Biological impacts

The character of the land surface, whether it is hardwood forest or grassland for example, is determined to a large extent by climatic forcing. Temperature is important of course, although it may be the coldest temperature of the year, or the warmest, rather than the annual average. Precipitation also plays a huge role in shaping the natural landscape.

The infinite complexity of the real landscape can be modeled by simplifying it into some manageable number of different biome types, such as "tropical deciduous" or "savanna" (Plate 12.5). Biomes can be modeled by keeping track of the essentials, the budgets of energy, water, and nutrients for example. Different biomes have different capabilities and tolerances, and they compete with each other for land surface area.

The equilibrium biome response to a new climate can probably be predicted fairly confidently because the distribution of biomes on Earth today is fairly well correlated with climate. The simplest model for terrestrial biomes could simply be a look-up table of the ranges of conditions inhabited by each biome type.

It is more difficult to forecast transitions between one climate state and another. When climate changes, the optimal biome type for some spot on Earth might change. In mountainous areas, biomes may be able to move to higher elevation where it is cooler (remember the lapse rate?). In flat places, the climate shift could be hundreds of kilometers. Some organisms, like insects, move immediately, but for others, like trees, the story is a bit more complicated. Of course we are not talking about walking trees, we are talking about seeds and new trees, and a process called ecological succession. When a forest grows after a clear cut, for example, the first set of plant and tree species will be different from the species that you would find in an old-growth forest under the same climatic conditions. The process of ecological succession is not trivial to understand in the real world, which makes it even more difficult to forecast for the future.

Coral bleaching events

Coral bleaching events

1980

1990 Year

Fig. 12.12 Coral bleaching events in Tahiti. Bleaching events occur whenever temperature exceeds a threshold value. A future warming of 2.5°C would be very large compared with the coral stress level. From Hoegh-Guldberg (2005).

1980

2.5°C warming

1990 Year

2000

Fig. 12.12 Coral bleaching events in Tahiti. Bleaching events occur whenever temperature exceeds a threshold value. A future warming of 2.5°C would be very large compared with the coral stress level. From Hoegh-Guldberg (2005).

The biotic response of the climate model from before is shown in Plate 12.5. The most striking change in the Earth's landscape is in the Arctic. The biome response is strong there because the climate change is intense because of (let's all say it together) the ice albedo feedback. The melting permafrost described above also changes the biotic landscape. The model in Plate 12.5 experienced a near total loss of the tundra biome by the year 2300, and the loss of most of it by 2100.

Melting of sea ice in the Arctic has the native polar bear on the brink of extinction. Polar bears only eat in the winter, by fishing for seals through holes in the ice. In summer, when the ice near the coast melts, the polar bears have to live on their accumulated fat. With further melting of Arctic ice, the extinction of natural polar bears is virtually certain.

In the ocean, coral reefs appear to be particularly vulnerable. Reefs are built by sedentary animals, the corals, that house symbiotic algae, plants that can perform photosynthesis to aid the nutrition of the corals. Coral reef ecosystems are among the most diverse on Earth. Reefs of one type or another have been found throughout the fossil record, yet coral reef systems today appear to be rather fragile. If the water is not clear enough, the symbiotic algae will not get enough light, and the coral will suffer. Corals build the reef from CaCO3, the production of which becomes more of a challenge as the seawater becomes acidified by rising CO2 concentrations. Overfishing threatens the coral community, in particular fishing by means such as dynamite or cyanide poison as practiced in some parts of the world. Corals have also been ravaged by diseases and by invasive species.

In addition to all of these struggles, corals are vulnerable to increases in temperature (Fig. 12.12). When corals are stressed, they respond by expelling their symbiotic algae. This is called coral bleaching because of their loss of color. Bleaching may be a mechanism for the coral to try to find new symbiotic algae that are more suited to the conditions they find themselves in, but it is a measure of desperation. Bleaching is often followed by the death of the coral. Figure 12.12 shows a record of temperatures in Tahiti, with arrows indicating times of coral bleaching events. The correlation between heat spikes and bleaching is very clear. Sediment cores in Caribbean reefs indicate that the degradation of reef communities is more widespread than has been seen in centuries. The projected warming in the future looks like it will have catastrophic effect on corals.

In general, the diversity of life (number of species) on Earth is already decreasing because the natural world is restricted and fragmented by human land use. Climate change can only amplify this extinction trend by demanding that natural ecosystems get up and move, just when they are hobbled and unable to do so.

Was this article helpful?

0 0
Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

Get My Free Ebook


Post a comment