in the last 10 years when the temperature did not get to freezing.

Did you mean when it did get down to freezing? That seems to be the sense you intended.