Planetary Climate Dynamics

Abstract:

© 2015 The Authors. Improving the late Quaternary paleoclimate record through climate interpretations of low-latitude glacier length changes advances our understanding of past climate change events and the mechanisms for past, present, and future climate change. Paleotemperature reconstructions at low-latitude glaciers are uniquely fruitful because they can provide both site-specific information and enhanced understanding of regional-scale variations due to the structure of the tropical atmosphere. We produce Little Ice Age (LIA) and Younger Dryas (YD) paleoclimate reconstructions for the Huancané outlet glacier of the Quelccaya Ice Cap (QIC) and low-latitude southern hemisphere regional sea surface temperatures (SSTs) using a coupled ice-flow and energy balance model. We also model the effects of long-term changes in the summit temperature and precipitiation rate and the effects of interannual climate variability on the Huancané glacier length. We find temperature to be the dominant climate driver of glacier length change. Also, we find that interannual climate variability cannot adequately explain glacier advances inferred from the geomorphic record, necessitating that these features were formed during past colder climates. To constrain our LIA reconstruction, we incorporate the QIC ice core record, finding a LIA air temperature cooling at the ice cap of between ~0.7 °C and ~1.1 °C and ~0.4 °C and regional SSTs cooling of ~0.6 °C. For the YD paleoclimate reconstructions, we propose two limits on the precipitation rate, since the ice core record does not extend into the Pleistocene: 1) the precipitation rate scales with the Clausius-Clapeyron relationship (upper limit on cooling) and 2) the precipitation rate increases by 40% (lower limit on cooling), which is an increase about twice as great as the regional increases realized in GCM simulations for the period. The first limit requires ~1.6 °C cooling in ice cap air temperatures and ~0.9 °C cooling in SSTs, and the second limit requires ~1.0 °C cooling in ice cap air temperatures and ~0.5 °C cooling in SSTs. Our temperature reconstructions are in good agreement with the magnitude and trend of GCM simulations that incorporate the forcing mechanisms hypothesized to have caused these climate change events.

Abstract:

An analysis of the climate impact of various forms of beef production is carried out, with a particular eye to the comparison between systems relying primarily on grasses grown in pasture (‘grass-fed’ or ‘pastured’beef) and systems involving substantial use of manufactured feed requiring significant external inputs in the form of synthetic fertilizer and mechanized agriculture (‘feedlot’beef). The climate impact is evaluated without employing metrics such asCO e 2 or global warming potentials. The analysis evaluates the impact at all time scales out to 1000 years. It is concluded that certain forms of pastured beef production have substantially lower climate impact than feedlot systems. However, pastured systems that require significant synthetic fertilization, inputs from supplemental feed, or deforestation to create pasture, have substantially greater climate impact at all time scales than the feedlot and dairy-associated systems analyzed. Even the best pastured system analyzed has enough climate impact to justify efforts to limit future growth of beef production, which in any event would be necessary if climate and other ecological concerns were met by a transition to primarily pasture-based systems. Alternate mitigation options are discussed, but barring unforseen technological breakthroughs worldwide consumption at current North American per capita rates appears incompatible with a 2 °C warming target.

Abstract:

A laboratory investigation is presented with the aim of studying systematically the occurrence and characteristics of low-frequency variability of flows resulting from the interaction of a baroclinic flow with periodic bottom topography. Low-frequency variability within the baroclinic wave regime occurred in two distinct forms in separate regions of parameter space. One corresponded to the transition region between the baroclinic travelling and stationary wave regimes. It involved primarily an interaction between the drifting baroclinic waves and stationary components of the topographically forced wave. The resulting flow had characteristics similar to amplitude vacillation and had a time-scale of 30–60 annulus revolutions (days), which also corresponded to the wave drift period. A new regime of low-frequency amplitude vacillation was discovered in the transition region with the axisymmetric flow regime. As the complexity of the flow increased the period of the vacillation cycles grew to ∼100–180 “days”. This slower vacillation seemed to involve a cyclic enabling and disabling of nonlinear interactions between the forced stationary wave and the growing and azimuthally drifting wave, which in turn was linked to a decrease in mean flow shear. Subsequent chains of wave-wave interactions characterised the complex but robust oscillation phenomenon. The resulting behaviour has several features in common with some recent models of intraseasonal oscillations in the mid-latitude troposphere and with sudden stratospheric warmings.