Universe Today

In our generation, the main causes of global warming are related to human activity. The production of greenhouse gases which have prevented heat from the sun from escaping back into space, are widely believed to come from fossil fuel burning vehicles, machines, and power plants. However, the widespread warming events that the Earth experienced in the past may have had other causes. Let's take a look at some of those causes, man made or not, now.

Variations in Solar Output

It has been observed that certain solar activities undergo a cyclical process. The most evident is the 11-year solar cycle a.k.a. the sunspot cycle. The amount of solar heat radiated is believed to be proportionate to the number of sun spots. That is, the greater the number of sun spots, the more heat energy is released.

Although not directly proving solar output as among the major causes of global warming, the occurrence of certain extreme climates in the past shows how sun spot activity may affect the climate. For instance, the Maunder Minimum, a long period of sun spot inactivity, is believed to have coincided with the Little Ice Age. The Little Ice Age is a stretch of time when Europe experienced long bouts of extreme coldness.

Milankovitch Cycles

There are other cyclical physical phenomena that affect the amount of solar heat that reaches the Earth. One is the group of events collectively known as Milankovitch cycles. Milankovitch cycles are cyclical movements of the Earth that includes its eccentricity, axial tilt, and precession.

Eccentricity refers to how elliptical the Earth's orbit is. Axial tilt is the degree of inclination of the Earth's axis relative to an imaginary line perpendicular to its orbital plane. Finally, Precession is the wobbling characteristic of the Earth. All these properties undergo cyclical variations that last tens of thousands of years.

Greenhouse Gases

The two causes of global warming mentioned earlier are however not given much credit for the warming experienced in the recent years. There is an overwhelming number of scientists who believe that the global warming we're experiencing now is caused by the accumulation of too much greenhouse gases in the atmosphere.

In the past, accumulated atmospheric greenhouse gases managed to prevent some amount of heat from being radiated back into space. This was a good thing, as it kept the Earth within just the right temperatures. The recent excessive build up of greenhouse gases, however, have caused the ocean's water temperature to rise and great chunks of ice in the Arctic to melt.

Unless mankind can figure out a (realistic) way to bring down greenhouse gas emissions, we may be in for a wetter, warmer planet.

Can rising temperatures really shut down plate tectonics? Find out here in Universe Today. Another interesting question: Could cosmic rays influence global warming?

An article in NASA talks about how the recent warming in the Arctic may affect worldwide climate. There's another one that discusses short-term ocean cooling and how it suggests a global warming 'speed bump'.

Relax and listen to some interesting episodes at Astronomy Cast. Want to know more about Ultraviolet Astronomy? How different is it from Optical Astronomy?

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A new national survey conducted by Pew Research shows that more Americans are growing skeptical of global warming. This, despite the fact that the scientific opinion on climate change remains steadfast in endorsing the position of the IPCC (Intergovernmental Panel on Climate Change), which attributes most of the global warming observed over the last 50 years to human activities.

So what exactly are the human-related factors that cause global warming?

The most impactful global warming causes fall under one general heading: the increasing concentration of greenhouse gases in the atmosphere. This is largely due to emissions brought about by human activity. First, we'll identify the greenhouse gases, then we'll pinpoint their most likely sources.

The gases that have been largely identified with the greenhouse effect are: water vapor, which accounts up to 70%, carbon dioxide (up to 26%), then methane and ozone.

It is in carbon dioxide emissions where humans are identified as accomplices to global warming causes. The rise in carbon dioxide emissions can be traced back to the start of the Industrial Revolution in the 18th century.

About 75% of the increase in atmospheric carbon dioxide over the past 20 years is attributed to fossil fuel burning, while much of the remaining percentage is believed to be caused by deforestation (also a man-made activity).

While fossil fuel burning results in emissions of up to 21 billion tonnes of carbon dioxide every year, only half of that can be used up by the environment. As such, the remaining 10.5 billion tonnes are accumulated in the atmosphere, preventing heat from the Sun from leaving.

Some products of fossil fuels are gasoline, diesel and coal. These materials are used in automobiles, coal-powered plants, and other machines. What machine do you know that doesn't run purely on these materials? Not many, right? The vehicles you ride each day and the electricity you consume in your homes and offices all rely heavily on fossil fuel.

Is it therefor still surprising that carbon dioxide levels are rising?

Not everyone is quick to point an accusing finger to human beings and their activities as major contributors to global warming causes. There are those who believe it (global warming) as a consequence of increased solar output, volcanic activity, and other variables related to the Earth's orbit around the Sun.

If the question however is, what does the scientific community say? Well, we already know the answer.

Want to see some pictures of global warming? We've got them here in Universe Today. Perhaps you'd also want to read the peculiar article: NASA Uses 90 Rubber Ducks to Study Global Warming.

Since we've mentioned NASA, here are some global warming related articles from their site.

Global Warming
NASA Study Predicts More Severe Storms With Global Warming

Here are some interesting episodes from Astronomy Cast:

Galileoscope, Black Hole Time, and What Exactly is Energy
Energy Levels and Spectra

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There is little room for doubt that the extreme weather conditions being experienced in many places in the world are among the effects of global warming. There was Typhoon Ketsana, which left a good part of Southeast Asia in shambles … then of course there was Hurricane Katrina.

High ocean temperatures lead to greater precipitation and stronger wind velocities. So as global temperatures continue to rise, we can expect far more powerful storms. Ironically, we can also expect other places in the world to be hotter and drier than usual.

As you're reading this, ice in the polar regions continue to melt. One of the effects of global warming that scientists are closely monitoring is the decrease of ice content in the Arctic.

What they fear is that, as the permafrost melts, a subsequent release of methane will ensue. Methane is known to be a very potent greenhouse gas – the group of gases recognized as the main culprits of global warming. The faster the permafrost melts, the faster methane is released – which can lead to further acceleration of global warming.

Then there's the Greenland Ice Sheet. It is predicted that the ice sheet on Greenland is sufficient to raise sea levels way above the streets of many of the world's biggest cities, Shanghai, New York, Tokyo, and London being the most notable.

The corresponding effects of rising sea levels alone are already disastrous. Imagine New York and Shanghai underwater – where will you relocate millions of people, vehicles, and infrastructure?

One of the lesser known effects of global warming is the imminent rise of ocean acidity. You see, increased carbon dioxide concentrations are not only experienced by the atmosphere. Part of the excess carbon dioxide are absorbed by the oceans, where they react and form carbonic acid.

Unfortunately, many animal species are very sensitive to pH levels. Raise or lower the pH levels of their habitat, and they cannot hope to survive. Therefore, an increase in the ocean acidity can wipe out certain marine species. Those that aren't as directly affected to changing acidity can be indirectly affected by the loss of certain organisms in the food chain.

The effects of global warming are not confined to the ocean. Warmer temperatures can lead to the melting of glaciers like those on the Tibetan Plateau. This can result in flooding of the villages and farmlands below. Worse, since these glaciers feed rivers, the loss of the source can eventually cause these rivers to dry up in the future.

Can rising temperatures really shut down plate tectonics? Find out here in Universe Today. Another interesting question: Could cosmic rays influence global warming?

An article in NASA talks about how the recent warming in the Arctic may affect worldwide climate. There's another one that discusses short-term ocean cooling and how it suggests a global warming 'speed bump'.

Relax and listen to some interesting episodes at Astronomy Cast. Want to know more about Ultraviolet Astronomy? How different is it from Optical Astronomy?

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Climate change is one of those gradual things that sneak up on you. It doesn't look like anything is happening, but if you look back over the years and decades, you can see dramatic climate change pictures that show glaciers are receding, water levels are rising, and the polar ice caps are melting. Here are a series of pictures of climate change that can show you what's happened so far, and where the world might be going.

This climate change picture shows you the retreat of the Jakobshavn Glacier in Greenland. You can see the point that the glacier ended from 1805 until the last couple of years. In fact, the glacier's retreat sped up in 1997, almost doubling the amount of ice it discharges into the oceans.

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This is a picture of the Larson B ice shelf in Antarctica. In just 35 days, an area larger than Rhode Island broke up and collapsed into the sea.

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This image shows temperature trends in the Arctic from 1983 to 2003. The redder regions have gotten warmer and the bluer regions have gotten cooler. As you can see, there aren't a lot of cooler regions.

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This is a model of sea surface temperatures developed by NASA. Red colors indicate rising temperatures, while blue colors indicate cooling temperatures.

We have written many articles about climate change for Universe Today. Here's an article about climate change and the Earth's cryosphere, and how past climate change can't be tied to the Earth passing through the galactic plane.

You can also get many more climate change pictures and animations from NASA here.

We have recorded a whole episode of Astronomy Cast about the Earth. Listen to it here, Episode 51: Earth.

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The Maunder Minimum is a long period wherein sunspot occurrence was noticeably very low. Although it is normal to observe the Sun having few sunspots over a certain duration, with some scientists even believing that an 11-year cycle of maximum and minimum solar power outputs exists, the period spanning the Maunder Minimum is at an unusually astounding 70 years, from 1645 to 1715.

The graph above should give you an idea how glaring it is. Although it is not shown in the graph, data gathered by astronomers reveal a 30-year duration within the Maunder Minimum wherein only 50 sunspots were accounted for. Compare that to the usual 40,000 to 50,000 recorded in more recent years.

This extended period of minimal sunspot activity is named after Edward Maunder, an astronomer who in the late 1800's and early 1900's studied variations in sunspot latitudes.

One feature of that 70-year sunspot drought might interest climate change advocates. This interval is said to have coincided with the coldest stretch of the Little Ice Age, a period of considerably low temperatures that affected vast parts of Europe and North America. During the Little Ice Age, Greenland was virtually inaccessible between 1410 to 1720 due to enormous structures of ice.

The effects of solar activity, much less the extent of it, to climate change is not well established. However, there are those who suggest we should look at other causes of climate change other than greenhouse gases, and solar activity is one of the alternative candidates.

Galileo is usually credited when it comes to the discovery of sunspots. However, it is Heinrich Schwabe who first noticed the cyclical rise and fall of their numbers. His findings were released in an articled entitled "Solar Observations in 1843". In that paper, he suggested a 10-year cycle, close enough to the currently accepted 11-years.

While it is definitely too early to tell whether we're about to go into an extended time of sunspot inactivity again, the sun is currently staying at a minimum a little longer than expected. After the anticipated minimum between 2007-2008, solar activity is already supposed to be on its way up but that doesn't seem to be happening. According to Mike Lockwood, a solar physicist from Southampton University, the Sun is currently "bumping along the bottom".

Since the next maximum is still estimated to be at 2013, there's absolutely no cause for alarm. If no substantial change occurs in the next couple of years, then perhaps that's the time when we should start worrying.

We have some articles in Universe Today that are related to the Maunder Minimum. Here are two of them:

• Where are the Sunspots? Are we in for a Quiet Solar Cycle?
• 2012: No Killer Solar Flare

Articles related to the Maundy Minimum brought to you by NASA and Physics World, here are the links:

• The Sun's Chilly Impact on Earth
• Where are the sunspots?

Tired eyes? Let your ears help you learn for a change. Here are some episodes from Astronomy Cast that just might suit your taste:

• The Sun, Spots and All
• Dangerous Solar Flares, Higgs Boson Insights, and Light Speed Flashlights

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Last week the US government released more than a thousand intelligence images of Arctic ice that have been used to help scientists study the impact of climate change. The images were taken by spy satellites, as part of the Medea program, which lets scientists request spy pictures from environmentally sensitive locations around the world. After they were taken, the Bush Administration released the photographs to the scientists but deemed them "unsuitable for public release." Earlier this month, the National Academy of Sciences recommended the Obama Administration declassify the photos, which they did within a few hours of the recommendation.

Various blogs are saying these dramatic images are faked, but since they are available through the US Geological Survey , that hardly seems likely. Over 700 images show changes of sea ice in various recent years from six sites around the Arctic Ocean, with an additional 500 images of 22 sites in the United States.
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Albedo is a measure of an object's reflection of the Sun's radiation. This term is important in Astronomy as many planetary bodies in the Solar System are visible due to the reflection of the sun's light off their respective surfaces. This is why we can see planets like Venus, Mars, and Jupiter.

The measurement of albedo is a subjective scale ranging from 0 for complete dark to 1 for completely bright. For example, snow has an Albedo of 0.9 and coal has an Albedo of 0.1. The Earth has varying Albedo scores. Dark soil has one of the lowest Albedo scores with .05 or 5%. The brightest are snow, deserts, and clouds with albedo scores at .09 or higher. On average the Earth's Albedo is around 30%. Some objects have lower albedo scores than expected. The moon for example has a surprisingly low Albedo of only 0.12.

There are two main kinds of albedo. One is black sky albedo and the other is white sky albedo. Black-sky albedo is the reflection of a surface under direct illumination. The white-sky albedo is reflection of a surface under diffuse or indirect light. Albedo is also important in Astronomy as it can give astronomers additional information about objects in the Solar System such as planets and other rocky objects. In the same way that spectroscopy analyzes wavelengths of light to find out the composition of a star, albedo can hint at the surface of a planet or other body because of changes in brightness. This even has an impact on the current discussion of the Earth's climate change

Another interesting fact about the albedos of objects in the Solar System is that the farther away from the Sun you get, the lower the albedo score. This is because the intensity of the Sun's radiation drops off over greater distances.

Albedo can also be used to detect if an celestial object in the Solar System is likely to have organic compounds. This probably because many organic compounds are carbon based and on the Albedo scale has one of the closest scores of 0.

To return to the more local effects of Albedo the reflection of the Sun's rays can change climates. It is commonly understood that cooling of the Earth is in part caused by the Sun's rays being reflected rather than absorbed. That is why there is concern about the polar ice caps melting since this would reduce the Earth's general albedo meaning more heat absorbed from the Sun which could accelerate global warming.

If you enjoyed there are other astronomical articles you might like. There is a great article about the Moon's Albedo. There is also an article that is more detailed about the Earth's Albedo.

There are also great resources on the web. There is a Georgia State University site which has a pretty concise explanation about Albedo and some comparison measurements to the Albedo of other objects in the Solar System. The National Snow and Ice Center site has an article that talks about the important role albedo has in regulating the Earth's temperature.

You might also like to listen to an episode of Astronomy Cast. Episode 50 Venus is one that might interest you.

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Earth's climate has changed over time, but the cause for the changes has been hotly debated. One idea (Shaviv and Veizer,2003), suggested that perhaps two-thirds to three-fourths of the variance in Earth's temperature over the past 500 million years may be attributable to when our solar system passes through the spiral arms of the Milky Way galaxy. The evidence seemed to fit: there appears to be a 140 million year cycle of global climate change, and that correlates when our solar system seems to move between spiral arms, too. Or at least it used to. Since 2003 we have revised our map of the galaxy, which changes the estimation of when Earth transits through the spiral arms.

"Although previous work found a correlation between the 140 Myr climate cycle on Earth and the intersection with spiral arms," write researchers Adrian Melott, Andrew Overholt, and Martin Pohl, "with new data on the structure of the galaxy, this correlation disappears."
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Researchers have been able to determine the atmospheric carbon dioxide levels over the past 2.1 million years in the sharpest detail yet by analyzing the shells of single–celled plankton. Their findings shed new light on CO2's role in the earth's cycles of cooling and warming, confirming many researchers' suspicions that higher carbon dioxide levels coincided with warmer intervals during the study period. But it also rules out a drop in CO2 as the cause for earth's ice ages growing longer and more intense some 850,000 years ago.
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