Earth’s ocean is mixed by a complex system of currents. Downwellings occur when currents move water from the surface to the depths and upwellings occur when nutrient-rich waters are pulled from the depths to the surface. Upwelling areas are some of the most productive waters in the world, including the California Coast where part of the California Current System upwells. The waters along the California Coast are more or less productive during some years, based on the strength and timing of this upwelling. Waters are less productive during years when the winter upwelling is delayed and weaker. This upwelling strength is indexed by the North Pacific Gyre Oscillation (NPGO) – in positive NPGO years, the upwelling starts about six weeks earlier than negative NPGO years. The NPGO is an expression of the variability in the pressure difference between a high pressure center located near Hawaii and a low pressure center in the Gulf of Alaska. This variability leads to changes in the strength and position of the winds that run along the California Coast and work to “pull” a current of water from the depths. Compared to negative NPGO years, average end of winter water conditions during positive NPGO years feature nitrate concentrations that are about 25 percent higher, chlorophyll concentrations about 15 percent higher and zooplankton numbers that are about 20 percent higher. These nutrients and zooplankton  feed commercially-important fish species and seabirds.

Seasons: Winter, Spring

Sources: Chenillat, F et al. “North Pacific Gyre Oscillation modulates seasonal timing and ecosystem functioning in the California Current upwelling system.” Geophysical Research Letters 39 (2012): L01606 and Di Lorenzo, E et al. “North Pacific Gyre Oscillation links ocean climate and ecosystem change.” Geophysical Research Letter 35 (2008): L08607.

Observers during recent annual Audubon Christmas Bird Counts are noticing different birds in their local areas during the winter months than observers did in the 1960s. Between 1966 and 2005, significant northward movement of 177 out of 305 observed species was documented. Not all species moved north and a few may be wintering a little farther south, but the general trend has been an average northward movement of 35 miles. More than 60 species are now wintering at least 100 miles farther north than they did in the 1960s. General trends of species movement toward or away from the poles happen during periods of climate warming and cooling, as species seek their preferred conditions. The average temperature in January in the lower 48 states rose by over five degrees Fahrenheit from 1966-2005. This means that temperatures are now more tolerable in more northerly areas, letting birds stop their southerly migrations sooner and remain closer to the north pole during winter. In the eastern United States, the range of the Purple Finch has advanced by 433 miles over the past 40 years. This is about the distance from the Virginia-North Carolina border to southern Connecticut.

Want to help scientists collect more data about winter bird ranges? Participate in the Christmas Bird Count from December 14, 2011 to January 5, 2012.

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Purple Finch (click for image download from U.S. Fish and Wildlife Service)

Photo courtesy of Dr. Thomas T. Barnes, U.S. FWS

Source: The Audubon Society. “Birds and Climate Change: Ecological Disruption in Motion.” February 2009. Accessed Online 2 December 2011 < http://birdsandclimate.audubon.org/>

Observers during recent annual Audubon Christmas Bird Counts are noticing different birds in their local areas during the winter months than observers did in the 1960s. Between 1966 and 2005, significant northward movement of 177 out of 305 observed species was documented. Not all species moved north and a few may be wintering a little farther south, but the general trend has been an average northward movement of 35 miles. More than 60 species are now wintering at least 100 miles farther north than they did in the 1960s. General trends of species movement toward or away from the poles happen during periods of climate warming and cooling, as species seek their preferred conditions. The average temperature in January in the lower 48 states rose by over five degrees Fahrenheit from 1966-2005. This means that temperatures are now more tolerable in more northerly areas, letting birds stop their southerly migrations sooner and remain closer to the North Pole during winter. In the Midwest United States, the range of the American Goldfinch has advanced by 250 miles over the past 40 years. This is about the distance from the southern to northern border of Missouri.

Want to help scientists collect more data about winter bird ranges? Participate in the Christmas Bird Count from December 14, 2011 to January 5, 2012.

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Goldfinch (click for image download from U.S. Fish and Wildlife Service)

Photo courtesy of David Brezinski, U.S. FWS

Source: The Audubon Society. “Birds and Climate Change: Ecological Disruption in Motion.” February 2009. Accessed Online 2 December 2011 < http://birdsandclimate.audubon.org/>

Observers during recent annual Audubon Christmas Bird Counts are noticing different birds in their local areas during the winter months than observers did in the 1960s. Between 1966 and 2005, significant northward movement of 177 out of 305 observed species was documented. Not all species moved north and a few may be wintering a little farther south, but the general trend has been an average northward movement of 35 miles. More than 60 species are now wintering at least 100 miles farther north than they did in the 1960s. General trends of species movement toward or away from the poles happen during periods of climate warming and cooling, as species seek their preferred conditions. The average temperature in January in the lower 48 states rose by over five degrees Fahrenheit from 1966-2005. This means that temperatures are now more tolerable in more northerly areas, letting birds stop their southerly migrations sooner and remain closer to the north pole during winter. In the western United States, the range of the House Finch has advanced by 270 miles over the past 40 years. This is about the distance from Fresno, California to the California-Oregon border.

Want to help scientists collect more data about winter bird ranges? Participate in the Christmas Bird Count from December 14, 2011 to January 5, 2012.

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House Finch (click for image download from U.S. Fish and Wildlife Service)

Photo courtesy of Dave Menke, U.S. FWS

Source: The Audubon Society. “Birds and Climate Change: Ecological Disruption in Motion.” February 2009. Accessed Online 2 December 2011 < http://birdsandclimate.audubon.org/>

For comparison: It is about 85 miles from Indianapolis, Indiana to Fort Wayne, Indiana. Small but noticeable temperature differences between these two locations exist.

Seasons: Winter, Spring, Summer, Fall

Source: Burrows, MT et al. “The Pace of Shifting Climate in Marine and Terrestrial Ecosystems.” Science 334 (2011): 652-655.

Every place in the world has its own climate with its own average temperature and precipitation levels. Some places around the world, such as most equatorial rainforests, experience little seasonal variation and are hot and wet throughout the year. Locations closer to the poles have more seasonal climates. The Northeast United States, for example, has rainfall evenly spread throughout the year, but the summer months are much warmer than the winter months. In some locations in the tropics, temperatures don’t change much throughout the year, but there are defined wet and dry seasons. Similarly, from year to year some places have little rainfall variance while other locations can be considerably wetter or drier. Such inter-annual variability in rainfall can be particularly pronounced in parts of Amazon. Inter-annual rainfall variability in the Amazon is driven by surface temperature shifts every few years in the waters of the equatorial Pacific Ocean, and shifts on longer time scales in the tropical and subtropical Atlantic Ocean. These water temperature shifts move winds, affecting rainfall patterns on land. If it was not for the plants of the Amazon, however, this variability would be even greater. Wetter years, or years with wetter wet seasons and/or shorter dry seasons, are years when vegetation flourishes. More vegetation means more evapotranspiration, the movement of moisture from the soil through plants to the atmosphere. More evapotranspiration means more rainfall. This increase in rainfall helps to keep the wet conditions going into the next year, even if other factors would favor drier conditions. Drier years tend to stress vegetation, leading to less evapotranspiration and less rainfall, which perpetuates these dry conditions into the following year. This means that years following severe droughts, such as the “once-in-a-century” 2010 Amazon drought, may be more susceptible to further droughts. It also means that there is more year-to-year continuity of rainfall levels than there would otherwise be.

Seasons: Winter, Spring, Summer, Fall

Source: Wang, G et al. “Vegetation dynamics contributes to the multi-decadal variability of precipitation in the Amazon region.” Geophysical Research Letters 38 (2011): L19703.

• Tree Cover: As temperatures have warmed since 1970, tree cover in areas that had not been burned or logged has increased by 40 percent.
• Salamander Decline: A two degree rise in average summertime temperatures means more water is evaporating from the Park, which has impacted local salamander populations. Many of the Yellowstone’s formerly permanent ponds are going dry in the summer and many seasonal ponds are gone. Whereas there were 43 ponds within the park that supported salamanders in the early 1990s, there are fewer than 21 today.
• Geysers: About half of Earth’s geysers are found in Yellowstone. How frequently these geysers erupt is connected to rainfall and groundwater levels, with drier periods having fewer eruptions. A good proxy for groundwater levels is the annual discharge of the Madison River, which has dropped by about 15 percent since 1970.

Seasons: Winter, Spring, Summer, Fall

Sources: Hurwitz, S et al. “Climate-induced variations of geyser periodicity in Yellowstone National Park, USA.”  Geology 36 (2008): 451-454 and “U.S. Temperature and Precipitation Trends.” U.S. National Oceanic and Atmospheric Administration (NOAA): Climate Prediction Center. 5 January 2005. Accessed Online 31 October 2008 and McMenamin, SK et al. “Climatic change and wetland desiccation cause amphibian decline in Yellowstone National Park.” PNAS 105 (43). Accessed Online 31 October 2008 and Science Daily. “Global Warming is Killing Frogs and Salamanders in Yellowstone Park, Researchers Say.” 29 October 2008. Accessed Online 31 October 2008 and Hansen, Andrew. “Conifer Cover Increase in the Greater Yellowstone Ecosystem: Frequency, Rates, and Spatial Variation.” Ecosystems 10 (2007): 204-216.

Florida Keys National Marine Sanctuary, the nation’s second largest marine sanctuary, provides a breeding ground for 5,500 species. This marine life supports a 20 million pound per year fishery and a coral reef tourism industry valued at 4.4 billion dollars. The richest parts of the sanctuary occur around coral reefs. While these reef ecosystems host some of Earth’s most visually stunning species, it is the microscopic, single-celled organisms called zooxanthellae that make these ecosystems possible. Zooxanthellae live inside the coral and pay “rent” by manufacturing sugars, which feed the coral. About 90 percent of the coral’s energy needs are provided by zooxanthellae. When ocean waters become too warm, however, corals expel zooxanthellae and “bleach,” losing their primary food source. Sea surface temperatures in the tropical and subtropical Atlantic are the warmest they have been since record keeping began in the 1880s. The last 15 years have been particularly hard on coral; in 1996 about 11.7 percent of the sanctuary was covered with living coral, but by 2005, too many frequent and prolonged periods of water temperatures exceeding 86 degrees Fahrenheit had reduced coral cover to 6.7 percent – a 180 square mile decrease in coral cover.

A likely contributor to this coral stress has been rising atmospheric carbon dioxide (CO2) levels. The oceans absorb excess carbon dioxide, about 22 million tons each day, and become more acidic as a result. More acidic waters mean less carbonate is available for coral, which need the carbonate to build their bodies. Ocean waters have become 30 percent more acidic in the last 200 years as the waters have absorbed an estimated 525 billion tons of CO2. How coral react to more acidic waters is influenced by the surrounding water temperature, with warm waters exacerbating the effect of increased acidity.

Seasons: Winter, Spring, Summer, Fall

Sources: United Nations Atlas of the Oceans: The Value of Coral Reefs. Accessed Online 8 October 2007: http://www.oceansatlas.com/ and Hoegh-Guldberg et al. “Coral Reefs Under Rapid Climate Change and Ocean Acidification.” Science 318 (2007): 1737 and “Oceans Becoming More Acidic, Potentially Threatening Marine Life.” Science Daily 23 February 2009. Accessed Online 25 February 2009 <http://www.sciencedaily.com/releases/2009/02/090223091752.htm> and Moy, AD et al. “Reduced calcification in modern Southern Ocean planktonic foraminifera.” Nature Geoscience 2 (2009): doi:10.1038/ngeo460  and Causey, Billy: “The History of Massive Coral Bleaching and other Perturbations in the Florida Keys.” In Chapter 6 of Coral Reefs in the U.S. and the Carribean. U.S. Coral Reef Information Service: National Oceanic and Atmospheric Administration and Wilkinson, C., Souter, D. (2008). Status of Caribbean coral reefs after bleaching and hurricanes in 2005. Global Coral Reef Monitoring Network and Reef and Rainforest Research Centre, Townsville, 152 p and Gaskill, Melissa. “Global bleaching goes from bad to worse.” Nature News 19 November 2010. Accessed Online 18 September 2011 < http://www.nature.com/news/2010/101119/full/news.2010.621.html>.

For comparison: 15 million pounds is about the same weight as 80 fully loaded Boeing 737-800s.

Seasons: Summer, Fall

Sources: Horvath, E et al. “Microscopic fungi as significant sesquiterpene emission souces.” Journal of Geophysical Research: Atmospheres 116 (2011): D16301 and Helmig, D et al. “Sesquiterpene emissions from loblolly pine and their potential contribution to biogenic aerosol formation in the Southeastern US.” Environmental Sciences 40 (2006): 4150-4157.

The Red Sea, which separates Africa from the Arabian Peninsula, hosts one of Earth’s most diverse marine ecosystems. The diversity in the Red Sea is particularly impressive because it is one of the least explored marine ecosystems, meaning that there are likely lots of life forms yet to be discovered there. The Red Sea’s diversity is largely due to the 1,240 miles of coral reefs that run near the sea’s shore. Coral reefs are considered the “rainforests of the ocean,” with the coral creating a matrix providing habitat for thousands of other species. One of the species, which actually inhabits coral bodies, is a type of algae called zooxanthellae. This algae has a symbiotic relationship with the coral: the coral provide a place to live, and the algae provide the coral with nutrients through photosynthesis, the process through which plant like species use the Sun’s energy to turn water and carbon dioxide into sugar. While coral can only survive in warm ocean waters, if temperatures become too warm the coral do not grow as well because the algae do not photosynthesize as efficiently. The already warm Red Sea has warmed at a particularly rapid rate over the last two decades. The ocean surface there is about 1.3 degrees Fahrenheit warmer today than it was in the early 1980s, with an abrupt temperature increase happening after 1994. This warming has been accompanied by a 30 percent decline in coral growth.

Sources: Raitsos, DE et al. “Abrupt warming of the Red Sea.” Geophysical Research Letters 38 (2011): L14601 and Cantin, NE et al. “Ocean Warming Slows Coral Growth in the Central Red Sea.” Science 329 (2010): 322-325.

Forests react to climate change through changes in species composition. The biodiversity, or collection of different species with different strengths and vulnerabilities, of a forest enables it to adapt to changing conditions. For example, a drought tolerant tree species may only have a few members standing when rainfall is plentiful, while drought intolerant species with other positive characteristics are flourishing. The tables turn if a sustained period of drying causes increased mortality amongst the water loving trees, a process that will leave gaps in the canopy which the drought-tolerant species will fill. A survey of which species are present in mature form and which species are the most common saplings provides a good indication of where a forest has been and where it is going. Analysis of a heavily studied forest plot on Barro Colorado Island in Panama shows a forest with many drought tolerant species, which gained the upper hand during a dry period that ran from the 1950s until the mid-1980s and was capped-off by the severe 1983 El Niño related drought. Since the 1970s, the average temperature in the plot has warmed by 3.6 degrees Fahrenheit. This temperature rise has been accompanied by an increase in average annual rainfall and this increased moisture is accompanied by an increased abundance of drought-intolerant saplings.

Seasons: Winter, Spring, Summer, Fall

Source: Feeley, KJ et al. “Directional changes in the species composition of a tropical forest.” Ecology 92 (2011): 871-882.

Afternoon summertime precipitation in the wet, humid and heavily vegetated eastern United States is related to the evaporation that happens in the morning. Lots of soil moisture can stimulate lots of evaporation, which can push cloud development over the threshold where precipitation happens. This positive land-atmosphere feedback means that soil moisture conditions are self-reinforcing. Dry soils mean less evaporation and less plant-nurturing rainfall, while wet soils mean more evaporation that can enhance the probability of a rainfall event by up to 25 percent. Soil moisture conditions do not appear to be particularly influential regarding rainfall intensity, however, with other factors such as large-scale convergence largely controlling how much rain falls during a given summertime afternoon event. This coupling of processes at the land surface and the atmosphere helps to explain the persistence of droughts, as dry soil conditions make the atmosphere less conducive to drought-mitigating rainfall. It also explains the persistence of wet periods where ample soil moisture stimulates the precipitation that keeps it moist.

Seasons: Summer

Source: Findell, KL et al. “Probability of afternoon precipitation in eastern United States and Mexico enhanced by high evaporation.” Nature Geoscience 4 (2011): 434-439.

After the snow melts in high-elevation meadows of the central Rocky Mountain region, pollinators hatch and flowers bloom. Flowers need pollinators for reproduction and pollinators need flowers for food via the nectar they provide. Many species of pollinators are generalists, meaning that they can feed on a variety of flowers, as opposed to specialists which usually rely on only one species. Generalists typically have longer lifecycles that extend throughout the warm season. They rely on a staggered system of flowering for a consistent supply of food, with different species of flowers growing on different sites and blooming at different times throughout the season. Sites include dry, rocky areas with shallow soils, wet soil sites at lower elevations often adjacent to streams, and mesic sites that are dryer than wet sites but have more developed soils than dry sites. Traditionally, the wet and dry sites have had two peak periods of flowering, one in the late spring and one in the late summer, with flowering that takes place on the mesic sites bridging the gap between these two peaks. A study of flowering behavior and temperature based on observations from Rocky Mountain Biological Laboratory collected between 1974 and 2009 showed that when compared to the seven years with the lowest July-August temperatures, the seven years with the warmest July-August temperatures featured second, late-season flowering peaks on the dry and wet sites that were an average of 25 days later in the season. These peaks tended to be smaller with fewer flowers. Warmer years also exhibited the development of a mid-season “valley” at the mesic sites when less flowering occurred. This means that warm years tend to include a mid-summer period where there is a lack of flowers and nectar that generalists like bumblebees and the broad-tailed hummingbirds need to survive. The average July-August temperature at the study site has increased by 2.5 degrees Fahrenheit since 1974.

Season: Summer

Source: Aldridge, G et al. “Emergence of a mid-season period of low floral resources in a montane meadow ecosystem associated with climate change.” Journal of Ecology 99 (2011): 905-913.

Water conditions along the Pacific Northwest coast are controlled by the Northern California Current (NCC) system, which features a strong alongshore northward flow of warm waters during winter and a southward flow of cool waters during the summer. On longer time scales, the Pacific Decadal Oscillation (PDO) is a cycle where abnormally warm and abnormally cool conditions shift across the North Pacific. During positive PDO phases, warm conditions in the northeastern Pacific accompany a stronger wintertime northward flow in the NCC that favors the survival of warm water plankton, fish and even seabird species in places as far north as Vancouver Island, Canada. Negative phases with cool conditions feature stronger summertime southward flows that favor the survival of cool water plankton, which tend to be richer in fats and more nutritious than their warm water counterparts. This variability in nutrition levels in the waters influences the survival rates of juvenile salmon, which enter the ocean and begin feeding on plankton in April and May, just after the current shifts. These salmon return upstream a year and a half later in the autumn to spawn in the place they were born. Water samples taken off the coast of Newport, Oregon during different phases of the PDO were used to analyze associated changes in plankton community compositions and then compared to Coho salmon survival rates. Years when more fat-rich plankton species were present were years when juvenile Coho salmon survival rates were the highest.

Seasons: Winter, Spring, Summer, Fall

Source: Hongsheng, B et al. “Transport and coastal zooplankton communities in the northern California Current system.” Geophysical Research Letters 38 (2011): L12607.

Range, the geographic area where a species is located, can shift in response to habitat changes such as land use changes, the introduction of a new species, the elimination of a competitor or internal species dynamics such as a genetic mutation that allows individuals to tolerate new conditions. It can also shift in response to climate change. Birds in midlatitude areas like the United States generally move their ranges closer to the Equator when Earth cools, such as during the ice age thousands of years ago, and closer to the poles as the Earth warms. While not all birds that have shifted their ranges in recent decades have moved northward, most species that have expanded their ranges have expanded them in that direction. This has been observed in both Europe and North America over the past five to six decades. The only factor that is consistent across both Eastern and Western Hemispheres since 1950 that could account for the general northward shift is a multi-seasonal warming with northern hemisphere spring maximum temperatures increasing by two degrees Fahrenheit. This has likely prompted Northern Hemisphere birds to travel farther north on their spring journeys to warm season breeding grounds. An analysis of similar bird taxa (several orders of arboreal and semiarboreal insectivores and granivores) demonstrates a northward range expansion at a rate of about 1.5 miles each year since the 1970s for southern species formerly limited by cool temperatures.

Two warbler species have been particularly quick to take advantage of the warmer conditions: the Kentucky Warbler and the Golden-Winged Warbler. The Kentucky Warbler’s mean breeding range latitude is now about 88 miles farther north than it was in the 1970s, while the mean latitude of the Golden-Winged Warbler is about 136 miles farther north.

Above: Mean range shifts for the Kentucky and Golden-Winged Warblers since the 1970s. This image is provided by Earth Gauge and is free for distribution and use on-air.

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Season: Summer

Source: Hitch, AT and Leberg, PL. “Breeding Distributions of North American Bird Species Moving North as a Result of Climate Change.” Conservation Biology 21 (2007): 534-539.

Range, the geographic area where a species is located, can shift in response to habitat changes such as land use changes, the introduction of a new species, the elimination of a competitor, or internal species dynamics such as a genetic mutation that allows individuals to tolerate new conditions. It can also shift in response to climate change. Birds in midlatitude areas like the United States generally move their ranges closer to the Equator when Earth cools, such as during the ice age thousands of years ago, and closer to the poles as the Earth warms. While not all birds that have shifted their ranges in recent decades have moved northward, most species that have expanded their ranges have expanded in that direction. This has been observed in both Europe and North America over the past five to six decades. The only factor that is consistent across both Eastern and Western Hemispheres since 1950 that could account for the general northward shift is a multi-seasonal warming with northern hemisphere spring maximum temperatures increasing by two degrees Fahrenheit. This has likely prompted Northern Hemisphere birds to travel farther north on their spring journeys to warm season breeding grounds. An analysis of similar bird taxa (several orders of arboreal and semiarboreal insectivores and granivores) demonstrates a northward range expansion at a rate of about 1.5 miles each year since the 1970’s for southern species formerly limited by cool temperatures.

In the Great Lakes region, two species have been particularly quick to take advantage of the warmer conditions: the Swainson’s Thrush and the Blue-gray Gnatcatcher. The Swainson’s Thrush mean breeding range latitude is now about 88 miles farther north than it was in the 1970s, while the mean latitude of the Blue-gray Gnatcatcher is about 195 miles farther north.

Above: Mean range shifts for the Swainson's Thrush and Blue-gray Gnatcatcher since the 1970s. This image is provided by Earth Gauge and is free for distribution and use on-air.

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Season: Summer

Source: Hitch, AT and Leberg, PL. “Breeding Distributions of North American Bird Species Moving North as a Result of Climate Change.” Conservation Biology 21 (2007): 534-539.

In the Southwestern United States, plant cover and plant behavior change with rainfall. Drought events are particularly instrumental in shaping plant community composition and response to drought varies among different plant species. Plants such as Ponderosa and Pinyon Pines are isohydric and always have a minimum amount of water in their leaves. Other plants, such as Juniper, are anisohydric and adjust how much moisture their leaves hold based on how much moisture is in the soil. Isohydric plants respond to drought by closing their gas exchange organs, called stomata, which minimizes water loss but restricts photosynthesis and growth; too little photosynthesis can mean insufficient carbon resources for metabolism and mounting defenses against hungry beetles. Anisohydric plants respond to drought differently and instead allow parts of themselves to die-off, which increases their root to shoot ratio, giving the remaining tissues a better chance of survival. These remaining tissues are still vulnerable to drought induced damage, called cavitation, that  occurs when the strong tension between the dry atmosphere and the moisture in the soil creates an air bubble in the plant vascular tissues. These air bubbles can burst, causing embolisms that impact the plant’s ability to move water and prevent canopy dieback. In August of 2002 in northern Arizona, annual precipitation was 56 percent of normal; 2002 became the third driest year in at least 1400 years. During this drought, the anisohydric Junipers had greater canopy dieback than the isohydric Pinyon and Ponderosa Pines, yet the Junipers had the lowest tree mortality rate. This suggests that during prolonged droughts, Juniper trees move up from lower elevations to replace the dying pines

(Source: Koepke, DF et al. “Variation in woody plant mortality and dieback from severe drought among soils, plant groups, and species within a northern Arizona ecotone.” Oecologia 163 (2010): 1079-1090.)

Boreal (Northern Hemisphere) spring is here. Even in the high northern latitudes, temperatures are beginning to warm and plants are beginning to come out of dormancy and photosynthesize, using the Sun’s energy to turn water and atmospheric carbon dioxide into sugar and grow. Snow cover may seem like a relic of winter, but snow also effectively reflects sunlight off the ground. In the boreal forests of the Northern Hemisphere, snow still covers much of the forest floor. Gaps in the tree canopy allow sunlight to hit snow on the ground, which reflects sunlight back towards the trees above. The amount of energy the trees receive from this reflection can even exceed the amount of energy they get from the initial downward wave of sunlight! It is likely that this reflection gives the trees a boost of energy, giving them the kick they need to “wake-up” and photosynthesize. This boost may be diminishing in importance as the duration of Northern Hemisphere snow cover has been shrinking at a rate of 5.5 days per decade over the past 40 years. Most of this decline in snow cover duration is due to melting in the late winter and early spring period.

Seasons: Spring

Sources: Choi, G et al. “Changing Northern Hemisphere Snow Season.” Journal of Climate 23 (2010): 5305-5310 and Pinty, B et al. “Snowy backgrounds enhance the absorption of visible light in forest canopies.” Geophysical Research Letters 38 (2011): L06404.

The Amazon Rainforest’s western terminus is the Andes Mountains. Along the eastern slope of the Andes, the perennially wet and warm rainforests of the western Amazon gradually transition into higher elevation forests, such as cloud forests, and eventually into alpine grasslands near the Andean peaks. The complex topography of the region leaves many valleys and peaks with a particular habitat type isolated amongst different surrounding habitat types. This dynamic discourages species adapted to a particular habitat from migrating, which reduces genetic exchange and has encouraged speciation. There are many species in these isolated peaks and valleys that are found nowhere else on Earth, highlighting the importance of the region to Earth’s biodiversity. This isolation also makes it difficult for species to migrate quickly when rapid climate changes happen. Such rapid changes appear to be happening now – the Andes have warmed by about 1.5 degrees Fahrenheit over the past 60 years. In Manu National Park in southeastern Peru, this has led to plants formerly found at low elevations moving upslope at a rate of about ten feet per year. This upslope movement may be problematic for plants adapted to living in isolated areas, particularly those at the highest elevations where upslope movement in response to temperature is not possible.

Seasons: Winter, Spring, Summer, Fall

Sources: Feeley, KJ et al. “Upslope migration of Andean trees.” Journal of Biogeography 38 (2011): 783-791 and Vuille, M et al. “20th Century Climate Change in the Tropical Andes: Observations and Model Results.” Climate Change 59 (2003): 75-99.

Trivia Question: As temperatures in the Arctic have warmed over the last 50 years, Alaska’s tree cover has…

a) Expanded
b) Shrunk
c) Not changed

The correct answer is a. As temperatures have warmed, tundra soils have begun to thaw at deeper levels for at least some part of the year. This has created a disturbance that allows trees, which have deeper roots than grasses and shrubs, to move into the tundra. Warmer temperatures also stimulate microbial activity in the soils, giving trees yet more of an incentive to move north. About 4,500 square miles of Alaska that were tundra in 1960 are covered by trees today.

Seasons: Winter, Spring, Summer, Fall

Sources: Hinzman, L et al. “Evidence and Implications of Recent Climate Change in Northern Alaska and Other ArcticRegions.” Climatic Change 72 (2005): 251–298 and Tape, K et al. “The evidence for shrub expansion in Northern Alaska and the Pan-Arctic.” Global Change Biology 12 (2006): 686-702.