We see far greater risk of massive irreversible sea level rise (SLR) at 2°C, on a scale of 12–20 meters or more in the long term. The climate record of the Earth over the pat few million years is quite clear:

Sea Level Rise from Ice Sheets
We see far greater risk of massive irreversible sea level rise (SLR) at 2°C, on a scale of 12–20 meters or more in the long term. The climate record of the Earth over the pat few million years is quite clear:

Sea Level Rise from Ice Sheets
Cryosphere Impacts of Overshoot
In pathways with no or limited overshoot of 1.5°C, anthropogenic CO2emissions [must] decline by about 45% from 2010 levels by 2030 (median 50%).
IPCC, 2018: Summary for Policymakers

Marine ice sheet instability in Antarctica and/or irreversible loss of the Greenland ice sheet
could result in multi-metre rise in sea level over hundreds to thousands of years.
These instabilities could be triggered at around 1.5°C to 2°C of global warming.
IPCC, 2018:
Summary for Policymakers
SEA LEVEL RISE FROM ICE SHEETS

Mid-latitude glaciers and snow in the Alps, southern Andes/Patagonia,
Iceland, Scandinavia, New Zealand and North American Rockies can survive at 1.5°,
but these glaciers will disappear almost entirely at 2°C, and snow cover decrease.
ICCI, 2019: Cryosphere1.5º: Where Urgency and Ambition Meet – Why Cryosphere Dynamics Must Mean 1.5° Pathways for 2020 NDCs
LOSS OF
GLACIERS & SNOW

The level of ocean acidification due to increasing CO2 concentrations associated with global warming of 1.5°C is projected to amplify the adverse effects of warming, and even further at 2°C, impacting the growth, development, calcification, survival, and thus abundance of a broad range of species, for example, from algae to fish.
IPCC, 2018:
Summary for Policymakers
POLAR OCEAN ACIDIFICATION