Impacts of climate change

Note: My knowledge about this subject is mainly based in what I read in 2004-2010, some in Japanese, some in English. Regrettably, I am not good at showing sources of each item.

Note: Not all are impacts of climate change in the strict sense. Some are impacts of change of CO₂ concentration.

Note: Damages are more emphasized than beneficial effects, partly because compensation is unlikely.

Impacts on ecosystems (mainly on land, as for this section)

• Habitable spatial range of each species will change according to rise of temperature, change of water availability, rise of sea level etc. Some species face risk of extinction. (see, e.g. Lovejoy & Hannah, 2005).
• Sometimes species cannot find where to migrate. (e.g. Species that have adapted to polar or alpine cold climate; species that need sea ice.)
• Even if species have mobility, the velocity of climate change may be too fast for the species to catch up. Also, human activities other than climate change (e.g. land use change, fences) may hamper migration.
• Combination of species that constitute local ecosystems may change. The basic principle of nature consevation "conservation of wild ecosystems in place" may not be achievable. Artificial relocation may be necessary.
• Such discourse as "the humans is making a mass extinction of species of a remarkable magnitude in the history of the earth."
  • I think it is probably correct. But, the main causes are direct human intervention on ecosystems, such as land use change and fisheries.
  • Extinction because of anthropogenic climate change does exist, but I think it is minor.
  • Combination of direct intervention and climate change makes the problem more severe.
• (In addition to impacts of changes of climate (temperature, water)) direct impacts of carbon dioxide concentration in the atmosphere also exist.
  • If the transmittance of the stomata in leaves remains the same, plants can take more CO₂ in, so, can produce more organic matter by photosynthesis.
  • If water is the limiting factor, plants will tend to close their stomata, and save water while keeping photosynthesis.
  • The effect of CO₂ concentration on photosynthetic production depends on the mechanisms of photosynthesis. "C4 cycle" is more efficient than "C3 cycle" at the present CO₂ concentration, but C4's efficiency does not increase so much as C3's as CO₂ increases.

Impacts on agriculture

• Increasing CO₂ concentration may lead to increase of yields, or to decrease of demand of water, but neither are guraranteed.
• As temperature rises, present crops may become out of range of adequate climate.
  • e.g. In south-western half of Japan, rice yields (of such varieties currently planted in Japan) will decrease in such climate as projected for the late 21th century.
• As temperature rises, potential evaporation will increase everywhere, but precipitation will increase somewhere and decrease elsewhere. Thus, some continental areas are likely to have deficiency of soil water (droughts). The parts of the world where production of wheat or cattle seem vulnerable.
• In snowy parts of the mid-latitude lands (such as Hokuriku region of Japan), springtime irrigation depends on snowmelt at present climate. As temperature rises, winter precipitation becomes rain, so, water availability in spring will become lower. On the other hand, more cropland and more water will be available in winter.
• As sea level rises, rice paddies of the low lands (e.g. Ganges delta, Mekong delta) may lose productivity because of waterlogging or salinity.
• As adaptation, people need to change crops, variety of crops, season of plantation., etc.
• In addition to change of climate of the country one lives, change of climate of importers, exporters, competitors etc. also affects industries (including agriculture) and economies of one's country.

Impacts on marine ecosystems and bio-resources

• Projection is difficult.
  • Impacts of human activities (fisheries, pollution, garbage etc.) other than climate change are large.
    • (Note: in some cases, pollution such as nitrogen and phosphorus in coastal region may be beneficial to fishery and aquaculture.)
  • It is known that fish resourses are affected by so-called "regime shift" which is related to (presumably natural) decadal-scale variation of climate.
  • (My opinion) Resource management including regulation of fisheries is necessary. But, because we cannot predict well, the way of management must be adaptive.
• Ocean acidification ... distinct from global warming, though the cause is same.
  • Increase of CO₂ concentration in the atmosphere results in increase of carbonate substance (CO₂, HCO₃^-, CO₃^2-) in seawater, and lower pH.
  • CaCO₃ becomes more soluble. Such organisms that produce CaCO₃ shells (sea shells, corals, etc.) have difficulty in survival.
• Rising temperature results in ...
  • Change of the geographical regions which are suitable to species. Can species migrate and adapt?
  • "Bleaching" of coral reefs (loss of algae that are in symbiosis with corals) becomes more likely.
  • Less vertical mixing of near-surface sea water
    • Less dissolved oxygen in sub-surface layer, perhaps less productivity
    • Less nutrients (such as phosphorus) in surface water, perhaps less productivity

Reference(s)

See [books] page, in particular the section of "Impacts of climate change on ecosystems and biodiversity, issues of their conservation".