If the world is to head off dangerous climate change and somehow keep a global temperature rise under 2 C, we need all hands on deck. That includes airlines.

Air travel is not only the fastest growing form of transport. It is also the most carbon intensive.

Few if any holidaymakers and business people boarding their flights know that the kerosene fuel powering their airliner is tax-free.

This gives air transport an unfair advantage over rail and road, and offers less incentive to aircraft designers and operators to accelerate a transition to ever-more fuel-efficient planes. Long-standing efforts to end this anomaly have failed.

A recent attempt to require aircraft flying to Europe to pay for their CO2 emissions under the European Union's Emissions Trading System triggered fierce opposition from many non-European countries.

The EU has suspended its plan for a year, putting the ball back in the court of the International Civil Aviation Organization and its 191 member states to find a solution.

This is the ideal place for aviation to begin cutting the 5 percent of global greenhouse gas emissions it now accounts for.

A global agreement would level the playing field so that all airlines pay the same fuel levy, so reducing the risk of "freeloaders".

But there is a deadline to the opportunity for helping aviators get a handle on their CO2 emissions by 2020. And they must flip them soon after.

In September a triannual decision-making ICAO assembly will meet in Montreal with a vote likely on whether a global market-based measure will be adopted to drive the industry to meet its responsibilities. If no decision is taken, the next assembly may not convene until 2016.

The world has waited long enough for aviation - and indeed shipping - to join international efforts to bridge the emissions gap.

Increased engine efficiencies, alternative fuels, air traffic management reform and technological enhancements can help, but are unlikely on their own to deliver the emissions reductions needed and at the speed required. Question marks also remain over how such investments would be paid for.

Seizing the moment to put in place a market-based structure to catalyze the low carbon innovations the industry needs - and guarantee its sustainable future - is thus both logical and desirable.

The resolution on the "Implementation of the Aviation Carbon-Neutral Growth Strategy" adopted at the International Air Transport Association annual general meeting earlier this month could prove to be an important step in the process.

A clear signal from industry that it supports a global market-based mechanism to be agreed at this year's ICAO Assembly has been one that governments have been waiting for.

Climate change remains an over-arching challenge not just for future generations, but also for those living with its early consequences today.

Impacts in the last 12 months, consistent with scientific projections, include: the largest melting of Arctic sea ice on record, a "once in a century" drought that hit the US Mid-West, followed by a once in a century hurricane that hit New York, the wettest-ever summer in the United Kingdom, followed by one of the coldest-ever springs.

As ever, the greatest tragedies have been suffered by those with the least resources to cope. But whether we are talking about floods in India, or droughts in east Africa, a climate crisis is emerging of profound proportions.

The complexity of the Earth's systems and feedback mechanisms prevent predictions being made with 100 percent certainty. But the risk assessments of the Intergovernmental Panel on Climate Change underline that humanity is playing a dangerous game of Russian roulette with our life support systems.

There are many encouraging actions underway from the rise of renewable energy investments to cuts in deforestation in countries such as Brazil.

Greenhouse gas emissions in the United States have fallen to 1994 levels according to recent estimates, and China is scheduled to invest over $1 trillion in clean energy, energy efficiency and other climate mitigation measures over the next five years.

Many other nations, large and small, rich and poor are building on the outcomes of last year's Rio+20 Summit to devise and define pathways to a low carbon, resource efficient Green Economy.

Yet despite many positive developments, the world has yet to turn the corner. Emissions into the atmosphere hit a new record high last year of over 35 billion tons - 58 percent above 1990 levels.

In order to realize the future we want, and need, economies must urgently begin decoupling economic growth from natural resource use, including fossil fuels.

Airlines must be part of that transformation. This can be the year when ICAO departs the runway and plots a course for a low carbon future. The first stop is a global deal in Montreal.

The author is UN under-secretary general and executive director of the UN Environment Programme.