The importance of solar insolation on temperature variations for the past 110 kyr on the Chinese Loess Plateau

The Chinese Loess Plateau is a large source of agriculture and home to the Yellow River, and thus plays an important role in Chinese civilization. Understanding how weather patterns and climate change affect the area is key to being able to prevent any major changes in the future. Since the 1960s data have been compiled on the monsoon patterns in the area, however there are few data on temperature changes. This gap is important to close if models and complete records are to be produced. Gao et al. (2012) collected temperature proxies in the Lanjian region of the Loess Plateau, using tetraether lipids from bacteria. Their findings suggest that insolation is the main driver behind temperature changes for the past 110 thousand years (ky). Their data records match up with other local records, as well as with global forcing records. The data the authors compiled will aid in creating more accurate models for understanding possible affects of climate change on the Loess Plateau. –Mathew Harreld
Gao, L., Nie, J., Clemens, S., Liu W., Sun, J., Zech, R., Huang, Y. 2012. The importance of solar insolation on temperature variations for the past 110 kyr on the Chinese Loess Plateau. Palaeogeography, Palaeoclimatology, Palaeoecology 317–318, 128–133.

            Local and global monsoon patterns are important indicators of climate shifts. On the Chinese Loess Plateau there are some of the best archives of monsoon profiles in the world, allowing scientists to recreate the East Asian Monsoon pattern for the past few million years. This information allows for the recreation and understanding of past local and global climates. Furthermore, the data collected have important implications for predicting future monsoon rainfall variations, especially in global warming scenarios. The Chinese Loess Plateau has a rich archive of surface soil magnetic properties, oxygen–18, and grain sizes, which all contribute to creating rainfall records. Because of the abundance of these proxies the rainfall patterns in the Chinese Loess Plateau are well understood. However, the temperature variations throughout the same periods are not very well documented. Gao et al. attempt to address the issue of missing temperature data by using tetraether lipids from bacteria in conjunction with known climatic forcings. Temperature plays one of the most important roles in understanding a climate, through the use as the primary source to parameterize climate models, through its influence on other proxies, and through its insight on local mountain glacier activities.
            Gao et al. compiled data from the Lantian region of the Chinese Loess Plateau. To optimize their data’s accuracy they compared it to recently published, high-resolution data sources. The differences between their data and the other sources are mostly due to general location, and thus different weather affects, and different modelling techniques.
            Variation in the Lantian region’s temperature matches closely with Northern Hemisphere absolute insolation maximum at 35°N. Thus, it seems likely that the insolation forcing of the sun and earth’s orbit drives temperature changes in this region. Maximum (94, 72, 22.5 ka) and minimum (105, 81, 58, 10.8 ka) insolations match with Lantian temperature maximum and minimum. The authors propose that insolation has such a large impact because of the postive feed back loop of monsoon intensities being increased greatly by high summer insolations, which then trap more heat, resulting in even higher temperatures. However, increased monsoon strength does not always occur along with higher temperatures because changes in insolation strengths don’t match up with monsoons changes.
            Another potential influence on temperature is changes in atmospheric CO2 levels. Increased temperatures coincide with high CO2 levels, and vice versa. This is to be expected on larger time scales, however on the short term it is more difficult to get a accurate understanding. The results found by Gao et al. further suggest the relationship between CO2variation and large scale temperature variations on the Chinese Loess Plateau.
            Glacial records from the nearby Tibetan mountain ranges show maximum local glacial advance earlier than global values. This is fairly common throughout the world, and is most likely due to abundant moisture availability and local cold temperatures. And the data compiled by the authors is consistent with other data compiled in the region. Furthermore, the lowest temperatures in the record are around 30 and 22.5 ka, which designates the local last glacial maximum. Temperatures increased rapidly from 22.5 ka years on, increasing about 9°C. This warming in earlier than global values, but this is also not unusual for local climates.
            Compiling a record of temperatures in the Lanjian region will greatly enhance understanding of monsoon changes in the past, as well as aiding in creating climate models for the region so we can begin to better understand future changes under climate change. It is clear that insolation is the main drive in temperature change in the Chinese Loess Plateau, and therefore any insolation maximum combined with monsoon changes and other climate change effects might vastly change the Chinese Loess Plateau region.

The Formation of Supercontinents, Old and New, based on the Orthoversion Model

The formation of supercontinents is a relatively unknown phenomenon, especially since humans have never observed it. But in understanding the processes of supercontinent formation, we may be able to predict future changes in Earth’s surface and mantle for millions of years to come, while also aiding in our understanding of Earth processes. Two theories predominate as to how supercontinents form: introversion and extroversion. Introversion postulates that a younger and interior body of water will close, forming a supercontinent in its place. Today this would be the closing of the Atlantic Ocean, about where Pangaea was located. Extroversion postulates that an older and exterior body of water will close, forming a supercontinent in its place. Today this would be the closing of the Pacific Ocean, opposite of where Pangaea was located. However, both of these theories have gapping holes in them, especially when compared to geological evidence of mantle movement, both in more recent times and on the million-year timescale. Mitchell et al. (2012) have proposed a new model, orthoversion. Orthoversion is the formation of supercontinent in the downwelling girdle of subduction (today the “ring of fire” in the Pacific) orthogonal (90°) to the predecessor supercontinent. Using seafloor spreading patterns and changes in paleomagnetic poles, the authors were able to recreate potential centers of former supercontinents Pangaea (~200 million years ago (Mya)), Rodinia (~600 Mya), and Nuna (~1000 Mya). Then using their orthoversion model, they were able to recreate the movement of continents from one supercontinent to the next. The significance of their model is that it clears up the gaps present in the other models. The orthoversion model provides the missing link in Pangaean formation, and is the only model that matches ocean records in showing that the Pacific Ocean rift has only existed since the creation of Pangaea. By creating and presenting the orthoversion model, Mitchell et al. have shown that orthoversion explains the connection between supercontinent decline and growth, and many other gaps in the other two. –Mathew Harreld
Mitchell, R.N., Kilian, T.M., Evans, D.A.D. 2012. Supercontinent cycles and the calculation of        absolute palaeolongitude in deep time. Nature 482, 208–211.

            It is now well-known that millions of years ago a “supercontinent,” named Pangaea, dominated Earth’s landscape. Since its formation about 200 million years ago (Mya), the continents, as we know them now, have been shifting. In the following millions of years the continents will continue to shift, once again forming a supercontinent, already named “Amasia”. Understanding the processes of how Amasia might form requires discovering how the supercontinents of the past have formed. Two general theories are prevalent in today’s scientific literature: introversion, extroversion. The introversion model is based on the idea that young interior oceans stop forming and then begin to close, creating a collision between two landmasses. In today’s terms this would mean the closing of the Atlantic Ocean, and the collision of the Americas, Europe, and Africa. This will mean Amasia will form where Pangaea once was. Extroversion is the process where the relatively older, exterior ocean closes, forming the supercontinent in its place as two landmasses collide. In today’s terms this would be the closing of the Pacific as Asia, Australia, and the Americas collide, forming Amasia opposite of where Pangaea formed. However, both of these theories have deep gaps in their explanations, especially when compared to geological evidence. Mitchell et al. have developed a new theory called orthoversion. Orthoversion is the prediction that a supercontinent will form orthogonal (90°) to its predecessor, in a region of downwelling, and in the subduction girdle formed by its predecessor. Today this would result in the closing of the Arctic Ocean, as North America and Northern Europe meet to form Amasia. Amasia would be formed in the Pacific region, based around the Pacific’s “ring of fire”, and eventually close the Atlantic Ocean and the Caribbean Sea. Each of the models shows that Amasia will be formed with Asia at its center.
            To show that any one of these models is more accurate than the others in forecasting the future, the models must first recreate the past. Using their orthoversion model, Mitchel et al. are able to show that previous supercontinents have orthoverted from one to the next, all the way back to 1000 Mya. By creating a model based on geological records of landmass centers and supercontinent centers, the authors were able to recalculate their movement, based on of the orthoversion model. The landmass and supercontinent data are acquired from seafloor-spreading records that allow for the precise calculation of Pangaea’s center. Then by working backwards they are able to recreate the older supercontinents, Rodinia (~600 Mya) and Nuna (~1000 Mya).
            Their results match what little understanding we do have of what these older supercontinents looked like. What is more important, however, is that authors’ method for deriving these supercontinents match movements being observed in the Earth’s mantle, and movements of the mantle in the past that have been reconstructed. Over a period of 800 Mya, Mitchell et al. are able to show the movement of Earth’s continents as they form one supercontinent into another, while also arriving at a picture that looks like Earth today. The orthoversion model also helps explain the movement of Australia, India, and Arabia. Each of those landmasses have moved eastward into the subduction girdle of post-Pangaea, and then moved northward. Only the orthoversion model can explain this movement. The orthoversion model also provides the missing link in Pangaean formation, and is the only model that matches ocean records in showing that the Pacific Ocean rift has only existed since the creation of Pangaea. By creating and presenting the orthoversion model, Mitchell et al. have shown that orthoversion explains the connection between supercontinent decline and growth, and many other gaps in the other two theories.
            

Recent contributins of glaciers and ice caps to sea level rise

Yearly glacier and ice cap melt contributes sea level changes. How the rate of this contribution to sea level changes is very important in understanding changes in Earth’s climate. Jacob et al. (2012) use the Gravity Recovery and Climate Experiment (GRACE) satellite to calculate changing masses of glaciers and ice caps around the world from 2003 to 2010. These values allow the authors to calculate the changes in the sea level. Their findings show that there are increasing rates of loss in most areas of the world that are ice-covered. The full contribution of ice mass loss around the world to sea level change is about 1.48±0.26 millimeters per year. However, their data did show difference from previously published work in some regions, specifically in High Mountain Asia (Northern India and the Himalayas). Looking at their data and the previously published data in more detail revealed that their data were most likely accurate, as there were little reasons for GRACE to miscalculate the data in the region. Furthermore, the final rate of change is sea level rise is nearly identical (difference of 0.2±0.6 millimeters per year, which is not significantly different from zero) to other recent studies that focus on physical calculations of sea level change. This paper demonstrates the firm understanding of glacier and ice cap contribution to sea level change in the scientific community. –Mathew Harreld
Jacob, T., Wahr, J., Pfeffer, W.T., Swenson, S. 2012. Recent contributins of glaciers and ice caps    to sea level rise. Nature (Online) 1-5.

            A major concern in a changing climate is its the impact on sea level changes. The melting of glaciers and ice caps throughout the world mostly drives the changes in sea level. Rising global mean temperature could mean a faster rate of glacier and ice cap melting, which in turn will increase sea level. The big question, however, is how much. Many studies have been done recently to calculate the changing sea level due to glacial melt, but Jacob et al. reevaluate those studies with one of their own. Using the Gravity Recovery and Climate Experiment (GRACE) satellite to calculate changing sea levels due to changing masses of glaciers and ice caps in the 8 year period from 2003 to 2010.
            GRACE observes monthly, global gravity field changes, allowing the authors to calculate changes in mass on Earth’s surface. Using data compiled from GRACE the authors calculated the rate of loss or gain of glaciers and ice caps from around the world, and converted that data into rates of sea level rise. The data from GRACE were split into 175 small arbitrarily defined regions of Earth, called “mascons”. The 175 mascons were then grouped into 20 regions based on location on the Earth’s surface. GRACE does not have high enough resolution to separate Greenland and Antarctic ice sheets from their peripheral glaciers and ice caps, and therefore the main part of the study focused on results without the peripheral glaciers and ice caps. The authors, however, used a different source for the peripheral glaciers and ice caps for the sake of completeness in their final results.
            The results without the peripheral glaciers and ice caps showed increasing rates of loss in most areas of the world. The authors do note that certain areas show positive increases in rate, but that the increases are not significantly different from zero. The total mass of glacier and ice cap rate loss between 2003 and 2010, with the peripherals,was calculated to be about –536±93 gigatons per year. The peripheral glacier and ice caps contribute about –236 gigatons to the total amount, a significant amount. Since the peripheral glacier and ice cap amounts were not derived from GRACE, the amounts could be brought into question. The authors calculated that the –536 gigaton per year loss of glacier and ice caps contributed to an increased rate of 1.48±0.26 millimeters per year of the sea surface between 2003 and 2010. The peripheral glaciers and ice caps contributed about 1.06 mm per year to the total.
            The findings of this paper were similar to the results of other papers, except for the High Mountain Asia region (Northern India and the Himalayas), which the authors calculated to have a much lower rate of loss than reported in another paper. A paper used GRACE to evaluated glacier and ice cap changes between 2002 and 2009 and determined that the same region rate of loss was around –55 gigatons per year, whereas Jacob et al. determined it to be around –4 gigatons per year. Due to this large discrepancy the authors decided to evaluate the region in more detail. It is possible that changes in the tectonic process under the region could be causing Jacob et al.’s difference in data, but this seems to be unlikely for a number of reasons. The amount of tectonic uplift needed to cause the large discrepancy is unlikely to work on such a short time period, or occur. For GRACE to not pick up these changes is even for unlikely, for the broad spatial changes must occur on a hundred to thousand year timescale. Another possibility is the absorption of melt water by the ground, effectively showing no change in mass in the studied area, when in fact the glaciers have decreased in size. But this too seems unlikely to contribute a large enough offset to result in such drastically different data.
            The authors determined that their derived data were accurate enough to add validity to changes in sea level rise. Their final results suggest that ice-covered regions are contributing an increase in sea level rise at a rate of 1.48±0.26 millimeters per year. Their findings differ from previous findings based on water-based measurements by 0.2±0.6 millimeters per year, which is not significantly different from zero. This suggests we have an accurate understanding of sea level changes due to glacial and ice cap melt. Future work needs to work on consolidating the data, and region changes.

The Weakening of the North Atlantic Current During the Late Pliocene and Early Pleistocene

The role of the North Atlantic Current (NAC) in regulating the Northern Hemisphere sea surface temperature (SST) gradient and the air temperature is huge. If the current were to weaken or stop, the effects could be drastic. Roughly 2.6 Ma that is exactly what happened, resulting in a major glacial event. Naafs et al. (2010) address how big an impact the NAC had on changing the climate, and show how the NAC may have weakened. Using coring samples from the middle of the Atlantic Ocean, Naafs et al. reproduce SST and productivity, to show how both change over time, and what those changes mean for the NAC. The shift of the Arctic Front southward, and the slow weakening of the NAC led to a major glacial event, changing the face of the planet. The findings of the authors highlight the long-term nature of change in Earth systems, while also showing how drastically they can be changed. –Mathew Harreld

Naafs, B.D.A., Stein, R., Hefter, J., Khélifi, N., Schepper, S.D., Haug, G.H. 2010. Late Pliocene changes in the North Atlantic Current. Earth and Planetary Science Letters 298, 434-442.

The North Atlantic Current (NAC) is hugely important in regulating the northern hemisphere climate. Warmer surface waters are pulled northward toward the Arctic Ocean, and some is downwelled into the deeper ocean, while some is sent back southward. This explains why England is more temperate than the Eastern Seaboard of the United States even though it is at a higher latitude. It is the warmer tropical waters from the south that keep the northern Atlantic Ocean at temperate temperatures. A topic of debate in current research is how might the slowing and stopping of this current affect local temperatures, and how might the NAC slow down. Naafs et al. raise this question in a previous epoch of Earth’s history. During the early Pliocene epoch, roughly 5 million years ago (Ma), there were warmer sea surface temperatures (SST) in the Northern Atlantic Ocean than there are today by nearly 10°C. This higher temperature meant that the NAC was more powerful than it is presently. However we also know that around 3.6 Ma an intense Northern Hemisphere glacial and interglacial cycle period began. Around 2.6 Ma, at the beginning of the Pleistocene epoch, the Earth fell into its first major glacial period that exhibited large Norther Hemisphere ice sheets.

During this shift into a deep glaciation the NAC is thought to have shifted dramatically. The extent of of the Arctic Front extends into lower latitudes, as ice sheets expand, and therefore there must be some change in NAC, which is carrying warmer waters that would otherwise melt the forming ice. In order for the ice to be expanding, and temperatures to be falling the NAC must have shifted. Naafs et al. hypothesize that that the NAC flattens out at a lower latitude, possibly even shrinking, while the Arctic Front expands southward, weakening the NAC. To test their hypothesis Naafs et al. use Deep Sea Drilling Project core samples from a site in the middle of the Atlantic Ocean on a latitude of 41°00’N. The core samples are used to remodel ocean productivity, which acts as a proxy for global average to temperature, and SST. They purposely chose a site that is currently right in the middle of the NAC because they believed it would show a greater effect of change in glacial conditions.

Having acquired the core samples, the authors used oxygen-18 data and organic compound data to remap SST and productivity. Oxygen-18 allowed the authors to remap SST because in colder temperatures there is more oxygen-18 present in oceans because oxygen-16 (a lighter isotope than oxygen-18) is frozen in the ice. The organic compounds allowed the authors to see levels of productivity because a higher level of organic compounds meant there were more organisms living in that area at that time. It should also be noted that there are higher levels of productivity when there are lower SSTs because that means there is less influence from the NAC, which would allow more nutrient-rich waters to stay in the area. Using both of these variables the authors were able to put together changes in SST and productivity, giving a better understanding of how the NAC might have changed over the million-year period being studied.

During mid/late Pliocene there were generally low levels of oxygen-18 in the oceans, reflecting high SST. This combined with the generally low amounts of organic compounds meant that there was a highly intense NAC affecting the coring area about 3.6 to 3.4 Ma. During this time, however, there are also periods of lowering SST and increasing productivity, but not enough to suggest any major shift.

In the period between 3.4 and 3.29 Ma there began a shift toward lower SSTs, and lower productivity. This suggests that the NAC was weakening of this time, but not enough to allow for nutrients to flow back into the area. This period also saw the beginning of the move of the Arctic Front southwards, and the initial build up of glaciers.

The next 0.5 million years saw the ocean return to a warmer climate. SSTs rose and productivity decreased, suggesting an increased influence of the NAC and a northern Arctic Front. This period did see a gradual shift downward of SST, but nothing like what was seen between 3.4 and 3.29 Ma.

Between 2.9 and 2.45 Ma SSTs plummeted and an increase in productivity was seen. The authors mention that there may be many factors that may have influenced an increase in productivity, but that such a large increase—more than 10 times—in productivity could only be attributed to the weakening of the NAC. This period at the end of Pliocene saw a significantly reduced NAC and a much lower latitude Arctic Front. The changes observed in the core sample are remarkable, and are supported by other findings in other core samples in the Northern Atlantic region.

The change that is expected in the NAC during a glaciation period is exactly what the authors predicted. The combination of increased ice albedo (reflectivity) and eastward movement of the NAC could have brought on the glaciation period. However there are still some variables that are not well understood about how the NAC could change so drastically. The authors suggest that perhaps changes in wind forcings may have played an important role, as might have orbital forcings. Either way it seems certain that the slowing and weakening of the NAC, pushing it southward, played a pivotal role in producing ice sheet growth southward, and drastic temperature drops in the higher and mid latitudes. The article also highlights the long-term nature of the changes that affect our planet greatly. And while it may be possible to predict such changes in their beginning stages, the full effects will not be observed for thousands or millions of years.

CO2 has a Major Role in Driving the Antarctic Glaciation 33.7 Million Years Ago

The Antarctic glaciation that occurred about 33.7 million years ago is a major turning point in Earth’s history. Pagani et al. (2011) look back to this glaciation to see what may have caused it, with a focus on CO2. Previous work done on CO2 levels during this time period have shown that CO2 was increasing, which contradicts greenhouse gas theory. However, Pagani. et al. determine that CO2 was overestimated, and that, in fact, CO2 was decreasing well before and during the Antarctic glaciation. This finding is pivotal in our understanding of how CO2 and the glaciation cycle are interlinked. –­Mathew Harreld
Pagani, M., Huber, M., Liu, Z., Bohaty, S.M., Henderiks, J., Sijp, W., Krishnan, S., DeConto, R.M., 2011. The role of carbon dioxide during the onset of Antarctic glaciation. Science 334, 1261–1265

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            About 33.7 million years ago a major glaciation in the Antarctic shifted the climate towards what it is today. The onset of this Antarctic glaciation has been studied intensively because CO2 levels at the time of its occurrence seem counter intuitively high. Previous papers have suggested that CO2 was increasing along with the new glaciation, but this is counter to current theory and understanding of the relationship between temperature and CO2. Pagani et al. revaluate the alkenone (a substrate found in phytoplankton)-based record to determine why this counter intuitive finding may be occurring. A more recent paper did, in fact, model global CO2 levels during the period to be decreasing, but used boron records to develop CO2 levels. Pagani et al. explored this curious contradiction, and looked to use alkenone records to correctly model CO2 during the Antarctic glaciation 33.7 million years ago.
            To evaluate the CO2 during the glaciation period, the authors used the same coring samples used by previous papers that used alkenone. The drilling sites were spread throughout the Atlantic, mostly near South America and the Southern Ocean, and one near New Zealand. Two of these drilling sites show evidence of increasing CO2 levels throughout the glaciation period, however the quality of the cores is very poor.
            The authors used the carbon-13 values from the alkenones from six drilling sites, allowing for a wide range of environments and algal-growth patterns. The carbon-13 is derived from methyl ketone, which is found in the coring samples. The authors also used carbon isotopes levels to determine algal growth. Using various testing methods the authors compiled the algal growth and carbon-13 values. Their analysis provided evidence for lower carbon-13 and algal growth levels in the Antarctic region than in northern regions. However the results here do not show lower levels than reported previously.
            The authors than ran tests on how cell size may affect the levels of CO2 in the oceans, but determined that the changes in cell size, which varied by location, had more to do with the available nutrient cycle than that of CO2. The authors also attempted to remodel possible ocean dynamics, which revealed that there were indeed lower levels of nutrients in the study region, as well as differing levels of other key materials used to study and calculate CO2. Many of the sites initially picked for this study are not of use because of this finding. The uncertainty of temperature and nutrient cycles in lower latitude regions makes it very difficult to determine CO2 levels, so the authors refocused their work on two sites at higher Southern latitudes, which are less susceptible to effects of the variables.
            The results from these two sites revealed that CO2 declined about two million years before the rapid glaciation, and that the decrease continues into the event. There are possible places where CO2 increased, but full evidence is still lacking. This paper’s results determined that previous papers did not take full account of pre-glaciation values, and thus were left with poorer results. The results from this paper and from boron-based testing match with model estimates of this Antarctic glaciation. The authors concluded that there was a certain CO2 decline during the period, but cannot yet determine the absolute values.
            This paper highlights the important role CO2 may have on affecting climate, and that CO2 decrease is critical for global cooling to occur and for the evolution of Earth’s cryosphere. The decrease in CO2 had a great effect on the earth’s climate 33.7 million years ago, but it didn’t act alone. The combination of long-term decreasing CO2 as well as many other important factors pushed the Earth’s climate into a long glaciation.

The Mathematical Proof that Obliquity and Precession Drive Glaciation Cycles Together

Glaciation cycles having been driving the Earth’s climate system for millions of years, changing the face of the planet every hundred thousand years or so. How these cycles began, why they began, how they continue, and how they might affect us in the future are large questions being asked by scientists today. The timing of glaciations is driven largely by orbital forcings of the Earth, in theory. Huybers (2011) attempts to quantify how two of these forcings, obliquity and precession, drive glaciations. Using oxygen-18 records Huybers is able to create a model and equation that shows how obliquity and precession cycles come together about every 10,000 years to drive an interglaciation period, that correlates with the oxygen-18 record available. Huybers’s work is an important step it turning a theory into mathematical understanding. –Mathew Harreld

Huybers, P., 2011. Combined obliquity and precession pacing of late Pleistocene deglaciations. Nature 480, 229-232.

The earth system is driven by many factors, but there are a few factors that dominate the pattern of climate change. One of these major factors is the glaciation cycle that has existed for the past million years. How these cycles began, why they began, and how they are changing are key questions to understanding our greater earth system. Early in the 20th century a scientist named Milutin Milankovich proved that the major drivers of the Pleistocene era glaciations were orbital forcings, and calculated how those orbital forcings changed. Milankovich hypothesized that changes in orbital eccentricity, changes in Earth’s obliquity, and precession, changes in the orientation of the spin axis with respect to Earth’s orbit affected the northern hemisphere insolation (solar radiation) levels. He determined that these affects came together to drive the glaciation cycles over first 40,000 year cycles (40 ky) and then 100 ky cycles. However, the technology and data available to Milankovich kept him from ever proving that obliquity and precession actually worked together in changing the Earth’s climate.

The understanding of how obliquity affects earth climate systems is now well understood, but many gaps remain in understanding precession and how the two might work together if at all. Huybers (2011) attempts to show that precession does in fact play a key role, and does so in conjunction with obliquity, while suggesting a larger role in southern hemisphere climate changes than previously believed.

The difficulty of proving the effects precession has on the earth’s climate comes down to its shorter cycle compared to that of obliquity. Obliquity changes on a 41 ky year cycle, however precession changes on a 26 ky cycle, making the mathematical proof sensitive to timing errors. Huybers takes the first steps forward in proving the affects of the precession cycle by using new statistical tests that nearly remove the timing errors.

Using oxygen-18 dating of layers in ice cores taken from ice sheets scientists have long been able to map the changes of glaciations for the past million years. The changes in these cycles from glaciations to interglaciations occur approximately on a 100 ky cycle. Huybers evaluated the combined affects of obliquity and precession to determine if they correlated with Milankovich maximums, the deglaciations. His first step was to estimate the time of the terminations (the maximums) using delta oxygen-18 records, as well as geomagnetic reversals. Second, Huybers defined insolation using a generic and broad formula that takes into account obliquity, precession, time, perihelion (point closest to the sun on earth’s orbit), and aphelion (point farthest from the sun on earth’s orbit). The equation allowed Huybers to model Milakovich’s hypothesis about warmer and longer Northern Hemisphere summer by setting certain parameters. Lastly, Huyber calculated a median value of the forcing maxima corresponding with termination points (Milakovich maximums). This method is key to Huybers work because it greatly detaches his results from timing errors. Median values are less sensitive to timing errors because only wrong forcing cycles could cause them and because median values’ outliers have little effect on the result.

What Huybers found was that both precession and obliquity are important in determing the patterns of glacial terminations.

Both obliquity and precession play important roles in affecting insolation during the periods of termination, and thus both affect the glaciation cycle. Also, the known cycle of obliquity and precession match up so that precession achieves a maximum during every above-average obliquity period. However, more research must be done to determine if precession affects the precise timing of terminations, especially during the early Pleistocene. Huybers also notes that when the summer solstice occurs near a perihelion for the northern hemisphere, the southern hemisphere also has longer summers at the aphelion, potentially releasing more CO2, and potentially aiding in the rate of deglaciation. This relationship highlights the complexity of the earth system, as well as the deep interconnectedness shared between the planet, the local forcings, and the sun.

No Correlation Between Yield Production and Biodiversity in Large-Scale Farming

There is a growing concern about the amount of food being produced and the growth of the human population. In an effort to meet the demands of population growth it is feared that many natural habitats will have to be replaced by agricultural land. This would be hugely detrimental to biodiversity, especially in tropical regions, which are home to most of the world’s biodiversity and 13% of human agriculture. Although more wildlife-friendly agriculture practices have been put forward, they are rarely used on a large scale because it is believed they decrease the total yield. Clough et al. (2011) explore this argument in Indonesian cocoa agroforestry plantations. They discovered that there is no correlation between biodiversity and agricultural yield, opening up many possibilities in large-scale wildlife friendly agricultural practices. They also explored possible ways to benefit yield and biodiversity in trees and birds, giving an example for a new way of thinking about farming and biodiversity conservation. While their findings do not suggest that wildlife friendly farming practices will end the depletion in biodiversity, as primary forests still are home to many more species than any other area on earth, it is a step forward as we attempt to feed our growing population and conserve the planet and the other species on it. –Mathew Harreld
Clough, Y., Barkmann, J., Juhrbandt, J., Kessler, M., Wanger, T.C., Anshary, A., Buchori, D., Cicuzza, D., Darras, K., Putra, D.D., Erasmi., S., Pitopang, R., Schmidt, C., Schulze, C.H., Seidel, D., Steffan-Dewenter, I., Stenchly, K., Vidal, S., Weist, M., Wielgoss, A.C., Tscharntke, T. 2011. Combining high biodiversity with high yields in tropical agroforests. PNAS 108:20, 8311–8316.

       The importance of food and agriculture in our culture is unquestionable, and the global importance of agriculture will continue to grow in the years to come. As human populations grow there is an increasing demand for food. Agriculture, however, is one of the main threats to global biodiversity. As farms try to increase yields to meet increasing demands, removing natural habitats and increasing farmland is often the action taken. If wild species are to survive then a balance must be found between agriculture and biodiversity. There is the potential for biodiversity-friendly farming. This farming method is often criticized for decreasing the yield quantity because of the focus on biodiversity preservation. Clough et al. explore this argument in Indonesian cacao farms. The argument that wildlife friendly farming practices is ineffective on larger scales is put to the test. The authors evaluated the possibility of combining high species diversity and high yields and where this might be done.
       The authors chose to focus on tropical regions in Indonesia because of the high biodiversity combined with the high human populations density. Furthermore, agriculture in tropic regions compasses 13% of the total agricultural system globally, and thus is an important area for future agricultural output.
       Clough et al. broke the study into two parts: a field study and a survey study. The field study consisted of data collected on yield and species richness in nine different taxonomic groups, during a two-year period. The authors used the land of 43 smallholder cacao agroforestry system in Sulawesi, Indonesia. Only mature plots ten to twenty years old were chosen for the study. Also, the authors studied the possible relationship between biodiversity and yield as distance to a natural forest changed.
       The survey portion of the study focused on 60 cacao plantations that were run only by the owners, and were not affected by the study. Only tree species were used as a measurement of biodiversity, however other agronomic data were recorded. These data were used mostly for a better understanding of general yield patterns throughout the regions.
       The authors discovered a surprising result once their data were collected, there was little to no correlation between species richness and yield. This general lack of correlation could potentially have large impacts on farming methods, but first the authors explored what does affect species richness and yield.
       They found that differences in region and altitude had large impacts on species richness, but it was mainly associated with distance from forests and shade by trees. There was a clear negative relationship between distance from forest and species richness. Plots with high levels of trees and shade had more bird species, but had fewer light-dependent species, such as herbs and butterflies.
       Yield was mainly negatively affected by the amount of shade a plot received, however distance to forest had a small positive effect. Other variables proved to have little effect on yield. Through the survey portion of the study, it was determined that labor and pesticide use were the largest determinants of yield.
       In an attempt to find a possible method of sustaining high yields and high biodiversity the authors focused on the effects of trees, yield, and birds. They found that birds were more dependent on tree height than total amount of shade, whereas yield was affected by shade. Therefore it may be possible to increase bird habitat with taller, but fewer trees, resulting in less shade.
          This study reveals that it is possible to have wildlife friendly farms that produce high yields. These findings suggest that wildlife friendly policies can be, and should be, implemented in agriculture without fear of yield loss. The authors also caution that their findings may be inaccurate because there may be a lag in time between the presence of farms and their effect on biodiversity. This is why the authors chose the most established and mature agroforestry sites. More data need to be collected to continue to record the effects on the practices of wildlife friendly agricultural on biodiversity and yield. At first glance, though, the findings of Clough et al. are quite stunning and exciting, leaving the potential for new wildlife friendly farming practices that produce high yields for a growing human population.

Genetically Modified Crops Benefit Biodiversity and Human Sustainability

The use of genetically modified crops in commercial agriculture has been in debate for many years now, and there exists a worry of how these crops may adversely affect humans, as well as other species. Carpenter (2011) reviews journal articles related to the effect of genetically modified crops on biodiversity, focusing the review on crop diversity, effect on non-target soil organisms, effect on target pests, changes in farming practices, weed diversity, use of pesticides and herbicides, and several other topics. The overall findings of Carpenter are that genetically modified crops have near negligible effects on non-targeted species, while being successful at reducing targeted species populations. There is also evidence that genetically modified crops are already aiding biodiversity by increasing farming yields, reducing the amount of land needed to convert from natural habitat to agricultural land. The increased yields, due to successful reduction of pests, has also resulted in more beneficial farming practices, including more conservative tillage practices and decreases in pesticide and herbicide use. The introduction of genetically modified crops has the potential to be extremely beneficial to both humans and our efforts in preserving biodiversity. –Mathew Harreld
Carpenter, J.E. 2011. Impacts of GM crops on biodiversity. Landes Bioscience 2:1, 1–17.

          High crop yields are essential as the human population continues to grow. Genetically modified (GM) crops offer an opportunity to increase our crop yields, but what effect do genetically modified crops have on the surrounding environment? Carpenter reviewed research papers and review articles on the effect GM crops have on crop diversity, non-target soil organisms diversity, weed diversity, land use, target organisms, non-target above ground invertebrates, birds, tillage practices, and pesticide use. Using this framework Carpenter was able to outline the potential effect of introducing GM crops on biodiversity. From the beginning it is clear that the largest threat to biodiversity is the conversion of natural habitats into agricultural land. Reviewing the impact of GM crops will give us a better sense if the benefits of GM crops outweigh the costs.
          The first issue at hand is changes in crop diversity. Over the history of commercial agriculture our crops have become less diverse as we seek to improve the economic efficiency of their production. This has the potential to put strain on our crops’ genetic resources, potentially lowering yield, pest resistance, and quality. The use of GM crops could be a source of re-diversifying our crop selection. The GM genetic strains might mix with wild strains, creating more diversity. It might also be the case that with GM crops lesser used, and previously less cost efficient crops, will be revitalized due to the development their GM varieties; sweet potato is one such example.
          The quality of the soil is regulated not as much by what fertilizers we add, as by the organisms that live in it. Fungi and invertebrate species play key roles in sustaining arable soil, and therefore it is important to understand the effect GM crops might have on them. Carpenter used a review of 70 journal articles, which stated there was little to no impact on soil organisms due to the introduction of GM crops. There have been reports that GM crops adversely affect microbial communities, but most of the effect is thought to be due to differences in geography, temperature, plant variety, and soil type. Papers published after this review reached similar conclusions of little to no effect on soil organisms by GM crops. One of the few documented adverse effects was that long exposure to GM corn as the only food source, reduced the growth of snails. From these articles it is clear that GM crops have little impact on soil organisms, and what impact might exist might be due to regional abiotic differences.
          The presence of weeds in farming communities has a large impact on local biodiversity. The more weeds present in an area the more herbicide needed, and more weeds will result in changes of tillage practices. In reviewing journal articles, Carpenter has found that the introduction of GM crops has resulted in declines of weed populations. In the U.S., a survey in six states found that farmers report a 36 to 70% decline in weed pressure. A study done in the U.K. found that introduction of GM sugar, beet, and oilseed rape resulted in declines of weeds and weed seed, but GM corn resulted in increased weed numbers. This resistance in corn fields is most likely due to the development of new strains of glyphosate resistant (GR) weeds, but however there are few reports of such weeds found globally.
          As mentioned earlier, the most direct adverse effect on biodiversity is the conversion of natural land to agricultural land, so Carpenter’s results show GM crops are more productive and require less land. Carpeter shows that GM crops increase crop yields from 0 to 7% in developed countries and 16 to 30% in developing countries. Thus, GM crops have the potential to save biodiversity by allowing farmers to avoid converting natural lands.
          Perhaps one of the more important direct aspects of use of GM crops is their effect on targeted pest species. Papers from around the globe unanimously show that GM crops decrease the levels of pest populations. Studies in China, California, Arizona, Mississippi, and Maryland all show declines in their respective pest populations over time. This has a very positive impact on other species biodiversity as the increase in pest control results in decreased use of pesticide.
          The effect of GM crops on above ground invertebrates has been found to be negligible. Over 360 journal articles were reviewed that covered this topic, and they almost all support the use of GM crops when compared to their effects against non-target invertebrates. Papers that did find that beneficial species were declining due to the introduction of GM crops due to inadvertent poisoning through multitrophic exposure lose of prey, or reduction in prey quality, stated that these effects were nothing compared to the effect that physical agriculture practices had on these species.
          The effect on birds was counter to theory; the decreased levels of invertebrates and weeds due to the introduction of GM crops was thought to decrease bird population levels, however crops of GM sugar beet and maize were found to have increased bird populations. This may be due, however, to local changes in bird populations outside of the introduction of GM crops.
          Another very important change in agricultural practices due to the introduction of GM crops is the change in tillage practices. With the introduction of the stronger, more resistant GM crops farmers are adopting conservative tillage and no-tillage policies. Tillage disturbs the land, and hastens erosion, as well as releasing herbicides and pesticides beyond the farmland. Introduction of GM crops aid in reducing these adverse effects.
          The introduction of GM crops, on a whole, seems to provide many more benefits than not. While there have been cases of GM crops hurting farming production, this has not been the case for most adopters. Carpenter concludes that the use of GM crops will greatly aid our fight to feed our growing population, while supporting our efforts to preserve local biodiversity. Many of the opined adverse effects of GM crops, if they exist, seem to be negligible. Thus, the future of GM crops is positive, especially as new technologies continue to be developed. The use of GM crops in commercial agriculture may go a long way to aiding efforts to preserve natural habitats.

The Need for More Research and More Conservation in Tropical Biodiversity

Tropical rain forests are home to most of Earth’s biodiversity. It is therefore paramount to understand the potential impacts human disturbances in the tropics have on biodiversity. Gibson et al. (2011) combine 138 studies to create a global meta-analysis on the impact of human disturbances on tropical biodiversity. The effect of humans differs throughout the world, but is present everywhere. Southeast Asian taxa show the largest sensitivity to human development, while birds are the hardest hit taxonomic group. However, not all species are negatively affected. Some mammals, specifically small mammals, benefited from human disturbances, and all mammals had a considerably lower sensitivity than birds. The resounding findings in this paper are the desperate need for more research to be done, especially in African tropics, as well as the need for conservation of primary forests. Secondary forests were potential habitats for biodiversity conservation, but this paper shows that secondary forests have substantially lower amounts of biodiversity than primary forests. Gibson et al. produce the first meta-analysis of biodiversity in the tropics, and reveal the great need for conservation efforts and for more research.—Mathew Harreld
Gibson L., Lee T.M., Koh L.P., Brook B.W., Gardner T.A., Barlow J., Peres C.A., Bradshaw C.J.A., Laurance W.F., Lovejoy T.E. 2011. Primary forests are irreplaceable for sustaining tropical biodiversity. Nature 478, 378–381.

          The preservation of primary tropical forests is key to the sustainability of biodiversity, and the dramatic increase of human development in tropical forests could have a huge impact on biodiversity. As more studies are done on the effects on biodiversity from forest degradation, we might be able to find some answers as to how to stop them. Current literature shows varied results depending on the type of impacts studied, most often reporting studies of a specific response in a specific region. Gibson et al. attempt to piece together the puzzle of biodiversity in the tropics by analyzing 138 studies. Their goal to deliver a better overall understanding of what is causing biodiversity to change and how it is changing.
          The 138 studies that were used in this study span the globe, with a focus on Central America and Southeast Asia. It is therefore important to keep in mind that the current data may be biased toward these two locations. The authors have discovered a huge gap in studies done in Africa, Central America, and India. There is a great need for more research in these areas, especially Africa since it is home to the second largest tropical forest.
          The authors used the data presented in the papers to create a metric for understanding the effect of biodiversity. Putting together the specific effects on biodiversity, they developed a standard method for understanding each paper’s specific results, allowing them to compare each of the results by region, taxonomic group, metric, and disturbance type.
          Even with this hole in the current data, the data on record reveal much. Southeast Asia, the focus of the Asian studies, is home to the most sensitive biota. The authors developed a metric of sensitivity by finding the median effect size, which was 0.51. Any numbers below zero reflected a benefit from the effects of human interference. The studies done in Southeast Asia reveal that there is an effect size of 0.95, which is much higher than any of the other regions studied. The authors suggest that this can be explained by the large increase in human development due to expansion of oil palm monoculture. Africa and South America showed effect sizes of about .35 and .42, respectively, while Central America showed an effect size of about 0.1. The stark difference between Asia, specifically Southeast Asia, and the rest of the regions demonstrates the urgent need for preventative measures against the adverse effects of human development.
          Among taxonomic groups there was little difference between arthropods, birds, and plants. Each had an effect size of about 0.6 to 0.7. Mammals, however, showed an effect size of –12, suggesting that some mammals substaintally benefitted from some human disturbances. The authors suggest that this is due to the higher abundance of small mammals in degraded forests, perhaps be because small mammals tend to have a high tolerance to disturbance. Birds showed the most vulnerability of the four taxa, however here it is important to look at what disturbance type affected each taxonomic group most.
          Birds were most sensitive to development of agricultural land, while plants are most sensitive to burned or shaded forests. Of the twelve-disturbance types, agricultural land use and abandonment had the largest impacts. The agroforestry and plantations (shaded and unshaded) were considerably lower, which is to be expected. The lowest effect was found in selective logging, however the value was still positive at 0.11. This finding is supported by other studies, which have found selective logging to preserve large numbers of local species. These findings suggest that selective logging is the best solution to preserve biodiversity. There is however still a large danger in logging. Logging and the long-term effects of logging roads through the forest have the potential to injure primary forests, increase risk of species extinction over the long-term, and further exacerbate already existing issues. So, these seemingly positive results should still be taken with a grain of salt.
          Next the authors split the various measures of biodiversity into five response metrics: abundance, community structure and function, demographics, forest structure, and richness. The most common of these metrics are abundance and richness, used in over 75% of the papers surveyed. Richness and forest structure are the most sensitive to human disturbance, with effect sizes of 0.83 and 0.7, respectively. Community structure and function was the next largest impacted, while abundance came next at 0.19. Demographics showed little effect at all. The high level of richness was deemed conservative by the authors because it considered forest specialists and generalists equally. If only specialists were considered richness would be 1.16. The authors, therefore, deem that species richness is a good measure of forest value, and how urgently conservation acts are needed.
          The need for more research is perhaps the most important finding of this study, especially in Africa. The other finding of great importance is that secondary forests are of little use in preserving biodiversity. It was believed that secondary forests may be a potential source of biodiversity habitat, but the authors have found secondary forests have significantly lower levels of biodiversity than do primary forests. The conservation of primary forests appear to be the only solution in our effort to preserve biodiversity.

The Amazon’s Growth into the Richest Area of Organisms in the World

The Amazon rainforest and the Amazon River support an abundant forest full of biodiversity. Yet, it is still a mystery as to how this region became so rich as it is today. Hoorn et al. (2010) pull together resources from around the scientific community to piece together the history of Amazonia. Their research focuses on the effect the development of the Andes had on the entire Amazonian region. The Andes changed its climate, redirected the water flow, distributed soil and nutrients, and brought a great influx of diverse species from North America down to the Amazon. Over a hundred million years the Amazon rainforest slowly developed into what it is today, but there are still many questions on how exactly this happened. Hoorn et al. attempt to answer some of these questions, while also raising more. What becomes clear is that the development of a large ecosystem, such as Amazonia, is not a simple process, but rather a long, complicated process dependent on many factors. —Mathew Harreld
Hoorn, C., Wesselingh, F.P., ter Steege, H., Bermudez, M.A., Mora, A., Sevink, J., Sanmartín, I., Sanchez-Meseguer, A., Anderson, C.L., Figueiredo, J.P., Jaramillo, C., Riff, D., Negri, F.P., Hooghiemstra, H., Lundberg, J., Stadler, T., Särkinen, T., Antoneli, A., 2010. Amazonia Through Time: Andean Uplift, Climate Change, Landscape Evolution, and Biodiversity. Science 330, 927–931.

          Protecting the Amazonian region of South America is critical in preserving regional and global biodiversity. The Amazon rainforest is home to what may be the most diverse and unique terrestrial species. The authors believe that the uplift of the developing Andes largely influenced the ecological development of the Amazonian region, and examine this thesis using a variety of new models and data in the fields of geology, paleontology, ecology, and molecular phylogenies.
In order to understand the effect the growth of the Andes had on the Amazonian rainforest, Hoorn et al. first studied the pre-Andean Amazonian region from 10 million years ago (MYA) to 135 MYA. Over the course of continental breakup (135 to 100 MYA) the Amazonian region developed the initial basins that would become home to the modern rainforest, as well as the beginnings of the mouth of the Amazon River. The tectonic plate shifts during this time also began the initial formations of the Andes Mountains. This entire region is known as pan-Amazonia, which existed up to 10 MYA, and extended past the present area of the Amazon into Orinoco, Magdalena, and sometimes into the northern Paraná region. Over the next few million years, pan-Amazonia became home to a variety of mammalian species, freshwater fish species, and even at some points saltwater fish species.
          Sixty-five to 34 MYA the movement of tectonic plates southward began creation of the Central Andes, and then about 23 MYA additional plate movement began the creation of the Northern Andes. This development also saw the first of modern plant and animal mountainous species rise in this region. About 12 MYA the region underwent its most intense mountain building. During this period the gap between South America and Panama was closed, giving way to the Great American Biotic Interchange. This brought a great number of new species to the Amazonian region from North America, furthering the diversity that was already taking place. During this time the land continued to advance, as mountains began to surpass 2000 meters in height and basins grew out of the mountainous regions. These changes in geological environment caused rainfall to increase in the southeast. The continued uplift and increased rainfall resulted in erosion and sediment dispersal. Over the next millions of years the sediments made their way westward.
          The development of the mountainous regions coincided with the development of a large wetland. The wetland, along with warmer temperatures, brought the rise of many large invertebrates, now extinct. Evidence of seasonal monsoons also gives evidence of a rapidly developing environment, as a water influx becomes a seasonal norm. Around this time there is also evidence of a rise of salinity, giving way to more marine species inland. The overall influence of these marine conditions on Amazonia is still in debate, however. The continued growth of the mountains resulted in the creation of valleys and advanced water systems. Around 10 MYA when the sea level dropped, the Amazon River became fully established by reaching the Atlantic Ocean. This also coincided with the change of the Western Amazon basin from a megawetland to more river conditions, as seen today. This change brought the end for many endemic species, and the rise of grasslands that would later give rise to the forests of today. In the last 3.5 million years the Andes have continued to rise, readjusting river patterns, and fully closing the gap between South America and Panama. The influx of North American plant and animal species, as well as African plant species played large roles in diversifying the Amazonian region during this time, creating the forest and animal species we know today.
          What these results mean for the current and future Amazonian region is still unclear, as further specific studies need to be done. However, Hoorn et al. show that tree diversity is dependent on wetter, less seasonal areas, and that animal diversity is affected by many factors that need further studying. The younger, western region of Amazonia is home to more species than the older, eastern half. This raises many questions over how diversification occurs, and what drives it. What these data do suggest is that wetter, less seasonal western Amazonia might play a key role in sustaining climates faced with change, while sustaining, and perhaps driving, diversity. What is clear is that there is no simple answer to how Amazonia became so diverse and abundant. There is no one large event in global history that single-handily affected the region, but rather it has been a mix of many events from the formation of the continents onwards.