The floods that have devastated Italy over the past week could become even more severe in the future, threatening food production and destroying the country's natural beauty, experts warn.

Storms have battered ancient towns and left large swaths of farmland in Tuscany under water, prompting a warning from the region's governor, Enrico Rossi, that "climate change is making us get used to ever more violent flooding".

Three people were found dead on Tuesday after their car fell from a collapsed bridge near Grosseto, while the town of Albinia was under two metres of water. As army units were called in to help locals evacuate, towns in neighbouring Umbria were also put on alert and sections of the main road linking north and south Italy were blocked by water. On Monday a 73-year-old man was drowned in his car by rising floodwaters near the walled town of Capalbio, with residents evacuated near Cortona, the setting for the novel Under the Tuscan Sun. Much of the rich farmland of the Maremma had become a lake of mud.

Rising temperatures due to climate change could mean wild arabica coffee is extinct in 70 years, posing a risk to the genetic sustainability of one of the world's basic commodities, scientists said on Wednesday.

Although commercial coffee growers would still be able to cultivate crops in plantations designed with the right conditions, experts say the loss of wild arabica, which has greater genetic diversity, would make it harder for plantations to survive long-term and beat threats like pests and disease.

Monsanto and other agribusiness and food companies have spent more than $45m (£28m) to defeat a California ballot measure that would require labelling of some GM foods. The measure, proposition 37, is one of the most contentious initiatives on California's election ballot on Tuesday.

If it passes, it would require labels on GM food sold in supermarkets, but would not cover restaurants. It also has a number of gaping loopholes. For example, the law would not require labels on meat from animals that were fed GM corn.

Retail bodies and charities have criticised the government for setting "weak" targets on the use of sustainable palm oil.

The Department for Environment, Food and Rural Affairs (Defra) yesterday asked retailers, manufacturers and charities to sign up to "work towards" ensuring that, by 2015, all palm oil used in food and other products is responsibly produced and does not contribute to deforestation.

But the British Retail Consortium (BRC) said that while the government deserved praise for putting the palm oil issue on the agenda, many of its members had already made more ambitious commitments. The BRC wants other sectors to commit to nothing less than the Roundtable on Sustainable Palm Oil (RSPO) standards for sustainable palm oil.