[Coral-List] Basic Question. Simple Answer ?

Mark Eakin Mark.Eakin at noaa.gov
Mon Jul 26 15:58:00 EDT 2004

Mike Risk gave a very good response, so I'll just highlight a few  

On Jul 24, 2004, at 9:42 AM, John Meaker wrote:

> 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?

No, what I mean is that generally temperatures in the polar and  
sub-polar atmosphere vary much more than tropical oceans.  When air  
temperatures change dramatically in Greenland, coral reefs in tropical  
waters see much smaller change.  The impacts of these smaller changes  
in tropical water temperature will vary among different parts of the  

> 	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?

Yes, but not necessarily in ways you might think.  A reduction in NADW  
formation could actually cause a direct warming effect on tropical  
oceans.  Remember that NADW formation intensifies the northward  
transport of ocean heat, warming northern oceans.  If you shut off the  
northward flow of heat, the tropics could warm.  Reduced northward flow  
also may reduce the southward flow of cool water, adding to this  
effect.  However, if reduced NADW cools the atmosphere, this could have  
cooling effects on tropical oceans that counteract the warming due to  
changes in ocean circulation.  The warmest areas in the oceans are  
unlikely to warm or cool.  However, the latitudinal extent of the warm  
pools would change.

> 	Additionally, the mid holocene warm period actually saw warmer
> global temperatures than we are currently experiencing.

Maybe.  The mid-Holocene thermal maximum was warmer than pre-industrial  
modern climate, and in some areas was warmer than today.  We don't have  
adequate records to provide full temperature reconstructions of global  
climate at the mid-Holocene, nor do we know for sure what the climate  
will look like in another 100 years as CO2 continues to rise.  Remember  
that atmospheric CO2 is now higher than any time in the last 450,000  
years and probably higher than any seen in the last 24 million years --  
since the major expansion of corals.

> 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.

The big difference is that those changes were natural.  The one we are  
causing is a global-scale, uncontrolled experiment.

>> 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?

Good question.  So far corals don't seem to be doing too well with what  
we are throwing at them, do they?

>> 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?"

My point exactly.


> --  
> 	John Meaker
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C. Mark Eakin, Ph.D.
Director of the World Data Center for Paleoclimatology

NOAA/National Climatic Data Center
325 Broadway E/CC23
Boulder, CO 80305-3328
Voice: 303-497-6172                  Fax: 303-497-6513
Internet: mark.eakin at noaa.gov

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