Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session G40: Invited Session: The Physics of Climate |
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Sponsoring Units: GPC Chair: James Brasseur, Pennsylvania State University Room: Mile High Ballroom 2B-3B |
Tuesday, March 4, 2014 11:15AM - 11:51AM |
G40.00001: Sea ice, climate, and multiscale composites Invited Speaker: Kenneth Golden In September of 2012, the area of the Arctic Ocean covered by sea ice reached its lowest level ever recorded in more than three decades of satellite measurements. In fact, compared to the 1980's and 1990's, this represents a loss of more than half of the summer Arctic sea ice pack. While global climate models generally predict sea ice declines over the 21st century, the precipitous losses observed so far have significantly outpaced most projections. I will discuss how mathematical models of composite materials and statistical physics are being used to study key sea ice processes and advance how sea ice is represented in climate models. This work is helping to improve projections of the fate of Earth's ice packs, and the response of polar ecosystems. A brief video of a recent Antarctic expedition where sea ice properties were measured will be shown. [Preview Abstract] |
Tuesday, March 4, 2014 11:51AM - 12:27PM |
G40.00002: Ice sheet-ocean interactions and sea level change Invited Speaker: Patrick Heimbach Mass loss from the Greenland and Antarctic ice sheets has increased rapidly since the mid-1990s. Their combined loss now accounts for about one-third of global sea level rise. In Greenland, a growing body of evidence points to the marine margins of these glaciers as the region from which this dynamic response originated. Similarly, ice streams in West Antarctica that feed vast floating ice shelves have exhibited large decadal changes. We review observational evidence and present physical mechanisms that might explain the observed changes, in particular in the context of ice sheet-ocean interactions. Processes involve cover 7 orders of magnitudes of scales, ranging from mm boundary-layer processes to basin-scale coupled atmosphere-ocean variability. We discuss observational needs to fill the gap in our mechanistic understanding. [Preview Abstract] |
Tuesday, March 4, 2014 12:27PM - 1:03PM |
G40.00003: The Role of Clouds in Climate Change Invited Speaker: Daniel Cziczo The role of greenhouse gases, predominantly CO$_{2}$, on climate has been understood since the work of Arrhenius in the late 1800's. The role of clouds on the Earth's radiative balance is far more uncertainty. It is known that small atmospheric particles act as the seeds on which water droplets and ice crystals form but projecting laboratory and field measurements of particles and clouds to climate projections remains the most uncertain aspect of climate change. Laboratory and field studies show that cloud formation occurs when the ambient water vapor exceeds the equilibrium saturation value. When the ambient temperature is above 0$^{\circ}$C and the relative humidity above 100{\%}, liquid water condenses on aerosol particles, known as cloud condensation nuclei. The spontaneous formation of ice within aqueous droplets of the size commonly found in the atmosphere does not occur until a level of supercooling exceeding -38$^{\circ}$C, and a saturation near that of liquid water, is reached. Consequently, ice nucleation from 0 to -38$^{\circ}$C requires the presence of a special particle, known as an ice nucleus. This talk will describe the current state of knowledge of cloud formation and what aspects remain uncertain. Information gained from laboratory and field studies will be compared to our understanding of Earth's current state and how climate is projected to change in the future. [Preview Abstract] |
Tuesday, March 4, 2014 1:03PM - 1:39PM |
G40.00004: Causes and consequences of time-varying climate sensitivity Invited Speaker: Kyle Armour While constraining climate sensitivity has long been a focus of climate science, this global and equilibrium metric provides only limited understanding of transient and regional changes over the coming centuries. Indeed, pronounced spatial and temporal variability of climate change has been observed, and climate models diverge strongly in projections of future warming. This intermodel spread is due, in part, to different representations of how global climate sensitivity (set by feedbacks linking surface warming to top-of-atmosphere radiative response) will vary in time as the Earth warms. Here I discuss mechanisms governing the time variation of climate sensitivity, and consider its implications for future climate prediction. I show that climate sensitivity depends fundamentally on the respective geographic patterns of local radiative feedbacks and surface warming, and thus it naturally varies in time as the pattern of surface warming evolves, activating feedbacks of different strengths in different regions. Further, the pattern of surface warming and the strength of local radiative feedbacks themselves (shortwave clouds feedbacks in particular) depend on regional ocean circulations and the resulting time-varying geographic pattern of ocean heat uptake. These results imply that equilibrium climate sensitivity cannot be reliably estimated from transient climate observations. [Preview Abstract] |
Tuesday, March 4, 2014 1:39PM - 2:15PM |
G40.00005: Causes and implications of the growing divergence between climate model simulations and observations Invited Speaker: Judith Curry For the past 15+ years, there has been no increase in global average surface temperature, which has been referred to as a 'hiatus' in global warming. By contrast, estimates of expected warming in the first several decades of 21st century made by the IPCC AR4 were 0.2C/decade. This talk summarizes the recent CMIP5 climate model simulation results and comparisons with observational data. The most recent climate model simulations used in the AR5 indicate that the warming stagnation since 1998 is no longer consistent with model projections even at the 2\% confidence level. Potential causes for the model-observation discrepancies are discussed. A particular focus of the talk is the role of multi-decadal natural internal variability on the climate variability of the 20th and early 21st centuries. The ``stadium wave'' climate signal is described, which propagates across the Northern Hemisphere through a network of ocean, ice, and atmospheric circulation regimes that self-organize into a collective tempo. The stadium wave hypothesis provides a plausible explanation for the hiatus in warming and helps explain why climate models did not predict this hiatus. Further, the new hypothesis suggests how long the hiatus might last. Implications of the hiatus are discussed in context of climate model sensitivity to CO2 forcing and attribution of the warming that was observed in the last quarter of the 20th century. [Preview Abstract] |
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