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Glaciers are important indicators of climate change. A recent study published in the leading journal Science shows that glaciers in the tropical Andes have now retreated further than at any other time in the entire Holocene – which covers the whole history of human civilisation since the invention of agriculture. These findings are likely to resonate beyond the scientific community, as they strongly support the lawsuit filed by a Peruvian farmer against the energy company RWE, which has returned to court this week.

Paleoclimatologists can determine how long bedrock beneath a glacier has been covered by ice using measurements of specific isotopes. When rock surfaces are exposed, isotopes such as carbon-14 and beryllium-10 form due to bombardment by cosmic radiation. If, however, the rock is covered by an ice sheet, it is shielded from this radiation, and these unstable isotopes gradually disappear through radioactive decay (with half-lives of 5,700 and 1.4 million years, respectively). This method, known as cosmogenic radionuclide dating, has been well-established for decades. I first encountered it myself 23 years ago during an excursion with glacier experts to New Zealand’s Southern Alps.

The new study applied this method to examine several glaciers in the tropical Andes (see Fig. 1).

In rock samples collected at the edges of the glaciers, researchers found isotope concentrations close to zero. From this, they conclude that these rocks must have remained covered by ice throughout the entire Holocene, shielding them from cosmic radiation. This indicates that these glaciers are very likely smaller today than at any point in at least the last 11,700 years.

This finding aligns with several previous studies showing that temperatures in the tropical Andes have never been warmer during the Holocene than they are today. For instance, reconstructions of the glacier margin of the Quelccaya Ice Cap demonstrate that it has not been smaller than today at any time in at least the last 7,000 years. Temperature reconstructions based on proxy data further support this conclusion.

Global Warming Means Global Glacier Retreat

The Andes are not an exception: according to current research, global average temperatures today are very likely higher than at any other point during the entire Holocene. Given that an ice age lasted for more than 100,000 years before the Holocene, today’s temperatures are probably the highest experienced in about 120,000 years. This unprecedented warming, which began in the 19th century and has so far reached around 1.3–1.4°C, is almost entirely driven by human activity – primarily the burning of fossil fuels. According to the Intergovernmental Panel on Climate Change (IPCC), natural factors have contributed very little to recent warming, probably even having a slightly cooling effect, due to declining solar activity since the mid-20th century (a fact reflected in the title of former RWE manager Fritz Vahrenholt’s book, Die kalte Sonne – The Cold Sun).

As a result, glaciers worldwide continue to lose mass (see Figure 2). In Germany, only four glaciers remain, following the disappearance of the Southern Schneeferner glacier in September 2022. Soon, there will be no glaciers left in Germany at all.

Implications for the RWE Case

The RWE case addresses, among other things, whether global warming caused by CO₂ emissions is responsible for the severe glacier melt, the substantial retreat of the glacier by approximately 1.5 km over the past 140 years and the thawing of permafrost above the city of Huaraz in Peru. A 2021 attribution study published in the respected journal Nature Geoscience has already conclusively demonstrated this connection; however, RWE appears to continue challenging these findings.

In this context, the new data from Gorin et al. are particularly relevant. The Queshque Glacier, now smaller than at any other time in at least the last 11,700 years, is located only 40 km from Huaraz, in the same mountain range as Lake Palcacocha (see Fig. 3).

It is highly likely that local climate changes across this area differ minimally at most. Although average climate conditions can vary over short distances due to local topography, climate warming typically has a correlation radius of more than 1,000 km. Therefore, there is no meaningful difference in climate change effects between Queshque Glacier and Lake Palcacocha.

This region is already experiencing the most significant climate warming in the history of human civilisation. It will undoubtedly continue until the global economy achieves climate neutrality, essentially, net-zero CO₂ emissions.

In the RWE trial, the central issue will be whether, and to what extent, the city of Huaraz and the plaintiff would be affected by a glacier flood. A systematic analysis of past glacial lake outburst floods (GLOFs) in the region has examined 160 such events based on satellite imagery. The findings clearly identify the Andes around Huaraz as a hotspot for this risk (see Fig. 4).

Additionally, this study shows that the frequency of such floods has increased significantly since 1980 (see Fig. 5). Before 1980, there was only one year with more than two recorded GLOFs: 1970 due to a severe earthquake. However, there are now repeatedly years with 3, 4 or even 5 glacial lake outbursts.

One thing is clear: given the existing research, it would be absurd to assume that the risk of a Lake Palcacocha outburst could be calculated based solely on historical data, without explicitly accounting for global warming caused by fossil fuels. Anyone who suggests that climate change is not happening in Huaraz – that there is no human fingerprint, and therefore no connection to RWE’s share of CO₂ emissions – may have their reasons for doing so. But the evidence clearly shows otherwise.