Thread by @yarrowaxford

Excited to share a new review paper w/Anne de Vernal & @biggreenplanet (bosses of paleoceanography and glaciochemistry) that asks: When in the Holocene was Greenland warmer than today, and WHAT did that look like on land and at sea? 1/10
annualreviews.org/doi/abs/10.114…

Arctic summers were warmer than today for a long chunk of the last 10,000 years. As a result, many of Greenland’s glaciers disappeared. Perennial sea ice north of Greenland retracted 1000 km. Marine species and warmth-needing shrubs migrated northward. 2/10

That past warmth was caused by very slow, predictable changes in the tilt of Earth’s axis (which, by the way, should be causing the Arctic to cool today, except fossil fuel CO2 took over). Sea ice loss and other environmental changes amplified the warming. 3/10

But how warm did it get? Did some places warm more than others, and why? And how did the Greenland Ice Sheet, Greenland’s 1000s of smaller glaciers, and polar ecosystems respond? To answer… 4/10

we brought together a colorful cast of ~75 summer temperature records from lake, ice & marine cores, all reaching back >7000 years. Plus bonus evidence from glaciers changing and beetles, fish and land plants migrating when temperatures shifted. 5/10

These data exist because so many scientists have worked at tough field sites & been super creative in their labs, all to find climate’s footprints in ice & mud. And because the people of Kalaallit Nunaat (aka Greenland) have so generously allowed us access to their homeland. 6/10

We find that, yowza, even under the Holocene’s relatively “stable” global climate, a seemingly modest forcing caused a BIG temperature change across Greenland (summers 3-5C warmer than today ~9-6000 years ago). & Greenland looked very different during that warmest period. 7/10

On a more inside-baseball note, the data overall don’t support widespread delayed (summer) warming in the early Holocene, despite modeling studies that simulate depressed temperatures due to effects of the nearby decaying Laurentide Ice Sheet. 8/10

Bringing together so many types of evidence (aka climate proxies), we also learned lessons about the proxies. Especially the importance of seasonality, ice sheet elevation change, vegetation analogs and lags, and how ice sheet meltwater affects nearshore marine proxies. 9/10

Study is available as an uncorrected proof until the final version comes out in March. Let me know if you can’t access it and I’m happy to share! 10/10