So far this year, the Intergovernmental Panel on Climate Change has released two reports.

On Feb. 2, the UN body looked at the scientific basis for climate change, and found that Earth's climate has warmed and that it's 90 per cent likely that human activity, primarily the burning of fossil fuels, is driving that warming.

On April 6, the IPCC looked at the likely impacts of climate change over the next 100 years. For example, a two-degree Celsius rise in the Earth's temperature could leave 2 billion people short of water by 2050 and cause about 20 to 30 per cent of the planet's species to become extinct.

On May 6, the IPCC released its third of four reports. This one tells how the world can mitigate climate change.

The goal

Climate scientists say while global warming can't be stopped, the most dangerous effects can be avoided if the temperature rise is held to a maximum of two degrees above the pre-industrial global temperature.

• This can happen, they say, but the following measures must be adopted, among others:
• The world must shift away from fuels like coal,
• Invest in energy efficiency,
• Reform the agriculture sector,
• Halt deforestation (forests absorb carbon dioxide from the air and store it), and
• Put a price on carbon and cut subsidies for fossil fuels.

GHG emission trends

• Between 1970 and 2004, global greenhouse gas emissions have risen by 70 per cent. If nothing is done, they will rise by another 25 to 90 per cent over the next 25 years.
• The single biggest area of growth has come from the energy supply sector, which is up 145 per cent.
• This overall rise has happened despite a 33 per cent rise in energy intensity, which is the means the amount of energy going into a given unit of output has fallen. However, global income grew 77 per cent and the population grew by 69 percent, offsetting those gains.
• The Montreal protocol on ozone-depleting substances, which also contribute to the greenhouse effect, also helped control GHG emissions. Those substances are at 20 per cent of their 1990 levels.
• There's a high likelihood GHG emissions will continue to grow over the next few decades.
• The report found there is technology available now to cut GHG output, and there should be significant new technologies commercially available by 2030.

Stabilizing GHG levels

The current C02 concentration in the atmosphere is about 380 parts per million, but when one adds in the effect of other greenhouse gases, that number rises to 425 ppm.

Many researchers think a safe target for GHG emissions would be a C02 equivalent level of 450 ppm.

The report suggests a level of 445 to 490 ppm would keep the global temperature rise to 2.0 to 2.8 degrees.

The argument for quick action

Climate scientists say that carbon dioxide, the main greenhouse gas driving climate change, accumulates and lingers in the atmosphere for a century or more.

As a result, the way to head off dangerous warming is not only to prevent more GHGs from reaching the atmosphere, but to start cutting emissions in absolute terms now.

The 1997 Kyoto Protocol set a global target of a five per cent cut in GHG emissions below the 1990 baseline by 2012. The treaty is to take effect in 2008, but it received global ratification in early 2005.

A generally accepted target is that GHG emissions must fall to at least 50 per cent below 1990 levels by 2050 to keep the rise below two degrees. Others set a target of 80 per cent.

The longer actual cuts are put off, the deeper they will have to be in the future, they say.

The cost of cuts

The cost varies with the stabilization level, and would likely vary from country to country.

A target of between 445 and 535 ppm for CO2 would cost an estimated three per cent of world GDP to achieve.

Are we already over?

Writing in Britain's The Guardian newspaper on May 1, author George Monbiot argued that the world is already above a safe target of the CO2 equivalent of 450 parts per million when one includes not just carbon dioxide, but the impact of other gases like methane and nitrous oxide.

"The European Union and the Swedish government have established the world's most stringent target. It is 550ppm, which gives us a near certainty of an extra 2°C. The British government makes use of a clever conjuring trick. Its target is also "550 parts per million", but 550 parts of carbon dioxide alone. When you include the other greenhouse gases, this translates into 666 ppm carbon dioxide equivalent (a fitting figure)."

That figure almost guarantees a rise of more than two degrees by 2050, he said.

China and the U.S.

Those two nations tried to have the report's language weakened.

The U.S. is currently the world's biggest total emitter of greenhouse gases.

Although it only has five per cent of the world's population, the U.S. accounts for about 25 per cent of the world's greenhouse gas output.

On a per capita basis, the U.S. is one of the world's biggest per capita emitters of GHGs, surpassed only by the tiny country of Luxembourg. Canada and Australia, the world's biggest coal exporter, round out the top four.

While Canada and the U.S. produced about five to six times more carbon dioxide per capita than China did in 2003, China has been rapidly narrowing the gap.

The world's most populous country had been expected to surpass the U.S. as the biggest total GHG emitter in 2010, but it will do so late this year.

About 80 per cent of China's electricity comes from coal -- more than twice the world average. To keep up with the demand created by its surging economy, a new coal-fired power plant opens every week to 10 days.

In 2001, new U.S. President George W. Bush announced his administration would not seek ratification of the Kyoto Protocol.

He complained that cutting U.S. emissions by seven per cent below 1990 levels would hurt his country's economy. He also said that the U.S. couldn't live with China and other major developing countries being excluded.

Kyoto supporters argue that industrialized nations have created the problem. China, India and other emerging economic powers are to be part of Kyoto's second phase.

Monbiot, author of the book Heat: How To Stop The Planet From Burning, also wrote the following in The Guardian on May 1 on what needs to be done:

"We must open immediate negotiations with China, which threatens to become the world's biggest emitter of greenhouse gases by November this year, partly because it manufactures many of the products we use. We must work out how much it would cost to decarbonize its growing economy, and help to pay.

"We need a major diplomatic offensive -- far more pressing than it has been so far -- to persuade the United States to do what it did in 1941, and turn the economy around on a dime. But above all we need to show that we remain serious about fighting climate change, by setting the targets the science demands."

Sources: IPCC, the Associated Press, New York Times, The Guardian