Ecology. Michael Begon

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Ecology - Michael  Begon


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in what is called the ‘greenhouse effect’. The greenhouse effect was of course part of the normal environment before the Industrial Revolution and was responsible for some of the environmental warmth before industrial activity started to enhance it. At that time, the greater proportion of the greenhouse effect was due to atmospheric water vapour.

      CO2 – but not only CO2

Graph depicts the total annual anthropogenic greenhouse gas emissions from 1970 to 2010 converted to gigatonne equivalents of CO2 per year.

      Source: IPCC (2014).

      It is possible to draw up a balance sheet of how the CO2 produced by human activities translates into changes in concentration in the atmosphere. Human activities have released more than 2000 Gt CO2 since 1750, but the increase in atmospheric CO2 accounts for only 40% of this (IPCC, 2014). The oceans absorb an estimated 30% of CO2 released by human activities. Furthermore, recent analyses indicate that terrestrial vegetation has been ‘fertilised’ by the increased atmospheric CO2, so that a considerable amount of extra carbon has been locked up in vegetation biomass. And more is to be found as soil carbon. This softening of the blow by the oceans and terrestrial vegetation notwithstanding, however, atmospheric CO2 and the greenhouse effect are increasing.

      ocean acidification

      A large proportion of anthropogenic CO2 is absorbed by the oceans, thus far reducing seawater pH by 0.1 units since the Industrial Revolution (equivalent to a 30% increase in acidity) as well as reducing carbonate ion concentrations. We have already seen that pH is a condition with significant influences on the success of organisms, but the fact that many parts of the ocean are also becoming undersaturated with calcium carbonate minerals is expected to have profound consequences for calcifying species such as corals, molluscs, sea urchins and calcareous plankton. On the other hand, photosynthetic production in the oceans is likely to benefit from higher CO2 concentrations.

      2.9.2 Global warming

Graphs depict annual land and ocean surface temperature anomalies and sea-level changes. (a) Globally averaged combined annual land and ocean surface temperature anomalies from 1850 relative to the average over the period 1986–2005. Colours indicate different datasets. (b) Globally averaged annual sea-level changes from 1900 relative to the average over the period 1986–2005.

      Source: IPCC (2014).

      Predictions of the extent of global warming resulting from the enhanced greenhouse effect come from two sources: (i) trends detected in measured datasets, including the width of tree rings, sea‐level records and measures of the rate of retreat of glaciers; and (ii) predictions based on sophisticated computer models that simulate the world’s climate according to a variety of possible mitigation scenarios. The latter range from the best case, where there is a concerted and international political drive to minimise the temperature rise by the use and development of efficient technologies (e.g. switching to renewable energy and bioenergy, carbon capture and geological storage) to the worst case where very little is done and the expected outcome is close to the no‐mitigation baseline scenario.

      global distribution of climate change

      Global warming so far has not been evenly distributed over the surface of the earth, and neither will it be in the future. Northern high latitudes are expected to change more rapidly than the tropics, land areas will change more rapidly than the oceans, and small islands and coastal regions will be particularly prone to associated rises in sea level.

      We have emphasised how the distributions of species are strongly influenced by temperature and water availability, and how many organisms are impacted by occasional extremes rather than by average conditions. Computer modelled projections imply that global climatic change will also bring greater variance in temperature, rainfall, hurricanes and so on. Hence, not only the predicted average climate changes, but also the increased frequency and severity of extremes, are certain to be accompanied by marked responses in the distribution of species and biomes.

      can the biota keep up with the pace?


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