🧊Donovan Dennis
(@donovanpdennis.com, @pik-potsdam.bsky.social ) is a glaciologist exploring the current state of glaciers and ice sheets, and what their loss means for our planet

Read the full report:
global-tipping-points.org

@pik-potsdam.bsky.social @gsiexeter.bsky.social @iceybethan.bsky.social @jeremyely.bsky.social @wwf.org.uk

A. Degree. Matters. Reducing emissions, holding the world to 1.5 (or 1.6, or 1.7) is infinitely better than throwing hands up. The only demonstrated way to prevent widespread ice loss for mountain glaciers (in Alaska, and globally) is to minimize global warming.

www.science.org/doi/10.1126/...

🅰️ There is no silver bullet. Geoengineering interventions implemented in other regions would be exceedingly expensive (we're talking in the $100,000,000 to $1,000,000,000 range given costs elsewhere) to implement for Áakʼw Tʼáak Sítʼ.

🅱️ The destiny is by no means set in stone!!! Every. Tenth. Of..

continues to retreat, and as other glaciers which feed Áakʼw Tʼáak Sítʼ disconnect (see feedback No. 2!), the threat of additional floods may increase.

There are many additional consequences, from aquatic ecosystems to tourism to national security. But two additional points we wanted to highlight:

Floods from Suicide Basin in '23, '24, and '25 each set records for the largest on record. Following the 2024 flood, which damaged 300+ homes, new temporary barriers were installed to protect the community, at a cost to homeowners of $6000+ dollars.

As Áakʼw Tʼáak Sítʼ...
www.juneauflood.com#/home

These Tlingit communities have expressed a deep sense of grief and loss, describing their culture and identity as being inseparable from the land, which is changing rapidly.

Additional consequences of glacier loss in Juneau relate to Glacial Lake Outburst Floods...

edition.cnn.com/2024/08/07/c...

But a MAJOR focus of the case study is not just on "how/why" Áakʼw Tʼáak Sítʼ may tip, but the consequences of it doing so.

Indigenous Tlingit communities have lived in and stewarded the coastal rainforests and waters of southeast Alaska and southwest Canada for at least the last 10,000 years...

Think about how mountain tops 🏔️ are colder than the valleys below them.

This is very important when the temperature gradients are large (like Greenland and Antarctica--see Section 2 of the GTPR!) but might be less important than the others in Juneau.

3️⃣: The "Ice-Elevation" Feedback. This feedback is not specific to the icefield, and might be less important here than elsewhere, like Antarctica. But when the surface elevation of the ice lowers due to melting, it lowers into elevations where temperatures are warmer...

... from the glacier's "tongue" below! Widespread disconnection is an thus another tipping feedback! @iceybethan.bsky.social, @jeremyely.bsky.social and co.'s paper here is a fabulous overview of the susceptibility of the icefield to disconnection.

onlinelibrary.wiley.com/doi/full/10....

...may follow, i.e., a "tipping point".

2️⃣: Glacier Disconnection. Where icefalls occur, the ice is much less cohesive and a larger surface area is exposed to ambient air temperature changes. This causes enhanced melting at the icefall. The consequence is that the source-area ice disconnects...

snowline. We call this line, in glaciology, the 'ELA'. If the ELA rises above the elevation of the glaciers' source area (the plateau), then little snow remains in the winter to nourish the glacier.

Thus, when the ELA rises above the elevation of the plateau for the JI, rapid loss...

flow off this high plateau, they cross over a steep lip, where icefalls like this form. This is key for several of the feedbacks that may lead to tipping:

1️⃣: 'ELA' rise. When average temperatures warm 📈, it decreases the amount of snow which remains through the winter, raising a glacier's...

In it, we've gone into quite a bit of detail on how smaller glacial systems tip, building off the major body of work by @iceybethan.bsky.social, @jeremyely.bsky.social and colleagues.

These studies showed that the Icefield's source areas predominantly sit on a flat, high plateau. As the glaciers..

Thanks so much to @nature.com for providing the space to share this and @annenotintokyo.bsky.social for her careful editorial guidance.

I only hope it’s useful for folks.

others are the “network” I talk about here.

In January, I finally defended a PhD here in Berlin. And the other happy ending is that Shivani, the other PhD who had to leave our group in Boston, joined us here at PIK last year as a post-doc. Finally we have the chance to work together on Antarctica.

resilient in case things go wrong.

Lindsey Nicholson, @allenpope.bsky.social, Brad Markle, Margi Rusmore, Scott Bogue, Ann Blythe—these were the folks who kept me on my feet during that horrible time, putting me in touch with everyone and anyone to find a new supervisor. 🙏 They and many (6/7)

protect themselves, but because I am a realist, and I know that there are others out there who will be called to task--that other students will go through similar situations. This is my advice for them, as well as advisors, and administrators on how to make their programs and experiences more (5/7)