Seminars
Atmosphere Ocean Science Colloquium
Investigating the causes and effects of Arctic climate change within a hierarchy of climate models
Speaker: Mark England, UCSC
Location: Online
Date: Tuesday, February 1, 2022, 4 p.m.
Synopsis:
In recent decades the Arctic has been warming over four times faster than the globe and the onset of the first ice-free Arctic summer could happen by the middle of this century. In this talk I will give an overview of my work investigating the drivers and effects of our rapidly changing Arctic climate. The talk will focus on two projects, showcasing how I have utilised models at the opposite ends of the climate model hierarchy to advance our understanding of recent and projected Arctic climate change.
The first half of the talk examines the widely used methodologies to attribute a climate response to Arctic sea ice loss in comprehensive climate model simulations. The results of these previous studies suggest that Arctic sea ice loss causes substantial warming both in the Artic and beyond. However, in this work we identify a common limitation among these methodologies; they all effectively add heat to the Arctic in order to melt the sea ice and this causes an artificial warming signal that is added to the warming that occurs due to sea ice loss alone. We illustrate this using an idealized climate model, in which the role of sea ice loss can be cleanly isolated. The results show that each methodology substantially overestimates the warming due to sea ice loss alone, overestimating the surface warming throughout the Northern Hemisphere by a factor of 1.5-2 in this model. Hence these results suggest that previous studies have substantially overestimated the climate warming response to sea ice loss.
The second half of the talk explores the role of ozone depleting substances (ODSs) in recent and future Arctic climate change using large ensembles of comprehensive climate model simulations. While the dominant role of carbon dioxide in the observed rapid Arctic warming is undisputed, another important set of anthropogenic greenhouse gases (GHGs) was also being emitted over the second half of the twentieth century: ODSs. These compounds, in addition to causing the ozone hole over Antarctica, have long been recognised as powerful GHGs. I will present work quantifying the contribution of ODSs to Arctic warming over the period 1955-2005. We show that, when ODSs are kept fixed, forced Arctic surface warming and sea ice loss are only half as large as when ODSs are allowed to increase. We also demonstrate that the large impact of ODSs on the Arctic occurs primarily via direct radiative warming, not via ozone depletion. I will also present work that shows the Montreal Protocol, which was signed in 1987 and heavily regulates the emission of ODSs, has had unintended, positive climate change mitigation effects. We show that the Montreal Protocol has helped us to avoid accelerated future warming in the Arctic and has delayed the projected date of the first ice-free summer in the Arctic by approximately a decade.