For decades, people have warned about this. Back in the early 1990s, a
poll of the world's leading climatologists showed that many feared
that the greenhouse effect could be unstoppable if emissions of
polluting gases were merely frozen and not cut. In December 1991,
Greenpeace asked 400 climate scientists if they thought the greenhouse
effect might reach the point of no return in the near future. Of the
113 scientists who returned their questionnaires, almost half thought
a runaway greenhouse effect is possible, and 13 per cent thought it
probable.

James Hansen, who heads the NASA Goddard Institute for Space Studies,
recently said that human activity is causing greenhouse gas levels to
rise so rapidly that his model suggests there is a risk of a runaway
greenhouse effect, ultimately resulting in the loss of oceans and of
all life on the planet: "In my opinion, if we burn all the coal, there
is a good chance that we will initiate the runaway greenhouse effect.
If we also burn the tar sands and tar shale (a.k.a. oil shale), I
think it is a dead certainty."

I discussed this danger in the article Venus' runaway greenhouse
effect a warning for Earth, originally posted and discussed at Gather.

Even if the risk of such scenarios occurring on Earth were small, it
makes sense to do the following:
- describe risk and estimate chances of manifestation, timelines, etc;
- identify tipping points, feedback mechanisms and give estimate
ranges of their combined impact;
- investigate ways to avoid it, mitigate it, etc;
- conduct comparative analysis of the various proposals; and
- make recommendations.

What evaluation criteria can be used in above comparative analysis?

=======
SCIENCE
=======

- EXISTING STUDIES - Are relevant studies available? Has there been
any peer-review?
- FURTHER STUDY - What further studies and modeling are required?
- EFFECTIVENESS - How effective will the proposal be in reducing
global warming?
- TIMESCALE - How long will it take to see results?
- CONCERNS - What are possible climate risks, side-effects, dangers?

===========
ENGINEERING
===========

- METHODS - How can it be done? Have specific methods been proposed?
- TECHNICAL PROBLEMS - Could the project run into technical problems?
- TECHNOLOGIES - Does the project require development of new
technologies?
- TESTING - Has any testing been done? At what scale?

==========
ECONOMICS
==========

- COST - Are there estimates as to what (each of the various stages
of) implementations would cost?
- FINANCING - How could the project be financed? Is there any backing
for the project?
- RESOURCES - Will there be access to the various resources needed to
make it work?
- IMPACT - What will be the economic impact? Who will profit from the
project?

========
POLITICS
========

- APPROVAL - What kind of approvals are needed to go ahead?
- SUBSIDIES - Are subsidies required for impact studies, feasibility
studies or for specific parts of the project?
- POLICY - How does the project fit in with specific policies, e.g.
offset policies, emissions trading or feebates?
- LEGAL - Does it require new laws or amendment of existing laws? Can
legal challenges be expected?
- DIPLOMACY - Would the project require international negotiations
between nations?
- ADMINISTRATION - From where will the project be administered?

===================
SOCIAL AND MEDICAL
===================

- SUPPORT - Is there public support for, concern about or resistance
against the project?
- CONSULTATION - Who will benefit, who could be harmed? Has the public
been consulted?
- CONTROL - What level of policing, supervision and security is
needed? What monitoring is needed?
- MEDICAL - Would the project pose safety and health concerns?
- CULTURAL - Does the project offend some people in some way?

=============
ENVIRONMENT
=============

- IMPACT STUDY - Has an environmental impact assessment been done? Are
further studies required?
- MAINTENANCE - Is any monitoring, maintenance or restoration
required, to prevent environmental damage?

These points could give some indication as to how hard it will be to
implement with a proposed project. Projects could be scored on each
point by asking whether this point will raise any difficulties for the
respective project. A high score would indicate that there can be
expected to be little or no difficulty on this point for the project,
while a low score would indicate that the project can be expected to
have difficulty on this point.

Each point could be given a specific weighting, resulting in overall
score for each of the projects. The higher the overall score, the more
the project should be of interest to members of this group. A high
overall score should indicate that there is sufficient confidence that
the project is safe, effective, feasible, viable, etc, with little or
no concern, risk or danger that things could go wrong or that a
proposal could cause damage or harm in some way.

Importantly however, this should not be seen as a race where only one
winner is selected. It is prudent to encourage diversity in approach
and to continue to study multiple ideas and suggestions in parallel. I
encourage others to suggest additions and changes to this post.

Cheers!
Sam Carana

"We all hope that things will turn out right, but we must think about
what to do, in case it doesn't!"

Links:
Clathrate Gun Hypothesis - Wikipedia
http://en.wikipedia.org/wiki/Clathrate_gun_hypothesis

Runaway greenhouse warming 'cannot be rule out' - by STEPHANIE PAIN -
February 15, 1992
http://www.newscientist.com/article/mg13318081.600

NASA scientist warns of runaway global warming - New Scientist -
December 22, 2008
http://www.newscientist.com/blogs/shortsharpscience/2008/12/nasa-scie...

Venus' runaway greenhouse effect a warning for Earth - by Sam Carana -
November 28, 2007
http://www.gather.com/viewArticle.jsp?articleId=281474977189423
http://geo-engineering.blogspot.com/2007/11/venus-runaway-greenhouse-...

Ranking the ideas - post by Sam Carana, December 27, 2008
http://groups.google.com/group/geoengineering/msg/751aa59e3cc5e8ff