About Lesson 9

We have seen now the projected potential future changes in climate. What practical impacts might they have? On human civilization? On ecosystems? Necessarily, the answers to these questions are complex and nuanced. They involve integrating a number of uncertain factors—the future greenhouse emissions pathways, the resulting changes in climate, and how human and natural systems might respond to those changes.

What will we learn in Lesson 9?

By the end of Lesson 9, you should be able to:

• Qualitatively assess the potential societal and environmental impacts of alternative future climate change scenarios.

What will be due for Lesson 9?

Please refer to the Syllabus for specific time frames and due dates.

The following is an overview of the required activities for Lesson 9. Detailed directions and submission instructions are located within this lesson.

• Watch the film "Before the Flood". Take note of any issues regarding the science and/or impacts of climate change that are worthy of discussion.
• Read:
  • IPCC Fifth Assessment Report, Working Group 2 [1]
    • Summary for Policy Makers [2], p. 1-8; Supplementary Material, p. 30-32;
  • Dire Predictions, p. 118-149.
• Take Quiz #3.

Questions?

If you have any questions, please post them to our Questions? discussion forum (not e-mail), located under the Home tab in Canvas. The instructor will check that discussion forum daily to respond. Also, please feel free to post your own responses if you can help with any of the posted questions.

As we saw in the last lesson, sea level is projected to rise more than a meter over the next century, and perhaps as much as five meters by 2300, given business-as-usual fossil fuel emissions. Scenarios such as 10 meters of sea level rise are not out of reach should, e.g., the west Antarctic ice sheet collapse more abruptly than is indicated by uncertain current model estimates.

The impacts of rising sea level will be differentially felt by different nations and regions. For low-lying island nations like the Maldives, even the lower-end sea level rise scenarios represent a distinct threat. In fact, some island nations, such as Tuvalu, have already made contingency plans for evacuation in the decades ahead.

Figure 9.1: Landing on the Island of Falalop in the Ulithi Atoll.

Credit: Public Domain

When asked about climate change impacts on Pennsylvania, I sometimes joke that Jersey Shore, PA [3] may have nothing to fear [4] from sea level rise directly, but all of those Pennsylvanians who make an annual summer pilgrimage to THE Jersey Shore would surely see the effects, as the beaches are increasingly eroded, and will ultimately be inundated.

Figure 9.2: Projected Sea Level Rise on the New Jersey shoreline.  Projections range from 2.5-6 feet.

Credit: Rutgers University Sea Level Fact Sheet [5]

Even moderate sea level rise (i.e., much less than a meter) can lead to significant increases in coastal erosion and other problems, such as salt water intrusion, wherein saline water penetrates increasingly inland through estuaries and tributaries, contaminating fresh water ecosystems and aquifers relied upon for fresh water supply.

There is also a natural component to changes in sea level in North America. As the Laurentide Ice Sheet that once covered a large part of Northern North America melted at the end of the last Ice Age, the Earth's crust beneath it has slowly rebounded, which has led to ascending motion of the ground in the regions where the ice load was greatest, e.g., the region of the Hudson Bay, and subsiding motion farther away, e.g., the east coast and especially the Gulf Coast. This so-called isostatic adjustment adds a local sea level change component which adds to, or subtracts from, the overall change in global sea level (the so-called eustatic sea level component). This regional component can be comparable to the overall global sea level rise over the past century.

Figure 9.3: Historical Changes in Sea Level for Various Coastal Cities of North America.

Credit: Mann & Kump, Dire Predictions

On the other hand, the local component is small compared to the 1 to 5 m sea level rise that is projected over the next one and two centuries under business-as-usual emissions. With 1 meter of sea level rise, we would see the disappearance of low-lying regions of the Gulf Coast, including the Florida Keys. At 5-6 meters of sea level rise we would see the loss of the southern 1/3^rd of Florida and many of the major cities of the Gulf Coast and East Coast of the U.S. At 10 meters of sea level rise, New York City would be submerged.

Figure 9.4: Map of Lost Northeast Coastal Land as a Function of Increasing Levels of Global Sea Level Rise. Most of New York City and Boston would be submerged if sea level were to rise by 6 meters.

Credit: Mann & Kump, Dire Predictions: Understanding Climate Change, 2^nd Edition
© 2015 Pearson Education, Inc.

Figure 9.5 Maps of Lost Southern Florida Coastal Land as a Function of Increasing Levels of Global Sea Level Rise.

Credit: Mann & Kump, Dire Predictions: Understanding Climate Change, 2^nd Edition
© 2015 Pearson Education, Inc.

One can measure the costs of increasing levels of sea level rise in terms of (a) the loss of land area, (b) the damage to our economy as measured by gross domestic project (GDP), and (c) the increase in population impacted either directly (by inundation or increased erosion) or indirectly (by, e.g., by saltwater intrusion into fresh water supply). In the scenario of 10 meters of sea level rise, not entirely out of the question on a timescale of a few centuries, the global costs as measured by any of the above metrics are rather staggering: more than 5000 square km of coastal land lost, nearly three trillion dollars of GDP lost, and more than a third of a billion people exposed to direct or indirect impacts of sea level rise.

As we will see later in this lesson, for many coastal regions the costs will be compounded by the added impact of greater hurricane damage.

Figure 9.6: Costs as Measured by Various Metrics of Increasing Levels of Global Sea Level Rise. Note that losses are sizeable even in the event of l meter of sea level rise, which could plausibly occur by the end of this century.

Credit: Mann & Kump, Dire Predictions: Understanding Climate Change, 2^nd Edition
© 2015 Pearson Education, Inc.

Climate change is already having a demonstrable impact on natural ecosystems and this is particularly evident when looking at niche (e.g., mountain and high-latitude) environments, where species are highly adapted to the prevailing past climatic conditions and have gone extinct, or are in the process of potentially going extinct because of rapidly shifting climatic conditions.

The poster child of climate change-related extinction is the Golden Toad. This magnificent amphibian once ranged throughout the high-elevation cloud forests of Monteverde, Costa Rica. First discovered in the 1960s, the toad appears to have gone extinct in the late 1980s. Scientist Alan Pounds and his colleagues have argued that the demise was due to climate change associated with a long-term drying as the cloud forests have been lifted to higher and higher elevations by a warming atmosphere (the warmer the atmosphere, the higher the so-called lifting condensation level at which clouds first form as one moves up in elevation). Other scientists have since noted that the influence of climate change in this extinction event was likely somewhat more subtle—with the immediate factor having been outbreaks of a fungus known as chytrid (this fungus has been implicated in globally-widespread decline in amphibian populations). The drying conditions may have made the golden toad more susceptible to these fungus outbreaks.

Figure 9.7: The Golden Toad (extinct).

Credit: Public Domain

Another poster child is the Polar Bear. Polar bears require a sea ice environment to hunt their primary food source—seals. As we saw in our previous discussion of climate change projections [6], it is very possible that with a little more than 1°C warming (which we likely commit to with ${\text{CO}}_{\text{2}}$ concentrations higher than 450ppm) that environment will essentially disappear within the next century—that is to say, there will be an increasingly long ice-free period from the spring through the fall over most of the polar bear's range. This means that the hunting season for polar bears is getting increasingly short. The impacts are already seen in the declining weights of adult females and the adverse impact this is having on the sustainability of current polar bear populations.

An adult female needs to maintain a minimum of roughly 200 kg of fat to bring a cub to term, and even more to bear twin or triplet cubs. Such reserves were achievable in the past by feasting on seals over a roughly 8-month hunting season. As the hunting season becomes shorter, females are finding themselves unable to sustain these fat reserves. The relative abundance of triplet and twin cub births has already largely given way to single cub births. One recent study by polar bear expert Andy Derocher of the University of Alberta indicates (see, e.g., this news article in the Calgary Herald [7]) that with as little as a one month additional shortening of the season, the majority of adult female polar bears will be unable to bring even a single polar bear cub to term. While some populations of polar bears in the Arctic have actually shown modest increases in the past (generally due to hunting restrictions and other miscellaneous factors unrelated to climate), a majority of well measured populations have indeed shown steady declines in recent decades (see, e.g., the detailed information on polar bear populations [8] provided by the organization Polar Bears International). Other species, such as walruses too may be under similar threat from Arctic warming and sea ice disappearance.

Figure 9.8: Polar Bears in Their Arctic Sea Ice Hunting Grounds.

Credit: Wikimedia Commons [9]

Because of the imminent threat to the species of ongoing warming and Arctic sea ice decline, the U.S. formally designated the polar Bear as a threatened species in May 2008 under the endangered species act.

We have looked at two particularly striking examples of climate change impacts on animal species, but it is worth stepping back and looking at the bigger picture, considering for example, entire ecosystems. There is no better example than coral reefs.

In polar regions, coastal regions, and a narrow band of wind-induced oceanic upwelling near the equator the upwelling of deep water supplies nutrients (e.g., phosphorus, nitrogen, oxygen, etc.) needed to maintain the rich trophic structure that characterizes these marine ecosystems. In contrast, almost all of the tropical and subtropical oceans lack the upwelling of deep water necessary to supply the nutrients. Therefore, these regions generally become oceanic "deserts" that are largely devoid of biological productivity. An important exception are coral reefs, made up largely of the dead calcium carbonate skeletons of previously live coral, which build over time to create elaborate natural reef structures. These structures provide an environment that is home to a rich oceanic food chain. While they occupy less than 0.1% of the world's oceans, they are home to 25% of all marine species, constituting a major reserve of marine biodiversity. Coral reefs, like many other ecosystems (e.g., tropical rainforests) provide so-called ecosystem services—that is to say, they provide resources (e.g., food, recreation and tourism, medicinal products, shoreline protection, etc.) that are of great value to civilization. It has been estimated that the average annual ecosystem services provided by coral reefs globally is a staggering nearly 0.4 trillion dollars. Of course, one could argue that no such dollar figure can truly capture the value of something like the world's coral reefs, and that simple economics and cost/benefit analysis cannot measure the true value to humanity of the ocean's biodiversity or of natural wonders such as the Great Barrier Reef of Australia. We will revisit these deeper, philosophical questions in a later lesson. For now, suffice to say that the loss of coral reefs could represent a monumentally great cost to civilization and our environment.

As it happens, coral reefs are under multiple assault by anthropogenic influences. The whole of these impacts is greater than the sum of their parts, since organisms subject to simultaneous stresses have a greatly reduced behavioral elasticity/adaptive capacity. In addition to the impacts of anthropogenic ${\text{CO}}_{\text{2}}$ increases, coral reefs are threatened by pollution, i.e., chemical contaminants that enter coastal waters through river runoff, and by physical destruction by humans via motorboat damages or misuse/overuse by the tourism industry. Increased damage by ultraviolet (UV) radiation due to ozone depletion is also a factor.

Increases in atmospheric ${\text{CO}}_{\text{2}}$, however, may be the proverbial straw that broke the camel's back. This is particularly true because it is a double whammy for corals. First, there is the effect of the warming itself. When ocean waters become exceptionally warm (e.g., into the low 30's °C), the algae that typically live with corals will flee, seeking cooler waters. Since the corals maintain an important symbiotic relationship with these algae, losing them is highly detrimental to the health of the coral. The algae are also what give the corals their color—hence, when these symbionts flee, they leave behind only the white color of the coral themselves, and the event is thus termed coral bleaching. There is little in nature that provides quite the contrast of the comparison between a healthy and bleached coral reef.

Figure 9.9: Healthy (left) vs Bleached (right) Coral Reef.

Credit: NOAA [10]

As sea surface temperatures increase, the frequency of bleaching events increases accordingly. Thus, ongoing global warming is projected to lead to increasing stress on coral reefs from bleaching alone. Coastal damage from more intense hurricanes are an added threat [11]. An even greater impact, however, is likely to arise from direct effects of the increasing atmospheric ${\text{CO}}_{\text{2}}$ concentrations, the phenomenon of ocean acidification [12] discussed in an earlier lesson.

Figure 9.10: Decline in Coral Growth Rate with Increasing ${\text{CO}}_{\text{2}}$ levels of Carbon Dioxide derived from a combined model and observation study.

Credit: Cantin, et al. 2010 Science [13]

Figure 9.11: Decline in Coral Growth Rate with Increasing ${\text{CO}}_{\text{2}}$ levels of Carbon Dioxide.

Credit: Mann and Kump, Dire Predictions: Understanding Global Warming (DK, 2008)

As atmospheric ${\text{CO}}_{\text{2}}$ concentrations increase, the increased dissolved ${\text{CO}}_{\text{2}}$ in the upper ocean acts to lower the pH of the ocean. As the ocean becomes more acidic (or, if you like, less basic—technically speaking the ocean is on average alkaline, not acidic), the ocean chemistry increasingly favors the dissolution of calcium carbonate (calcite)—the very substance corals use to grow their skeletons. This means that coral growth rates decline. If we extrapolate this relationship based on a middle-of-the-road future fossil fuel emissions scenario, we reach the point of zero coral growth by the end of this century. In reality, the collective effects of other impacts, in particular increased bleaching from warming ocean waters, has lead scientists to project a far more imminent demise of coral reefs worldwide—as soon as a few decades from now—if we continue with business-as-usual fossil fuel emissions (see, e.g., this news article about a UNESCO-funded scientific study [14] of this issue).

It is convenient to summarize the impacts on animal species, ecosystems, and biodiversity in terms of a "thermometer" scale that characterizes the degree of species loss, etc., as a function of additional warming. We already saw that amphibians in particular are under threat from global warming. With less than 2°C additional warming, we might see widespread disappearance of amphibians, and above 2°C warming, a loss of as much as a third of all species. At 3°C additional warming, we could see as much as a 50% loss of all species worldwide. At 4°C warming, that rises to as much as 70%.

Figure 9.11: Threat to Species and Ecosystems, a Function of Degree of Future Warming.

Click Here for Text Alternative for Figure 9.11

Biodiversity Impact Scale:

1. +0.6 Degrees Celcius: Widespread extinction of amphibians begins
2. +1 Degree Celcius: Krill populations reduced, threatening penguin survival
3. +1.6 Degrees Celcius: 9 percent to 31 percent species extinction, Arctic ecosystems damaged with half of wooded tundra lost, All coral reefs undergo bleaching.
4. +2.2 Degrees Celcius: 15 percent to 37 percent species extinction, Up to 25 percent of large mammals in Africa threatened or extinct
5. +2.6 Degrees Celcius: Major loss of tropical rainforests, with biodiversity losses from climate change exceeding those due to deforestation
6. +2.9 Degrees Celcius: 21 percent to 52 percent species extinction
7. +3.1 Degrees Celcius: Corals Extinct
8. +3.7 Degrees Celcius: Ecosystems lose 7 to 74 percent of areal extent
9. + > 4.0 Degrees Celcius: 40 - 70 percent species extinction

Credit: Mann & Kump, Dire Predictions: Understanding Climate Change, 2^nd Edition
© 2015 Pearson Education, Inc.

Water is essential to life and it is essential to human civilization. Either too much or too little is a problem. And as we have seen in Lesson 7 [15], climate change may, ironically, give us both.

Figure 9.12: Examples of Flooding (left) and Drought (right).

Credit: Both photos are in the public domain

As atmospheric circulation patterns and storm tracks shift, and changing rainfall patterns combine with the effects of changing evaporation and changing runoff patterns, one thing is for certain—water resources will be impacted. The greatest threat is the uncertainty of increasingly irregular and shifting patterns of precipitation.

In some regions, like the desert southwest of the U.S., climate change threatens to reduce fresh water availability due to both decreased winter rainfall and snowfall that ultimately feeds major reservoirs through spring runoff. Current projections are that Lake Powell, which provides southern Nevada with much of its fresh water supply, may run dry within a matter of decades, extrapolating recent drying trends. These decreases in water supply are on a collision course with demographic trends, as population centers, such as Las Vegas and Phoenix, continue to expand in size. Similar scenarios are likely to play out in Southern Europe and the Mediterranean, the Middle East, Southern Africa, and parts of Australia.

Other regions, meanwhile, are projected to get too much water. Bangladesh, already threatened by rising sea level, is likely to see increased flooding from the intense rainfalls expected with a warmer, more moisture-laden atmosphere.

Figure 9.13: Shifting Water Resources [Enlarge [16]].

Click Here for Text Alternative for Figure 9.13

• Serious Negative Impacts: The negative impacts of changing precipitation patterns outweigh the benefits. For example, the increases in annual rainfall and runoff in some regions are offset by the negative impacts of increased precipitation variability, including diminished water supply, decreased water quality, and greater flood risks. There is hope, however, that in some cases, adaptations (e.g. the expansion of reservoirs) may offset some of the negative impacts of shifting patterns of water availability.
• More Frequent Extreme Drought Events: Climate model simulations predict that the spacing between consecutive extreme drought events (defined as once-in-a-hundred-years events) will decrease sharply in many regions by the 2070s for the "middle of the road" emissions scenario.
• Future Climate Change Impacts on Water
  • U.S. - A steady increase in the population of cities in desert climates such as Phoenix and Las Vegas is occurring at precisely the same time that drought conditions are worsening
  • South America - Aquifers will be depleted 75% by 2050. 
  • Southern Europe and the Mediterranean - Many arid and semi-arid regions, such as the Mediterranean and parts of Southern Europe, Southern Africa, and much of Australia, are likely to suffer from increased drought. Electricity production potential to hydropower stations may decrease by more than 25% by 2070.
  • Africa - The spread of disease will increase due to more heavy precipitation events in areas with poor water supplies and an overtaxed sanitation infrastructure. 
  • India - In many coastal regions there will be plenty of water, but it will be the wrong kind! A sea level rise of 0.1 m (0.3 ft) by 2040-2080 will threaten the fresh water supply. 
  • Bangladesh - Areas with increased rainfall and runoff will suffer from an enhanced risk of flooding. The impacts are likely to be especially harsh for regions like Bangladesh, which is already facing the pressures of rising sea level. 
  • Worldwide - More than 15% of the world's population depends on the seasonal melt of high elevation snow and ice for fresh water. The melting of glaciers and ice caps represent a serious threat. 

Credit: Mann & Kump, Dire Predictions: Understanding Climate Change, 2^nd Edition
© 2015 Pearson Education, Inc.

Climate change is likely to challenge global food security, but the situation is complicated. Longer growing seasons in northern latitudes could prove favorable for growing crops, but even moderate warming is likely to lead to substantial decreases in productivity for key cereal crops grown in the tropics—rice, wheat, sorghum, maize. These crops are growing at what is essentially their optimal temperature, and any warming leads to substantial decreases in yield. Added to the mix is the direct impact of the increase in ambient ${\text{CO}}_{\text{2}}$ concentrations. There is empirical evidence that the impact of so-called ${\text{CO}}_{\text{2}}$ fertilization could also lead to increases in productivity. Plants require ${\text{CO}}_{\text{2}}$ for photosynthesis, so, to the extent that ${\text{CO}}_{\text{2}}$ is a limiting factor in cereal crop growth, increasing ${\text{CO}}_{\text{2}}$ levels might increase productivity. Yet, there are additional factors that might mitigate this effect. As we have seen previously in Lesson 7 [15], large parts of the tropical and subtropical continents are projected to see drying soils as a result of anthropogenic climate change (one exception is central and eastern equatorial Africa—but there is little consensus among models). To take in ${\text{CO}}_{\text{2}}$ for the purpose of photosynthesis, plants must maintain open stomata—but at the same time, this increases evapotranspiration, which is a problem as conditions become drier, and water itself becomes a limiting factor. Indeed, any increase in drought stress could easily offset the benefits of longer growing seasons in extratropical regions.

Thus, projecting precisely how agricultural yields will respond to ongoing climate change is quite uncertain, because it requires knowing not only how seasonal temperature patterns will change, but also knowing how regional rainfall and drought patterns will be impacted. This uncertainty notwithstanding, best estimates based on driving theoretical crop models with climate change projections suggest that for 1 to 2°C additional warming we could see modest increases in agricultural productivity in extratropical regions, but substantial decreases in tropical regions. Similar patterns hold for livestock yields, which themselves rely on feedstocks (see the map below). For warming exceeding 3°C, however, we begin to see sharp decreases in global agricultural yields. Some of the limitations of these projections should be kept in mind. Indeed, they may be overly optimistic because they do not account for other potentially detrimental climate change impacts, such as decreased fresh water supply (see the previous section on water resources) for irrigation, or severe weather events, such as the catastrophic Pakistan floods and Russian wildfires last summer, which devastate crops and impair distribution system, and which have been blamed for recent spikes in global food prices. These additional aggravating factors could have devastating consequences for agriculture (see, e.g., this article in The Economist [17]).

Figure 9.14: Projected Climate Change Impacts on Agricultural Productivity by Mid 21st Century Given Moderate Emissions.

Credit: Mann & Kump, Dire Predictions: Understanding Climate Change, 2^nd Edition
© 2015 Pearson Education, Inc.

In our next lesson on adaptation to climate change, you will investigate these impacts in detail in the context of possible adaptive strategies for mitigating the impacts. For now, we will neglect the prospects for adaptation and simply focus on the projected impacts of climate change on agriculture. To be precise, we will focus on three key cereal crops: wheat, rice, and corn/maize. The impacts are taken from the results of theoretical crop models driven by global warming projections. One limitation that should be kept in mind is that the crop model predictions do not account for other potentially important factors, such as decreased precipitation and fresh water supply. That having been said, such models provide, at the very least, some basic framework for assessing specific potential climate change impacts—as we will see in the next lesson, they can also inform the process of climate change adaptation.

Play around with the interactive application below, and investigate the impacts on the various cereal crops for different amounts of future projected warming, for both tropical and extratropical regions. Be prepared to discuss your findings in next week's discussion. This analysis will be useful to you in advance of our next project, in which we will use a similar interactive application to investigate possible adaptation measures for mitigating climate change impacts on agricultural productivity.

We have already seen that climate change is likely to increase the frequency and severity of many types of severe weather impacts, [18] including heat waves, intense precipitation events, and more intense hurricanes [19].

In North America, we have already seen increased damages, likely related to these increases. Among these is the rise in tropical storm-related damages (though there is some debate about precisely how much of a role has been played by the increase in storm intensity, and how much of a role has been played by increases in coastal infrastructure, real estate values, etc.). We have also seen an increase in damages due to increases in "fire weather", i.e., meteorological conditions such as warm and dry weather, which favor destructive wildfires.

Figure 9.15: Pattern of temperature change over North America in recent decades. The greatest warming is found in the northwest, but all regions have warmed. 

Credit: Mann & Kump, Dire Predictions: Understanding Climate Change, 2^nd Edition
© 2015 Pearson Education, Inc.

Figure 9.16: Severe Weather-Related Damages in North America.

Click Here for Text Alternative of Figure 9.16

Earth

This graph shows how relative sea levels on the North American coast have changed over the last century. In some regions, such as eastern Canada, the rising of the coastline due to Earth's slow rebound from the last ice age has largely offset the sea level rise resulting from global warming. In other regions, such as the Gulf Coast of the United States, this rebound is having the opposite effect and compounding sea level rise.

Wind

Hurricane energy and powerfulness have increased in recent times in the United States. It is interesting to note that while damage from storms is increasing--not only due to escalating stomr energy and power, but also because of growing coastal populations and more coastal development--mortality hasn't. This is thanks largely to better warning systems and evacuation measures. Still, punishing stomrs have the potential to wreak havoc, especially on property and infrastructure, in many coastal communities.

Fire

This graph compares trends in surface temperature and forest area burned in Canada over the past 100 years. Warming temperatures mean longer fire seasons, larger forest fires, and a heightened threat to human communities and forest ecosystems. A confluence of record-breaking heat, drought, and fuel load has led to unprecedented wildfires in the western U.S. in recent years. Extreme heat and dryness in Eurasia led to an unprecedented outbreak of hundreds of wildfires in Russia during the summer of 2012. The combined record heat and smoke generated smog that led to over 50,000 deaths across Russia. Damages were estimated to exceed U.S. $15 billion.

Credit: Mann & Kump, Dire Predictions: Understanding Climate Change, 2^nd Edition
© 2015 Pearson Education, Inc.

We saw earlier in this lesson that shifting water resources represent a potential climate change threat. In Europe, for example, both extreme drought and flooding due to intense rainfall are likely to incur damages. More powerful winter storms are likely to impact the economies of both Europe and North America (see, e.g., this news article discussing the impact of especially severe winter storms [20] during 2011 winter on air travel in North American and Europe).

Figure 9.17: Severe Weather-Related Damages in Europe.

Click Here for Text Alternative of Figure 9.17

Selected potential climate change impacts in various parts of Europe:

• More frequent forest fires
• Biodiversity losses escalate
• Negative impact on summer tourism
• Heat wave impacts grow more serious
• Cropland losses as well as losses of lands in estuaries and deltas
• Thawing of permafrost
• Substantial loss of tundra biome
• More coastal erosion and flooding
• Greater winter storm risk
• Shorter ski season
• More Coastal flooding and erosion
• Stressing of marine ecosystems and habitat loss
• Increased tourism pressure on coasts
• Greater winter storm risk and vulnerability of transport systems to high wind conditions
• Increased frequency and magnitude of winter floods
• Heightened health threat from heat waves
• Decreased Crop yield
• More soil erosion
• Increased salinity of inland seas
• Severe fires in drained peatland
• Disappearance of glaciers
• Shorter snow-cover period
• Upward shift of tree line
• Severe biodiversity losses
• Shorter ski season
• More frequent rock slides

Credit: Mann & Kump, Dire Predictions: Understanding Climate Change, 2^nd Edition
© 2015 Pearson Education, Inc.

Climate change is likely to impact human health in a number of ways. On the one hand, we might expect decreased mortality from extreme cold, but the flip-side is a dramatic increase in warm extremes and heat waves. The young and the elderly, as well as the poor—who are less likely to have access to modern air conditioning, etc., are most at risk. The toll of the unprecedented heat wave in Europe of summer 2003 [21], where more than 30,000 lives were lost, is a possible harbinger of the impact of future, more frequent and intense heatwaves, and to a lesser extent, so are the European heat waves of 2006 [22] and 2010 and, in North America, of 2006 and 2010.

Other weather extremes may have human health impacts. In some cases, such as the physical damage and loss of life from land falling hurricanes, this is obvious. But there are many other examples. Intense rainfall events leading to flooding can cause physical harm or create conditions that favor the spread of disease or lead to various ailments. Drought conditions pose the obvious threat of limiting fresh water supply, but they can also favor disease and malnutrition. Once again, the impacts fall disproportionately on the poor, who are the least able to afford clean water, electricity, and modern health care.

Climate change is also likely to lead to the spread of various types of infectious disease. Many of these diseases are spread by so-called vectors—pests, such as insects and rodents, which are capable of spreading the disease far and wide. In many cases, the ranges of vectors are restricted by climate. Diseases such as West Nile Fever and Malaria, for example, are spread by mosquitoes. Temperate regions with killing frosts are thus relatively inhospitable to the disease, as they interrupt the life cycle of the vector and thus the disease itself. As the globe warms and cold regions retreat poleward, we can expect the regions where diseases currently classified as "tropical diseases" are endemic to spread well into the extratropics. The outbreak of West Nile Virus in New York State in 2005, for example, was likely due to an unusually warm winter, which allowed mosquitoes to persist through much of the year.

Figure 9.18: Regions of the World Where Malaria is Endemic.

Credit: NASA Outreach

The story is not quite as simple as that, however. Consider malaria. There are reasons why malaria can be found far into the subtropics of Asia and South America, but not, in the U.S. This has to do with the fact that industrial nations, like the U.S., have adequate resources to eradicate Malaria through the use of appropriate health practices and technology that is not available to third world nations.

Moreover, the connection with climate is a bit more complex than warmer temperature = more malaria. Here at Penn State, we have experts who are studying the potential impacts of warming temperatures on the spread of malaria [23]. The problem is complicated, in part, because it is not just the average temperature that determines how rapidly the malaria parasite can reproduce. It turns out that there is a threshold dependence on temperature (recall our discussion of thresholds in the context of climate tipping points [24]). The malaria parasite reproduces at an exponentially greater rate above a particular threshold temperature, roughly 20°C. This is why highland tropical African cities such as Nairobi, with an elevation of nearly 5000 feet and a mean annual temperature of 19°C, are generally free of malaria, even while surrounding lowland regions must contend with the disease. This threshold dependence on temperature also implies that one must not only consider the mean temperatures, but also the variability of temperatures, to assess possible impacts on the spread of malaria. Let us demonstrate this through an example.

The threshold dependence of malaria on temperature means that the problem of projecting climate change influences on malaria is even more challenging than we might have thought. One must be able to project not only how mean temperatures will change, but also how the diurnal temperature range, the seasonal cycle, and even the inter-annual variability might change. And since there is much uncertainty about whether, e.g., ENSO events will be larger or smaller as a result of anthropogenic warming, there is much uncertainty, too, in how the amplitude of inter-annual variability in temperatures will change in many parts of the world.

Of course, temperature is not the only climate variable that might influence malaria. Rainfall matters too: the fewer breeding spots available for the disease vector (anopholes mosquitoes), the less likely that malaria takes hold. Unfortunately, as we have seen, projections of future changes in precipitation in regions such as Kenya is quite uncertain (see the Precipitation and Drought page of Lesson 7 [15]), largely because of uncertainties in ENSO. This makes projecting impacts of climate change on infectious disease particularly challenging.

Opponents to action often present the challenges of climate change as if they are the sole concern of "granola-crunching tree huggers [25]". While it may be convenient, from a rhetorical perspective, for climate change deniers to caricature concern over the climate change threat in this manner, it is not very accurate at all. In reality, the national security community—hardly a bunch of environmental extremists—are among the communities most concerned about the potential impacts of projected future climate changes.

We have already seen that climate change could threaten food security, water security and health security. As there has often been the fierce competition for limited resources—be it food, water, land, etc.—it is reasonable to draw the conclusion that climate change may challenge national security. In fact, that is the conclusion of the U.S. Military. You can hear Dr. David Titley (formerly a Rear Admiral, the Navy's official oceanographer, and most recently a Professor of Practice at Penn State University and Director of the Center for Solutions to Weather and Climate Risk) discussing the potential national security threats of projected future climate change in this video:

Video: TED Talk - "How the Military Fights Climate Change" (7:41)

You can also find a thorough discussion of the potential national security threats of climate change in this report, The Age of Consequences: The Foreign Policy and National Security Implications of Global Climate Change [27], published by the Center for Strategic International Studies, and co-authored by leading national security experts including former CIA director James Woolsey [28].  There is also a documentary of the same name looking at climate change and national security.

One recurring theme in discussions of U.S. national security impacts is the potential military implications of retreating Arctic sea ice. In recent years, the mythical "Northwest Passage" has finally opened up on a semi-regular basis. That is to say, it is now possible, over part of the year, for ships and submarines to travel unimpeded from the Labrador sea through the Arctic ocean, into the Pacific ocean. As the trajectory of sea ice retreat continues and the open channels widen and deepen, it will likely be possible for large military vessels (ships and submarines) to make this route. That would have deep implications for U.S. national security. Suddenly, the U.S. would need to defend a new (Arctic) coast line against potential invasion and military attack.

Figure 9.19: Opening of the Northwest Passage.

Credit: Mann & Kump, Dire Predictions: Understanding Climate Change, 2^nd Edition
© 2015 Pearson Education, Inc.

Other scenarios involve the idea that increased conflict between nations and cultures may arise from so-called environmental refugeeism—people fleeing regions no longer fit for habitation for other currently occupied regions, thereby increasing the competition for resources. As parts of Sub-Saharan Africa, such as Senegal, become too dry and inhospitable for subsistence agriculture, for example, there may be a flood of human refugees fleeing this environment to the less arid south, e.g., to Ghana (indeed, there is evidence this is already happening). Another scenario is that the extremely large populations of interior Nigeria, driven by drying conditions, flee for the mega-city of Lagos to the south, where there is heightened competition for food and water resources. Adding to the incendiary mix is the skirmishes that might break out among groups and individuals fighting over the last remains of the disappearing oil reserves of the Niger River Delta, and the cronyism and political corruption that may ensue. Consider also the impact of an increasingly dry Middle East. Author Daniel Hillel has argued in Rivers of Eden [29]that it is the competition for scarce water resources over the years that has driven much of the Middle East conflict. Imagine adding further fuel to the fire as water resources continue to disappear. New York Time's columnist (and Nobel Prize winner in economics) Paul Krugman has argued that climate change-related stresses on food supply [30] may have had a role in recent unrest and uprisings in the region, such as that recently witnessed in Egypt. A more recent article on water supply [31] can be found here.  Could that be a sign of things to come?  

The worst-case scenarios that researchers have envisioned are not entirely unlike the dystopian futures portrayed in 1970s and 1980s apocalyptic films such as Soylent Green and Mad Max.

Figure 9.20: "Mad Max" - a Dystopian Vision of Our Future.

Credit: Moviefone [32]

In this lesson, we looked at the potential impacts of projected climate change on civilization and our environment. The key impacts under continuing anthropogenic carbon emissions are:

• Projected sea level rise could threaten many coastal and low-lying regions of the world by the end of this century; low-lying island nations could be submerged. Within two centuries, major east coast and Gulf coast cities would be severely impacted. Costs from damage to coastal infrastructure could rise to a third of a billion dollars for the U.S., and millions of individuals could be displaced.
• Certain species such as the Golden Toad have already gone extinct, at least in part due to climate change. Many other amphibians, and iconic megafauna such as the Polar Bear, are already under threat from climate changes. Projected losses of species could approach 1/3 with only 2°C additional warming, and well over half of all species with 3°C warming. The combined impact of warming oceans and increasing ocean acidity from anthropogenic greenhouse emissions, combined with other human-caused threats such as pollution and ozone depletion, place coral reefs—which account for 25% of the ocean's biodiversity—under threat of disappearance in as soon as a few decades.
• Shifting water resources threaten damage to societal infrastructure through increased precipitation intensity and flooding during certain seasons in some regions, and increased drought during other seasons in other regions. In regions such as the desert southwest of the U.S., decreasing water supply is on a collision course with increasing populations in cities such as Las Vegas and Phoenix.
• Health impacts of climate change are likely to include increased mortality due to more frequent and intense heat waves, increased spread of disease from more widespread flooding and drought, threats to health and life from more increased storm damage, and the poleward spread of tropical disease with warming temperatures.
• National security impacts of climate change include increased conflict arising from the competition between nations and groups for diminishing land, food, and water resources, and the need for additional national defense as new shipping routes and coastlines open as a result of diminished arctic sea ice.

Reminder - Complete all of the lesson tasks!

You have finished Lesson 9. Double-check the list of requirements on the first page of this lesson to make sure you have completed all of the activities listed there before beginning the next lesson.