Pollution in plane sight: The fight against contrails goes to Montreal

Have you ever looked up in the sky after a plane has passed and saw white fuzzy lines that look like clouds? These lines are called contrails. Sometimes these contrails are short-lived and look like hairline streaks in an otherwise blue sky and other times they are persistent and spread so wide they begin to look like clouds themselves.

Persistent contrails in the sky caused by planes


Satellites have observed clusters of contrails lasting as long as 14 hours, though most remain visible for four to six hours.

Can you imagine if half an hour after you drove down the road, someone could still see your exhaust? With all the vehicles on the road, that would be quite the sight, or we’d be too busy coughing at that point.

Long-lived, spreading contrails are of great interest to climate scientists because they reflect sunlight and trap infrared radiation. A contrail in an otherwise clear sky reduces the amount of solar radiation that reaches Earth’s surface, while increasing the amount of infrared radiation absorbed by the atmosphere. This is the Greenhouse Effect.

Greenhouse Effect
Greenhouse Effect

Garbage Patch in the Sky

Contrails are what happens to a plane’s exhaust when it’s in the upper reaches of our atmosphere. CO2 attaches itself to ice particles and can’t break down. It’ll be up there for thousands of years, like a floating garbage patch. The only thing we can do now at this point is stop adding to it.

Planes are major contributors to climate problems, in two ways: first they combust fossil fuels and emit gases and aerosol to the atmosphere, second they fly in the same elevation as ice-saturated regions of the atmosphere which messes up natural cloud formation.

Consider this: a nonstop round-trip transatlantic flight averages about one tonne of CO2 emissions per passenger, equivalent to emissions from a 35-km daily commute in a Toyota Prius over a work year.

International aviation produced more than 492 million tonnes of carbon dioxide in 2014 and that number is projected to skyrocket in coming years, with more than 56,000 new aircraft projected to hit the skies by 2040.

CO2 emissions from air travel and transport could increase by a factor of three or four over that period. The next time you’re at the grocery store take a look at what you’re buying and find out if it was flown in from the other side of the world.

September 27th could be our last chance to do something about plane pollution. Next week in Montreal the ICAO General Assembly is going to vote whether to impose a market cap on plane emissions. This is crucial because CO2 emissions from aviation are likely to grow by 300% between now and 2050.

If aviation were a country, it would be a top ten emitter. Contrails and contrail cirrus are not part of any climate agreement. Why was this overlooked? This sector alone could prevent us from limiting global warming to 2°C which is what was set out in the Paris Agreement (COP21). There has to be a reduction in plane emissions by 50% if this goal can be reached.

Plane exhaust

Aviation fuel contains carbon dioxide (CO2), nitrogen oxides, (NOx), hydrocarbons (HC), sulfur (SOx), black carbon (BC), and water vapor (H2O). Greenhouse gases, especially CO2 and water vapor, trap heat and elevate surface temperatures.

In addition, a lot of unburned plane fuel is released which contains hydrocarbons and carbon monoxide. A lot of times, planes will dump their excess fuel as they fly over the oceans before they land. This is equally harmful, but not too much study has been done about this.

There has only been one study in recent years on pollution from planes and that was using data from 2005. Why is that? Has the aviation industry muzzled just about every scientist? Many people can’t even agree on how to measure changes in the atmosphere caused by dumping fossil fuels but we know it’s happening.

Is there a solution to contrails? Yes.

Contrails expert David Fahey
Contrails expert David Fahey

Scientists like David Fahey say that aviation’s total global warming impacts are more than double those estimated from its CO2 emissions. Nitrogen oxide emissions and aviation’s impacts on clouds add significantly to the warming effect of carbon dioxide.

There is a simple solution to the worst contrails – fly at a different level. According to Dr. David Fahey, just by modifying aircraft routes can make a difference. He says that ice-supersaturated regions tend to be tens of kilometres across but often shallow vertically, so a change of one or two flight levels en route may avoid them.