Western Australian towns along the coastline are among the most at risk in global climate change, according a new report from the Climate Commission.

The report, titled "The Critical Decade: Western Australia Climate Change Impact" estimates that areas of Western Australia including Mandurah, Bussleton, Rockingham and Bunburry are particularly threatened with flooding and coastal erosion. The report estimates that between 18,700 and 28,900 residential buildings are at risk from rising sea levels.

"A sea-level rise of 50 centimetres will lead to very large increases in the frequency of coastal flooding; flooding that is currently considered a one-in-100-year event would occur every year in most parts of WA and even more frequently in Perth," the report says.

More than 2,100 commercial buildings in WA and up to 9100 kilometers of roadway along the coast are also in danger.

"A sea-level rise of 50 centimetres will lead to very large increases in the frequency of coastal flooding; flooding that is currently considered a one-in-100 year event would occur every year in most parts of WA and even more frequently in Perth," the report says.

"Flooding events are likely to damage cities, towns and the supporting infrastructure in low-lying coastal areas and will lead to erosion of sandy beaches."

The report also says that the changing climate will affect crop yields in the state's wheatbelt and threaten the world-famous Ningaloo Reef and iconic Western Australian species such as the quokka and Carnaby's Cockatoo.

Climate Commissioner and report author Will Steffen warned that government should immediately act to reduce carbon emissions.

"We are more certain of the climate change risks for water resources for south-western WA than any other part of Australia," he said.

"Over the last 40 years we've watched the south-west of the state become markedly drier with significant impacts for agriculture and urban water supplies."

The state government has announced that it would double the Southern Seawater Desalination Plant at Binningup, north of Bunbury.

"Failing to take sufficient action today entails potentially huge risks to our environment, economy, society and way of life into the future," the report says.

Professor Steffen recommended a move to reduce carbon emissions in the economy and a shift to clean energy resources by 2050.

"The risks have never been clearer and the case for action has never been more urgent," Professor Steffen said.

"This is the critical decade. The decisions we make this decade will determine the severity of climate change impacts our children and grandchildren suffer."