Contents

Cause of Arctic Amplification

Arctic Amplification is a prominent feature of global warming!

What is Arctic Amplification (AA)?

  • Near-surface of the Northern Hemisphere high latitudes are warming at rates double that of lower latitudes (Cohen et al., 2014).

../_images/acw_giss_map_1960_2019.png

Fig. 7 Trends in mean surface air temperature over the period 1960 to 2019. The fact that Arctic warms more than the rest of the globe in the past decades signatures the Arctic amplification. Credit: NASA GISS.

Why AA is important?

  • Local impacts on human dimension

  • Local impacts on nature system

  • Remote impacts

Quantitative definition of AA

  • Arctic amplification factor (AAF): Arctic surface air temperature change divided by global surface air temperature change.

  • Arctic amplification efficacy (AAE): AAF\(_{XX}\) divided by AAF\(_{CO_2}\), where \(XX\) is the forcing agent.

AA in Observational Records and Models

  • Paleoclimate records

  • Present-day observations

  • General circulation model

  • State-of-the-art climate model and future projection

AA Structure

  • AA has distinct seasonal and meridional structures.

Physical Mechanisms Causing AA

Climate Forcing

../_images/ipcc_rad_forc_ar5.jpeg

Fig. 8 Radiative forcings by emissions and climatic drivers from IPCC AR5 report. The story of evolution of radiative forcing bar charts can be seen here.

Climate Feedbacks

A thorough review of these feedbacks’ contributions to Arctic warming can be seen in Goosse et al. 2018. We will go through each feedback in class.

  • Temperature feedbacks:

    • Planck feedback

    • Lapse-rate feedback

  • Surface albedo feedback

  • Water vapor feedback

  • Cloud feedback

  • Other feedbacks:

    • Northward shift of boreal forest and overall greening of the Arctic

    • Large evaporation increases in low latitudes

    • Oceanic heat fluxes in Arctic Ocean

../_images/feedback_polar.png

Fig. 9 A schematic of some important radiative and non-radiative feedbacks in polar regions involving the atmosphere, the ocean, sea ice and ice sheets. Source: Goosse et al. 2018.

Poleward Energy Transport

  • Atmospheric transport:

    • Dry static energy

    • Moiste static energy

  • Oceanic transport

    • Circulation anomalies

    • Heat anomalies

  • Remote forcing from tropics?

  • Timescale affects the portion of atmospheric and oceanic heat transports

Coupling Between Mechanisms

Climate State Dependence

Sea Ice Arctic-Midlatitude Linkage