Last Thursday, the eight-country Arctic Council was reminded of the issues they face by an event faraway in Hawaii. For the first time in probably three million years, the level of carbon dioxide in the atmosphere averaged above 400 parts per million for an entire day.

That's based on readings at the key monitoring station at Mauna Loa, Hawaii, and the best available scientific evidence. Carbon dioxide readings above 400 ppm were first seen in the Arctic last year, but did not stay above that level for an entire 24-hour period.

Sweden's Foreign Minister Carl Bildt welcomes Canada's Health Minister Leona Aglukkaq, the new chair of the Arctic Council, in Kiruna, Sweden, May 14. (Charles Dharapak/Associated Press)

Canada, which hosted the founding conference of the Arctic Council in 1996 and was its first chair, again took on that responsibility at the meeting in Kiruna, Sweden, on Wednesday. Federal Health and Northern Development Minister Leona Aglukkaq was scheduled to become the council chair.

During Wednesday's sessions, the conference agreed to let nations that are far from Earth's north observe the council's operations.

The decision boosts rising superpowers China, India and Korea, which seek to mine the north of its untapped energy and other natural resources. The European Union also was tentatively granted observer status but must first address several questions about its bid, including concerns about its ban on Canadian seal exports.

Here are six of the most important issues on the table at the moment, from A to F:

Acidification of the Arctic Ocean

According to the council, "ocean acidification is occurring at a rapid and accelerating pace, and the Arctic Ocean is on the frontline of this global change."

Acidification "will have a negative effect on Arctic marine ecosystems at all scales," including marine food chains and fish stocks, it says.

Commercial fishermen and other mariners send the message 'SOS acid ocean' to spread word about ocean acidification caused by fossil fuel emissions, in Homer, Alaska, Sept. 6, 2009. 'Acidification is occurring at a rapid and accelerating pace,' the Arctic Council says. (Lou Dematteis/Reuters)

One example, calcifying species may become unable to form hard shells, which would then affect other animals up the food chain.

The acidification results from rising temperatures and melting sea ice, which leads oceans to absorb larger quantities of the carbon dioxide in the atmosphere and turn the gas into a weak acid.

The council estimates that "Over the past 200 years, the average acidity of surface ocean waters worldwide has increased by about 30 per cent."

What's more, carbon dioxide "is more readily absorbed into cold water and the increasing amounts of fresh water entering the Arctic Ocean from rivers and melting ice are reducing the Arctic Ocean's capacity to neutralize acidification."

Black carbon reduction

Scientists say that one of the best ways to limit climate change in the Arctic is to reduce black carbon or soot emissions, which get carried to the Arctic and deposited on snow and ice.

Created by the incomplete combustion of fossil fuels and biomass, this black carbon both absorbs solar radiation and reduces the amount that is reflected away from the Earth, adding to the warming cycle.

Last year, the Arctic Council called on the international community to prioritize cutting emissions of black carbon as well as other of what are called short-lived climate forcers such as ozone, methane and hydrofluorocarbons.

In January, an international study concluded that black carbon's direct influence on global warming is probably twice as high as previous estimates, including those by the Intergovernmental Panel on Climate Change in 2007.

According to Tami Bond of the University of Illinois at Urbana-Champaign, a lead author of the report, since black carbon is short-lived, the impacts of curbing emissions "would be noticed immediately."

In April, the Arctic Athabaskan Council, an indigenous group in Canada with status at the Arctic Council, filed a petition concerning black carbon with the Inter-American Commission on Human Rights.

Council membership

U.S. Secretary of State John Kerry, left, is seated with, clockwise, Michael Stickman, of the Arctic Athabaskan Council and James Stotts, chair of the Inuit Circumpolar Council, in Kiruna, Sweden, May 14, ahead of the Arctic Council meeting. The council may decide to give observer status to as many as 14 additional countries. (Charles Dharapak/Associated Press)

China, India and a dozen other countries, along with the European Union, are requesting observer status at the Arctic Council.

Council decisions are reached by consensus of the eight member states that ring the Arctic Circle, and so far the Nordic states appear to be in support, with Canada and Russia opposed. The White House, despite unveiling its own Arctic strategy on Friday, did not state a position on the new observer applications.

China's interest stems from mining operations in the region and the expectation, due to climate change, of the opening of a northern passage through the Arctic that would dramatically shorten shipping distances between China and Western Europe.

Disappearing ice cover

Last month, scientists at the U.S. National Oceanic and Atmospheric Administration released a study that predicted the Arctic will be ice-free in summer by 2050, much earlier than previous estimates.

By last September, thick ice cover had already shrunk to half the average for that month during the years 1979-2000, researchers found.

Other scientists, including Carlos Duarte, the director of the Oceans Institute at University of Western Australia, have warned that "the Arctic could be free of ice in summer by 2015."

Last year, Duarte wrote a paper about how the receding ice cover and other climate change factors could lead to a snowball effect of "dangerous" changes in the Arctic and globally.

Emergency preparedness

Shell's Arctic Challenger oil containment barge docked in Bellingham, Wash., Feb. 27. Shell is dropping plans to drill in the Arctic waters off Alaska this year. An oil spill cleanup in the Arctic faces huge challenges, experts say. (Philip A. Dwyer/Bellingham Herald/Associated Press)

On Wednesday, the ministers of the eight Arctic states will sign the Marine Oil Pollution Preparedness and Response agreement.

It will be only the second time they've signed a legally binding accord.

With oil drilling in the Arctic Ocean looming, the agreement aims to prevent accidents and codify response actions should a spill happen.

"There isn't any effective equipment deployed in the Arctic that can handle an oil in ice spill," Lars-Otto Reiersen, head of the Council's Arctic Monitoring and Assessment Program (AMAP), told CBC News last year.

With half the year in darkness, extreme cold, strong winds and fog, Reiersen said any oil-spill cleanup faces huge challenges.

In February, Greenpeace received a leaked copy of the draft, which the environmental group called "a disappointingly weak document."

The draft was also criticized by Finland's environment minister who said he would push for changes.

Food chain pollution

Pollutants carried by air and water to the Arctic are accumulating in the food chain, yet another threat for the region's indigenous people. (Jonathan Hayward/Canadian Press)

Pollution and other threats to Arctic biodiversity, which is on the agenda for the meeting in Sweden, have a direct effect on indigenous people in the region.

The council says it has special responsibility for indigenous peoples in the Arctic and certain indigenous organizations are included as permanent participants in council meetings.

Reiersen says that the main challenge from pollution in the North comes from the mercury, industrial chemicals and persistent organic compounds in pesticides, which are often transported via the atmosphere and rivers.

These accumulate in the food chain and the foods indigenous people eat, and can lead to cancers and developmental problems in infants.