Transient and quasi-equilibrium climate states at 1.5{degree sign}C
and 2{degree sign}C global warming
Abstract
Recent climate change is characterised by rapid global warming, but the
goal of the Paris Agreement is to achieve a stable climate where global
temperatures remain well below 2°C above pre-industrial levels.
Inferences about conditions at or below 2°C are usually made based on
transient climate projections. To better understand climate change
impacts on natural and human systems under the Paris Agreement, we must
understand how a stable climate may differ from transient conditions at
the same warming level. Here we examine differences between transient
and quasi-equilibrium climates based on greenhouse gas-only model
simulations at 1.5°C and 2°C global warming. We find substantial local
differences between seasonal-average temperatures, with mid-latitude
land regions in boreal summer considerably warmer in a transient climate
than a quasi-equilibrium state at both 1.5°C and 2°C global warming. Our
research demonstrates that the rate of global warming must be considered
in regional projections.