More than half of all frogs, toads and newts living in Europe could be driven to extinction within 40 years as climate change, diseases and habitat destruction take their toll, scientists warned last night.

The majority of the most threatened species live in Mediterranean regions, which are expected to become warmer and drier. Island species, such as the Mallorcan midwife toad and Sardinian brook newt, are especially at risk because they are unable to move to cooler climates.

In Britain, where viruses are already wiping out many hundreds of amphibians a year, conservationists fear for the future of the common toad, natterjack toad and crested newt.

Researchers described the bleak outlook for Europe's amphibians at a meeting of the Zoological Society of London last night. Sir David Attenborough, who was due to attend the symposium, said: "Amphibians are the lifeblood of many environments, playing key roles in the function of ecosystems, and it is both extraordinary and terrifying that in just a few decades the world could lose half of all these species."

One in three of the world's amphibians are already on the International Union for the Conservation of Nature's red list of endangered species, with some estimates suggesting 150 species have already become extinct since the 1980s.

The expansion of towns and cities into natural habitats is chiefly to blame for the amphibians' precarious future, but many scientists believe climate change and diseases are acting together as a double whammy. "A lot of European amphibians, especially those found in the Mediterranean, cannot move to find more suitable habitats, because they are surrounded by sea water, which they can't tolerate, or they are blocked off by mountain ranges," said Trent Garner, research scientist at the Zoological Society of London.

Snakes, fish and birds that prey on the amphibians are already showing some signs of decline as the staple of their diet dies out. The disappearance of some amphibians is also expected to lead to a rise in insects and other creatures that amphibians feed on. "Given that many of the things that amphibians eat are the things that destroy our crops or bite us and suck our blood, we might be feeling some of the effects a bit more directly than we've expected," said Garner.

Ten years ago, scientists raised the alarm after finding vast numbers of amphibians were being wiped out by chytrid fungus, which infects the skin through which many of the animals drink and breathe. Scientists in Australia now suspect they have lost nine species to the infection.

In recent decades chytrid fungus has spread rapidly, appearing almost everywhere there are amphibians. Some scientists believe the fungus has become more deadly as a result of climate change. One alarming case has been seen in the Peñalara national park near Madrid, where the climate has become more humid and the fungus has caused mass mortality among amphibians.

Garner and his colleagues based their assessment on published research into the effects of climate change on amphibian habitats, and believe more than 40 species could be extinct by 2050. One study showed that as global warming alters the climate in Europe, almost every amphibian habitat would be affected. "It's horrifying to think that you can have a large group of organisms suffer such a catastrophic decline. Over 150 species may have gone extinct already in the past few decades and to me that is unacceptable," said Garner.

In Britain, infections caused by a family of pathogens called ranaviruses, which emerged in the 1980s, are causing widespread deaths among some of the most common amphibians. "When people find frogs in their gardens that look emaciated with sores all over their bodies, and quite often with toes missing, that is probably ranavirus," said Garner.

Scientists at the meeting will emphasise the need to reduce the effects of climate change by reining in greenhouse gas emissions, but for many species that will come too late. In the short term, conservationists are urging zoos to set up captive breeding programmes for the most threatened amphibians.