Tag Archives: albedo

Feedback Accelerates Global Warming

Positive feedback to global warming keeps climate scientists up at night. Feedback can accelerate the rate of change in the climate. The worst-case scenario involves tipping points where the heating of the air and water make parts of the planet uninhabitable.

A frightening irony concerning global warming is the use of air conditioning to combat the heat. We obviously don’t think about cooling our homes and offices right now, but that is part of our problem. Using air conditioning requires power to generate the necessary electricity. The electricity comes to a large degree from burning fossil fuels which contribute to global warming. This short term reaction to a meteorologic phenomenon contributes to a long term climatological phenomenon.

Climate scientists call this positive feedback. Burning fossil fuels to run air conditioners contributes carbon dioxide to the atmosphere which traps heat and makes the planet warmer, which requires more air conditioning, which causes carbon dioxide release which causes more heating which… You get the picture.

In this case, the feedback has a human element. Other feedback loops are purely physical phenomena. These feedback loops add to the complexity of climate modeling. Predictions of future climate rely on computer calculations, the accuracy of which depends on how well the variables in a climate system are understood.

Water vapor in the atmosphere is without question the most important of the global warming feedback loops. Water vapor is a strong greenhouse gas itself; that is, its presence in the atmosphere traps heat and contributes to global warming. The positive feedback comes about because the amount of water vapor in the atmosphere is directly proportional to the temperature of the atmosphere. The hotter the atmosphere the more water vapor, the more water vapor in the atmosphere, the more heat trapped in the atmosphere, the more water vapor in the atmosphere, the more… you get the picture.

When natural gas (methane) is burned it produces carbon dioxide, a major greenhouse gas. Unburned methane released to the atmosphere is itself a potent greenhouse gas. There are vast stores of methane trapped in the permafrost of the tundra and the continental shelf under the oceans. As the planet warms, the permafrost thaws which releases methane. Methane release warms the planet thawing more permafrost which releases more methane which… you get the picture.

The amount of solar heating of the planet is a function of the albedo, the reflectivity of the planet. Sunlight is strongly reflected by snow-covered expanses near the north and south poles. As the climate warms due to global warming, the snow melts exposing soil which is much less reflective.

The less reflective soil traps more heat, warming the planet further, melting more snow, which traps more heat… you get the picture

The same is true of sea ice and the oceans. Ice is more reflective than water. As the ice cover melts, more heat is trapped, as more heat is trapped more ice melts… you get the picture.

A final irony is that as the area of the oceans covered with ice shrinks, it opens more area to exploration and untimely production of crude oil. Burning these fossil fuels adds more carbon to the atmosphere, which warms the planet… I hope you get the picture.

Dr. Bob Allen is Emeritus Professor of Chemistry, Arkansas Tech University.

Antarctica and Global Warming

Antarctica, the southernmost continent is literally the last place on earth. It occupies about 14 million square kilometers (5.4 million sq. miles.) For comparison, it is about twice the size of Australia and half the size of North America. Because of the tilt of earth’s axis and local elevation, it is obviously the coldest with an average wintertime temperature of – 60°Celsius, and summers averaging -28° C.

Interestingly Antarctica is also the driest, windiest and highest. Annual precipitation is 20 centimeters (8 inches) and most of that falls on coastal areas with the interior even drier. Ironically, although it is a desert based on precipitation, it contains 70% of the world’s fresh water as ice.

Wind speed averages 23 mph across the continent, but straight line winds of 200 mph have been recorded. Compare this with a category 5 hurricane whose winds are a puny 156 mph. Only an F5 tornado creates wind speeds equivalent to that encountered routinely on Antarctica.

One of the reasons for the cold weather in Antarctica, as noted earlier is its average elevation. The North Pole is at sea level, actual below it because the land mass at the North Pole is under the Arctic Ocean. The average elevation however for Antarctica is over 8,000 feet. The South Pole itself is over 9,000 feet and the highest point is 16,300 ft. Ice over much of Antarctica is a mile or more thick.

So what’s up (pun intended) with Antarctica? The temperatures? Well, it’s complicated as parts of the continent are warming while others aren’t. First the warming part. Both computer climate models and recorded data over decades show that while the planet is warming as a whole, the polar areas are warming even faster. This is a result of several different phenomena. Clouds, ice cover, water vapor and large scale weather patterns have all be implicated.

Ice is shiny stuff and reflects much sunlight. As ice over the sea melts the sun warms the less shiny water more. The term for light reflected divided by light absorbed is albedo. For very shiny snow or ice the albedo is about 0.9 (total reflection would result in a value of 1.0). Open oceans are much less reflective hence absorb more heat and have an albedo of less than 0.1.

The south pole has a confounding variable – the ozone hole. Essentially the reduced amount of ozone over the south pole reaches a maximum in the austral spring. The ozone hole is gradually decreasing due to international protocols which banned the use of chlorofluorocarbons. As the amount of ozone returns to normal the temperatures in the south pole are expected to rise as rapidly as in the north. As the Antarctic continent warms and sea ice melts, some of the land based, 1 to 3 mile thick layer of ice will begin to melt.

Were all this ice to melt sea levels would rise over 200 feet. This catastrophic sea level rise would inundate Manhattan Island, Miami, New Orleans, Houston and on and on. This won’t be happening soon, but without first recognition of human impact to global warming, it will happen.