By Matt McGrath
Environment reporter, BBC News
One of the world's biggest research programmes of the past 50 years has been launched in Paris.
Scientists warn Arctic summer sea ice could disappear by 2040
International Polar Year (IPY) is a $1.5bn (£763m) collaborative effort to study the north and south poles.
Thousands of researchers will be carrying out more than 200 projects, with climate change top of the agenda.
Some nations, including the UK and US, unveiled their IPY programmes earlier this week, but the Paris event sees the official start of the two-year study.
This is the fourth IPY since 1882 but the first one in which the impact of man-made global warming will be clearly visible at both poles.
Ice sheet melt
Using ice breaking ships, satellites and submarines, an army of researchers from more than 60 countries will be studying the polar regions in unprecedented detail over the next two years.
And climate change will be at the heart of many of the research projects.
Scientists say rising temperatures are warming the polar regions faster than the rest of the planet.
One of the key questions that scientists will hope the research effort will shed new light on is the potential rise in sea level caused by melting of ice sheets in Greenland and Antarctica.
The southern polar ice sheet holds 90% of the world's fresh water. If it all melted, global sea levels would rise by 60m (197ft).
There will also be projects to study the impacts of climate change on the millions of people who live in the Arctic and there will be efforts to study exotic marine life under the Antarctic ice.