From being a marginal and even mocked issue, climate-change litigation is fast emerging as a new frontier of law where some believe hundreds of billions of dollars are at stake.

Compensation for losses inflicted by man-made global warming would be jaw-dropping, a payout that would make tobacco and asbestos damages look like pocket money.

Imagine if a country or an individual could get redress for a drought that destroyed farmland, for floods and storms that created an army of refugees, or for rising seas that wiped a small island state off the map.

In the past three years, the number of climate-related lawsuits has ballooned, filling the void of political efforts in tackling greenhouse-gas emissions.

Eyeing the money-spinning potential, some major commercial law firms now place climate-change litigation in their Internet shop window.

Seminars on climate law are often thickly attended by corporations that could be in the firing line - and by the companies that insure them.

But legal experts sound a note of caution, warning that this is a new and mist-shrouded area of justice.

Many obstacles lie ahead before a Western court awards a cent in climate damages and even more before the award is upheld on appeal.

"There's a large number of entrepreneurial lawyers and NGOs (non-governmental organizations) who are hunting around for a way to gain leverage on the climate problem," said David Victor, director of the Laboratory on International Law and Regulation at the University of California at San Diego.

"The number of suits filed has increased radically. But the number of suits claiming damages from climate change that have been successful remains zero."

Lawsuits in the United States related directly or indirectly to climate change almost tripled in 2010 over 2009, reaching 132 filings after 48 a year earlier, according to a Deutsche Bank report.

Elsewhere in the world, the total of lawsuits is far lower than in the US, but nearly doubled between 2008 and 2010, when 32 cases were filed, according to a tally compiled by AFP from specialist sites.

The majority of these cases touch on regulatory issues and access to information, which can have many repercussions for coal, gas and oil producers and big carbon-emitting industries such as steel and cement.

"In this area, the floodgates have opened," said Michael Gerrard, director of the recently opened Center for Climate Change Law at Columbia Law School in New York, who contributed to the Deutsche Bank report.

In the United States, many cases seek clarification on the right of the US Environmental Protection Agency to regulate carbon dioxide (CO2) emissions, while in Europe, the main issue has been emissions quotas allotted to companies in Europe's carbon market.

In some cases, courts have thrown out the suits, admitted part of them or declared themselves unfit to issue a ruling and booted the affair to a higher authority.

The legal fog is especially thick when it comes to so-called nuisance suits, which seek to determine blame, and open the way to damages.

"There are billions of potential plaintiffs and millions of potential defendants," said Gerrard. "The biggest problem, though, is causation."

Gerrard and others pointed out some of the dilemmas for establishing liability, starting with the fact that fossil fuels are used, by all of us, in complete legality.

And a molecule of CO2 is no respecter of national boundaries.

Then there is the business of distinguishing between weather and climate. For instance, hurricanes, droughts and floods have always occurred in human history. Can one, or even several, of these be pinned to human meddling in the climate system?

So who is to blame? And to what degree?

Some of the wrangling can be seen in a 2006 case in which California sued three US and three Japanese carmakers, arguing that emissions from their vehicles had caused among other things a melting of mountain snowpack on which the state depends for its water.

That case was dismissed by a district court in 2007, which ruled that the issues were "political questions" that should be tackled by the US president and Congress.

It also noted that the cars were sold legally, that the car emissions had not violated any current laws or regulations and climate change had many contributing factors.

Two other big cases touching on liability have gone to the Supreme Court to adjudicate on competence.

In the most eagerly awaited case, whose ruling is expected by the end of June, the state of Connecticut is demanding an injunction against major power companies to reduce greenhouse-gas emissions.

"That will definitely be the big one," said Gerrard. "Everyone is waiting to hear what the Supreme Court says."

Christoph Schwarte, a lawyer with a British charity called FIELD (Foundation for International Environmental Law and Development), said that even if today's lawsuits come to nothing, "some of these cases may be winnable in the future."

"Case law in the future might evolve, and scientists' claims to determine the percentage of human contribution to certain extreme-weather events may be recognized in some way or another."

Today's lawsuits may also spur thinking about future liability risks among major emitters, Schwarte argued.

Many tobacco and asbestos lawsuits, for instance, hinged on arguments that firms knew their product was dangerous at the time, but concealed this evidence from the public.

"(The lawsuits) create awareness and thus also may have an impact on the actions of governments and corporations," said Schwarte.