The biosphere as part of the physical Earth System: Just to review, we have discussed:

  • The origins and consequences of global climate change from a physical science perspective.

  • We have discussed the importance of the biosphere to human society.

    The general uncomfortable relationship between human civilization and biodiversity is well known. A synopsis of major events that relationship that have unfolded in North America might include:

    The climate change connection The last four items on this list are arguably connected. Now let's consider the effects of global change on the biosphere. Remember, the physical processes in which climate change is manifested, involve basic requirements of organisms. Thses include changing:

    The oceans: The most basic fact of global climate change is the accumulation of CO2 in the atmosphere. CO2 is notoriously water soluble, so the atmospheric CO2 concentration increase is followed by an increase in dissolved CO2 in the shallow oceans. Remember, deep and shallow ocean water don't mix much, so the CO2 is not making it into the deep oceans in quantity. Alas, most marine biomass inhabits this shallow sunlit layer.) What are the consequences?

    Oceanic acidification: The increase in oceanic CO2 concentration sets off a chain of consequences. The two big ones:

    This is a problem because:

    Observations to date include:

    No feel-good solutions: One problem with acidification of oceans is that it requires a direct solution to the problem of rising CO2 emissions. Schemes to block sunlight with artificial aerosols in order to lower global temperature have no effect.

    The past: We have already seen geologic records of the effects of ocean acidification:

    How does climate change effect life on land? It is tempting to think that as Earth warms and climate zones shift, critters can just follow the climate zones to which they are adapted. Sometimes, it works like that but more often not.

    Lessons from the past:

    No place to go: Organisms adapted to high latitudes/altitudes have no place to go. Those most directly effected are creatures of the arctic like polar bears, but creatures at home near the snow line of mountain slopes like the pika (right) are running out of space also.
    Artificial barriers and habitat fragmentation: Organisms requiring large home ranges, lacking the ability to move long distances to new habitats, or unable to cope with human conversion of landscapes to agriculture or urbanization are unable to navigate the patchwork of natural environments left by human encroachments.

    A recent analysis by Thomas et al. models the probability of species extinction based on expected changes in species ranges by 2050 and determine that depending on whether you assume minimum or maximum climate change, between 18% and 35% of species will be "committed to extinction" by 2050.

    "Temperature" does not equal "Climate": But all of that that takes a simplistic view in which we talk about shifting climate zones but really mean shifting temperature zones. Climate involves the interplay of many factors. E.G. Changes in the location and timing of rainfall will complicate the climate zone picture in many cases. Current observations are consistent with predictions:

    But this doesn't even consider the time scale. Evolutionary change normally occurs on the scale of million of years, ecological change on the order of millenia. Here we have a major climate change happening on an order of decades. Favors ecological generalists (i.e. weeds and pests).

    The changing ecology of the human animal

    Humans have the same basic needs as other animals, but most of us can't provide for those needs without the help of complex and fragile cultures, technologies, and structured societies. Thus, the consequences of global climate change for human society must take its cultural and political consequences into account. What follows is an oversimplification of diabolically complex topics that, nevertheless, sets the general tone.

    Context: The food crisis

    Human population is expected to top nine billion by 2050. Recent studies indicate that we will need between 70 and 100% more food than is currently harvested to feed these people. The green revolution of the 1970s addressed a similar need through the modernization of Asian agriculture, expansion of fisheries, and the bringing of more land under cultivation. Now the task is more difficult:

    The result is a yield gap. To meet future demand: But what that means is that agricultural monocultures have to be encouraged, despite the inherent risks. Finally, no projection of changing crop yields with the introduction of foreseeable technologies enables us to close the yield gap by 2050. Also, increasing the efficiency of global transport exacerbates the threat of CO2 production and transport of invasive species and disease.

    Add to this three major components of global climate change:

    1) Changing agricultural growth zones

    What changes can we expect in the behavior of our crops? We have said before, agricultural technology is tied to a given region. Thus, North American wheat couldn't just be grown in the Soviet Union, and today, however much we may wish it, the green revolution technologies that revolutionized farming in East Asia don't export to Africa. When the climate zone for American wheat shifts into Canada can we expect the wheat to transplant itself nicely?

    Plants are adapted to more than climate. They have specific soil requirements. In the central plains of the US, we have some of the world's best agricultural soils, combining loess, silt from glacial outwash, with copious humus. In contrast, Northern Canada's soils were largely stripped away by the glaciers and have barely recovered. Will those soils sustain our wheat yield?

    Assume that every major food crop faces a similar future.

    2) Changing rainfall distribution

    More than plants depend on rainfall. So does human civilization. In some regions of the world, water is the limiting factor to economic growth. (Indeed, the American west is dotted with ghost towns from optimistic overreach of the mid 20th century. E.G. Gotebo, OK, Merck's mother-in-law's home town)

    How is climate change expected directly to effect our access to water? We've noted changing rainfall patterns. Right now, water is the limiting factor on the increase of agricultural yield. Technical analyses suggest that 20% more irrigation water will be needed to close the yield gap by 2050 than are currently available. The projected impact of expected water resource changes by 2050 will be to double this shortfall in irrigation water. Southern China, the US southwest, and South Asia are expected to be especially hard hit. The net effect is significantly to exacerbate the future food crisis.

    3) Changing health threats

    Access to clean water is a major factor in world health. In some developing countries, water-born pathogens are major threats to public health. How will climate change effect this sector of human society? These issues are reviewed in 2003 by the Union of Concerned Scientists.

    Global climate change has two major components:

    Both factors favor increasing geographic range and longer active seasons for vector organisms that spread diseases, including: For example, mosquitoes are sensitive to temperature. Malaria-bearing Anopheles mosquitoes can't breed at temperatures below 16° C. (61° F). Dengue-bearing Aedes require 10° C (50° F). Also, mosquitoes would be more active at higher temperatures. Models indicate that a 3° C global temperature rise would increase annual malaria cases by 50-80 million. At greatest risk would be regions adjacent to current areas in which the diseases are active.

    Currently, outbreaks of malaria are occurring at higher elevations in the Andes and central Africa than previously. this spread is consistent with the retreat of alpine glaciers and the upward shift (on the order of 150 meters) in the 0° isotherm.

    Will it get too warm for mosquitoes? Not quickly. Recall that minimum temperatures are increasing faster than maximum temperatures. Thus, the range of Anopheles will expand faster, as a result of warmer minimum temperatures, than it will contract as temperatures approach it's maximum of 40°.

    Precipitation is the limiting factor for diseases spread by small mammals and their parasites, such as plague. In New Mexico, human plague infections first appeared in the 1940s and have risen substantially due to wetter winters and springs. Moister winters seem to favor either the fleas that spread the plague or the rodents that carry the fleas.

    We can expect tropical diseases and their vectors to spread into the mid latitudes. These include some of the most medically intractable diseases there are.
    The Human Response

    Major long-term environmental changes have been fatal to civilizations (E.G. the classic Maya, the Anasazi, and the Greenland Norse.) Modern society differs from preindustrial ones in two big ways:

    A 2007 review of global security threats from global climate change by the Center for Strategic and International studies, reviews the human dimension of the issues cited above in detail, but they focus on the lessons of history. Looking at previous major environmental changes and natural disasters, they note:

    The CSIS report examined expected, severe, and catastrophic scenarios for global change. They say:

    ANY scenario calls invokes three huge threats: