Environmental change and natural hazards the impact in the twentyfirst century

From the perspective of the first year of a new millennium, the impact of rapid-onset geophysical hazards over the course of the next century is difficult to forecast, particularly in light of the major uncertainties attached to predictions of environmental change over this period. Perhaps some constraints can be imposed, however, on the basis of climate change impact forecasts made in a recent report by the UK Meteorological Office (1999) (Box

8.1), and based upon the second Hadley Centre climate model. Assuming unmitigated greenhouse emissions, the report predicts a global temperature rise of 3 degrees Celsius by 2080, accompanied by a 41-cm rise in global mean sea level. Substantial diebacks of tropical forests and grasslands are forecast, while forest growth is promoted at higher latitudes. Water availability is predicted to fall in some parts of the world while rising in others, and patterns of cereal yields are expected to undergo similar dramatic changes. In natural hazard terms, an increase in coastal flooding is the most obvious consequence of the forecast changes, and the UK Met Office itself predicts a rise in the number of people affected annually from 13 to 94 million. Population growth in coastal zones is estimated using a projection of existing trends and assumes that the frequency of storms remains constant. Changes in either of these parameters would result in an even greater rise in coastal flood impact. In addition to an increase in major discrete flood events, elevated and rising sea levels will ensure progressive impacts on many coastlines, including inundation and increased erosion with the potential to cause instability, slumping and landslide formation. A consequence of the dieback of tropical forests and grasslands -forecast to affect 3 million km2 by the end of the century - is an increase in desertification, which is likely to lead to a rise in the numbers and severity of dust storms in the affected regions. Desertification is likely also to be exacerbated in some regions, such as Australia and southern Europe, by reduced river run-off, while

Box 8.1 Forecast environmental change: the world in 2080 assuming unmitigated greenhouse gas emissions

Climate change

Global average temperature increase 3 degrees C

Natural ecosystems

Substantial dieback of tropical forests and tropical grasslands (particularly in northern South America and central South Africa)

Considerable growth of forests in North America, northern Asia and China

Water resources

Substantial decrease in the availability of water from rivers in Australia, India, Southern Africa, most of South America, and Europe Increase in the availability of water from rivers in North America, Asia (particularly Central Asia), and central eastern Africa Three billion people will suffer increased water resource stress

Agriculture

Increase in cereal yields at high and mid-Source: UK Meteorological Office (1999)

latitudes such as North America, China, Argentina and much of Europe Decrease in cereal yields in Africa, the Middle East and, particularly, India

Coastal effects

Sea level will be about 41 cm higher than today

The average annual number of people flooded will increase from 13 million to 94 million. The majority of the increase will occur in South Asia (from Pakistan, through India, Sri Lanka and Bangladesh, to Burma) and South-East Asia (from Thailand to Vietnam, and including Indonesia and the Philippines)

Sea-level rise will compound the decline of coastal wetlands

Sea-level rise will produce a range of progressive impacts on coastal lowlands and on low-lying coastal islands

Human health

An estimated 290 million additional people will be at risk of falciparum malaria (clinically more dangerous than the more widespread vivax malaria), mainly in China and Central Asia increased run-off in North America and parts of Asia and Africa may contribute to more flooding.

Prospects for windstorm frequency and severity in the late twenty-first century are unclear and at present difficult to model, owing to inadequate resolution in current climate models. Nevertheless, some recent modelling and theoretical studies predict a modest increase in the intensity of both tropical and extratropical cyclones, which, coupled to possible changes in circulation patterns, could result in significant increases in the windstorm hazard for some regions.

The UK Met Office report (1999) also includes alternative scenarios assuming stabilisation of atmospheric carbon dioxide at 550 ppm and 750 ppm. Stabilisation at the lower figure would delay a rise of 2 degrees C (expected by the 2050s with unmitigated emissions) for 100 years, while stabilisation at the higher figure would result in a 50-year delay. The coastal flood impacts of sea-level rise would also be reduced under the stabilisation scenarios. However, the warming already incurred will ensure that global sea-level rise continues for many centuries.

Continue reading here: Natural hazards the human dimension

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