Join me for this New Year walk, marking the edge of the low tide and the rise of the full moon. We’ll think about presence and absence in Princeton-by-the-Sea, a neighborhood on the site of a former Ohlone village.

A little background. This phrase — tideline as timeline — occurred to me earlier this year while writing my Master’s thesis. I didn’t know what it meant then, except in the poetic sense of the daily pulsing of the ocean, in and out. Yet as I’ve taken a deeper dive into geology, sea levels, and climatic change, I now see the phrase as both more literal and more meaningful.

In fact, the tideline has shifted dramatically over time in response to tectonic shifts and the effect of global temperature on planetary ice levels. Over much of the last 500 million years, the planet was significantly warmer than it is now; there was no ice anywhere during much of that time, and sea levels were as much as 600 feet higher than they are now, due to the very different continental configurations of the distant past.

More recently — that is, since North America joined the South American plate 3.5 million years ago — the planet has had a consistent sea level range. When ice ages develop, as they have about every 100,000 years for at least a million years, sea levels drop about 400 feet. When the ice partially melts, as it has systematically done as part of this cycle, sea levels have risen to about where they are right now.  It’s as if the planet has been breathing in and out in a deep time, mirroring the ocean’s daily pulsing at a different scale. We are currently at the bottom of the cyclical exhale, when things are warm and wet.

Knowing this makes it even more alarming that our global temperatures and sea levels are about to spike. The planet has spent the past 20,000 years exhaling (i.e. warming) and we are about to exhale again, without any in breath to sustain us. We have never been here before.

When all the ice melts, as it likely will over the coming 500-1000 years, sea levels will be 212 feet higher than they are today. Where will our tideline be then? It’s one of the things we’ll think about on the Tideline as Timeline walk, the first in a series I’m developing with fellow artist and ocean lover, Zoe Farmer.