Overview

Principles of sustainable development

Gated communities

ISSUES

ISSUES

CLIMATE CHANGE

Climate change once again poses a threat to life on the planet, but whereas past climate change occurred through natural processes, human activity is strongly implicated in the present changes. It is now generally accepted that climate change is a reality. There are many indicators that average global surface temperatures are steadily increasing, with the 14 hottest years since measurement began occurring in the last two decades of the 20th century, 1998 being the warmest year on recordⁱ. A study of global warming fingerprints by seven organizations, drawing on reports by scientists from across the world, has shown that many of the world's lower altitude glaciers are disappearing. At the current rate of disappearance, scientists predict the loss of all central and eastern Himalayan glaciers by 2035. Furthermore, mean surface temperatures in the Arctic and Antarctic have risen, with subsequent melting of permafrost causing land subsidence of as much as ten meters in the Alaskan interior and the loss of ice shelves in Antarctica.ⁱⁱ

Climate change, coupled with the impact of human activity, is also linked to an increase in the occurrence of natural disasters. The world has experienced three times as many natural disasters in the 1990's as in the 1960'sⁱⁱⁱ. While the number of geophysical disasters has remained fairly steady, the number of hydro-meteorological disasters since 1996 has more than doubled. During the past decade over 90 per cent of those killed by natural disasters lost their lives in hydro-meteorological events such as droughts, windstorms and floods^iv. In his 1999 Report the UN Secretary-General described 1998 as the worst on record for weather-related natural disasters. It is estimated that the extreme weather events of 1998 cost the world about 90 billion US dollars. In the 2001 World Disaster Report^v, 1998 has been replaced by 2000.

Several factors contribute to climate change, the most important of these being our emissions of greenhouse and ozone-depleting gasses. Since pre-industrial times, atmospheric concentrations of CO2 has increased from a relatively stable 286ppm to 367ppm in 1998, that of methane has doubled. The percentage of gaseous chlorine, a major ozone depleting substance, has increased with 85% since measurement started in 1978. The Mauna Loa record shows a 16.6% increase in the mean annual concentration of CO2, from 315.83 parts per million by volume (ppmv) of dry air in 1959 to 368.37 ppmv in 1999. The 1997-98 increase in the annual growth rate of 2.9 ppmv represents the largest single yearly jump since the Mauna Loa record began in 1958.^vi While there are arguments that the increase in CO2 levels is a natural phenomenon, it cannot be denied that human activity is responsible for almost 45% of current global CO2 emissions, and that this contribution is increasing^vii. It is predicted that at current rates of consumption, CO2 levels will have doubled within the next 100-150 years. However, if consumption rates are adjusted at present growth levels, the effect may be a tripling of CO2 levels in 400 years^viii.

The construction industry's activities are responsible for 20-30% of greenhouse gas emissions. The biggest culprits are the materials that form the basis of modern construction - concrete and steel. Twice as much concrete is used in construction around the world than the total of all other building materials including wood, steel, plastic and aluminium. World production of cement is 1.56 billion metric tonnes. Cement production is, after the burning of fossil fuels, the biggest anthropogenic contributor to greenhouse gas emissions. Cement kilns have been identified as a stationary source of nitrogen oxides, releasing more than 25 tonnes per year.^ix Although cement makes up only 12-14% of the final concrete mix, further embodied energy comes from the transportation and extraction of aggregates, and in the case of reinforced concrete, the manufacturing of steel. Steel is one of the most energy-intensive materials. Together the production of iron and steel is responsible for 4.1% of global energy use^x . The manufacturing and final use of both these materials are also very water-intensive. Table 4 gives an indication of the water use and CO2 emissions of the most popular modern materials.

Material	CO2 emissions*	Water use
Cement	1.1t CO2/t cement	3.6 t of water/t of dry cement
Clay brick	0.25 tCO2/t of brick	0.5t of water/t of clay brick product
Glass	2 t CO2/t glass	--
Steel	1.2 t CO2/t steel	300 t of water/t of steel

*Source: European Commission. 1999. A Green Vitruvius. London: James & James.
Data in metric tonnes

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