Human influence at least doubled the risk of last year's Europe-wide heatwave. That is the conclusion of leading scientists who say they are more than 90 percent sure of the fact. The research, published in Nature magazine, is a significant milestone on the road to establishing liability for climate change damage.
It boosts the argument that greenhouse gas emissions have increased temperatures both globally and regionally, and it brings nearer the day when courts will be asked to decide where liability lies.
This "detection and attribution science," as it is known, lies behind the many efforts of lawyers and campaigners around the world to enforce the law to combat the causes and impacts of climate change.
In 2001, the world's scientists said that globally, most of the warming was due to human activities. Since then, at least three peer-reviewed papers have revealed human influence on regional temperatures; human influence, found for the first time, on a climate variable other than temperature - sea-level pressure; and now "the first successful attempt to detect man-made influence on a specific extreme climatic event," according to Christoph Schar, at the Institute for Atmospheric and Climate Science in Zurich, and Gerd Jendritzky, of the German Weather Service.
The courts have already responded positively to these findings. The legal relevance of climate change has now been accepted by US and Australian judges in cases where decisions leading to more coal mining and electricity transmission were found to be illegal. And a California appeals judge has rejected the idea that "injury to all is injury to none" where "global environmental impact is threatened by a federal statutory wrong."
In addition, the range of legal theories used is broadening. Cases began in 2002, with the collaboration of US cities, non- governmental organizations and citizens against the US export-credit bodies. These were followed by US states, American Samoa, cities and NGOs challenging the failure of the US environmental protection agency to regulate greenhouse gas emissions under the Clean Air Act.
These are what lawyers call traditional public law cases. Since then, the Inuit Circumpolar Conference has announced its development of a case against the US in the InterAmerican Commission for Human Rights, alleging violations of Inuit human rights.
Climate change litigation arrived in Europe in June this year, when NGOs went to court under freedom of information rules to challenge the German government's secrecy about export credit support for fossil fuel projects since 1997.
Meanwhile, in Argentina, citizens have successfully used the Accion Informativa mechanism (whereby public bodies, where responsible, are legally required to respond to questions from the public) after the Santa Fe floods, the country's worst climate-related disaster.
The first private law action was brought in July by eight US states, New York city and NGOs against the five main US power companies, arguing for a court order to compel them to reduce their emissions of carbon dioxide. And in November, the impact of climate change on some of the most beautiful parts of the planet was highlighted when an alliance of NGOs, climbers and others initiated legal moves in Unesco to protect Mount Everest, world heritage glaciers in the Andes and coral reefs in Belize from the impacts of climate change.