The Relationship Between Recent Arctic Amplification and Extreme Mid-Latitude Weather

The Arctic region has warmed more than twice as fast as the global average — a phenomenon known as Arctic amplification. The rapid Arctic warming has contributed to dramatic melting of Arctic sea ice and spring snow cover, at a pace greater than that simulated by climate models. These profound changes to the Arctic system have coincided with a period of ostensibly more frequent extreme weather events across the Northern Hemisphere mid-latitudes, including severe winters. The possibility of a link between Arctic change and mid-latitude weather has spurred research activities that reveal three potential dynamical pathways linking Arctic amplification to mid-latitude weather: changes in storm tracks, the jet stream, and planetary waves and their associated energy propagation. Through changes in these key atmospheric features, it is possible, in principle, for sea ice and snow cover to jointly influence mid-latitude weather. However, because of incomplete knowledge of how high-latitude climate change influences these phenomena, combined with sparse and short data records, and imperfect models, large uncer - tainties regarding the magnitude of such an influence remain. We conclude that improved process understanding, sustained and additional Arctic observations, and better coordinated modelling studies will be needed to advance our understanding of the influences on mid-latitude weather and extreme events.

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Recent Arctic amplification and extreme mid-latitude weather

The slowdown in global average surface warming has recently been linked to sea surface cooling in the eastern Pacific Ocean. This work shows that strengthening trade winds caused a reduction in the 2012 global average surface air temperature of 0.1–0.2 °C. This may account for much of the warming hiatus and is a result of increased subsurface ocean heat uptake.

Recent intensification of wind-driven circulation in the Pacific and the ongoing warming hiatus

Tropical forests provide many ecosystem and climatic services. This Review provides a synthesis of the effects of tropical deforestation on climate and implications for agriculture, both in the tropics and worldwide. Tower, ground-based and satellite observations indicate that tropical deforestation results in warmer, drier conditions at the local scale. Understanding the regional or global impacts of deforestation on climate, and ultimately on agriculture, requires modelling. General circulation models show that completely deforesting the tropics could result in global warming equivalent to that caused by burning of fossil fuels since 1850, with more warming and considerable drying in the tropics. More realistic scenarios of deforestation yield less warming and less drying, suggesting critical thresholds beyond which rainfall is substantially reduced. In regional, mesoscale models that capture topography and vegetation-based discontinuities, small clearings can actually enhance rainfall. At this smaller scale as well, a critical deforestation threshold exists, beyond which rainfall declines. Future agricultural productivity in the tropics is at risk from a deforestation-induced increase in mean temperature and the associated heat extremes and from a decline in mean rainfall or rainfall frequency. Through teleconnections, negative impacts on agriculture could extend well beyond the tropics.

Effects of tropical deforestation on climate and agriculture

https://www.geo.umass.edu/climate/papers2/Pollard_EPSL_2015.pdf

Potential Antarctic Ice Sheet retreat driven by hydrofracturing and ice cliff failure

[1] The Naval Research Laboratory three-dimensional simulation code SAMI3/ESF is used to study the response of the postsunset ionosphere to circular gravity waves. We model the coupling of both circular (local) and plane wave (nonlocal) gravity waves to the bottomside F layer as a mechanism for triggering equatorial plasma bubbles. Results support the hypothesis that nonplane gravity waves can more strongly couple to the F layer than plane gravity waves. Results also show that the coupling of the seed wave to the F layer depends on the (nonlocal) growth rate and the local electron density at the position of the seed wave.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2012GL054022

Matthew Hei

Papers

Simulation of the seeding of equatorial spread F by circular gravity waves