[Coral-List] La Nina and global warming

[David M. Lawrence]

Some [arguably biased] highlights from the Geological Society of London 
statement:

What are the grounds for concern?

* Evidence from the geological record is consistent with the physics 
that shows that adding large amounts of carbon dioxide to the atmosphere 
warms the world and may lead to: higher sea levels and flooding of 
low-lying coasts; greatly changed patterns of rainfall2; increased 
acidity of the oceans 3,4,5,6; and decreased oxygen levels in seawater7,8,9.

* There is now widespread concern that the Earth’s climate will warm 
further, not only because of the lingering effects of the added carbon 
already in the system, but also because of further additions as human 
population continues to grow. Life on Earth has survived large climate 
changes in the past, but extinctions and major redistribution of species 
have been associated with many of them. When the human population was 
small and nomadic, a rise in sea level of a few metres would have had 
very little effect on Homo sapiens. With the current and growing global 
population, much of which is concentrated in coastal cities, such a rise 
in sea level would have a drastic effect on our complex society, 
especially if the climate were to change as suddenly as it has at times 
in the past. Equally, it seems likely that as warming continues some 
areas may experience less precipitation leading to drought. With both 
rising seas and increasing drought, pressure for human migration could 
result on a large scale.

What is the Greenhouse Effect?

* The Greenhouse Effect arises because certain gases (the so-called 
greenhouse gases) in the atmosphere absorb the long wavelength infrared 
radiation emitted by the Earth’s surface and re-radiate it, so warming 
the atmosphere. This natural effect keeps our atmosphere some 30ºC 
warmer than it would be without those gases. Increasing the 
concentration of such gases will increase the effect (i.e. warm the 
atmosphere more)19.

Has sudden climate change occurred before?

* Yes. About 55 million years ago, at the end of the Paleocene, there 
was a sudden warming event in which temperatures rose by about 6ºC 
globally and by 10-20ºC at the poles22. Carbon isotopic data show that 
this warming event (called by some the Paleocene-Eocene Thermal Maximum, 
or PETM) was accompanied by a major release of 1500-2000 billion tonnes 
or more of carbon into the ocean and atmosphere. This injection of 
carbon may have come mainly from the breakdown of methane hydrates 
beneath the deep sea floor10, perhaps triggered by volcanic activity 
superimposed on an underlying gradual global warming trend that peaked 
some 50 million years ago in the early Eocene. CO2 levels were already 
high at the time, but the additional CO2 injected into the atmosphere 
and ocean made the ocean even warmer, less well oxygenated and more 
acidic, and was accompanied by the extinction of many species on the 
deep sea floor. Similar sudden warming events are known from the more 
distant past, for example at around 120 and 183 million years ago23,24. 
In all of these events it took the Earth’s climate around 100,000 years 
or more to recover, showing that a CO2 release of such magnitude may 
affect the Earth’s climate for that length of time25.

How did levels of CO2 in the atmosphere change during the ice age?

* The atmosphere of the past 800,000 years can be sampled from air 
bubbles trapped in Antarctic ice cores. The concentrations of CO2 and 
other gases in these bubbles follow closely the pattern of rising and 
falling temperature between glacial and interglacial periods. For 
example CO2 levels varied from an average of 180 ppm (parts per million) 
in glacial maxima to around 280 ppm during interglacials. During 
warmings from glacial to interglacial, temperature and CO2 rose together 
for several thousand years, although the best estimate from the end of 
the last glacial is that the temperature probably started to rise a few 
centuries before the CO2 showed any reaction. Palaeoclimatologists think 
that initial warming driven by changes in the Earth’s orbit and axial 
tilt eventually caused CO2 to be released from the warming ocean and 
thus, via positive feedback, to reinforce the temperature rise already 
in train28. Additional positive feedback reinforcing the temperature 
rise would have come from increased water vapour evaporated from the 
warmer ocean, water being another greenhouse gas, along with a decrease 
in sea ice, and eventually in the size of the northern hemisphere ice 
sheets, resulting in less reflection of solar energy back into space. 
[DML: Note that this excerpt addresses Gene's point about warming 
preceding CO2 increases.]

How has carbon dioxide in the atmosphere changed in recent times?

* Atmospheric CO2 is currently at a level of 390 ppm. It has increased 
by one third in the last 200 years33. One half of that increase has 
happened in the last 30 years. This level and rate of increase are 
unprecedented when compared with the range of CO2 in air bubbles locked 
in the ice cores (170-300 ppm). There is some evidence that the rate of 
increase in CO2 in the atmosphere during the abrupt global warming 183 
million years ago (Early Jurassic), and perhaps also 55 million years 
ago (the PETM), was broadly similar to today’s rate34.

When was CO2 last at today’s level, and what was the world like then?

* The most recent estimates35 suggest that at times between 5.2 and 2.6 
million years ago (during the Pliocene), the carbon dioxide 
concentrations in the atmosphere reached between 330 and 400 ppm. During 
those periods, global temperatures were 2-3°C higher than now, and sea 
levels were higher than now by 10 – 25 metres, implying that global ice 
volume was much less than today36. There were large fluctuations in ice 
cover on Greenland and West Antarctica during the Pliocene, and during 
the warm intervals those areas were probably largely free of 
ice37,38,39. Some ice may also have been lost from parts of East 
Antarctica during the warm intervals40. Coniferous forests replaced 
tundra in the high latitudes of the Northern Hemisphere41, and the 
Arctic Ocean may have been seasonally free of sea-ice42.

In conclusion - what does the geological record tell us about the 
potential effect of continued emissions of CO2?

* Over at least the last 200 million years the fossil and sedimentary 
record shows that the Earth has undergone many fluctuations in climate, 
from warmer than the present climate to much colder, on many different 
timescales. Several warming events can be associated with increases in 
the ‘greenhouse gas’ CO2. There is evidence for sudden major injections 
of carbon to the atmosphere occurring at 55, 120 and 183 million years 
ago, perhaps from the sudden breakdown of methane hydrates beneath the 
seabed. At those times the associated warming would have increased the 
evaporation of water vapour from the ocean, making CO2 the trigger 
rather than the sole agent for change. During the Ice Age of the past 
two and a half million years or so, periodic warming of the Earth 
through changes in its position in relation to the sun also heated the 
oceans, releasing both CO2 and water vapour, which amplified the ongoing 
warming into warm interglacial periods. That process was magnified by 
the melting of sea ice and land ice, darkening the Earth’s surface and 
reducing the reflection of the Sun’s energy back into space.

* While these past climatic changes can be related to geological events, 
it is not possible to relate the Earth’s warming since 1970 to anything 
recognisable as having a geological cause (such as volcanic activity, 
continental displacement, or changes in the energy received from the 
sun)43. This recent warming is accompanied by an increase in CO2 and a 
decrease in Arctic sea ice, both of which – based on physical theory and 
geological analogues - would be expected to warm the climate44.

* In the coming centuries, continued emissions of carbon from burning 
oil, gas and coal at close to or higher than today’s levels, and from 
related human activities, could increase the total to close to the 
amounts added during the 55 million year warming event – some 1500 to 
2000 billion tonnes. Further contributions from ‘natural’ sources 
(wetlands, tundra, methane hydrates, etc.) may come as the Earth 
warms22. The geological evidence from the 55 million year event and from 
earlier warming episodes suggests that such an addition is likely to 
raise average global temperatures by at least 5-6ºC, and possibly more, 
and that recovery of the Earth’s climate in the absence of any 
mitigation measures could take 100,000 years or more. Numerical models 
of the climate system support such an interpretation44. In the light of 
the evidence presented here it is reasonable to conclude that emitting 
further large amounts of CO2 into the atmosphere over time is likely to 
be unwise, uncomfortable though that fact may be.

Dave

On 11/16/2010 2:36 PM, Eugene Shinn wrote:
> Dear Listers, Good to see the neurons are firing on all cylinders.
> The Geological Society of London statement
> http://www.geolsoc.org.uk/gsl/views/policy_statements/climatechange
> is well done. It pretty much says what I have been trying to say. I
> was a little concerned that they did not put more emphasis on water
> vapor as the greatest green house gas or methane and others. But then
> the IPCC said little as well. Why are we all so stuck on Co2? Plants
> love it!
>       Also, there was no mention that ice cores show warming occurred
> before Co2 peaked by at least 400 years. Shouldn't it be the other
> way around?  I would like to suggest a new book by Robert Carter a
> well-respected Australian geologist/paleontologist. The title is,
> "Climate: The Counter Consensus.:
> The book is technical but easy reading and is not strident like so
> many anti AGW/IPCC publications. He even discusses corals and ocean
> acidification oops! I meant alkalinity shift, which he clearly
> explains. There is a lot about sea level rise and fall and how it
> depends on where you are. His major point is the IPCC is all about
> "projections" (their words) not predictions as the mass media and
> warming enthusiasts call it. Gene
>

-- 
------------------------------------------------------
  David M. Lawrence        | Home:  (804) 559-9786
  7471 Brook Way Court     | Fax:   (804) 559-9787
  Mechanicsville, VA 23111 | Email: dave at fuzzo.com
  USA                      | http:  http://fuzzo.com
------------------------------------------------------

"All drains lead to the ocean."  -- Gill, Finding Nemo

"We have met the enemy and he is us."  -- Pogo

"No trespassing
  4/17 of a haiku"  --  Richard Brautigan