Ch-ch-change

If climate is a measure of weather averaged over many decades, then climate change is the fluctuation of climate as time progresses. When we read about climate change in the newspaper or see reports on television, it is often expressed in terms of temperature (for example, “global warming”). There are good reasons for this:

• Instrumental temperature observations comprise the longest and most widespread measurements of climate that exist…the longest record, from England, dates back 350 years! Noninstrumental estimates of temperature fluctuations extend back even further – thousands of years – and are measured from chemicals extracted from “paleo” records such as ice cores, ocean sediments, and dead organic material.
• Temperature is a measure of climate that all humans can relate to. We all have a sense for “hot” and “cold” that is based on the climate where we live.
• Temperature changes can be linked to nearly all other types of climate change. For instance, glaciers melt faster when temperatures increase.

This third reason helps us answer the original question: could a very active hurricane season in the Gulf of Mexico be caused by climate change? Consider that warm ocean temperatures are the heat engine that fuels hurricane development. And, if climate change leads to warmer atmospheric temperatures, global ocean temperatures will also increase. In the tropics, where hurricanes form, the surface area of the regions with ocean temperatures that are warm enough to support hurricane development will increase, which will likely cause more hurricanes. The fuel source – ocean water – will become even warmer, which will lead to stronger tropical storms, more of which will be categorized as hurricanes.

While it is difficult to say that a single, more-active-than-normal hurricane season is related to climate change, if hurricane seasons in the future consistently produce more and stronger hurricanes than in the past, these changes in the weather are likely linked to climate change. As a matter of fact, climate change can affect all sorts of weather events. Most climate scientists believe that global warming will lead to more “extreme” weather events such as droughts, heat waves, and flood-intensity rainfall episodes.

Cool It!

The polar regions of Earth – the Arctic in the Northern Hemisphere and the Antarctic in the Southern Hemisphere – play important roles in modulating climate across the entire globe…even the tropics. For example, the cold temperatures near the poles are favorable for the formation of sea ice. Sea ice, when it is formed, leads to the “rejection” of the salty brine in the water, and the water under the sea ice becomes saltier – and denser – than the water surrounding it and sinks to the bottom of the ocean. The polar water flows along the bed of the ocean toward the equator, and warmer water from the tropics (think Gulf Stream) in turn flows toward the poles to replace the polar water. In this manner, heat is transported away from the tropical regions toward the poles by the ocean currents, and therefore the ocean acts as a sort of “thermostat” that modulates the temperatures across the globe.

Thus, if we are to truly understand and address global climate change, it is necessary to study the climates of the Arctic and Antarctic even though few people live in either region. Because the Arctic and Antarctic are sparsely populated, and because they have cold, harsh conditions, conducting research is difficult. However, there have been great gains in our knowledge of polar climates in recent years due to increased funding from international science agencies and through technological advances, especially spaceborne measurements from satellites. In a nutshell, the general climates as well as climate change are vastly different between the Arctic and the Antarctic. Next, we’ll examine why.

Upside Down and Inside Out

The Antarctic, as its name suggests, is truly the opposite of the Arctic. The Arctic is essentially an ocean surrounded by land, while the Antarctic is a chunk of land surrounded by an unbroken expanse of ocean. Plus,   Antarctica has a permanent ice cover and is very high – the elevation at the South Pole, for example, is about 9,000 feet above sea level. These geographic differences lead to important distinctions in climate.

Antarctica, with its high elevation – which prevents most storms from penetrating its interior – and its permanent ice cover, is on average much colder and drier than the Arctic. As a matter of fact, a polar desert larger than the United States is situated on the Antarctic Plateau. In the much lower-elevation Arctic (Greenland aside), more storms reach even the highest latitudes, transporting warm, moist air from temperate latitudes. Additionally, since relatively warm ocean water lies under only a few feet of sea ice over much of the Arctic, the ocean also plays a role in keeping Arctic temperatures milder than they would be otherwise. As we will see next, the warmer climate of the Arctic has led to an entirely different response to recent climate change compared to that in the Antarctic.

Red circles outline the Arctic (left) and the Antarctic (right). Image courtesy of the Polar Meteorology Group, Byrd Polar Research Center, The Ohio State University

How ’bout Some Feedback?

Regions with climates that have temperatures near the freeze/thaw point, such as the Arctic, are more sensitive to change than climates with much colder temperatures. This is due to climate triggers, called “feedbacks” by scientists, which are released when melting occurs. Some key feedbacks include:

• The reflectivity (called “albedo” by scientists) of bright, icy surfaces is much higher than that of darker surfaces that do not have ice or snow cover. About 70-80 percent of the sunlight that reaches icy surfaces reflects back to space, and therefore only about 20-30 percent of the Sun’s energy is absorbed and can in turn heat the ice. The opposite is true for water: only about 5 percent of the Sun’s energy is reflected back to space from the relatively dark ocean surface, and the other 95 percent is absorbed and can heat the water. In the Arctic where temperatures near the surface of the sea ice are near the freeze/thaw point for much of the summer, warming causes melt to occur near the edges of the Arctic sea ice pack, which in turn exposes the ocean water. The darker water absorbs much more energy than the ice that used to lie on top of it, which then accelerates the melting of the sea ice from below. Therefore, even small increases in the average summer temperatures can trigger a disproportionate amount of melting of Arctic sea ice, which causes even more warming.

• A similar effect occurs on Arctic land masses. As temperatures increase, and the season for which snow blankets the North becomes shorter, the comparatively darker tundra and taiga (forest) environments under the snow absorb additional energy from the Sun, which exacerbates the warming.

• Permafrost is the term given to soils that have been frozen for a very long time. In the Arctic, these soils contain vast stores of dead, ancient organic material (mainly from yearly plant growth) that would have decayed each year if it had died in a more temperate climate. Organic material is comprised primarily of carbon. Thus, when organic material decays, carbon dioxide and methane – two of the most important greenhouse gases – are released. These gases in turn trap additional heat near the Earth’s surface, amplifying warming.

Due to these climate feedbacks, as well as some other unique features of the Arctic atmosphere, warming in the Arctic during the past 50 years has outpaced global warming by a factor of two, with temperature increases on average of 2 degrees Fahrenheit, and much larger in some particularly sensitive regions. Arctic sea ice concentration has decreased by about 25 percent over the past three decades. In the summer of 2007, the summertime sea ice minimum was a record 40 percent lower than normal and 20 percent lower than the previous record (set in 2005). Scientists are also concerned that the recent increase of melting from Arctic alpine glaciers and the Greenland Ice Sheet will cause an acceleration of sea level rise that is much faster than previously expected.

Deep Freeze with a Twist

Due to its colder climate, higher topography, permanent ice cover, and isolation from the rest of the global climate system by an unbroken expanse of ocean, climate change in Antarctica has been much slower than in the Arctic and the rest of the globe. Ironically, the slower warming in Antarctica may be caused in part by increases in greenhouse gases and depletion of ozone (the “ozone hole”), both of which humans have contributed to. The interaction of these two gases with the atmosphere has caused the belt of westerly winds that circles Antarctica to strengthen, in a sense acting to inhibit the transport of warmer air from lower latitudes toward Antarctica. There are signals, however, that this situation may only be temporary and that Antarctica may soon begin to warm in step with the rest of the globe.

One small region comprising about 5 percent of Antarctica – the Antarctic Peninsula, which has a milder climate than the mainland – has already undergone substantial warming that has led to the breakup of several large ice shelves (floating masses of glacial ice). One of the largest ice shelves, about the size of Rhode Island, had been there for at least the last 10,000 years, indicating that the recent regional warming is unprecedented. Additionally, some large glaciers on or near the Antarctic Peninsula have begun to accelerate toward the ocean, enhancing their contribution to sea level rise. Some scientists fear that as these glaciers retreat, much larger volumes of ice trapped behind them may also retreat into the ocean as part of a domino effect that could raise global sea level by many feet within a short period. Only time will tell!

Resources

Global and Regional Temperature Change
This web page maintained by the NASA Goddard Institute for Space Studies explains temperature changes that have occurred globally over the past century, and provides an interactive database of temperature records from around the globe that can be plotted and viewed by users.

Arctic Climate Change
The Arctic Climate Impact Assessment is the most comprehensive synthesis of knowledge about climate change in the region currently available. While this document is often technical, the executive summary provides a brief overview written for nonscientists.

Arctic Sea Ice
This resource from the National Snow and Ice Data Center explains sea ice processes and documents the alarming decline of Arctic sea ice.

West Antarctica
The West Antarctic Ice Sheet (WAIS) has been the research focus of many scientists due to its uniqueness and its potential role in climate change. This web site gives a comprehensive overview of the climate, research, glaciers, and animals of WAIS, written for nonscientists.

SciencePoles
This web site from the International Polar Foundation has educational resources for studying climate change at both poles.

International Polar Year (IPY)
The IPY web site contains educational resources, blogs, and research results for both polar regions.

National Science Education Standards: Science Content Standards

A study of weather and climate aligns with the Earth and Space Science content standard for grades K-4 and 5-8 and the Science in Personal and Social Perspectives content standard for grades K-4 and 5-8.

Earth and Space Science

K-4 Changes in the Earth and Sky

• Weather changes from day to day and over the seasons. Weather can be described by measurable quantities, such as temperature, wind direction and speed, and precipitation.

5-8 Structure of the Earth System

• The atmosphere is a mixture of nitrogen, oxygen, and trace gases that include water vapor. The atmosphere has different properties at different elevations.
• Clouds, formed by the condensation of water vapor, affect weather and climate.
• Global patterns of atmospheric movement influence local weather. Oceans have a major effect on climate, because water in the oceans holds a large amount of heat.

Science in Personal and Social Perspectives

K-4 Changes in Environments

• Changes in environments can be natural or influenced by humans. Some changes are good, some are bad, and some are neither good nor bad. Pollution is a change in the environment that can influence the health, survival, or activities of organisms, including humans.
• Some environmental changes occur slowly, and others occur rapidly. Students should understand the different consequences of changing environments in small increments over long periods as compared with changing environments in large increments over short periods.

5-8 Natural Hazards

• Human activities also can induce hazards through resource acquisition, urban growth, land-use decisions, and waste disposal. Such activities can accelerate many natural changes.
• Natural hazards can present personal and societal challenges because misidentifying the change or incorrectly estimating the rate and scale of change may result in either too little attention and significant human costs or too much cost for unneeded preventive measures.

Read the entire National Science Education Standards online for free or register to download the free PDF. The content standards are found in Chapter 6.