Glaciers and icebergs of the Greenland ice cap are seen over Greenland on Aug. 17, 2005. Patterns show the ice is being pressed away from the middle of the island, with glaciers sliding slowly between mountains before breaking off into icebergs that float out of the fjords. Rising temperatures in Arctic regions is one of the likely scenarios of climate model predictions. (Associated Press)

For years, scientists have known the Earth was becoming a warmer place and at a faster rate in recent times: 11 of the highest average global annual temperatures recorded have come in the past 12 years. But despite growing evidence, the science behind our changing climate has continued to be hotly debated in legislatures and boardrooms around the world.

On Feb. 2, 2007, the UN's Intergovernmental Panel on Climate Change released a report — backed by 2,000 climate scientists from 113 countries — that attempts to put aside lingering doubts about the human role in the phenomenon.

The IPCC report says man-made activities such as the burning of fossil fuels and to a lesser extent intensive agriculture are "very likely" — more than 90 per cent certain — to be behind the hotter temperatures and rising sea levels.

The major findings of the report:

Global warming is 'very likely' caused by man-made greenhouse gas emissions. Exisiting greenhouse gas levels will lead to rising temperatures, higher sea levels and more extreme weather such as heat waves, droughts and more intense hurricanes.

Average worldwide annual temperatures will increase between 1.8 and four degrees over the next century.

Sea levels will rise between 18 and 59 cm over the same time period.

(Source: IPCC Summary for Policy Makers)

The report represents the strongest language yet from the United Nations organization on climate change since it issued its first report in 1990.

It's a stance reflective of a growing confidence within the scientific community in the depth, scope and predictive value of the research, said John Fyfe, a research scientist at Environment Canada's Centre for Climate Modelling and Analysis and one of the contributors to the report.

"All of these different lines of evidence are telling us the same story," said Fyfe.

Here, we examine their findings and what they could mean for Canadians.

What does the report tell us?

The essence of the report is simple: the warming of the world's climate is "unequivocal" and man's fingerprints are all over the phenomenon, particularly through the emissions of carbon dioxide.

Global warming is the increase over time of the Earth's average surface temperature. In general, it works like this: the sun shines on the Earth. Most of those rays pass through the Earth's atmosphere, although some are reflected back into space. The planet's surface — either the land or water — absorbs the energy. Some of that heat energy is re-emitted and travels back up into the atmosphere.

Greenhouse gases like carbon dioxide, methane and nitrous oxide in the atmosphere can trap that heat on the way up, however, warming up the Earth's surface even more. The climate of the Earth has always been in flux, including periods of sustained warming and cooling, and greenhouse gases have played a role in those changes. Without naturally-occurring greenhouse gases, the Earth would be about 33 degrees Celsius colder than it is, a temperature hostile to human life.

"Carbon dioxide is by far the biggest contributor to warming," said Fyfe. "Part of the reason is that it is so long-lived. Unlike aerosols, it can exist perpetually in the atmospheric system."

The IPCC report's findings have shown global atmospheric concentrations of carbon dioxide were 379 parts per million in 2005, far above the natural range of between 180 to 300 ppm over the past 65,000 years and significantly higher than in the pre-industrial era. And levels of the gas in the atmosphere have continued to rise in the past 15 years alone.

The new analysis of the warming and cooling effects on the planet connects the rise in carbon dioxide to rising temperatures, with researchers saying with "very high confidence" that the net effect of human activities since 1750 has been one of warming.

"Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising mean sea level," the report states.

"We have said the warming is unequivocal," said Ken Denman, a senior research scientist at the Canadian Centre for Climate Modelling and Analysis and one of the authors of the study.

"When physical scientists say something, they don't like to say 'certain,' but I think that means certain," he told CBC News.

Alarming predictions

The bones and a skull from dead cattle lie at a water hole in the village of Hadado in northern Kenya on Sept. 20, 2006. Climate models predict more severe droughts in subtropical regions. (World Food Program/Associated Press)

Even more disturbing are the report's projection of the Earth's climate 100 years from now.

The report predicts that, at current carbon dioxide levels, the global temperature will rise by 1.8 to 4.0 degrees Celsius — an increase that will be even greater at higher latitudes including Canada, according to René Laprise, a specialist in regional climate modelling at the University of Quebec in Montreal.

"These temperature increases could exceed 10 degrees [Celsius]," he told CBC News. "Warming on average in Canada would increase four to six degrees Celsius, with a smaller change in the south and an increase of 10 degrees in the north."

The report also predicts sea levels will rise between 18 and 59 centimetres, a development that could be disastrous for island nations lying at low altitudes.

The prediction could be even worse if the melting of polar ice sheets continues to accelerate.

Among the other predictions:

• Increased atmospheric carbon dioxide will lead to increasing acidification of the ocean.
• Warming is expected to be greatest over land and at high latitudes, with some models predicting rises of 10 degrees Celsius in the next 100 years in the Arctic.
• Sea ice is expected to sink, with some projections predicting late-summer Arctic sea ice to disappear almost entirely in the latter part of the 21st century.
• Hot extremes, heat waves and heavy precipitation are highly likely to become more frequent.
• Hurricanes are likely to become more intense, though there is less confidence in whether they will decrease in number.
• Precipitation is very likely to move toward the poles, with an increase at higher latitudes and a decrease in subtropical regions.

How is this different from the last report?

The differences between the IPCC's report six years ago and the latest findings come down to certainty.

The 2001 report said human activities were only "likely" to have an impact on global warming, a range of assurance that translates to 66 per cent certainty. The new report now puts our involvement as "very likely" or 90 per cent certain.

Many of the ranges for future projections have also been refined and in most cases narrowed. The changes in certainty reflect the growing maturity and resources of the scientific community, said Fyfe.

Scientists have observational data from a wider range of sources.

The carbon dioxide concentrations found in ice core samples provide an assessment of concentrations of the gas from thousands of years ago.

Balloon-borne and satellite measures of atmospheric warming rates have supplemented and helped correct inconsistencies in temperature trends gleaned mostly from data primarily taken from the surface of the planet.

And new investigations from a more widespread and diverse group of locales have provided a broader perspective on the changes in the planet, said Fyfe.

"It's an explosion of observation," he said.

Another development behind the increased confidence of the 2,000 climate scientists behind the report can be attributed to the success of past climate models.

Fifteen years ago, climate models were projecting global average temperature increases between 0.15 and 0.3 degrees per decade for the time between 1990 and 2005. The actual observed value of 0.2 degrees per decade falls in that range, strengthening confidence in these forecasts.

Adding to numbers suggesting today's researchers are on the right track are greater resources in producing these models and greater access to the work of other groups, said Fyfe.

Where do we go from here?

Future reports from the IPCC in 2007:

April 6: Impacts, Adaptation and Vulnerability

May 4: Mitigation of Climate Change

Nov. 17: The Synthesis Report

February's report is the first of four IPCC releases expected in 2007. The others are expected to deal with vulnerable regions and recommendations for policy makers.

But while the United Nations group has substantial influence on policy makers throughout the world, translating its findings into action will fall to world leaders.

Under the Kyoto accord that went into effect in 2005, 141 nations have committed to reducing emissions by an average of five per cent below 1990 levels by 2012.

But the agreement does not include the world's biggest emitter of greenhouse gases — the United States — and also excludes developing countries like China and India.

U.S. Energy Secretary Sam Bodman downplayed America's role as a greenhouse gas emitter, saying "we are a small contributor when you look at the rest of the world. It's really got to be a global discussion."

Prime Minister Stephen Harper said the report confirmed that "these changes are occurring, they're serious and we must act."

But Harper defended his government's decision to move away from the Kyoto protocol and pursue "targets that can reached."

"I think the first … realistic step in any such plan would be to try over the next few years to stabilize emissions. Obviously over the longer term to reduce them, but as I said before, realistically, the only way to get … reductions is to develop technologies," Harper said.

Fyfe said climate models suggest our future is far from certain, as long as changes in greenhouse gases are addressed.

"We're locked into a temperature increase of about 0.5 degrees by 2025 regardless of what we do, but the increases start to diverge depending on the levels of emissions when you look a hundred years from now," said Fyfe. "So what we do now can make a difference."