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Donovan Dennis @donovanpdennis.com · 1d

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

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

Global Tipping Points | understanding risks & their potential impact

Harmful tipping points in the natural world threaten humanity by disrupting life support systems and societal stability.

global-tipping-points.org

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Donovan Dennis @donovanpdennis.com · 1d

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/...

Global glacier change in the 21st century: Every increase in temperature matters

Glaciers are melting more rapidly than expected due to global warming.

www.science.org

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Donovan Dennis @donovanpdennis.com · 1d

🅰️ 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..

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Donovan Dennis @donovanpdennis.com · 1d

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:

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Donovan Dennis @donovanpdennis.com · 1d

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

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Donovan Dennis @donovanpdennis.com · 1d

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...

Watch the glacier outburst that sent a surge of water into Juneau, causing ‘unprecedented’ flooding | CNN

A rush of water unleashed by an ailing glacier swelled an Alaska river to record levels Tuesday causing unprecedented flooding in Juneau nearly a year to the date of a similar destructive event.

edition.cnn.com

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Donovan Dennis @donovanpdennis.com · 1d

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...

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Donovan Dennis @donovanpdennis.com · 1d

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.

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Donovan Dennis @donovanpdennis.com · 1d

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...

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Donovan Dennis @donovanpdennis.com · 1d

... 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....

Topographic controls on ice flow and recession for Juneau Icefield (Alaska/British Columbia)

We provide a detailed glaciological and geomorphological map that outlines the neoglacial geomorphology and contemporary glaciology (in 2019 AD) of Juneau Icefield, USA/Canada. The contiguous area of...

onlinelibrary.wiley.com

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Donovan Dennis @donovanpdennis.com · 1d

...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...

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Donovan Dennis @donovanpdennis.com · 1d

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...

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Donovan Dennis @donovanpdennis.com · 1d

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...

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Donovan Dennis @donovanpdennis.com · 1d

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..

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Donovan Dennis @donovanpdennis.com · 1d

The #JuneauIcefield is a deeply meaningful place for me and many others, part of the reason we put so much care into our case study on tipping of Áakʼw Tʼáak Sítʼ (Mendenhall Glacier), one of the icefield's major outlet glaciers.

The study is out today as part of the Global Tipping Points Report.

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Donovan Dennis @donovanpdennis.com · 6d

Ready for @berlinscienceweek.bsky.social?! Come by the Diverse Minds, Shared Future event on 1 Nov from @berlin-soapbox.bsky.social and LGBTQIA+ STEM Berlin. You’ll hear six great talks, including one about glacier tipping points 😉. No PowerPoints, just props!

berlinscienceweek.com/programme/di...

Diverse Minds, Shared Future

Our event brings the fascinating world of science to the streets, merging scientific inquiry with artistic expression. The invited speakers, women and queer scientists, present their research in a jar...

berlinscienceweek.com

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Donovan Dennis @donovanpdennis.com · May 14

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.

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Donovan Dennis @donovanpdennis.com · May 14

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.

Me and Shivani smiling at my defense in Berlin, 7 years after leaving Boston.

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Donovan Dennis @donovanpdennis.com · May 14

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)

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Donovan Dennis @donovanpdennis.com · May 14

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)

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Donovan Dennis @donovanpdennis.com · May 14

precarity of dreams (and grad school). Unfortunately, because of the "little fiefdom" structures of academia, it's often students and those with less autonomy who also endure the consequences of those abusers' actions.

I wrote this commentary not because I believe students should *have* to (4/7)

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Donovan Dennis @donovanpdennis.com · May 14

saved in an album at home in Montana. Joining the BU Antarctic group was my absolute dream.

Like Jane, I was from a small town in a big, empty state, with dreams of seeing every corner of this world, with science as my ticket. Leaving that group 18 months later was a reality check in the (3/7)

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Donovan Dennis @donovanpdennis.com · May 14

power and were held to account for their actions.

I remember exactly where I was when I received his call… when he told me I would be joining his lab group and going to Antarctica. I still have the letter of admission from B.U., signed by the administrators who would later scrap my funding, (2/7)

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Donovan Dennis @donovanpdennis.com · May 14

It's hard to believe that nearly a decade has passed since @geojane.bsky.social went to B.U.'s administration and detailed her shocking experiences as a grad student under my then-adviser, Dave Marchant.

In the years since, we have learned of so, so, so many others who likewise abused their (1/7)

Nature @nature.com · May 13

My main advice is this: students, treat your PhD as you would a job

https://go.nature.com/457wUqv

My PhD adviser was fired and I was collateral damage. I learnt how to build resilience into graduate school

Students and institutions should treat PhD degrees as they would a job.

go.nature.com

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Donovan Dennis @donovanpdennis.com · May 7

supporting #PinkSummits who've invited me to join. (Follow them both, as well as fellow speaker, Fabian on Insta, they're not yet Bluesky). You can still sign up to participate but spaces are already very limited, so do so soon! (www.eventbrite.ca/e/pride-hike...)

Pride Hike & Climb 2025 Austria for LGBTIQ+ Visibility Outdoors

We will hike, rock-climb and climb some via ferratas in the Kaiser Mountains (Kaisergebirge) and celebrate pride

www.eventbrite.ca