Ask a Scientist

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Q: How were the polar ice caps formed, and where did the water that they are made of come from?

--Jessica, Lake Peekskill, NY, USA

A: Dear Jessica,

The polar ice caps formed from snow fall, and the moisture in the snow originally came from the ocean. Water is picked up by the atmosphere and dropped on ice caps. These ice caps are also called ice sheets, which cover most of Greenland and Antarctica, over 2 miles thick in places. The North Pole is an ocean with thin layer of frozen ocean, called sea ice. Snow falling on ice sheets packs into solid ice, and the ice flows back into ocean, some as icebergs and some as water where caps melt at edges in summer. We don't know whether the ice sheets are growing or shinking now, but the laser altimeter on NASA's ICESat(to be launched in the summer of 2002)is designed to tell us whether the ice sheets are getting thicker or thinner.

Q: How can scientists measure fluctuations in carbon sequestration in the forest?

--Akbar, Kuala Lumpur, Malaysia

A: Dear Akbar,

This is a question that a lot of scientists are thinking about now. We can't measure fluctuations in sequestration any where near as well as we need to in order to judge forest impacts on atmospheric CO2 concentrations.

Carbon sequestration in forests can occur by storage in above ground wood (trunks and limbs) resulting from more trees or bigger trees. It can also occur through increases in below ground wood (large roots). Another way is through accumulation of dead material both above ground and below ground and is caused by slower decomposition (or fire suppression) relative to production.

Most measurements are of above ground living wood (because of its direct economic value) and involve many simple measurements of girth and heights. One can also look at tree rings to study past fluctuations. Because these measurements are of individual trees and each tree is exposed to slightly different conditions (soil type, slope exposure, pathogens, etc) you have to make a lot of measurements to get an average for a particular area. It is possible to measure the regrowth of forests using satellite observations. As forests get thicker the sunlight reflected into space changes and we use this signal to estimate changes in forest growth from year to year.

Q: Has the spinning sphere shape of the Earth allowed its atmosphere to flow over the entire Earth creating a planet where life can exist? If the Earth had been cube-shaped, could life exist?

--Johnna, Folkston, GA

A: Dear Johnna,

This is a great thought question for a Ph.D. exam! I would say "probably yes" to your second question. We'll ignore the issue that the Earth, though solid, is not nearly rigid enough to avoid the near-spherical shape. And, let's assume that the masses of solid Earth, water, and atmosphere are about the same on "Cube World" as on Earth. Even though the solid Earth is cubic, the water and atmosphere would still respond to gravity. So, they would puddle on each face of the cube, which is the part of the planet that is closest to its center of mass. Compared to the volume of solid Earth, the other two components are small, so each face would have some ocean, deepest in the center, and then land surrounding that. The atmospheric pressure would be greatest at the ocean's surface and decrease as you climbed toward the edges of the cube. Without doing the calculation, I'm not sure what the pressure distribution would be, but it might well turn out that the edges would have pressures too low to support life. Thus, life forms on each face might have to develop independently. Finally, there are some important parameters left unstated. Does Cube World rotate? How fast? Is the axis of rotation tilted? Where on the cube is the North Pole? Each combination of parameters might give a different environment, some less hospitable than others.

Q: How high above the earth must one go in order to see a curved horizon instead of a flat horizon?

--Bob, Little Rock, AR

A: Dear Bob,

Any time you're above the surface of a smooth sphere you see a curved horizon! In the limit of being far away, the "horizon" is the edge of the disk that the Earth obscures in your field of vision. [Think of the pictures of the Earth taken from lunar orbit.] As you move down toward the surface the apparent size of the disk grows, but fundamentally continues to be a disk (with a curved edge) right up until your nose is touching the ground. In that case the "disk" covers half your 360-degree field of view and appears to be a flat plane. Having a rough surface complicates the picture a little, but compared to the radius of the Earth, even Mt. Everest is pretty small. Furthermore, our normal experience is so close to ground level (again, compared to the radius of the Earth), that the curvature of the horizon is imperceptible.

Q: If we keep burning fossil fuels and natural gases and keep driving our cars every day, and the pollution rate does not decrease, how long will the earth be inhabitable?

--Anthony, Zephyr Hills, Florida

A: Dear Anthony,

You've asked an incredibly important question, but also one that is difficult to answer. We don't have a very good idea of how to define at what point the planet will become uninhabitable because its hard to predict how the earth will respond to the impact of human activities on the climate. From ice core data we know that over the past 450,000 years there has been a natural oscillation in atmospheric CO2 levels and average global temperature, with warmer temperatures occurring with higher CO2 levels.

In this time period, until the start of the industrial revolution, atmospheric C02 varied between 200-300 parts per million (ppm). Now, with the increased burning of fossil fuels and deforestation, this level has surpassed 370 ppm, a condition that the earth has not experienced in the last half a million years.

So the task is to understand how the earth, as a system, will respond to this sudden large perturbation, and a tremendous amount of research is currently being done to address this question. To do this one must view the earth as a whole, and look at the interactions between the atmosphere, oceans and land. The oceans play an important role in the global carbon cycle because CO2 is very soluble in seawater, there is 50 times as much carbon dissolved in the ocean as exists in the atmosphere. Most of the research involves computer models that simulate the circulation in the atmosphere and ocean, and the interactions between them to try to understand the long-term effects of increased C02.

However the models are only as good as the knowledge of the processes that are put into them and there are feedbacks in the systems that are still not understood well enough to be modeled correctly. One of the big questions involves what is referred to as the "missing sink" of carbon. The amount of excess CO2 in the atmosphere is less than the amount that has been emitted into the atmosphere from fossil fuel burning, even accounting for the amount of carbon that the oceanic and terrestrial systems have taken up. This means that there must be another sink for the C02 that we are not aware of. The issue of the missing carbon sink underscores the fact that we do not fully understand fundamental aspects of how the earth is currently operating, which undermines our ability to predict how it will behave in the future. Current models suggest that a doubling of atmospheric CO2 will increase the global temperature by 1.5-5.5°C. However this is a global average and to understand its impact on humans, it also necessary to know what will be the regional patterns of this response. Certainly coastal areas will be heavily impacted by rising sea levels as glaciers and the polar ice caps melt. How well humans will be able to adapt to the changing conditions will depend on how fast the changes occur among other things.

Q: What causes the high (in 1971,82, 83, 84, 95, 96) and low (in 1963, 65, 67, 76, 78, 85, 97)fluctuation of the annual percipitation in Northwest Oregon (Willamette Valley)?

--Heidi, Marina, California

A: Dear Heidi,

There are two main processes that affect the long term climate variability in the Northwest USA: El Niño events and the Pacific Decadal Oscillation (PDO). El Niño events, and their counterpart, La Niña events, are part of a natural oscillation of the coupled ocean-atmosphere system in the tropical Pacific referred to as ENSO (El Niño-Southern Oscillation). While the dominant effects are seen near the equator, these events can also impact the climate further away. Spring and fall seasons tend to be drier in the NW Pacific during El Niño events, and La Niña events, which usual follow directly after El Niño events, cause wetter falls and winters. El Niño events typically start in the fall and last through to the following spring. The last three biggest El Niño events occurred in 1972/73, 1982/83 and 1997/98.

Precipitation in the NW Pacific is also impacted by the PDO, which is a type of oscillation like ENSO, but the events last much longer, persisting 10 or more years as opposed to ENSO events which typically are over in less than a year. Also the main signatures of the PDO are seen in the North Pacific/North America region, not in the tropics. A cool and wet phase of the PDO existed during 1947-1976, which would tend towards wetter conditions in Oregon. Since 1977 the PDO has been in a warm and dry phase, which would tend towards drier conditions in Oregon.

While not all the anomalous years that you listed fit the patterns outlined above, a more detailed comparison between NW Pacific precipitation and the ENSO cycle and the PDO shows a correlation between them.

Q: Can you please give me more information about the radiation levels on Earth. Just on the three types: Reflected Solar Radiation and Longwave Radiation and Net Radiation. Are there significent changes of these levels? Is radiation increasing on Earth from the ozone and the microwave, man-made radiation?

--Michelle, Melbourne, Victoria, Australia

A: Dear Michelle,

Just to make sure we're all on the same page, the "radiation" being discussed here is the radiant energy in various parts of the electromagnetic spectrum, which we experience as radiant heat (longwave), light (shortwave), various radio waves (including microwave, AM, FM, etc.), and cosmic rays. The Sun is so hot that much of the radiant energy it emits is in the form of visible light. About 40% of the sunlight striking the Earth is reflected by the Earth system (including clouds), and the rest is absorbed by the ocean, land, and atmosphere (in order of importance). In turn, different parts of the Earth system pass around the heat by conduction (into and out of the solid earth); transport (by ocean and wind currents); conversions among gaseous, liquid, and solid water (evaporation, condensation, sublimation, deposition, freezing, melting); and emission and absorption of radiant energy. Finally, the Earth emits as much radiant energy back to space as it receives from the Sun. This emission to space occurs mostly in the longwave band because the Earth system is relatively cool.

The point of the concern over the increase in CO2 and the other "radiatively active trace gases" (which includes water vapor) is that they change the way in which the solar energy captured by the Earth is redistributed on its way back to space. In isolation, increases in these gases act to slow the rate at which radiant energy returns to space, heating the earth's surface and atmosphere. What we do not yet know with precision is how other parts of the Earth system react when this heating tendency is inserted into the real Earth system. In particular, the response of clouds is still an active area of study. One major barrier to understanding is that the energy budget is highly complex and variable in space and time.

The direct human contribution of radiant energy, including microwave signals, is tiny compared to the total energy budget. Our release of CO2 is much more important.

Q: Was the Gulf of Mexico created by a giant meteor that Impacted the earth? And if so, does this strange oil leak that seeps out of this gulf have anything to do with this event? could this place be the site of origin of the Microbial soup theory?

--Antonio, Santa Rosa, CA U.S.A.

A: Dear Antonio,

The Gulf of Mexico is too large to have been formed by a meteor impact. However, the Chicxulub crater, which is believed to be the largest meteorcrater on the earth, is found off the Yucatan Peninsula in the Gulf of Mexico. The Chicxulub crater is 150-300 km in diameter, whereas the Gulf of Mexico is more than 1500 km in diameter. The Gulf of Mexico already existed when the Chicxulub meteor hit. The origins of the oil in the Gulf of Mexico have to do with its geological history. Oil is formed from unoxidized organic material, organic material being decaying plant and animal matter. During the Jurassic Period (140 million years ago) the entire Gulf of Mexico dried up, as it evaporated the water became depleted in oxygen and layers of black shale were deposited. Geological heating of these shales over millions of years created the oil.

The type of environment that first led to the creation of life is still debated. Some scientists have suggested this could have occurred at hydrothermal vents. Hydrothermal vent environments are in some ways similar to the seeps found in the Gulf of Mexico, but they are usually found in areas of the ocean with active volcanic activity. In contrast to the gulf seeps hydrothermal vents emit very hot water (300�C, three times hotter than boiling water!) and it is this extreme heat that is thought to have been the catalyst for reactions leading to the formation of life. While we will probably never be able to locate exactly where this happened, we can be fairly certain that it did not occur in the Gulf of Mexico. The earliest evidence of life on earth is 3.5 billion years ago, and at that time the continents and oceans had a very different configuration, and the Gulf of Mexico did not exist as it does today.

Q: With all the talk of global warming and the cause (many blaming human release of various gases), didn't the eruption of Mount Pinatubo produce a higher percentage of the harmful gases that cause global warming than humans ever did or will?

--Julie, Niagra Falls, NY U.S.A.

A: Dear Julie,

There is no question that Pinatubo and similar volcanic eruptions spew massive amounts of gunk into the atmosphere. ["Gunk" is a technical term for "gases and particulates that you wouldn't want to take home."] However, the particular materials ejected normally have the net effect of cooling the Earth, rather than warming it. The volcano only has a global effect when the eruption is powerful enough to send its plume into the lower stratosphere, in regions where there is relatively little mixing and turbulence. In a short time the heavier particles fall out and most of the gases chemically convert to aerosols. However, the remanents can persist for years and spread over most of the globe, acting principally to reflect sunlight and thus cool the Earth. In the case of Pinatubo the cooling lasted for about a year, during which time the stratospheric contamination was visible as faint pink shading just after sunset on the clearest evenings.

Q: Where did Earth's atmosphere come from?

--Ronald, Plainfield, NJ U.S.A.

A: Dear Ronald,

The atmosphere, as well as the ocean and solid earth, is the result of a long process of accretion, first from the original disk of tiny fragments that surrounded the early Sun, and subsequently from meteors and comets. As well, the formation of a free atmosphere depended on the formation and release of gaseous molecules, such as molecular oxygen (O2), as opposed to the constituents being bound in solid molecules, such as silicon dioxide (SiO2). A few gases were so light that the molecular or atomic forms have largely escaped from the atmosphere, including hydrogen and the well-named rare gases. Finally, the present composition of the atmosphere is the result of long-term interactions between the atmosphere and the biosphere. For example, it is thought that molecular oxygen only appeared when plants started giving it off as a by-product of photosynthesis.