"What if some major ocean current or atmospheric oscillation shuts down or changes to a completely different state, as will almost certainly be the case?"

why is that almost certainly the case, is the author not being equally arrogent by presuming to know what gaia would do?

Well either arrogance or ignorance or a combination of both has got us to the point where experts in climate science are now debating if it is too late.

Humans have attempted a humungous geoengineering and landed all life in a dangerous state where death is a likely outcome for much of life through flooding the atmosphere with greenhouse gases.

GAIA's describer, Lovelock, has proposed huge tubes in the ocean to sink carbon rich warm water to the depths, a replication of the ocean circulation that is one regulator of the climate.

If this draws up low carbon cold water to increase the rate of carbon consumption by ocean life how many will we need to draw the CO2 down from 384ppmv and thus to stabilize the climate if we continue to emit CO2 at ever increasing rates by burning killer coal and poison oil and gas.

Is it a mistake to replicate nature by geoengineering?. Here I am discounting the mirrors as a space industry grab for money.

And getting such a system to work when we could simply fund energy efficiency and currently proved alternatives whilst developing new ones with the money spent on any of these geoengineering projects makes one wonder what the proponents know about the future.

Copenhagen in 2009 will determine if the world grasps the importanc of strong and immediate action to reduce CHG emissions.

Anything like Australia's business as usual target of a 5% reduction by 2020 will ensure that the danger of runaway climate instability, that scientist are now debating, will be assured.

Trying to stabilize a system in chaos with geoengineering will be the actions of desperation, the results unknown as other tipping points, if they have been crossed may require us to return to a much lower CO2 level, [perhaps as low as that of before the industrial revolution of 272ppmv] to stop those other gases released from nature.

And still we have to change our behavior.

Geoengineering without the evidence it will be effective and is absolutely necessary seems like a sidetrack to action we need to take now.

The dream phase is over, the cliamte has been changed to one of less stability and we must act with effective and timely comprehensive reductions in emissions now.

Per this part of Jason Moody's comment:" [I]s the author not being equally arrogent by presuming to know what gaia would do?"

Nowhere in Dr. Barry's essay did I see him say anything about exactly what the new climate state would be. Quoting Dr Barry, "What if some major ocean current or atmospheric oscillation shuts down or changes to a completely different state, as will almost certainly be the case?"

It makes no sense that the climate will stay the same when energy retention and energy transfer changes. Also, atmospheric chemistry changes are occurring in many well documented ways. It is also "beaten into the ground" documented that earth's climate has been different in the past and responds in a buffered way to these changes.

Let's say for experimental purposes that the climate of the earth can exist in one billion ways exactly. So, take one billion pennies and throw them in a pile to represent the one billion ways the earth's climate can exist. Now trade one of those pennies for a marked penny and stir the pennies well. Now picking a random penny, pick out the marked penny on the first try! Climate change is likely like that. We will have something different than what we had.

Also, hat I mean by "buffered" is like a light switch. It takes energy to turn it on or off. When the switch is changed to a new position it then also takes energy to change it back to the old position. Also when the switch is changed it does not respond immediately. The light says on until the filament cools and the light doesn't come on until the filament heats up, although it may seem to a casual observer that the change is instantaneous.
In other words, after a climate switch is thrown it takes some time for us to see the new state and recognize it. Once we do recognize a new state, it then takes energy to return to the old state if in fact that is even possible.(Consider the billion pennies!) I urge you to think about the consequences of those concepts.

Dr. Barry is correct...more of the same techno-meddling will not cure the disease caused by human technology run amok. The only way out is a complete change of paragdigm to a truly wholistic and organic life-centered life style. Gaia is a vast interconnected web of relationship, and by putting up mirrors, or dumping iron in the oceans, or any such "cure" we are going to break the web somewhere else in our short sighted attempts. We are like the addict, who rationalizes they can continue to use their drug if they counter it with some other behavior, etc. We must immediately halt our consumption of the world if their is any hope. The disease of the planet is us...so can we mutate to a non-destructive form?

R. Gates

What we need is serious behavior modification!! Reduce by say 80% all household household consumption, taxing both individuals and greedy corporations, shut down fossil fueled transportation and power plants, shut down cement, steel and aluminum production. UN enforced population control. Eliminate deforestation by taxing with UN monitoring and enforcement (call it the UN Deforestation Admininstration, UNDA) especially Indonesia, Brazil, Malaysia, Russia, Philippines, Turkey and other major "land use problem countries" (representing around ~15% of total CO2e emissions). Close down international trade and leisure travel. This is just a "for starters."

Hi, Nature systems tend to a state of equilibrium, and climate isn't diferent, the problem is that human activity change the ins & outs of the equation, so that the system must rearrange...
We have already interfere with Nature in the wrong way, now it's time we interfere the right way, not permanently but until we strongly develop alternatives to fossil fuels and reach a sustainable development...it may seems utopian but it worth a try.

My personal favourite in the "let's just do it even though we have no idea what will happen" category is Professor Tim Flannery's suggestion that sulphur be added to the atmosphere - such as by adding it to airplane fuel. Refer http://www.news.com.au/story/0,23599,23724412-2,00.html

Greening Infrastructure: How engineering can protect ecosystems and ensure livelihoods. Innovative engineering and water management techniques are being employed to restore environmental flows on a permanent basis. At the same time, the economic benefits for which these river systems were initially developed are retained. However, can these approaches really restore rivers and get all sides to find a common solution? These are some of the discussions during the 5th World Water Forum, held between 16 and 22 March.

These Political Processes will not stop at he 5th World Water Forum. Their results will not only be used as a foundation for the 6th World Water Forum, but will also actively engage other international dialogues such as the G8, UN-CSD or UNFCCC. These meetings, and the results of the 5th World Water Forum, will raise the priority of water management strategies and actions on the international agenda.

The World Water Forum is the world’s premier event on water. It gathers over 15 000 participants from around the world to bring concrete solutions to the world's water challenges. A stepping stone towards global collaboration on water problems, the Forum offers the water community and policy-and-decision- makers from all over the world the unique opportunity to come together to create links, debate and attempts to find solutions to achieve water security.

The World Water Forum is organized every three years as a joint venture between the World Water Council and the government of the host country. After previous Forums in Morocco (1997), the Netherlands (2000), Japan (2003) and Mexico (2006), the 5th World Water Forum will be held in Istanbul, Turkey in March 2009. Get involved!

Here's a perfect example of how human meddling has unintended consequences:

http://news.yahoo.com/s/ap/20090113/ap_on_re_au_an/as_australia_rabbit_infestation_1

It's a complicated web of relationship...and as we try to engineer the planet...we'll only make it worse...

R. Gates

I do so totally agree with Dr. Barry's analysis of geoengineering that I hardly have anything to add. In agreement though I would like to say that Who do we think we are? Do we possibly think that we can adjust the earth better than the earth can adjust itself? Do we think that even the absolute smartest scientists know every detail of how the scenario could play out? We've gotten ourselves into this mess by thinking we knew what we were doing. We need to get back to some old fashioned basics of how to live with respect for the earth. We have to stop being selfish and wasteful and appreciate what we have. The earth can live without us but we cannot live without the earth.