Thursday, 24 December 2009

Climate change – nature or human nature?

The key question is this: climate change is now widely accepted as being a reality, so, is it a natural process in a sequence of climate changes that have occurred over the paleoclimatic record or is it being driven by humans? If we hold to the former view then all we can hope for is to adapt as best we can to the climate disruption. On the other hand, if we accept that it is largely human induced, then it follows that we ought to be able to do something about it.
There is widespread agreement among climate scientists worldwide that the present clear evidence of climate change is 90 per cent certain to be due to human activity mainly though the burning of fossil-based energy. This should be good enough to persuade us that human action can ultimately put a brake on the progress of global warming and its climate consequences.
Once the issues are understood, a commitment to renewable energy sources and bioclimatic architectural design should become unavoidable. Inspiring that commitment is the purpose of the first part of the book which then goes on to illustrate the kind of architecture that will have to happen as part of a broader campaign to avert the apocalyptic prospect of catastrophic climate change.

The carbon cycle
Carbon is the key element for life on Earth. Compounds of the element form the basis of plants, animals and micro-organisms. Carbon compounds in the atmosphere play a major part in ensuring that the planet is warm enough to support its rich diversity of life.
The mechanism of the carbon cycle operates on the basis that the carbon locked in plants and animals is gradually released into the atmosphere after they die and decompose. This atmospheric carbon is then taken up by plants which convert carbon dioxide (CO2) into stems, trunks, leaves, etc. through photosynthesis. The carbon then enters the food chain as the plants are eaten by animals.
There is also a geochemical component to the cycle mainly consisting of deep ocean water and rocks. The former is estimated to contain 36 billion tonnes and the latter 75 million billion tonnes of carbon. Volcanic eruptions and the weathering of rocks release this carbon at a relatively slow rate.
Under natural conditions the release of carbon into the atmosphere is balanced by the absorption of CO2 by plants. The system is in equilibrium, or would be if it were not for human interference.
The main human activity responsible for overturning the balance of the carbon cycle is the burning of fossil fuels which adds a further 6 billion tonnes of carbon to the atmosphere over and above the natural flux each year. In addition, when forests are converted to cropland the carbon in the vegetation is oxidised through burning and decomposition. Soil cultivation and erosion add further carbon dioxide to the atmosphere.
If fossil fuels are burnt and vegetation continues to be destroyed at the present rate, the CO2 in the atmosphere will treble by 2100. Even if there is decisive action on a global scale to reduce carbon emissions, atmospheric concentrations will still double by this date.
With the present fuel mix, every kilowatt hour of electricity used in the UK releases one kilogram of CO2. The burning of one hectare of forest gives off between 300 and 700 tonnes of CO2.
These are some of the factors which account for the serious imbalance within the carbon cycle which is forcing the pace of the greenhouse effect which, in turn, is pushing up global temperatures.

The greenhouse effect
A variety of gases collaborate to form a canopy over the Earth which causes some solar radiation to be reflected back from the atmosphere, thus warming the Earth’s surface, hence the greenhouse analogy. The greenhouse effect is caused by long-wave radiation being reflected by the Earth back into the atmosphere and then reflected back by trace gases in the cooler upper atmosphere, thus causing additional warming of the Earth’s surface (Figure 1.1).

Figure 1.1: The greenhouse ‘blanket’

The main greenhouse gases are water vapour, carbon dioxide, methane, nitrous oxide and tropospheric ozone (the troposphere is the lowest 10–15 kilometres of the atmosphere).
The sun provides the energy which drives weather and climate. Of the solar radiation which reaches the Earth, one third is reflected back into space and the remainder is absorbed by the land, biota, oceans, ice caps and the atmosphere. Under natural conditions the solar energy absorbed by these features is balanced by outgoing radiation from the Earth and atmosphere. This terrestrial radiation in the form of longwave, infra-red energy is determined by the temperature of the Earthatmosphere system. The balance between radiation and absorption can change due to natural causes such as the 11-year solar cycle. Without the greenhouse shield the Earth would be 33C cooler, with obvious consequences for life on the planet.
Since the industrial revolution, the combustion of fossil fuels and deforestation has resulted in an increase of 26 per cent in carbon dioxide concentrations in the atmosphere. In addition, rising population in the less developed countries has led to a doubling of methane emissions from rice fields, cattle and the burning of biomass. Methane is a much more powerful greenhouse gas than carbon dioxide. Nitrous oxide emissions have increased by 8 per cent since pre-industrial times (IPCC 1992).

Architecture in a Climate of Change: Peter F. Smith

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