6.4: Beneficiaries of Climate Change - Biology

6.4: Beneficiaries of Climate Change

Climate change, range shifts, and the disruption of a pollinator-plant complex

Climate change has significant impacts on the distribution of species and alters ecological processes that result from species interactions. There is concern that such distribution shifts will affect animal-plant pollination networks. We modelled the potential future (2050 and 2070) distribution of an endangered migratory bat species (Leptonycteris nivalis) and the plants they pollinate (Agave spp) during their annual migration from central Mexico to the southern United States. Our models show that the overlap between the Agave and the endangered pollinating bat will be reduced by at least 75%. The reduction of suitable areas for Agave species will restrict the foraging resources available for the endangered bat, threatening the survival of its populations and the maintenance of their pollination service. The potential extinction of the bat L. nivalis will likely have negative effects on the sexual reproduction and genetic variability of Agave plants increasing their vulnerability to future environmental changes.

6.2 What are the options for reducing greenhouse gas emissions?

6.2.1 Since 1995, there has been significant and faster than anticipated technical progress in greenhouse gas emissions reduction. The options over the next 20 years would include improving energy efficiency for buildings, transport and manufacturing, conversion to natural gas for energy supply, as well as low-carbon energy supply systems such as biomass, wind, nuclear and hydroelectric power systems, the reduction of methane and nitrous oxide emissions in agriculture and, with some applications, the minimization of fluorinated gas emissions (see Table SPM.1 for estimates half of these potential emissions reductions may be achieved with direct benefits exceeding direct costs). More.

6.2.2 Forests and agricultural lands provide significant carbon mitigation potential, which would not necessarily be permanent but it may allow time for other options to be further developed and implemented. The global potential could be in the order of 100 GtC by 2050, equivalent to about 10% to 20% of the fossil fuel emissions during that period. More.

6.2.3 Social learning and innovation, as well as changes in institutional structures could contribute to climate change mitigation. Changes in collective rules and individual behavior may have significant effects on greenhouse gas emissions, but would take place within complex institutional, regulatory and legal settings. More.

Changes in the Sun’s Energy Affect how Much Energy Reaches Earth

Climate can be influenced by natural changes that affect how much solar energy reaches Earth. These changes include changes within the sun and changes in Earth’s orbit. Changes occurring in the sun itself can affect the intensity of the sunlight that reaches Earth’s surface. The intensity of the sunlight can cause either warming (during periods of stronger solar intensity) or cooling (during periods of weaker solar intensity). The sun follows a natural 11-year cycle of small ups and downs in intensity, but the effect on Earth’s climate is small. Changes in the shape of Earth’s orbit as well as the tilt and position of Earth’s axis can also affect the amount of sunlight reaching Earth’s surface.

Changes in the sun’s intensity have influenced Earth’s climate in the past. For example, the so-called “Little Ice Age” between the 17th and 19th centuries may have been partially caused by a low solar activity phase from 1645 to 1715, which coincided with cooler temperatures. The Little Ice Age refers to a slight cooling of North America, Europe, and probably other areas around the globe. Changes in Earth’s orbit have had a big impact on climate over tens of thousands of years. These changes appear to be the primary cause of past cycles of ice ages, in which Earth has experienced long periods of cold temperatures (ice ages), as well as shorter interglacial periods (periods between ice ages) of relatively warmer temperatures.

Changes in solar energy continue to affect climate. However, solar activity has been relatively constant, aside from the 11-year cycle, since the mid-20th century and therefore does not explain the recent warming of Earth. Similarly, changes in the shape of Earth’s orbit as well as the tilt and position of Earth’s axis affect temperature on relatively long timescales (tens of thousands of years), and therefore cannot explain the recent warming.

Dissecting tough calls

As part of his research, Francis has looked at hard decisions governments across the world have made regarding climate change.

Some of the cases he has examined include the debate over fracking technologies in the United States and the energy crisis in Pakistan.

Over the past several years, Pakistan has been dealing with a shortage of electricity as a result of its weak supply and infrastructure that leads to frequent blackouts affecting millions of citizens.

The country struggled with the decision of whether to convert to renewable energy, extract more coal or continue to rely on importing oil for its energy needs. Officials eventually decided to extract more coal despite the adverse environmental effects.

“This has helped me get a sense of the stakes involved in these types of debates,” Francis said.

Subsidized gas prices are another example of a moral challenge nations face, he said.

“Americans aren’t paying the true price of gasoline,” Francis said. “And I think there is something very worrying about the fact that because of government subsidies we are not paying that true cost. But it’s complicated because we know that keeping gas prices low is really good for the poor and the middle class.”

In addition to examining specific cases, Francis is studying climate change policies and their evolution on the national and international level to determine the current moral assessment the public has about actions that lead to global warming. He is also researching the rules of organizations, such as the World Bank and the World Health Organization, regarding climate change, the restrictions they put on projects they help finance and how those policies were decided.

The information and insight Francis gains will be used to help create the moral framework so that nations can choose wisely when it comes to climate change policy. But that framework will require a long time and an effort from experts of all disciplines.

“Ultimately, it’s a big interdisciplinary task that philosophers by themselves won’t be able to accomplish,” Francis said. “But I think there is a big chunk of it having to do with what counts as a harm, how to trade off benefits and harms and when emitting is wrong that I could have a say in.”

44.5 Climate and the Effects of Global Climate Change

By the end of this section, you will be able to do the following:

  • Define global climate change
  • Summarize the effects of the Industrial Revolution on global atmospheric carbon dioxide concentration
  • Describe three natural factors affecting long-term global climate
  • List two or more greenhouse gases and describe their role in the greenhouse effect

All biomes are universally affected by global conditions, such as climate, that ultimately shape each biome’s environment. Scientists who study climate have noted a series of marked changes that have gradually become increasingly evident during the last sixty years. Global climate change is the term used to describe altered global weather patterns, especially a worldwide increase in temperature and resulting changes in the climate, due largely to rising levels of atmospheric carbon dioxide.

Climate and Weather

A common misconception about global climate change is that a specific weather event occurring in a particular region (for example, a very cool week in June in central Indiana) provides evidence of global climate change. However, a cold week in June is a weather-related event and not a climate-related one. These misconceptions often arise because of confusion over the terms climate and weather.

Climate refers to the long-term, predictable atmospheric conditions of a specific area. The climate of a biome is characterized by having consistent seasonal temperature and rainfall ranges. Climate does not address the amount of rain that fell on one particular day in a biome or the colder-than-average temperatures that occurred on one day. In contrast, weather refers to the conditions of the atmosphere during a short period of time. Weather forecasts are usually made for 48-hour cycles. Long-range weather forecasts are available but can be unreliable.

To better understand the difference between climate and weather, imagine that you are planning an outdoor event in northern Wisconsin. You would be thinking about climate when you plan the event in the summer rather than the winter because you have long-term knowledge that any given Saturday in the months of May to August would be a better choice for an outdoor event in Wisconsin than any given Saturday in January. However, you cannot determine the specific day that the event should be held on because it is difficult to accurately predict the weather on a specific day. Climate can be considered “average” weather that takes place over many years.

Global Climate Change

Climate change can be understood by approaching three areas of study:

  • evidence of current and past global climate change
  • drivers of global climate change
  • documented results of climate change

It is helpful to keep these three different aspects of climate change clearly separated when consuming media reports about global climate change. We should note that it is common for reports and discussions about global climate change to confuse the data showing that Earth’s climate is changing with the factors that drive this climate change.

Evidence for Global Climate Change

Since scientists cannot go back in time to directly measure climatic variables, such as average temperature and precipitation, they must instead indirectly measure temperature. To do this, scientists rely on historical evidence of Earth’s past climate.

Antarctic ice cores are a key example of such evidence for climate change. These ice cores are samples of polar ice obtained by means of drills that reach thousands of meters into ice sheets or high mountain glaciers. Viewing the ice cores is like traveling backwards through time the deeper the sample, the earlier the time period. Trapped within the ice are air bubbles and other biological evidence that can reveal temperature and carbon dioxide data. Antarctic ice cores have been collected and analyzed to indirectly estimate the temperature of the Earth over the past 400,000 years (Figure 44.26a). The 0 °C on this graph refers to the long-term average. Temperatures that are greater than 0 °C exceed Earth’s long-term average temperature. Conversely, temperatures that are less than 0 °C are less than Earth’s average temperature. This figure shows that there have been periodic cycles of increasing and decreasing temperature.

Before the late 1800s, the Earth has been as much as 9 °C cooler and about 3 °C warmer. Note that the graph in Figure 44.27b shows that the atmospheric concentration of carbon dioxide has also risen and fallen in periodic cycles. Also note the relationship between carbon dioxide concentration and temperature. Figure 44.27b shows that carbon dioxide levels in the atmosphere have historically cycled between 180 and 300 parts per million (ppm) by volume.

Figure 44.27a does not show the last 2,000 years with enough detail to compare the changes of Earth’s temperature during the last 400,000 years with the temperature change that has occurred in the more recent past. Two significant temperature anomalies, or irregularities, have occurred in the last 2,000 years. These are the Medieval Climate Anomaly (or the Medieval Warm Period) and the Little Ice Age. A third temperature anomaly aligns with the Industrial Era. The Medieval Climate Anomaly occurred between 900 and 1300 AD. During this time period, many climate scientists think that slightly warmer weather conditions prevailed in many parts of the world the higher-than-average temperature changes varied between 0.10 °C and 0.20 °C above the norm. Although 0.10 °C does not seem large enough to produce any noticeable change, it did free seas of ice. Because of this warming, the Vikings were able to colonize Greenland.

The Little Ice Age was a cold period that occurred between 1550 AD and 1850 AD. During this time, a slight cooling of a little less than 1 °C was observed in North America, Europe, and possibly other areas of the Earth. This 1 °C change in global temperature is a seemingly small deviation in temperature (as was observed during the Medieval Climate Anomaly) however, it also resulted in noticeable climatic changes. Historical accounts reveal a time of exceptionally harsh winters with much snow and frost.

The Industrial Revolution, which began around 1750, was characterized by changes in much of human society. Advances in agriculture increased the food supply, which improved the standard of living for people in Europe and the United States. New technologies were invented that provided jobs and cheaper goods. These new technologies were powered using fossil fuels, especially coal. The Industrial Revolution starting in the early nineteenth century ushered in the beginning of the Industrial Era. When a fossil fuel is burned, carbon dioxide is released. With the beginning of the Industrial Era, atmospheric carbon dioxide began to rise (Figure 44.28).

Current and Past Drivers of Global Climate Change

Because it is not possible to go back in time to directly observe and measure climate, scientists must use indirect evidence to determine the drivers, or factors, that may be responsible for climate change. The indirect evidence includes data collected using ice cores, boreholes (a narrow shaft bored into the ground), tree rings, glacier lengths, pollen remains, and ocean sediments. The data shows a correlation between the timing of temperature changes and drivers of climate change. Before the Industrial Era (pre-1780), there were three drivers of climate change that were not related to human activity or atmospheric gases. The first of these is the Milankovitch cycles. The Milankovitch cycles describe the effects of slight changes in the Earth’s orbit on Earth’s climate. The length of the Milankovitch cycles ranges between 19,000 and 100,000 years. In other words, one could expect to see some predictable changes in the Earth’s climate associated with changes in the Earth’s orbit at a minimum of every 19,000 years.

The variation in the sun’s intensity is the second natural factor responsible for climate change. Solar intensity is the amount of solar power or energy the sun emits in a given amount of time. There is a direct relationship between solar intensity and temperature. As solar intensity increases (or decreases), the Earth’s temperature correspondingly increases (or decreases). Changes in solar intensity have been proposed as one of several possible explanations for the Little Ice Age.

Finally, volcanic eruptions are a third natural driver of climate change. Volcanic eruptions can last a few days, but the solids and gases released during an eruption can influence the climate over a period of a few years, causing short-term climate changes. The gases and solids released by volcanic eruptions can include carbon dioxide, water vapor, sulfur dioxide, hydrogen sulfide, hydrogen, and carbon monoxide. Generally, volcanic eruptions cool the climate. This occurred in 1783 when volcanos in Iceland erupted and caused the release of large volumes of sulfuric oxide. This led to haze-effect cooling , a global phenomenon that occurs when dust, ash, or other suspended particles block out sunlight and trigger lower global temperatures as a result haze-effect cooling usually extends for one or more years before dissipating in intensity. In Europe and North America, haze-effect cooling produced some of the lowest average winter temperatures on record in 1783 and 1784.

Greenhouse gases are probably the most significant drivers of the climate. When heat energy from the sun strikes the Earth, gases known as greenhouse gases trap the heat in the atmosphere, in a similar manner as do the glass panes of a greenhouse keep heat from escaping. The greenhouse gases that affect Earth include carbon dioxide, methane, water vapor, nitrous oxide, and ozone. Approximately half of the radiation from the sun passes through these gases in the atmosphere and strikes the Earth. This radiation is converted into thermal (infrared) radiation on the Earth’s surface, and then a portion of that energy is re-radiated back into the atmosphere. Greenhouse gases, however, reflect much of the thermal energy back to the Earth’s surface. The more greenhouse gases there are in the atmosphere, the more thermal energy is reflected back to the Earth’s surface, heating it up and the atmosphere immediately above it. Greenhouse gases absorb and emit radiation and are an important factor in the greenhouse effect : the warming of Earth due to carbon dioxide and other greenhouse gases in the atmosphere.

Direct evidence supports the relationship between atmospheric concentrations of carbon dioxide and temperature: as carbon dioxide rises, global temperature rises. Since 1950, the concentration of atmospheric carbon dioxide has increased from about 280 ppm to 382 ppm in 2006. In 2011, the atmospheric carbon dioxide concentration was 392 ppm. However, the planet would not be inhabitable by current life forms if water vapor did not produce its drastic greenhouse warming effect.

Scientists look at patterns in data and try to explain differences or deviations from these patterns. The atmospheric carbon dioxide data reveal a historical pattern of carbon dioxide increasing and decreasing, cycling between a low of 180 ppm and a high of 300 ppm. Scientists have concluded that it took around 50,000 years for the atmospheric carbon dioxide level to increase from its low minimum concentration to its higher maximum concentration. However, beginning only a few centuries ago, atmospheric carbon dioxide concentrations have increased beyond the historical maximum of 300 ppm. The current increases in atmospheric carbon dioxide have happened very quickly—in a matter of hundreds of years rather than thousands of years. What is the reason for this difference in the rate of change and the amount of increase in carbon dioxide? A key factor that must be recognized when comparing the historical data and the current data is the presence and industrial activities of modern human society no other driver of climate change has yielded changes in atmospheric carbon dioxide levels at this rate or to this magnitude.

Human activity releases carbon dioxide and methane, two of the most important greenhouse gases, into the atmosphere in several ways. The primary mechanism that releases carbon dioxide is the burning of fossil fuels, such as gasoline, coal, and natural gas (Figure 44.29). Deforestation, cement manufacture, animal agriculture, the clearing of land, and the burning of forests are other human activities that release carbon dioxide. Methane (CH4) is produced when bacteria break down organic matter under anaerobic conditions. Anaerobic conditions can happen when organic matter is trapped underwater (such as in rice paddies) or in the intestines of herbivores. Methane can also be released from natural gas fields and the decomposition of animal and plant material that occurs in landfills. Another source of methane is the melting of clathrates. Clathrates are frozen chunks of ice and methane found at the bottom of the ocean. When water warms, these chunks of ice melt and methane is released. As the ocean’s water temperature increases, the rate at which clathrates melt is increasing, releasing even more methane. This leads to increased levels of methane in the atmosphere, which further accelerates the rate of global warming. This is an example of the positive feedback loop that is leading to the rapid rate of increase of global temperatures.

Documented Results of Climate Change: Past and Present

Scientists have geological evidence of the consequences of long-ago climate change. Modern-day phenomena such as retreating glaciers and melting polar ice cause a continual rise in sea level. Meanwhile, changes in climate can negatively affect organisms.

Geological Climate Change

Global warming has been associated with at least one planet-wide extinction event during the geological past. The Permian extinction event occurred about 251 million years ago toward the end of the roughly 50-million-year-long geological time span known as the Permian period. This geologic time period was one of the three warmest periods in Earth’s geologic history. Scientists estimate that approximately 70 percent of the terrestrial plant and animal species and 84 percent of marine species became extinct, vanishing forever near the end of the Permian period.

Organisms that had adapted to wet and warm climatic conditions, such as annual rainfall of 300–400 cm (118–157 in) and 20 °C–30 °C (68 °F–86 °F) in the tropical wet forest, may not have been able to survive the Permian climate change.

Link to Learning

Watch this NASA video to discover the mixed effects of global warming on plant growth. While scientists found that warmer temperatures in the 1980s and 1990s caused an increase in plant productivity, this advantage has since been counteracted by more frequent droughts.

Present Climate Change

A number of global events have occurred that may be attributed to climate change during our lifetimes. Glacier National Park in Montana is undergoing the retreat of many of its glaciers, a phenomenon known as glacier recession. In 1850, the area contained approximately 150 glaciers. By 2010, however, the park contained only about 24 glaciers greater than 25 acres in size. One of these glaciers is the Grinnell Glacier (Figure 44.30) at Mount Gould. Between 1966 and 2005, the size of Grinnell Glacier shrank by 40 percent. Similarly, the mass of the ice sheets in Greenland and the Antarctic is decreasing: Greenland lost 150–250 km 3 of ice per year between 2002 and 2006. In addition, the size and thickness of the Arctic sea ice is decreasing.

This loss of ice is leading to increases in the global sea level. On average, the sea is rising at a rate of 1.8 mm per year. However, between 1993 and 2010 the rate of sea level increase ranged between 2.9 and 3.4 mm per year. A variety of factors affect the volume of water in the ocean, especially the temperature of the water (the density of water is related to its temperature: water volume expands as it warms, thus raising sea levels), as well as the amount of water found in rivers, lakes, glaciers, polar ice caps, and sea ice. As glaciers and polar ice caps melt, there is a significant contribution of liquid water that was previously frozen.

In addition to some abiotic conditions changing in response to climate change, many organisms are also being affected by the changes in temperature. Temperature and precipitation play key roles in determining the geographic distribution and phenology of plants and animals. ( Phenology is the study of the effects of climatic conditions on the timing of periodic life cycle events, such as flowering in plants or migration in birds.) Researchers have shown that 385 plant species in Great Britain are flowering 4.5 days sooner than was recorded earlier during the previous 40 years. In addition, insect-pollinated species were more likely to flower earlier than wind-pollinated species. The impact of changes in flowering date would be mitigated if the insect pollinators emerged earlier. This mismatched timing of plants and pollinators could result in injurious ecosystem effects because, for continued survival, insect-pollinated plants must flower when their pollinators are present.

Supporting Information

Dataset S1. Dated Woolly Mammoth Occurrences in Eurasia

Max Ca BP l and Min Cal BP represent the 95% confidence interval for the age for radiocarbon dates. Radiocarbon ages have been converted using CalPal 2005 SFCP. Woolly mammoth occurrences for each time interval were defined as those having their calibrated 95% confidence intervals within these time intervals (42 ± 3 ky BP, 30 ± 3 ky BP, 21 ± 3 ky BP, and 6 ± ky BP, respectively), resulting in 270 records being included for modelling the climatic niche of the woolly mammoths. Data summary references are listed below.

Figure S1. A Visual Example of the Climatic Niche Concept, Its Geographical Location, and Niche Conservatism

The climatic niche represents the climatic conditions where a species is able to persist. It would encompass many climate variables (n dimensions). The climatic niche has a location in geographical space. On the left, we show an example of a climatic niche (yellow ellipse) defined by the distribution (black outlined symbols equal presence) of a species in three different periods of time, t1 (orange squares), t2 (green circles), and t3 (blue triangles), within a climatic space defined by two dimensions (two climatic gradients represented by precipitation and temperature). The mean climate conditions are symbolized by the black cross. On the right, we observe the geographical location of the climatic niche in the three periods of time and its projection to a fourth one, t4. Note that while the climatic conditions where the species is present remains constant (i.e., the records of the species in the three periods can be placed anywhere within the ellipse of the environmental scatterplot), climate change modifies the geographical location and the extent of the areas with conditions suitable for the species.

Figure S2. The Climatic Niche of Woolly Mammoths

Records (n = 270) of woolly mammoth presence during OIS 3 Warm Phase, 42 ky BP (orange dots), OIS 3 Cold Phase, 30 ky BP (green dots) and LGM, 21 ky BP (blue dots). The niche is plotted in a three-dimensional space and also in three plots of two-dimensions to enable an easier interpretation of the results. Mean temperature of the coldest month, Tcm mean temperature of the warmest month, Twm annual precipitation, Rann.

Figure S3. Number of Grid Cells (2° Resolution) in Relation to MD Scores

Red bars: 6 ky BP period blue bars: 21 ky BP period green bars: 30 ky BP period orange bars: 42 ky BP period. Deviation from the mean conditions is associated with higher MD scores. The reduction in the area of mean climatic conditions for woolly mammoths in Eurasia shows a clear trend, irrespective of the different ways (e.g., quartiles) in which the niche could be described.

Figure S4. The Projected Climatic Niche of Woolly Mammoths and the Vegetation for the 6 ky BP Period

The map shows in more detail the climatic niche of woolly mammoths projected by our model for the 6 ky BP period. The most suitable climatic conditions are plotted in red (Q1). Q3 is plotted in yellow and Q4 in green. The dark green line represents the limit of the distribution of the birch forest, Betula spp., for the 6 ky BP period as published by MacDonald et al. [23] based on radiocarbon-dated macrofossils. Treelines for larch ( Larix spp.) and spruce ( Picea obovata ) were located at similar latitude [23]. Small divergences between the red areas and the green line are the result of the coarse resolution of the maps generated by GENESIS 2 (2° × 2°). The use of bioclimatic models to assess the extent to which niches may or may not be reduced for many species, has been suggested [18] as one of the future steps of research on the Late Quaternary extinctions debate. Martínez-Meyer et al. [58] is an example of the use of bioclimatic models to assess past changes in the potential geographical range of species.

Figure S5. Bootstrap Plots of the Covariance Matrix C

MD technique relies on a mean vector and a covariance matrix. Blue bars are the real covariance values and the black lines are the covariance values simulated by the bootstrapping procedure. Tcm, mean temperature of the coldest month Twm, mean temperature of the warmest month and P, annual precipitation.

Figure S6. Bootstrap Plots of the Distances to the Most Suitable Climatic Conditions: Mean Vector m

The MD technique relies on a mean vector and a covariance matrix. Blue bars are the observed mean vector values and the black lines are the mean vector values simulated by bootstrapping. Tcm, mean temperature of the coldest month Twm, mean temperature of the warmest month and P, annual precipitation.

Protocol S1. BIOCLIM and Maxent Models of Woolly Mammoth's Niche.

Table S1. Kruskal-Wallis Test Statistics (see Material and Methods)

Table S1A filtered out 216 cases of 270 Table S1B filtered out 129 cases of 270. Table S1C did not filter out any case (n = 270). Significance levels above 0.05 indicate that the climate conditions do not differ between 42 ky BP, 30 ky BP, and 21 ky BP periods.

Table S2. HIt Values through Time

Number of woolly mammoths (NK) that should be killed per year in each time interval and hunting intensity (HIt) measured as woolly mammoths killed by human individual per year necessary to drive the entire population to extinction. CR, cull rate (individuals/y) Dm, woolly mammoth population density (individuals/km 2 ). Values are calculated assuming the minimum human population densities for each period (see Table S3 for densities of human populations)

Table S3. Demographic Density of AMH in Europe up to 40 °E in Four Different Cultural Periods [56]

Climate Change Threatens Tropical Birds

Rainbow-billed toucans like the one shown here normally are confined to lower elevations in Costa Rica, but global warming is allowing them to colonize mountain forests, where they compete with resident birds for food and nesting holes, and prey on their eggs and nestlings.

The resplendent quetzal (shown here) of Costa Rica’s highlands is one of the main victims of the rainbow-billed toucan’s move to higher elevations due to warming climate. The quetzal’s mountain forest habitat also is growing drier. The quetzal was venerated by the Mayas and Aztecs as the "god of the air" and is the bird most sought-after by birdwatchers visiting Costa Rica.

Venezuela’s scissor-tailed hummingbird has an existing habitat of less than 100 square miles of humid mountain forest. It is currently considered threatened with extinction, and computer models of expected extinctions due to climate change indicate that this species will be among the most likely to go extinct by the end of the century if global warming continues.

A New World warbler, the collared redstart lives in cloud forests in the mountains of Costa Rica and western Panama. Scientists have documented that it has shifted its limited habitat toward higher elevations. The redstart population could be seriously affected by global warming.

Newswise — SALT LAKE CITY, Feb. 16, 2012 – Climate change spells trouble for many tropical birds – especially those living in mountains, coastal forests and relatively small areas – and the damage will be compounded by other threats like habitat loss, disease and competition among species.

That is among the conclusions of a review of nearly 200 scientific studies relevant to the topic. The review was scheduled for online publication this week in the journal Biological Conservation by Çağan Şekercioğlu (pronounced Cha-awn Shay-care-gee-oh-loo), an assistant professor of biology at the University of Utah.

There are roughly 10,000 bird species worldwide. About 87 percent spend at least some time in the tropics, but if migratory birds are excluded, about 6,100 bird species live only in the tropics, Şekercioğlu says.

He points out that already, “12.5 percent of the world’s 10,000 bird species are threatened with extinction” – listed as vulnerable, endangered or critically endangered by the International Union for Conservation of Nature (

Şekercioğlu’s research indicates about 100 to 2,500 land bird species may go extinct due to climate change, depending on the severity of global warming and habitat loss due to development, and on the ability of birds to find new homes as rising temperatures push them poleward or to higher elevations. The most likely number of land bird extinctions, without additional conservation efforts, is 600 to 900 by the year 2100, Şekercioğlu says.

“Birds are perfect canaries in the coal mine – it’s hard to avoid that metaphor – for showing the effects of global change on the world’s ecosystems and the people who depend on those ecosystems,” he adds. Şekercioğlu reviewed the scientific literature relevant to climate change and tropical birds with Richard Primack, a biologist at Boston University, and Janice Wormworth, a freelance science writer and ecological consultant in Australia.

Wormworth and Şekercioğlu coauthored the 2011 book, “Winged Sentinels: Birds and Climate Change.” The new article is an updated condensation of that book and another 2011 book Şekercioğlu coauthored, “Conservation of Tropical Birds.”

The review was funded by the Christensen Fund – which finances community-based conservation projects – the University of Utah and National Science Foundation.

Putting the Heat on Tropical Birds

Scientists expect climate change to bring not only continued warming, but larger and-or more frequent extreme weather events such as droughts, heat waves, fires, cold spells and “once-in-a-century” storms and hurricanes. Birds may withstand an increase in temperature, yet extreme weather may wreck habitats or make foraging impossible.

“The balance of evidence points to increases in the numbers of intense tropical hurricanes (though hurricane frequency could decrease overall),” Şekercioğlu and colleagues write. “This would predominantly affect tropical bird communities, especially species living in coastal and island habitats.”

Şekercioğlu says it is difficult to predict how habitat loss, emerging diseases, invasive species, hunting and pollution will combine with climate change to threaten tropical birds, although “in some cases habitat loss [from agriculture and development] can increase bird extinctions caused by climate change by nearly 50 percent.”

In addition, “compared to temperate species that often experience a wide range of temperature on a yearly basis, tropical species, especially those limited to tropical forests with stable climates, are less likely to keep up with rapid climate change.”

The researchers say studies indicate:

-- Climate change already has caused some low-elevation birds to shift their ranges, either poleward or to higher elevations, causing problems for other species. Global warming helped rainbow-billed toucans move from Costa Rican lowlands to higher-elevation cloud forests, where they now compete for tree-cavity nest space with the resplendent quetzal. The toucans also eat quetzal eggs and nestlings.

-- Birds with slower metabolisms often live in cooler tropical environments with relatively little temperature variation. They can withstand a narrower range of temperature and are more vulnerable to climate change.

-- Climate change may spread malaria-bearing mosquitoes to higher elevations in places like Hawaii, where the malaria parasite can threaten previously unexposed birds.

-- Longer and less regular dry seasons and droughts expected during global warming may reduce populations of tropical birds that often time their breeding with wet seasons when food is abundant.

Şekercioğlu acknowledges that “not all effects of climate change are negative, and changes in temperature and precipitation regimes will benefit some species. … Nevertheless, climate change will not benefit many species.”

Scenarios for Extinction

A 2008 study by Şekercioğlu and late climatologist Stephen Schneider calculated 60 scenarios of how tropical land bird extinction rates will be affected by various possible combinations of three variables: climate change, habitat loss and how easily birds can shift their range, meaning move to new habitat. Citing those estimates, the new review paper says that “depending on the amount of habitat loss, each degree of surface warming can lead to approximately 100 to 500 additional bird extinctions.”

The Intergovernmental Panel on Climate Change has predicted 1.1 to 6.4 degrees Celsius (2 to 11.5 degrees Fahrenheit) of global warming of the Earth’s surface by the year 2100, which Şekercioğlu’s study converted into a best case of about 100 land bird extinctions and a worst case of 2,500.

He says the most likely case now is considered to be 3.5 C (6.3 F) warming by 2100, resulting in about 600 to 900 land bird species going extinct. These estimates are conservative because they exclude water birds, which are 14 percent of all bird species.

Because they don’t travel far, “sedentary” birds “are five times more likely to go extinct in the 21st century than are long-distance migratory birds,” says Şekercioğlu. The review found:

--Tropical mountain birds are among the most vulnerable to climate change. Warmer temperatures at lower elevations force them to higher elevations where there is less or no habitat, so some highland species may go extinct.

--Climate change and accompanying sea-level rise pose problems for birds in tropical coastal and island ecosystems, “which are disappearing at a rapid rate,” Şekercioğlu and colleagues write. Many such ecosystems already have been invaded by non-native species and exploited by humans.

-- Birds in extensive lowland forests with few mountains – areas such as the Amazon and Congo basins – may have trouble relocating far or high enough to survive.

-- Tropical birds in open habitats such as savanna, grasslands, scrub and desert face shifting and shrinkage of their habitats.

-- Rising sea levels will threaten aquatic birds such as waders, ducks and geese, yet they often are hemmed in by cities and farms with no place to go for new habitat.

-- Tropical birds in arid zones are assumed to be resilient to hot, dry conditions, yet climate change may test their resilience by drying out oases on which they depend.

More Research and Conservation Needed To better understand and reduce the impact of climate change on tropical birds, Şekercioğlu urges more research, identification and monitoring of species at greatest risk, restoration of degraded lands, relocation of certain species, and new and expanded protected areas and corridors based on anticipated changes in a species’ range. “Nevertheless,” Şekercioğlu and colleagues write, “such efforts will be temporary fixes if we fail to achieve important societal change to reduce consumption, to control the emissions of greenhouse gases and to stop climate change.” “Otherwise,” they add, “we face the prospect of an out-of-control climate that will not only lead to enormous human suffering, but will also trigger the extinction of countless organisms, among which tropical birds will be but a fraction of the total.”

6.3 Exposure Pathways and Health Risks

Humans are exposed to agents of water-related illness through several pathways, including drinking water (treated and untreated), recreational waters (freshwater, coastal, and marine), and fish and shellfish.

Drinking Water

Extreme precipitation events have been statistically linked to increased levels of pathogens in treated drinking water supplies.

Although the United States has one of the safest municipal drinking water supplies in the world, water-related outbreaks (more than one illness case linked to the same source) still occur. 33 Public drinking water systems provide treated water to approximately 90% of Americans at their places of residence, work, or schools. 34 However, about 15% of the population relies fully or in part on untreated private wells or other private sources for their drinking water. 35 These private sources are not regulated under the Safe Drinking Water Act. 36 The majority of drinking water outbreaks in the United States are associated with untreated or inadequately treated groundwater and distribution system deficiencies. 33 , 37

Pathogen and Algal Toxin Contamination

Between 1948 and 1994, 68% of waterborne disease outbreaks in the United States were preceded by extreme precipitation events, 38 and heavy rainfall and flooding continue to be cited as contributing factors in more recent outbreaks in multiple regions of the United States. 39 Extreme precipitation events have been statistically linked to increased levels of pathogens in treated drinking water supplies 40 and to an increased incidence of gastrointestinal illness in children. 21 , 41 This established relationship suggests that extreme precipitation is a key climate factor for waterborne disease. 42 , 43 , 44 , 45 The Milwaukee Cryptosporidium outbreak in 1993—the largest documented waterborne disease outbreak in U.S. history, causing an estimated 403,000 illnesses and more than 50 deaths 46 —was preceded by the heaviest rainfall event in 50 years in the adjacent watersheds. 10 Various treatment plant operational problems were also key contributing factors. 47 (See future projections in the Milwaukee Case Study). Observations in England and Wales also show waterborne disease outbreaks were preceded by weeks of low cumulative rainfall and then heavy precipitation events, suggesting that drought or periods of low rainfall may also be important climate-related factors. 48

Small community or private groundwater wells or other drinking water systems where water is untreated or minimally treated are especially susceptible to contamination following extreme precipitation events. 49 For example, in May 2000, following heavy rains, livestock waste containing E. coli O157:H7 and Campylobacter was carried in runoff to a well that served as the primary drinking water source for the town of Walkerton, Ontario, Canada, resulting in 2,300 illnesses and 7 deaths. 43 , 44 , 50 High rainfall amounts were an important catalyst for the outbreak, although non-climate factors, such as well infrastructure , operational and maintenance problems, and lack of communication between public utilities staff and local health officials were also key factors. 44 , 51

Likewise, extreme precipitation events and subsequent increases in runoff are key climate factors that increase nutrient loading in drinking water sources, which in turn increases the likelihood of harmful cyanobacterial blooms that produce algal toxins. 52 The U.S. Environmental Protection Agency has established health advisories for two algal toxins (microcystins and cylindrospermopsin) in drinking water. 53 Lakes and reservoirs that serve as sources of drinking water for between 30 million and 48 million Americans may be periodically contaminated by algal toxins. 54 Certain drinking water treatment processes can remove cyanobacterial toxins however, efficacy of the treatment processes may vary from 60% to 99.9%. Ineffective treatment could compromise water quality and may lead to severe treatment disruption or treatment plant shutdown. 53 , 54 , 55 , 56 Such an event occurred in Toledo, Ohio, in August 2014, when nearly 500,000 residents of the state’s fourth-largest city lost access to their drinking water after tests revealed the presence of toxins from a cyanobacterial bloom in Lake Erie near the water plant’s intake. 57

Water Supply

Climate-related hydrologic changes such as those related to flooding, drought, runoff, snowpack and snowmelt, and saltwater intrusion (the movement of ocean water into fresh groundwater) have implications for freshwater management and supply (see also Ch. 4: Extreme Events). 58 Adequate freshwater supply is essential to many aspects of public health, including provision of drinking water and proper sanitation and personal hygiene. For example, following floods or storms, short-term loss of access to potable water has been linked to increased incidence of illnesses including gastroenteritis and respiratory tract and skin infections. 59 Changes in precipitation and runoff, combined with changes in consumption and withdrawal, have reduced surface and groundwater supplies in many areas, primarily in the western United States. 58 These trends are expected to continue under future climate change , increasing the likelihood of water shortages for many uses. 58

Future climate-related water shortages may result in more municipalities and individuals relying on alternative sources for drinking water, including reclaimed water and roof-harvested rainwater. 60 , 61 , 62 , 63 Water reclamation refers to the treatment of stormwater, industrial wastewater, and municipal wastewater for beneficial reuse. 64 States like California, Arizona, New Mexico, Texas, and Florida are already implementing wastewater reclamation and reuse practices as a means of conserving and adding to freshwater supplies. 65 However, no federal regulations or criteria for public health protection have been developed or proposed specifically for potable water reuse in the United States. 66 Increasing household rainwater collection has also been seen in some areas of the country (primarily Arizona, Colorado, and Texas), although in some cases, exposure to untreated rainwater has been found to pose health risks from bacterial or protozoan pathogens, such as Salmonella enterica and Giardia lamblia. 67 , 68 , 69

Projected Changes

Runoff from more frequent and intense extreme precipitation events will contribute to contamination of drinking water sources with pathogens and algal toxins and place additional stresses on the capacity of drinking water treatment facilities and distribution systems. 10 , 52 , 59 , 70 , 71 , 72 , 73 Contamination of drinking water sources may be exacerbated or insufficiently addressed by treatment processes at the treatment plant or by breaches in the distribution system, such as during water main breaks or low-pressure events. 13 Untreated groundwater drawn from municipal and private wells is of particular concern.

Climate change is not expected to substantially increase the risk of contracting illness from drinking water for those people who are served by treated drinking water systems, if appropriate treatment and distribution is maintained. However, projections of more frequent or severe extreme precipitation events, flooding, and storm surge suggest that drinking water infrastructure may be at greater risk of disruption or failure due to damage or exceedance of system capacity. 6 , 58 , 70 , 74 , 75 Aging drinking water infrastructure is one longstanding limitation in controlling waterborne disease, and may be especially susceptible to failure. 6 , 13 , 74 For example, there are more than 50,000 systems providing treated drinking water to communities in the United States, and most water distribution pipes in these systems are already failing or will reach their expected lifespan and require replacement within 30 years. 6 Breakdowns in drinking water treatment and distribution systems, compounded by aging infrastructure, could lead to more serious and frequent health consequences than those we experience now.

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