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Human Carbon Dioxide Emissions Dwarf Annual Volcanic Emissions

Human Carbon Dioxide Emissions Dwarf Annual Volcanic Emissions

Yes, aerosols from volcanic eruptions cool the climate, but don’t carbon dioxide emissions from the same eruptions counteract this
cooling? No, at least not significantly.

Terrance Gerlach, scientist with the U.S. Geological Survey, untangles this commonly misconstrued reality in the American Geophysical Union’s EOS June 2011 issue. The amount of carbon dioxide emitted by volcanoes, Gerlach affirms, is inconsequential when compared to human emissions. He calculates that humans emit the equivalent amount of carbon dioxide as the 1991 Mt. Pinatubo eruption every 12.5 hours. Every 2.7 days, we emit the equivalent amount of carbon dioxide released by volcanoes during an average year. Our ubiquitous and unabated emissions easily dwarf volcanic emissions, and the cooling effect of volcanic aerosols from a single catastrophic event is much larger than the average annual warming effect of volcanoes worldwide.

There have been periods in Earth History, however, when volcanic carbon dioxide emissions may have been more significant in global climate. Roughly 640 million years ago, for example, volcanic emissions may have pulled the Earth out of a global glaciation. During this glaciation, called Snowball Earth, the Earth is thought to have been sealed in ice as thick as 1 kilometer in some regions, tapering down to less than than 2 meters at the equator. In such a scenario, the atmospheric-oceanic-terrestrial carbon cycle would have slowed down to a near standstill, seriously hindering the Earth’s natural thermostat. Volcanic eruptions, both sub-marine and sub-glacial, may have been the one source of carbon dioxide available to thaw the snowball.

According to studies led by Paul Hoffman, Professor Emeritus at Harvard University and a leader in Snowball Earth research, carbon dioxide from volcanic emissions could have leaked through weakly-frozen regions of the equatorial ocean and cracks in terrestrial glaciers, slowly warming the atmosphere. With essentially all carbon sinks sealed off, this carbon dioxide would have built up unabatedly in the atmosphere. Over the course of millions of years, enough could have accumulated to end Snowball Earth.

So, yes, volcanoes may contribute to significant climate warming, but only over the extended course of geologic time. Over the course of the 21st century, a mere blink in geologic time, we can safely assume that, if anything, volcanoes will cool global climate.

Posted by Laura Poppick, Assistant Editor of Maine Climate News.

Image Description: Volcanic eruption as seen from space

Small Volcanic Eruptions Cool the Climate

Small Eruptions Cool the Climate

On August 27, 1883, civilians on the Indian Ocean island of Rodrigues heard an explosion. What they initially assumed was cannon fire from a neighboring ship turned out to be a more distant threat: the sound of a volcano erupting on Krakatoa, Indonesia, nearly 3,000 miles away.

Traveling 50 miles through the atmosphere into the stratosphere, aerosols from the volcano’s ash plume billowed over the Earth along air currents that tinted the global sky for several years to follow. This veil of aerosols reflected enough incoming solar radiation to lower global temperatures by 2.2°F, and cast a dramatic red glow on skies above the U.S., Europe, and Asia. The brilliant sunset in Edvard Munch’s The Scream was allegedly inspired by these Krakatoan skies.

Until recently, atmospheric scientists assumed that only such catastrophic eruptions could significantly alter Earth’s climate. Other eruptions of similar scale have been documented to have temporarily cooled global climate, with the 1815 eruption of Mount Tambora in Indonesia causing a ‘year without a summer’, and the 1991 eruption of Pinatubo in the Phillippines cooling global temperatures by nearly 1.0°F.

Now, NOAA scientists say that even small volcanic eruptions can manipulate global climate. In a paper published last month in Science, Susan Solomon and her team report that ‘background’ levels of global stratospheric aerosols have nearly doubled over the past decade and have slowed the trajectory of climate warming. Given that no catastrophic volcanic eruptions have occurred since the 1991 Pinatubo event, other sources must account for this recent increase in aerosols. Some argue for coal burning power plants in China, but NASA scientist John Vernier and his team point to a series of moderate low-latitude tropical volcanic eruptions.

Low-latitude volcanic plumes rise above the equator and spread across both the Northern and Southern Hemispheres like tape in a cassette. High-latitude volcanic plumes, on the other hand, generally remain contained within their hemisphere of origin. Vernier shows that a series of increasingly more intense but still relatively moderate tropical eruptions have substantially contributed to the steady rise in global stratospheric aerosols over the past decade.

While the cooling effect of stratospheric aerosols is relatively fleeting, lasting up to 2 or 3 years, it is still significant in global climate. And yet models that predict future climate change do not generally account for volcanic aerosols. Solomon and Vernier both encourage climatologists to place more weight on volcanic aerosols to improve the accuracy of climate models.

Posted by Laura Poppick, Assistant Editor of Maine Climate News.

Image Description: Edvard Munch's 'The Scream'

Loops of Change: the Positive Feedback Loops that Drive Climate Change (Part IV)

 Permafrost Thaw and Bogland Loss

You may or may not be familiar with the bog man named Tolland Man. Tolland Man lived during the 4th century BCE and is believed to have been ritualistically sacrificed and buried in a bog in what is now Tolland, Denmark. The relatively low temperature, acidic, and oxygen-poor conditions of the waterlogged bog inhibited decay of his body, allowing his skin and other soft tissues to be remarkably well preserved. So much so that the Danish woman who discovered him in 1950 while harvesting peat to burn in her stove assumed that she had come across a recent murder victim. Only after the local police hired an archaeologist to investigate the site was Tolland Man discovered to have lived more than 2,000 years prior, during the Iron Age. His body now sits in the Silkeborg Museum in Denmark.

Fascinating from an archaeological standpoint, the preservation capacity of bogs is also an important component of the global climate system. That is, the same chemical and physical properties that slowed decomposition of Tolland Man’s body also do so for dead plant material. Since decomposition releases greenhouse gases like carbon dioxide and methane, the limited decay rates in bogs allows them to serve as a significant terrestrial carbon sink.

For a terrestrial habitat to be a carbon sink, plants need to grow and photosynthesize (absorb carbon) at a faster rate than they respire or decay (release carbon). The waterlogged nature of bogs creates an anoxic, or oxygen-depleted, environment that greatly slows decomposition and allows carbon absorption to outpace release. Over time, accumulated layers of partially decayed plant matter, or peat, form a secure bank of sequestered carbon similar to the sedimentary deposits created by marine snow on the sea floor.

Climate change may drain bogs of their characteristic waterlogged conditions, thereby threatening their role as a global carbon sink. Bogs are susceptible to warming because they rely on permafrost, or frozen soil, to maintain their structure. Generally occurring in northern boreal forests, bogs form when seasonal snowmelt pools at the soil surface above a barrier of permafrost below. As permafrost thaws with climate change, this barrier weakens and bog water drains from the surface. Soils that were once waterlogged and anoxic become aerated, thereby increasing decomposition rates and carbon dioxide emissions. As permafrost continues to thaw in this positive feedback loop, drained bogs become carbon sources.

Still, while permafrost drives bog hydrology, other factors affect bog health and carbon sequestration capacity. For example, in a paper published last month in Nature Geoscience, University of Victoria professor Christopher Avis and his research team suggest that increased precipitation with climate change could help bogs maintain waterlogged conditions as permafrost degrades. On the other hand, they point out, warmer conditions will increase both aerobic and anaerobic decay rates. Anaerobic decomposition produces methane, a stronger greenhouse gas than carbon dioxide. Since bog decay occurs primarily anaerobically, methane emissions are expected to increase, thereby expediting further warming.

Tolland Man would likely be surprised to know of the global climatic implications of the bog conditions that preserved his skin and allowed him to gain fame more than 2,000 years after his death. Now imagine yourself waking up 2,000 years from today. What will the global climatic landscape look like then? Though we are in an era of rapid change now, the Earth system will eventually reclaim equilibrium over the course of geologic time. We can’t know if this will occur 200, 2,000 or more years from now.

As chaotic as 21st century climate change may seem, it at least provides us a chance to understand the Earth as a unified system in a way that Tolland Man could never have conceived. Perceiving the Earth as a unified system, and understanding the strengths and vulnerabilities of this system, may help ground us through a future of change.

Posted by Laura Poppick, Assistant Editor of Maine Climate News.

Loops of Change is a weekly series through July exploring the major positive feedback loops that drive climate change.

*Cai, S., and Yu, Z. 2011. Response of a warm temperate peatland to Holocene climate change in northeastern Pennsylvania. Quaternary Research: 75. 531 – 540.

Image Description: Tolland Man

Image Description: Map of northern north america with peatland distribution

Loops of Change: the Positive Feedback Loops that Drive Climate Change (Part III)

The Biological Pump

Earlier this week, the National Snow and Ice Data Center reported that Arctic sea ice extent declined at an average rate of 46,000 square miles per day during the first two weeks of July. You can track daily images of sea ice extent here.

While sea ice naturally melts every summer, this summer’s melt area already surpasses the 1979 – 2000 average by 865,000 square miles. This, in part, results from this year’s early onset of melting, which occurred two weeks to two months earlier than the 1979 – 2000 average in certain regions. Early spring melting produces colonies of melt water ponds on top of the ice that decrease ice albedo and induce further melting. While sea ice extent is currently at record low levels, predictions for the duration of the summer suggest that ice extent will not ultimately surpass the record minimum levels of September 2007.

The direct climatic effects of increased melting, such as decreased net albedo,  are relatively easy to identify. The indirect effects, on the other hand, can be more elusive. For example, what are the implications of melting sea ice on the phytoplankton community of the ocean? Why does this question concern climate scientists?

Marine phytoplankton drive the biological pump, a carbon sequestration mechanism that, along with the solubility pump, makes the ocean a major global carbon sink. Phytoplankton suck carbon dioxide out of the atmosphere during photosynthesis. When they die, or are released as fecal pellets of zooplankton, they aggregate and sink out of reach of the atmosphere. The resulting mass of ‘marine snow’ showers the sea floor with sequestered carbon dioxide, and slowly accumulates over geologic time as a layer of sedimentary rock. The White Cliffs of Dover are an example of an exhumed phytoplankton graveyard and vault of ancient atmospheric carbon dioxide.

Global climate both manipulates, and is manipulated by, the efficiency of the biological pump. As sea ice melts, the ocean surface freshens and absorbs more heat. This fresh, warm water is more buoyant than the cold, saline water below, and forms a floating layer that stratifies the water column. The resulting density barrier near the surface of the ocean can prevent deep, nutrient rich bottom waters from upwelling and fertilizing plankton blooms. With a limited nutrient supply, plankton blooms atrophy and the efficiency of the biological pump decreases.

Given the wide variability in temperature, salinity, and currents across the global ocean, melting sea ice will not have a uniform effect on the biological pump. In some regions, its efficiency may remain unaltered, or may improve for unrelated reasons. Ultimately, climate-induced changes in the solubility pump will likely have a larger impact on the role of the ocean as a carbon sink.  Still, the biological pump remains an active area of research for climate scientists.

As oceanic carbon sinks begin to weaken, will terrestrial sinks compensate? Stay tuned for next week’s post on Permafrost Thaw and Wetland Decay, where we will leave the oceans to trek through a terrestrial loop of change.

Posted by Laura Poppick, Assistant Editor of Maine Climate News.

Loops of Change is a weekly series through July exploring the major positive feedback loops that drive climate change.

Image Description: Arctic Sea Ice Extent

Image Description: Image of marine snow

Loops of Change: the Positive Feedback Loops that Drive Climate Change (Part II)

The Solubility Pump: An Oceanic Cooling System

In a paper published earlier this week in Nature Geoscience, oceanographer Galen McKinley and her research team reveal that rising North Atlantic ocean temperatures are dampening the ocean’s ability to absorb atmospheric carbon dioxide. They present data from the past 29 years, long enough to overcome natural oscillations in the ocean system and expose a real trend. Since the ocean is one of the most important global carbon sinks, absorbing a quarter of all atmospheric carbon emissions, these findings have significant implications for the Earth’s carbon cycle and future climatic system.

But why does a warmer ocean reject carbon dioxide? For the same reason that drinking a lukewarm carbonated beverage is generally underwhelming. Lacking the crispness that we crave in such refreshments, these drinks have been subjected to gas laws that make it hard for warm water to keep gas in solution. As a result, they lose their bubbles to the atmosphere and become ‘flat’.

Even if kept cool, beverages eventually lose their fizz, and their appeal, to the atmosphere. This is because, according to Henry’s Law, gases constantly try to attain equilibrium with their surroundings. Beverages maintain carbonation over some time because manufacturers pump beverage containers to the brim with carbon dioxide. Upon opening, gas bubbles immediately begin to escape and equilibrate with the atmosphere.

The ocean, unlike carbonated beverages, naturally contains less carbon dioxide than the ambient atmosphere and thus absorbs atmospheric carbon dioxide. This natural carbon sequestration mechanism is called the Oceanic Solubility Pump, and is an important cooling knob on the global thermostat discussed in last week’s post. But, as McKinley’s team reveals, this pump weakens in a warming climate system and, in some regions, may begin to hose carbon back into the atmosphere.

Famously, carbon dioxide warms our atmosphere. As the carbon-grabbing tendrils of the ocean begin to loosen with warming waters, the following positive feedback loop takes hold:

More carbon dioxide accumulates in the atmosphere, thereby

  1. increasing atmospheric and ocean temperatures,
  2. further weakening the ocean’s grip on atmospheric carbon dioxide,
  3. further raising atmospheric carbon dioxide concentrations,
  4. leading to further warming.
Still, the Solubility Pump is just one of several other ocean features that manipulate Earth’s climate. Stay tuned for next week’s post on its living counterpart, the Biological Pump, to see why gas laws do not entirely dictate the ocean’s carbon sequestration capacity.

Post and photo by Laura Poppick, Assistant Editor of Maine Climate News. 

Loops of Change is a weekly series through July exploring the major positive feedback loops that drive climate change.

Image Description: image of the ocean

Loops of Change: the Positive Feedback Loops that Drive Climate Change (Part I)

Sea Ice-Albedo: Earth’s Chilling Reflection

Last month, the European Space Agency (ESA) released the first ever map of polar sea ice thickness. While two-dimensional maps of sea ice extent have been available since 1979, this is the first project to present total ice thickness in addition to extent. The ESA plans to continue updating the map in the future, providing climate scientists with an invaluable record of sea ice response to climate change.

Climate-induced changes in polar sea ice extent depend largely on ice thickness for 2 reasons, the first more obvious than the second: 1) thin ice melts away faster than thick ice, and 2) the absence of ice promotes further melting in a positive feedback loop called the sea ice-albedo climate feedback mechanism.

The sea ice-albedo mechanism is rooted in the simple concept that light-colored surfaces reflect light and dark surfaces absorb light. When you choose to wear light-colored rather than dark-colored clothing on a warm summer day, you are increasing your body’s albedo, or its reflectivity power, and allowing yourself to feel cooler. The same is true on a local scale of dark pavement absorbing more heat and feeling hotter to walk on than the grass around it, and on a global scale of Earth’s surface and atmosphere reflecting more sunlight in light regions (polar ice caps) than in dark regions (open ocean). As the hues of your clothing affect your personal climate, Earth’s surface features collectively manipulate global climate.

Earth’s net albedo, or the percentage of incoming solar radiation reflected back into space, changes with shifts in surface features. It is susceptible to cloud cover, vegetation growth, and even your wardrobe choices. My particularly pale geologist friend jokes that she increases Earth’s albedo when she bares her skin outside — and she’s right.

While everything under the sun does contribute to Earth’s net albedo, only vast expanses can significantly manipulate Earth’s climate. Polar sea ice, for example, is an especially important component of net albedo because it is far reaching, highly reflective, and dynamically involved in global climate as follows:

When sea ice melts, it exposes dark, heat-absorbent open ocean which, in turn,

  1. decreases net albedo,
  2. increases regional heat absorption,
  3. induces further melting,
  4. further decreases net albedo,
  5. further increases regional heat absorption,
  6. and ultimately warms global climate.

This is the sea ice-albedo positive feedback loop.

So why doesn’t sea ice melt away completely during polar summers? Because albedo is just one knob on Earth’s natural thermostat, which hosts many other knobs working in tandem to maintain a relatively stable climate system. ESA’s new ice thickness mapping program will help determine the future stability of this thermostat. Meanwhile, stay tuned for next week’s post on the Solubility Pump: an Oceanic Cooling System to learn how ocean chemistry balances global climate.

Posted by Laura Poppick, Assistant Editor of Maine Climate News.

Loops of Change is a weekly series through July exploring the major positive feedback loops that drive climate change.

Image Description: map of sea ice thickness in the Arctic ocean

‘Climate Change in the American Mind’

Today, 97 percent of American scientists agree that climate change is happening. According to a survey published in May 2011 by the Yale Project on Climate Change Communication, only 13 percent of Americans know of the near universality of this consensus.

The Yale Project on Climate Change Communication is one of many emerging efforts addressing the disconnect between climate science advancement and communication (see also Climate Central). These initiatives aim to strengthen public engagement with cutting-edge climate science by offering outlets of accessible and relevant climate science news.

The Maine Climate News Blog joins this effort by addressing fundamental concepts in climate change and discussing related recent findings. During the month of July, our theme will be Loops of Change: the Positive Feedback Loops that Drive Climate Change. We will explore a different positive feedback loop each week, gradually illustrating the extended web of Earth-Ocean-Atmosphere interactions that drive climate warming.

Stay tuned for next week’s installment, Sea-Ice Albedo: Earth’s Chilling Reflection, and for intervening updates on climate-related events in Maine!

Laura Poppick
Assistant Editor, Maine Climate News

Image Description: 'Climate Change in the American Mind' cover, image of earth


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