By Gerard Wynn

VENICE, May 16 (Reuters) - Eighteen months before a new climate pact must be agreed, the world appears to be drifting in negotiations that could be the most complex ever, experts said.

The pact is needed to replace or extend the Kyoto Protocol on tackling global warming, whose first round ends in 2012.

Some 190 countries have agreed to clinch by November 2009 a new or amended pact, mindful it would take at least two years for so many national governments and parliaments to ratify it.

"At this point it's not clear about a path forward," said Robert Stavins, co-director of a Harvard University project to help design a new climate agreement, which hosted a meeting of academics, business, policymakers and environmental groups in Venice on Friday.

"You have to think creatively, take into account the science and politics. Not any world challenge requires this kind of collaboration. Sometimes it just takes political will for the obvious way forward."

The talks are complicated by an election in the United States, a top emitter of greenhouse gases, which will see a new president elected in November but not inaugurated until January, with senior officials in place as late as June 2009.

The present Kyoto binds 37 developed nations to cut emissions by 5 percent below 1990 levels by 2008-12, while the next treaty aims to include all countries, although at very different levels of commitment.

The problem is sharing the cost of re-deploying the world's entire energy system away from fossil fuels, and deciding how soon emerging economies adopt binding caps on greenhouse gases.

Academics may help, for example, by allaying rich countries' fears about the economic impact of adopting caps first.

The most affected, energy-intensive and traded sectors like steel and cement account for less than 5 percent of employment and wealth in industrialised nations, one economist told the Venice conference, and while the impacts mattered, they were small, said another.

Many climate scientists say the world has only 10 years or so to halt year on year increases in greenhouse gas emissions or face dangerous climate change including more droughts, floods and sea level rise.

COST

Cap and trade schemes, designed by environmental economists, are now spreading beyond the European Union to other industrialised countries as a way to force industry to buy permits to emit the greenhouse gas carbon dioxide.

But such schemes add to industry costs and western governments fear they will hand an advantage to competitors in developing nations which have no such caps. The European Union has not ruled out border tariffs to level that effect.

One policy tweak could give developing countries carbon offsets, to sell to rich nations, if their steel and cement industries surpassed western-style national efficiency standards or "sectoral targets", academics told the Venice conference.

Analysts say the difficulty of agreeing a treaty is stark. Developed nations may not have the political will, for example, to pay poorer ones perhaps tens of billions of dollars annually for carbon offsets, as a way to meet tough emissions caps.

"Developed countries have to know when developing countries will participate," said Richard Bradley, head of energy efficiency and the environment at the International Energy Agency, energy adviser to rich countries.

While economists say the costs of fighting climate change are negligible compared to the size of the global economy and the risk of catastrophic climate change, those costs will be borne most by a few rich countries now, while benefits will be felt worldwide in avoided climate change, which may seem unfair. "It's getting over the first hump," said Bradley. (Reporting by Gerard Wynn; editing by James Jukwey)

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