As the first phase of the Kyoto Protocol draws to a close, the world will dissect its record for successes to emulate in the fight against global warming -- and pitfalls to avoid.

If all goes well, Kyoto will eventually be superseded by a new worldwide treaty, whose design is being negotiated at UN talks in Doha, Qatar.

Its job would be to limit global warming to a manageable two degrees Celsius (3.6 degrees Fahrenheit) from pre-industrial levels.

But what should this much-trumpeted post-2020 pact look like?

Searching for an answer, many are scrutinising Kyoto, the most ambitious but also the most contested climate pact ever seen.

"The protocol was the best we could produce in 1997. Now things are different. The situation has changed radically," Argentine diplomat Raul Estrada, a midwife at Kyoto's birth, told AFP.

Adopted in 1997 after 30 months of tough negotiations, the protocol was then held up by further wrangling over its rulebook before finally taking effect in 2005.

It bound 37 industrialised nations and the European Union (EU) to curbing Earth-warming greenhouse gas emissions by five percent on average in 2008-2012 from 1990 levels. In Doha, negotiators are wrangling over a second set of pledges that would run from 2013.

Kyoto has always excited passions.

Developing countries and greens like it because countries that historically are to blame for today's warming have legally-binding commitments on their emissions.

Critics, though, say it is flawed.

Their sharpest barbs are reserved for a rich country/poor country divide that may have held true in 1997 but is badly out of date today.

Developing countries have no targeted commitments, the idea being that they should be able to use cheap fossil fuels to power their rise out of poverty.

This category includes bone-poor economies such as Niger and Burkina Faso -- and newly-rich ones like South Korea, Saudi Arabia, Kuwait, Singapore and Malaysia.

As a result China, which has emerged since 1997 as the world's No. 1 CO2 spewer, has no specified targets.

Nor does the United States, the No. 2 emitter today, which signed Kyoto but refuses to ratify it citing unfairness.

"In practice, the 1997 treaty did little to curb emissions of greenhouse gases," the science journal Nature commented on Wednesday.

"Most of the parties to the treaty met their commitments easily but, because the Kyoto Protocol did not set limits for developing countries, the total emissions of greenhouse gases are rising faster than ever thanks mainly to massive growth in coal consumption by China."

According to the International Energy Agency, global energy-related CO2 emissions rose 3.2 percent in 2011 to reach a record high of 31.2 gigatonnes -- pointing to potential warming of 3.6 C (6.5 F).

Even so, Kyoto spawned innovations that are likely to remain part of the climate landscape, say analysts.

These include carbon markets that allow countries to trade emissions allowances and the Clean Development Mechanism by which rich nations earn credits for sponsoring cleaner fuel projects in poor countries.

"The success of the Kyoto Protocol depends on your measure," said Kelly Rigg, executive director of the Global Campaign for Climate Action.

"Has it cut emissions down to levels that would stop climate change and was it ever expected to do that? No!

"Was it instrumental in triggering investments and legislation in pioneer countries that will eventually lead the world economy towards a low-carbon transition? Yes!"

Rigg argued: "We need the Kyoto Protocol now, and its binding rules need to inspire a new treaty, as voluntary actions alone simply won't do the trick." But punishing climate violators is easier said than done.

Kyoto is larded with compliance clauses. Countries who exceeded their targets by 2012 have to make good in the follow-up period, with a 30 percent penalty on top.

But nothing prevents them from simply walking away from Kyoto without facing the bill, as Canada did in 2011 after years of exceeding its carbon cap.

"The problem is the way that international law works," lamented Estrada. "You cannot go to the Security Council of the UN asking to make an expedition" to a defaulting country."

In this light, many observers contend that there are far simpler measures, such as taxes or industry-wide incentives, that set a price on carbon and get countries to pollute less.