Global warming and Reefs

[michaelg]

There is a really interesting discussion (to me anyway) on coral list that I will try to share.  A lot of good points to think about.  It is a bit long, and I'm sure will grow longer, but hopefully at least one person will find the read interesting.

 

Here is what started it off-

"A simple question"

> > Greetings all,

> > My sincerest apologies for wasting time and bandwidth with what Im sure

> > is an eye-rolling question for you all.

> > I have tried to answer this question myself but have found

> > insufficient research

> > to back up my response.

> > Can anyone help me ?

> >

> > "Why are marine biologists so worried by a forecast global warming

> > rise of 1.4-5.8 degrees occurring over the next century, when the

> > coral obviously survived a far more rapid and greater increase (~7

> > deg over 10 years) about 15000 years ago (Younger Dryas) ?"

> >

> > My response is this:

> >

> > 1. Greenland never had hard corals and the temperature change was

> > probably local not global.

> > 2. Just because some corals survive, doesnt mean losing massive

> > diversity was a minor effect.

> > 3. Tropical coral reefs have been stable for a long time now - sudden

> > change will be disasterous.

> > But thats the best I can offer.

> > Hope someone out there has some patience.

> > Sorry again.

> > Chris.

On Fri, 23 Jul 2004, Mark Eakin wrote:

 

> While air temperatures rose dramatically in Greenland at the end of the

> Younger Dryas, it is unlikely that tropical oceans warmed anywhere near

> that much.

 

Do you mean that the warming trend was not at great in terms of

number of degrees of temperature change or that the change had less impact

on the ecosystem?  Does it not take a smaller temperature change in water

to impact the marine environment than air for a terrestrial environment?  

 

Also, many scientists believe that North Atlantic Deep Water

(NADW) circulation was a large part of the reason for those dramatic

temperature changes.  If the North Atlantic limb of the Conveyor did

indeed shut down, would it not have had a major impact on tropical oceans?  

 

Additionally, the mid holocene warm period actually saw warmer

global temperatures than we are currently experiencing.  Then, of course

there was the "Little Ice Age."  My point is that there have been periods

of tremendous volitility in climate in the earth's history.  We currently

(for the last 3,000 or so years) have been experiencing an unusual period

of stability.  This is extremely unusual and I doubt that is normal, at

least in the long term scheme of things.  

 

We know that the recent stability in climate has been extremely

favorable for us and that nature is capable of throwing some really nasty

climatological changes our way. Large glacial melts, dramatic eustatic

seal level rises, meltwater pulses causing salinity changes and other

effects are not only possible but a normal part of global change.  I am

not trying to say that they are good for the ecology (or for mankind

either) but that they are "normal" in some sense.  

 

> More important were changes in the area of warmth in the tropics.  That

> was also an increase from cold (glacial) conditions to warm

> (interglacial).  Your question regarding global warming is a further

> increase in interglacial temperatures.

 

But (so far, at least) not as warm as the Mid-Holocene?

 

> If corals were not under a wide range of other anthropogenic stresses,  

> then the warming would probably be less of an issue.  The temperature  

> problem is really compounded by the additive and synergistic effects of  

> other stress imposed on the corals at the same time as the warming.

 

How about the additive stresses of a meltwater pulse?  How did the

interplay of change in salinity, temperature, sea level and sediment

loading affect the coral ecosystem?  

 

> Corals are not likely to go extinct.  However, it can take a long time  

> for coral reef ecosystems to recover from severe stresses like those we  

> are likely to see in the next century.

 

Just because dramatic global global change is natural does not

mean it isn't devistating.  Natural disasters in the past have virtually

wiped out life on Earth as it was known at the time.  I believe that the

difference here is that manking can forsee the effect that he has.  The

larger question is, "Is mankind willing to change to protect the

environment and not kill himself off?"  

 

--

John Meaker

I had already replied privately to "Fishy" with some comments on his

question, but here is a general response:

 

The Younger Dryas (about 11,000 years BP, not 15,000) involved a sudden

shift in the climate of (mostly) the North Atlantic. This is believed

to have been caused by a shutdown/cessation/diversion of the Gulf

Stream. At this time, the globe was gradually warming, as we shifted

from glacial to interglacial. During the Y-D, there was a return to

glacial conditions for those regions influenced by the Gulf Stream.

 

It is true that this reversal took less than 5 years (Smith et al,

Nature 1997)-but that refers to the turnaround, not the entire

temperature range. (Sweden would have felt cooler very quickly, but the

rumble of oncoming glaciers was a few years away...) The entire event

lasted more than 1,000 years.

 

The reason why this event is so important to us now is that most

theories of origin of the Y-D involve disruption of the thermohaline

circulation of the Atlantic by meltwater-a situation which is perhaps

coming soon.

 

Greenland in fact has tons of corals-all deepwater. Our work at Orphan

Knoll (in the path of the Gulf Stream Return Flow) suggests that there

was, in fact, a mass death of these deep corals at that time.

 

It is true that corals/coral reefs are often described as

"resilient"-but all you biologists out there, be careful. Those

descriptions have been written by geologists and paleontologists, such

as Darwin, to whom a million years is a blip. We know that it takes

more than 1,000 years for reefs to colonise newly-flooded continental

shelves-if the water is nice and clean. Similarly, this "resiliant"

behaviour is an ecosystem response. Seen any nice bryozoan reefs

recently? They were common in the Ordovician...the take-home lesson of

the geologic record is that, in fact, corals die like flies.

 

Finally, although I await the outcome of the survey, I worry that there

may be too much emphasis on the results. I fear that there may be

attempts to use the survey to set policy.(Example: there are probably

100 reef scientists right now working on bleaching for every one doing

research on land-based pollution, yet there is no doubt which of the

two has, to this date, done more damage.)I would be more satisfied by a

study which objectively evaluted the damage to reefs done by the

different sources of stress than I would be by the collected opinions

of those responding to a survey. In fact, this is an excellent time to

consider the fallability of opinion polls...

 

Mike

[michaelg]

I came across this source of good references today from Eric's website.  There are downloadable pdfs of most of the articles.

http://www.esig.ucar.edu/kleypas/pubs.html