Some of the major impact of global warming on climate and living organisms are as follows:
(A) Climate Change (B) Climate Change and Plant Communities (C) Effect on Sea Levels (D) Reduction of Biodiversity (E) Effect on Agriculture (F) Effect on Arctic Ecosystems (G) Overall Effect.
(A) Climate Change:
It is believed that increased levels of greenhouse gases that cause global warming, have affected the global climate already and these effects will increase in future. According to IPCC (1996), the world climate has warmed from 0.3 to 0.6°C during the last century. Complex computer models of global climate predict that temperatures will increase further by 1°C to 3.5°C over the next century as a result of increased concentrations of carbon dioxide and other greenhouse gases.
The increase in temperature will be greatest at high latitudes and over large continents (Myneni et al, 1997). However, some scientists also predict an increase in extreme weather events such as flooding, regional drought and hurricanes associated with this warming (Karl et al. 1997). It seems likely that many species will be unable to adjust quickly to global warming and associated climate change.
As a result, biological communities may suffer profoundly. More than 10% of plant species in many temperate parts wall not be able to survive the new climatic conditions, they must migrate northward or die. This change has already been observed with alpine plants found growing higher on mountains and migratory birds spending longer times on their summer breeding grounds.
However, the effects of global climate change on rainfall and temperature are expected to be less drastic in the tropics than in the temperate zones. But even small changes in the amount and timing of rainfall will effect species composition and plant reproduction cycles. Changes in temperature and global climate can be expected to influence the biogeochemical cycles, which have already been perturbed by anthropogenic disturbances.
(B) Climate Change and Plant Communities:
Climatic changes as a result of global warming will naturally affect the biotic communities on this earth. Some plant species may utilize the increased CO2 concentrations and high temperature to increase their growth rates, but less adaptable species will decrease in abundance. Such unpredictable fluctuations in plant communities and associated herbivorous insect species could lead to the extinction of many rare species and great population increases in some other species.
As a result, the global climate change may restructure biological communities and change the distributional ranges of many animal and plant species. Some species may be in danger of going extinct in the wild and therefore new conservation strategies including captive breeding, will have to be adopted.
(C) Effect on Sea Levels:
Rising temperatures will cause glaciers to melt and the polar ice caps to shrink. As a result of this, sea levels may rise by 0.2 to 1.5 m and flood low lying coastal areas and their biotic communities. There is evidence that this process has already started. Sea levels have already risen by 10 to 25 cm over the last 100 years, possibly due to rising global temperatures (IPCC, 1996). If the trend continues, many low lying areas may be submerged in near future.
It is possible that rising sea levels may significantly change or destroy 20% -80% of the coastal wetlands. In tropical areas, mangroves will be adversely affected as seawater will be too deep in existing mangrove areas to allow the seedlings to develop. Rising sea levels are detrimental to coral reef species, which grow at a precise depth with optimum temperature and water movement.
It is possible that slow growing coral reefs will be unable to keep pace with the rise in sea level and will be gradually submerged and die and only fast growing coral reef species will be able to survive. This threat to coral reefs may be further compounded by increasing seawater temperatures. Abnormally high water temperatures in the Pacific Ocean during 1982 and 1983 caused the death of symbiotic algae that live inside the coral. Subsequently, the “bleached” coral suffered a massive dieback of 70%-95% coral cover of die area to depths of 18m (Brown and Ogden, 1993).
(D) Reduction of Biodiversity:
As mentioned above increased temperatures, inundation of some coastal biological communities and changes in the pattern of distribution of many species over a long period of time are likely to cause reduction in biodiversity in aquatic and terrestrial ecosystems.
(E) Effect on Agriculture:
The global climate change may have important effects on agriculture (Rosenweig and Parry, 1994). However, the effects of this change will vary for C3 (e.g., wheat, rice, beans) and C2 (e.g., maize, millet, sugarcane) plants. As temperatures increase with rising levels of CO2, some crop plants may no longer be grown in certain regions. According to Ricklefs and Miller (2000), under the most common models of global climate change, global temperature increases will have negative effects on both C2 and C4 plants unless the higher levels of CO2 in the atmosphere increase plant growth.
(F) Effect on Arctic Ecosystems:
Global climate change will have profound effects on arctic ecosystems. Studies on the response of arctic Tundra to elevated CO2 indicated that the Tundra is more sensitive to global climate change than most other ecosystems on earth. According to Shaver et. al (1992), warmer temperatures may increase primary production, thereby increasing carbon input and soil respiration, thereby increasing carbon output. The extent to which production may be increased is constrained by the availability of nitrogen.
(G) Overall Effect:
The overall effect of global warming on world climate has many dimensions, some of which are discussed above. The natural greenhouse maintains the earth’s temperatures within the limits for physiological functions. But studies suggest that even a moderate increase in the average global temperature could result in significant changes in biotic communities including reduction in biodiversity both in terrestrial and aquatic ecosystems.