The town of Huarez, nested high in the Peruvian Andes at 10,000ft altitude, is at risk. Water, once held securely within the Palcaraju glacier now rests in the nearby and unstable Lake Palcacocha, threatening the town with a devastating outburst flood that could inundate it. The risk is so acute that it is now the subject of a landmark legal case currently taking place in the German courts. Saúl Luciano Lliuya, a farmer from Huaraz, is suing RWE, Germany’s largest electricity producer, for the costs of preventing harms which would result if an outburst flood took place.
One of the key issues at the heart of this case is the question of fault. Should this high-emission company be held responsible, or could natural climate change have caused the glacier to retreat, resulting in the unstable lake? According to a new study from the University of Oxford and the University of Washington (which was undertaken independently of the legal case but which will now be used as evidence) the answer to the latter is unequivocally no. The researchers conclude that it is ‘virtually certain’ that the retreat of Palcaraju glacier to the present day cannot be explained by natural variability alone. In turn, they demonstrate that this retreat has increased the flood risk, establishing a direct link between emissions and the need to implement protective measures, as well as any damages caused by flooding in the future.
‘It’s up to the courts to decide how scientific evidence is interpreted,’ says Rupert Stuart-Smith, lead author of the study, ‘but this is the first attribution study which looks at the role of human-caused climate change – greenhouse gas emissions – all the way through to the hazards of a glacial outburst flood. What we found was that, from a scientific point of view, the role of climate change in causing this flood risk is very clear indeed.’
To establish this link the researchers took a three- stage approach, separating the causal chain into stages. ‘The first is the link between emissions and the global and regional change in the climate. So in particular, the change in the temperature around the glacier itself,’ says Rupert. This involved using standard Intergovernmental Panel on Climate Change methods. ‘Then we look at the relationship between this change in temperature, and the retreat of the glacier, which leads directly to the expansion of the lake from which the flood threat comes. And then we looked at how this glacial retreat and lake expansion changes the flood hazard and used some hazard ranking indices to do so.’
The team were also able to go further, concluding that not only is man-made climate change a relevant factor, it is likely to be entirely responsible for the glacial retreat. ‘Our best estimate is that in the absence of human influence on the climate, it is as likely that the glacier would have lengthened as it is that the glacier would have retreated. And so, basically, 100 per cent of the retreat of this glacier and therefore 100 per cent of the expansion of the lake which delivers the flood risk, is the result of this temperature change, which we also find is almost entirely due to human influence.’
It now remains to be seen what prosecutors can make of this evidence. With several similar cases now cropping up against high emitters it has the potential to set a powerful precedent. ‘Whether or not this particular case proceeds, it shows there is huge potential to leverage the power of the law to hold private companies liable for climate-change related impacts,’ said Professor Thom Wetzer, founding director of the Oxford Sustainable Law Programme.