Flex-mechs:
As laid down in the 1997 Kyoto Protocol, these are the clean development mechanism, emissions trading and joint implementation - all legitimate ploys that developed countries may use to lower the cost of cutting their own greenhouse gas emissions.
As far as the global climate is concerned, it doesn't matter where emissions originate. And because it can be cheaper to reduce emissions in less developed countries, the "flex-mechs" should help to achieve the Kyoto target as inexpensively as possible.
The protocol text authorising these mechanisms is brief and leaves it to the current negotiations to determine how they should operate. The Hague meeting must devise a system of credits and debits as well as ways to measure each project's contribution to reducing net emissions.
Clean Development Mechanism:
The CDM is intended to promote sustainable development by encouraging governments and industry to invest in projects in developing countries that reduce or avoid emissions - for example, generating electricity from wind or solar power.
Under the Kyoto regime, developed countries would receive credit against their targets for the emissions avoided by these projects. In addition, a levy would be charged to help vulnerable developing countries adapt to climate change.
But since CDM deals are not regarded as "a zero-sum game within the Kyoto envelope", even UN officials accept that the accounting system "will need to be particularly rigorous to uphold the protocol's environmental credibility". For example, should planting trees be included?
Joint Implementation:
Known by insiders as "JI", this offers the prospect for developed countries to get more credits for contributing to environmentally positive projects in other countries, principally those in central and eastern Europe and the former Soviet Union.
And since all of these countries are subject to Kyoto targets, unlike the developing nations that would stand to benefit from the CDM, JI deals occur within a zero-sum game where credits obtained by the investing country are offset by debits to the country hosting the project.
Emissions trading:
Another linchpin of the Kyoto Protocol, this will allow developed countries to transfer emissions credits to each other. The idea is that developed countries that successfully reduce emissions will be able to sell "excess emissions credits" to countries that find it more difficult.
A key issue with emissions trading has been concern that certain countries - notably Russia and Ukraine - would be able to meet their targets with minimal effort and could then sell emission credits to others.
Sinks:
These raise the technically complex and politically charged question of how much credit countries should receive for promoting reforestation or ending deforestation. Rigorous accounting will be needed, even if it is hard to estimate just how much carbon trees absorb.
Also needed are clear definitions of what counts as a "sink", and decisions on whether or not to give credit for non-forestry sinks, such as agriculture and soils, and on other issues, such as ensuring that climate-driven activities do not have negative environmental impacts.
"No Regrets" measures:
Promoting energy efficiency in homes, offices, industries, farms and vehicles makes economic and environmental sense, irrespective of climate change. In cities and towns, better public transport and less reliance on private cars would also cut emissions.
Compliance:
To be credible, the Kyoto Protocol must have rules for determining compliance and measures for responding to cases of non-compliance. The key question is what the consequences of non-compliance should be.