■ Snow cover duration falling to zero in most alpine regions. ■ Sea level rise of up to about 1.1 metres, likely increasing to more than seven metres over subsequent centuries even for no further global warming. The ratio of record high temperatures to record lows increased over the 20th century, and stands at greater than 2-to-1 for the last decade. Fire weather conditions showed a rapid increase in the late 1990s to early 2000s across much of south-eastern Australia. Looking into the future, the authors said models indicated a 4-degrees warmer scenario would lead to increases in record high temperatures and rainfall, extreme fire weather, large hail events on the east coast and more intense (but less frequent) cyclones. Yesterday's papers considered some of the impacts of such environmental changes on human health, cities, agriculture, oceans and terrestrial biodiversity.

For more information, go to www.fourdegrees2011.com.au Agriculture AUSTRALIA'S agricultural output will have shrunk so severely by the latter half of this century that it will no longer grow enough food to feed its populace, forcing the nation to rely on imports to meet demand. Climate scientists predict that if countries meet their current targets to reduce greenhouse gas emissions, global temperatures will rise by 4 degrees some time between 2055 and 2100. Australian agriculture will have been radically transformed and diminished by then, according to a paper presented in Melbourne yesterday by CSIRO scientist Mark Howden, at the Four Degrees or More? conference.

"Given the projections we've got, core cropping areas will become more marginal," said Dr Howden, chief research scientist with the CSIRO's climate adaptation flagship. Australia's vast wheat belt will have shrunk dramatically and crop yields for everything from rice and nuts to fruit and vegetables would increasingly be subject to drier, more sporadic rainfall patterns. The Murray-Darling Basin and its irrigated farmlands would be one of the areas hardest hit, as autumn, winter and spring rain decreased. In northern Australia, the dry season would become drier and the wet season would likely become wetter. Tropical crops such as bananas would be hit by more frequent extreme weather such as cyclones. Dr Howden said Australia's extreme weather would include "cyclones and storms, hailstorms, frosts, heatwaves, highly intense rainfall events, and sometimes high wind". Soil salinity would become less of a problem than it is now as the underground water table dwindled, but water-based soil erosion would increase.

Dr Howden said there already were examples of climate-based changes in Australian agricultural practices, including wine growers moving to Tasmania for its cooler climate and peanut producers moving from south-east Queensland to wetter parts of the Northern Territory. ADAM CAREY Oceans MARINE life in Australia's oceans will be radically changed by a 4-degree increase in the earth's temperature, with "catastrophic" results expected for the natural environment and the national economy. "Under the broad range of changes that are now being reported, it is hard to conclude that anything other than a collapse of marine ecosystem resources is likely as we move towards average global temperatures of 4 degrees or higher," marine scientist Ove Hoegh-Guldberg told the conference on global warming in Melbourne yesterday.

Professor Hoegh-Guldberg, the director of the Global Change Institute at the University of Queensland, said the Great Barrier Reef and many of Australia's fisheries would have changed "beyond recognition" by the end of this century. Changes in ocean temperature would greatly reduce stocks of phytoplankton - an essential fish food - during breeding times, causing widespread starvation. "The costs of this collapse, associated with other impacts from rising sea levels, are likely to cost the Australian taxpayer billions of dollars and reduce our quality of life significantly," Professor Hoegh-Guldberg said. The economic value of Australia's ocean territory is estimated by the CSIRO to be about $52 billion a year - 8 per cent of gross domestic product. Tourism would also be hit by large reductions in fish and coral life in the Great Barrier Reef.

Professor Hoegh-Guldberg rejected the theory that the reef would simply migrate south as the ocean warmed, saying that coral would have to move at 40 kilometres a year to keep pace with a 4-degree change in the earth's temperature. "The ability for coral species to disperse significantly over one generation is probably 10 kilometres or less," he told the conference. ADAM CAREY Cities AUSTRALIA'S 20 biggest cities could compete against each other to be recognised as the nation's most sustainable under a plan floated at the Four Degrees conference in Melbourne yesterday.

Sydney University's Phil McManus wrote that Australia's 20 biggest cities should consider becoming part of a "sustainability index" so that each city's vulnerability to climate change could be compared. "Given Australia's economic wealth, human resources and capacity for change, its cities should be leading the world in mitigation and adaptation measures," Professor McManus said. In his paper, Professor McManus said Australia was one of the world's biggest contributors of carbon equivalent emissions. "While Australia contributes less than 1.5 per cent of global greenhouse gas emissions, the rate of emissions per capita is among the highest in the world." Professor McManus argued cities could best mitigate climate change by reducing the consumption of products "where their manufacture and transportation generate significant greenhouse gas emissions". This

meant moving towards local production and reducing emissions from homes and businesses.

One of the proposals to help capture the imagination of residents was to develop a comparative index of the ways each city had adapted to climate change. Loading The index would look at issues such as what percentage of buildings and infrastructure were being resited away from areas of high vulnerability and the proportion of food grown locally. Separate criteria would include temperature and rainfall changes in each city, and the risk of flooding. Such an index would "foster

a spirit of friendly competition and have media salience", Professor McManus wrote. CLAY LUCAS