YSM Issue 89.1

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FOCUS environment ICE IN ACTION by Zach Smithline art by Ashlyn Oakes Sea ice at the North Pole has something to say about climate change. Talk of climate change in the news is ubiquitous. Everywhere we look, headlines are popping up, from deadly record-breaking heat waves in Pakistan and India to the notoriously cold and rainy London reaching a record high of 98 degrees Fahrenheit this past July. Earth’s climate cycle is becoming increasingly erratic, which has two conflicting effects — mapping these patterns is simultaneously more important than ever, and more difficult than ever. In many ways, climate change is a complicated beast. In a single season, we might see intense spikes in temperature in one area of the world and colder than normal weather elsewhere. It is a problem fueled largely by human activity, and so motivating environmentally friendly behavior is important. But change takes time: The climate concerns we are experiencing now are the result of hundreds, if not thousands, of years of change. Similarly, the positive lifestyle choices we might implement in service of our planet will not fix climate disruption overnight. These positive changes in human activity are crucial, but the sobering truth is that the planet does not respond immediately to change. These complex issues are exacerbated by the fact that measuring climate change is equally complicated. Reliable, hard and fast data on climate change patterns would perhaps be universally convincing and motivating, but is extremely hard to come by. Scientists use diverse parameters in quantifying climate change: They might measure sea surface temperatures or precipitation. Maybe they track volcanic eruptions. One method stands out as particularly effective, and that is measuring the thickness of Arctic sea ice. The existing tactic to understand the distribution of sea ice thickness up by the North Pole is centered on a partial differential equation. This formula depends on three 14 Yale Scientific Magazine December 2015
environment FOCUS variables, one of which is particularly problematic. A Yale duo has found a way to circumvent this problem, updating the partial differential equation so that it can more accurately convey information about Arctic sea ice, and about global climate change. The team consists of John Wettlaufer, a professor of geophysics, mathematics, and physics at Yale, and Srikanth Toppaladoddi, a graduate student. Their new model for calculating Arctic sea ice thickness could make a big splash in the field of climate science. All eyes on the Arctic Wettlaufer and Toppaladoddi’s model is significant not only because it is a more accurate measure of sea ice thickness, but because Arctic sea ice thickness is a highly sensitive indicator of the Arctic climate as a whole. And changes in Arctic climate have long been understood as a harbinger for what is to come farther south. An important reflection of Earth’s climate regulation is the hydrologic cycle, more commonly known as the water cycle — a staple of elementary school education. At lower latitudes, this cycle is regulated by the flux between evaporation and precipitation. But in the polar regions, the processes of freezing and melting are extremely important, as they create density differences that drive global water circulation. Earth’s cryosphere — its frozen water — has a global impact on climate, and disruptions can cause temperatures to plunge in some regions and skyrocket in others. Not all Arctic ice is created equally. The Greenland ice sheet sits three kilometers thick upon a landmass and influences global sea levels. This is one way to facilitate the effects of global warming, namely a rise in sea level. In contrast to Greenland, sea ice is only a few meters thick and does not alter sea level at all. Instead, sea ice affects global climate because it rejects salt when it forms, making it uniquely responsible for patterns in global ocean circulation. Large ocean currents, in turn, move warm and cold water around the globe, and thus impact weather events. In addition, small changes in climate at lower latitudes are amplified up in the Arctic, a phenomenon known as polar amplification. Thus, sea ice thickness up north is a strong signal for the global climate condition. In 1969, Russian climatologist Mikhail Budyko developed a simple energybalance theory of climate that captured a key feature of polar amplification. We know from common experience that the bright light reflected from a snow-covered field in the winter is far more glaring than that reflected from grass in the summer. The reflectivity of a material, called albedo, underlies Budyko’s theory of ice-albedo feedback: Floating white ice has a much higher albedo, or greater reflectivity, than the adjacent blue ocean. Since the latter absorbs more of the sun’s radiant energy than does ice, the ocean warms and melts the ice. This in turn exposes more ocean, which absorbs more energy, which again melts more ice. The cycle causes a runaway effect, and the Arctic shoulders much of the burden. Budyko’s theory only emphasizes the need for a reliable means of tracking Arctic sea ice, which is likely to be in flux as the planet warms. Prior methods were insufficient. Enter Wettlaufer and Toppaladoddi — and a new, tractable equation. The microscopic and the macroscopic Geophysicists in 1975 developed a partial differential equation that would in principle allow for the calculation of the distribution of Arctic ice thickness. The equation has three terms that describe the dynamics of sea ice. The terms that characterize how wind and heat affect ice thickness have a firm grounding. But the term that describes the mechanical redistribution of ice floes, or floating ice sheets, is difficult to characterize mathematically. Without a sound mathematical model, there is no way to test the partial differential equation observationally. Until recently, this intransigent term has been a roadblock, getting in the way of our complete understanding of Arctic sea ice and global climate change patterns. Yale’s Wettlaufer and Toppaladoddi have devised a different approach to the problem of Arctic ice thickness. The duo December 2015 Yale Scientific Magazine 15
Page 1 and 2: Yale Scientific Established in 1894
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Page 5 and 6: Science can be intimidating. It is
Page 7 and 8: in brief NEWS Professor Dylan Gee R
Page 9 and 10: mathematics NEWS BEAUTIFUL, SIMPLE,
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Page 21 and 22: forestry FOCUS PHOTO BY RAIN TSONG
Page 23 and 24: TO Strip a donor lung of its cells
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Page 37 and 38: ALUMNI PROFILE RICHARD LETHIN (YC
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