Fast and slow subpolar ocean responses to the North Atlantic Oscillation: thermal and dynamical changes
Geophysical Research Letters Wiley 49:24 (2022) e2022GL101480
Abstract:
Climate model hindcasts are analyzed to reveal the impacts of the North Atlantic Oscillation (NAO) on the North Atlantic subpolar ocean, which exhibits variability on seasonal to decadal timescales. The ocean response to a single winter NAO event is separated into fast and slow responses. The fast response persists over winter–spring seasons, during which wind stress and heat flux anomalies associated with the NAO rapidly modify ocean temperatures via changes in Ekman transport and ocean-atmosphere heat exchanges. The slow response persists for 3–4 years, during which overturning and gyre circulations redistribute opposing-signed surface temperature anomalies created by the NAO. This redistribution modifies east-west temperature contrasts altering the meridional heat transport associated with gyres and changing the strength of the overturning circulation. Hence, the fast and slow responses lead to opposing-signed subpolar temperature anomalies in time from the competing effects of local forcing and horizontal heat convergence.CO2 ocean bistability on terrestrial exoplanets
Journal of Geophysical Research: Planets American Geophysical Union 127:10 (2022) e2022JE007456
Abstract:
Cycling of carbon dioxide between the atmosphere and interior of rocky planets can stabilize global climate and enable planetary surface temperatures above freezing over geologic time. However, variations in global carbon budget and unstable feedback cycles between planetary sub-systems may destabilize the climate of rocky exoplanets toward regimes unknown in the Solar System. Here, we perform clear-sky atmospheric radiative transfer and surface weathering simulations to probe the stability of climate equilibria for rocky, ocean-bearing exoplanets at instellations relevant for planetary systems in the outer regions of the circumstellar habitable zone. Our simulations suggest that planets orbiting G- and F-type stars (but not M-type stars) may display bistability between an Earth-like climate state with efficient carbon sequestration and an alternative stable climate equilibrium where CO2 condenses at the surface and forms a blanket of either clathrate hydrate or liquid CO2. At increasing instellation and with ineffective weathering, the latter state oscillates between cool, surface CO2-condensing and hot, non-condensing climates. CO2 bistable climates may emerge early in planetary history and remain stable for billions of years. The carbon dioxide-condensing climates follow an opposite trend in pCO2 versus instellation compared to the weathering-stabilized planet population, suggesting the possibility of observational discrimination between these distinct climate categories.The strong role of external forcing in seasonal forecasts of European summer temperature
Environmental Research Letters IOP Publishing 17:10 (2022) 104033
Abstract:
Since the 1980s, external forcings from increasing greenhouse gases and declining aerosols have had a large effect on European summer temperatures. These forcings may therefore provide an important source of forecast skill, even for timescales as short as a season ahead. However, the relative importance of external forcings for seasonal forecasts has thus far received little attention, particularly on a regional scale. In this study, we investigate forcing-induced skill by comparing the near-surface temperature skill of a multi-model ensemble of seasonal predictions from the Copernicus Climate Change Service archive to that of an uninitialised ensemble of Coupled Model Intercomparison Project phase 6 projections for European summers (June–July–August) spanning the years 1993–2016. As expected, predictive skill over southern Europe is larger for initialised seasonal predictions compared to uninitialised climate projections. However, for northern Europe, we find that predictive skill is generally small in current seasonal models and surprisingly even smaller compared to uninitialised climate projections. These results imply that further research is necessary to understand the role of external forcing on seasonal temperature variations over Europe.Explaining and predicting earth system change: a world climate research programme call to action
Bulletin of the American Meteorological Society American Meteorological Society 104:1 (2022) E325-E339
Abstract:
The World Climate Research Programme (WCRP) envisions a world “that uses sound, relevant, and timely climate science to ensure a more resilient present and sustainable future for humankind.” This bold vision requires the climate science community to provide actionable scientific information that meets the evolving needs of societies all over the world. To realize its vision, WCRP has created five Lighthouse Activities to generate international commitment and support to tackle some of the most pressing challenges in climate science today. The overarching goal of the Lighthouse Activity on Explaining and Predicting Earth System Change is to develop an integrated capability to understand, attribute, and predict annual to decadal changes in the Earth system, including capabilities for early warning of potential high impact changes and events. This article provides an overview of both the scientific challenges that must be addressed, and the research and other activities required to achieve this goal. The work is organized in three thematic areas: (i) monitoring and modeling Earth system change; (ii) integrated attribution, prediction, and projection; and (iii) assessment of current and future hazards. Also discussed are the benefits that the new capability will deliver. These include improved capabilities for early warning of impactful changes in the Earth system, more reliable assessments of meteorological hazard risks, and quantitative attribution statements to support the Global Annual to Decadal Climate Update and State of the Climate reports issued by the World Meteorological Organization.Attribution of multi-annual to decadal changes in the climate system: The Large Ensemble Single Forcing Model Intercomparison Project (LESFMIP)
Frontiers in Climate Frontiers Media 4 (2022) 955414