Top scientists say the latest international report on climate change shows that Canadians must wake up to the impact of warming temperatures on land, on water and in communities across the country.

They say the Intergovernmental Report on Climate Change, released Sunday in Japan, shows changes are on their way and further delays in responding to them only narrow the options.

"We no longer have the option of choosing between mitigation and adaptation," Debra Davidson, a University of Alberta sociologist and lead author on the report, said Monday.

"We're already locked into a global warming scenario in which adaptation will be absolutely necessary if we want a reasonable quality of life," said Davidson, one of more than 2,000 scientists and expert reviewers from 70 countries who contributed.

The report says crop patterns will need to shift. Although some studies predict better growing conditions in more northern latitudes, disruptions to normal rain and snowfall patterns will cause problems, it suggests.

"There's always been some predictions in some areas that some crops will do better," said John Smol, a biologist at Queen's University in Montreal. "But if the drought frequency continues, what's the economic cost of a 10-year drought?"

Some Canadian lakes are already seeing algae blooms increase at rates that can't be explained by agricultural run-off, he said. Popular fish such as lake trout could be threatened by changing patterns of spring thaw and winter freeze-up.

Floods, too, will be an issue for Canada, predicted Andrew Weaver, a British Columbia Green party legislature member, climate modeller and lead author on previous editions of the report. The number and value of insurance claims are already on the rise in Canada, he pointed out.

The report warns the entire fresh-water ecosystem of the vast boreal forest that stretches almost across the country is under threat.

"Rates of climate change associated with medium- to high-emission scenarios pose high risk of abrupt and irreversible regional-scale change in the composition, structure and function of terrestrial and fresh-water ecosystems," it says. "Examples that could lead to substantial impact on climate are the boreal-tundra Arctic system."

Look for other nations to eye Canada's abundant fresh water with envy, Weaver warned.

"If you look at the climate projections, we get a heck of a lot more water and the southern U.S. gets a heck of a lot less. Where we have water, we get more, where they don't have water, they get less.

"There are issues of water transportation that are going to raise their head in the near future whether we like it or not."

Davidson warned that the consequences of climate change will fall more heavily on poor communities. Wealthy centres have more money to upgrade homes, build seawalls or buy more insurance. They're more likely to have better infrastructure in the first place.

And if they need to change how they fish or farm, they can make the investments more easily.

"A poor community will have relatively fewer resources at the household level," Davidson said.

Canada needs to stop thinking about climate change as something that only affects sea ice or low-lying tropical islands, said Smol.

"These are things that many people in the scientific community have known and have been saying 'It's getting worse and worse and worse and worse. And if anything, the rate of getting worse is accelerating.'

"The longer we wait, the harder it is to do anything. And we're losing options."

An Environment Canada scientist was one of the lead authors of the study. The department declined to make him available for an interview and instead outlined in an email the measures the federal government has taken to fight climate change.

A 2012 report by Environment Canada acknowledged the country will miss its 2020 greenhouse gas reduction targets by nearly one-third.

In question period in Ottawa on Monday, Liberal MP Joyce Murray from British Columbia took Prime Minister Stephen Harper's Conservatives to task.

"Rather than doing its part to fight climate change, the government's track record is clear: take credit for provincial actions, mock all proposals to make polluters pay, cut Environment Canada's climate change and clean-air budget massively, heckle from across the aisle and cheat future Canadians of their right to climate security," Murray said.

Environment Minister Leona Aglukkaq said the government has been "committed to protecting the environment while keeping the Canadian economy strong since 2006.

"Our government has invested significant funds in more efficient technology, better infrastructure and adaptation of clean energy."

Megan Leslie, NDP environment critic, pointed out that Canada now ranks dead last among OECD countries when it comes to climate change.

"The ... report is clear," she said. "Canadians are already dealing with the stark realities of climate change and it is only going to get worse."

Aglukkaq again replied that the government has invested "more than $10 billion in green infrastructure, energy efficiency, adaptation, clean technology and cleaner fuels."