Treading on Thin Ice. By Daniel Pollak

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1 Treading on Thin Ice By Daniel Pollak Nearly 20,000 fuzzy polar bears call the Arctic s expansive sea ice their home and it is the only platform from which the bears can hunt. Unfortunately, this sea ice is rapidly disappearing and is threatening their very existence. The simple reason for Arctic sea ice melting: a warming climate. In fact, the International Union for Conservation of Nature lists global warming as the largest threat to the existence of polar bears. Even sadder still is that it s not just the polar bears that are treading on thinning ice. Currently, there are approximately one and a half million people living north of the Arctic Circle, a mere half percent of the world s population. But, since most people don t live in the Arctic, who cares about this warming and melting, right? It s not like these changes would have any effect on us in the rest of the world, right? Wrong. A decrease in Arctic sea ice and an increase in arctic temperatures could have substantial impacts on the entire world s climate. With the global human population nearing 7 billion, it is impossible to ignore the footprints that we leave on planet Earth. The burning of fossil fuels for transportation, agriculture, and industry has caused increases in greenhouse gas concentrations. In moderate amounts, these greenhouse gases act as a protective shield for the Earth. However, large concentrations of these gases can act as a stronger insulator leading to warming conditions at the Earth s surface. Concentrations of carbon dioxide (CO 2 ), a key greenhouse gas, have increased by 15% percent during the last thirty years and are related to the warming of globally averaged temperatures seen since records began in the 1880s. The National Climatic Data Center s 2010 state of the climate global report revealed that out of these 120 years of data, the warmest 10 years have occurred since In particular, the polar regions are heavily susceptible to the effects of increasing greenhouse gases. In 2010, a study by National Center for Atmospheric Science (NCAR) climate scientist Marika Holland indicated that a consensus of climate models predict an increase of Arctic basin temperatures by 2 to 3 times the comprehensive global warming trend by the year Finding the main culprit behind this amplified Arctic warming brings us once again back to the melting Arctic sea ice. Sea ice is intricately connected to the ocean and atmosphere and changes to any component can destabilize this delicate balance. Arctic sea ice, which is frozen ocean, has an annual natural cycle of growth and melt which waxes and wanes with the seasons. Maximum ice extent is realized in March, after winter s round the

2 clock darkness; minimum ice extent is realized in September, after the summer s characteristic midnight sun comes to an end. A visual representation of this seasonal cycle is distinct in Figure 1 as well as the decreasing sea ice trend realized over the last 30 years the years since satellites observing sea ice began operations. These maps, compiled by the National Snow and Ice Data Center (NSIDC), illustrate the concentrations of sea ice; Dark blue represents open ocean, light blue indicates partial sea ice coverage, and solid white indicates a solid sea ice pack. The seasonality is indicated by the larger sea ice coverage seen in March versus September. The distinct downward trend of sea ice from increasing greenhouse gases and global warming is captured through the comparison between the 1979 and 2007 panels. The 29 year spread from alone saw a 30% reduction in annually averaged sea ice extent. Figure 1. Observed monthly ice concentrations seen by satellites. The seasonal trend is seen between March and September, but most pronounced is the large change seen between 1979 and 2007 (NSIDC). These drastic changes seen in Arctic sea ice and the Arctic climate are a result of what is called a climate feedback. A climate feedback is defined as a process that can either increase or decrease the rate of a change that is already occurring, in response to external forcings such as increases in greenhouse gas concentrations. A feedback that increases the rate of change is a positive feedback loop and one that decreases the rate of change is a negative feedback loop. One feedback known to be a major player in the recent and projected acceleration of sea ice melt is Figure 2. Illustration of the concept behind the surface albedo feedback. Snow and ice have a high albedo of greater than 0.8, and open ocean the ice snow surface albedo feedback, a positive feedback loop. While seemingly complicated, its basis is simple. This surface albedo feedback involves interactions between radiation from the sun and the surfaces that it hits. In the Arctic these surfaces are either sea ice or ocean. The term albedo refers to the amount of sunlight that is reflected by the surface of the earth. It is essentially

3 a percentage. When incoming solar radiation (yellow arrows in figure 2), approach the Earth s surface, they are either reflected (white arrows in figure 2) or absorbed (red arrows in figure 2). The proportions between each are dependent on surfaces encountered. Clean snow and ice reflect upwards of 80% (Albedo=0.8) of incoming solar radiation, absorbing less than 20%. This large sum of reflected sunlight (high albedo) from sea ice and snow is the reason why you need to wear good sunglasses on a sunny day after a snowstorm. Opposite, ocean in the Arctic absorbs 90% of the sun s radiation reflecting a mere 10% (Albedo=0.1). Given the profound albedo spread between the two surfaces, increasing open ocean and decreasing sea ice (as seen in recent years) is a striking and fundamental factor driving the surface albedo feedback. When sea ice extent decreases and larger cracks develop, additional open ocean is exposed, leading to increased shortwave absorption by the ocean. This increases air and ocean temperatures which subsequently melts more snow and sea ice. As a result, ice thickness and ice area decrease. These changes decrease the amount of bright surfaces there are to reflect sunlight and thus continue to accelerate this positive surface albedo feedback loop (Figure 3). Figure 3. Flow chart describing the positive surface albedo feedback. Given the short record of sea ice observations, it is of critical importance to simulate these recent changes through climate models. That way, we can help predict and understand determinants behind future changes and prepare humanity (including you!) to take action to mitigate and adapt to these changes. We utilized NCAR s newly released (April 2010) Community Climate System Model Version 4. These models use a system of complex equations to describe Earth processes and provide a comprehensive view of the climate system.

4 Future projections, as simulated by this robust model are worrisome. Between now and 2050 it is projected that annually averaged sea ice thickness will decrease from two meters to one meter. Additionally, by 2100 it is possible that the entire Arctic would be ice free during parts of the summer months. Consequences would have many layers and could occur in a domino effect. Through the surface albedo feedback, there is no doubt that this would cause an enhancement of global warming. Additionally, melting sea ice infuses the ocean with freshwater that decreases the overall salt content of the ocean. While small amounts of this freshwater discharge would be accommodated, studies summarized in the American Meteorological Society s 2008 State of the Climate indicate that significant freshening of the Arctic Ocean could affect ocean circulations. These consequences are not aspects that would seemingly affect the daily lives of people. But, given that 70% of the Earth is ocean and 100% of space we live in is part of the atmosphere, it is impossible that over your lifetime that you would not see and feel a change. Now that you understand the importance that melting sea ice plays in our climate system I urge you to remember the reasons why the ice is melting rapidly and why our climate is changing drastically increased carbon dioxide in the atmosphere. America is the land of the free, but also the land of the automobile. We drive anywhere and everywhere and often don t think of the cumulative effects that our daily habits have over a lifetime multiplied by the global population of 7 billion. Not everyone reading short scientific articles such as this will make a change in their daily life, and I do not expect them to. My objective as a student scientist is to inform you of one of the many human factors that are changing the state of our Earth s climate through climate feedbacks and also how every action we as individuals, communities, and countries take has effects that are beyond the current day and our lifetime. If we however do not address the environmental issues facing our climate, the polar bears may not be the only creatures finding their very habitat s existence at risk.

5 References: Holland, Marika M., 2010: Arctic Sea Ice and the Potential for Abrupt Loss, Geophysical Monograph Series doi: /2008gm Holland, Marika M., 2007: Projected changes in Arctic Ocean freshwater budgets, Journal of Geophysical Research doi: /2006jg Peterson, T. C., and M. O. Naringer, Eds., 2009: State of the Climate in Bull. Amer. Meteor. Soc., 90 S1 S196. State of the Climate: Global Analysis for December 2010, January 2011, NOAA National Climatic Data Center, retrieved February 15, 2011, <