The Oxford English Dictionary defines a ‘chemtrail’ as –

A visible trail left in the sky by an aircraft and believed by some to consist of chemical or biological agents released as part of a covert operation, rather than the condensed water of a vapour trail.

Wikipedia says –

According to the chemtrail conspiracy theory, long-lasting trails left in the sky by high-flying aircraft are chemical or biological agents deliberately sprayed for sinister purposes undisclosed to the general public.

Greenpeace have not seen sufficient evidence to justify further investigation into whether this is a real problem. As far as we are concerned, chemtrails are an urban myth - a conspiracy theory with no conspiracy.

We are aware of various vaguely similar but confirmed phenomena:

Carbon emissions – aviation is the fastest growing source of carbon emissions, and the fact these emissions are produced at altitude increases their impact upon the climate. For this reason we believe aviation growth needs to be constrained to keep us within ‘safe’ emission limits. This is a particular problem in the UK, where we fly more than any other country in the world, and yet are still told that we urgently need more runways. CO2 is invisible, and emitted as an unavoidable side-effect of burning kerosene.

Cloud seeding – emitting silver iodide or other chemicals into clouds causes the water vapour held in those clouds to condense around the silver iodide into rain, and fall to the ground. This can be used to encourage rain, by seeding the clouds over a site which needs more water, or to discourage rain by seeding clouds before they reach a site where people want dry weather. The most famous example of cloud seeding was during the Beijing Olympics, where it was used to prevent rain over the Olympic sites. This process would be carried out by rockets, as in Beijing, or light aircraft, not by passenger jets, and it is not particularly common.

Geoengineering – Geoengineering is the science of deliberately altering the global climate and is currently almost entirely theoretical. All geoengineering techniques are regarded as potentially hazardous, as they can only work by having very large impacts on how our atmosphere functions, with the possible risks being equally large. There are many different techniques proposed, some of which could include aircraft emitting substances to block sunlight from reaching the earth. The very few techniques which have had some limited, localised testing do not utilise aircraft. If the chemtrail conspiracy is real, then it is not a geoengineering project, as it has had no discernible impact on the climate.

HAARP – the High-frequency Active Auroral Research Program was an ionospheric research programme conducted by various dodgy outfits connected to the US and UK military. God knows what it was intended to do, but it closed last year. It may have been something worth worrying about, but it doesn’t seem to have utilised large numbers of aircraft, and did not receive the level of funding that would be required to do so on the scale of the alleged chemtrail conspiracy.

None of these phenomena explain visible vapour trails from commercial passenger jets. Fortunately, there is an explanation. The visible trails are contrails (short for ‘condensation trails’) and they consist of water vapour condensed due to the temperature differential created by the pressure differential between the upper and lower surfaces of the wings, the wing tips, or engines.

If you would like to communicate with Greenpeace about one or more of the confirmed phenomena described above, please avoid using the term ‘chemtrails’ as it may cause confusion.

Evidence

Greenpeace has been sent an enormous number of pictures and videos of vapour trails, all of which look like normal contrails behaving exactly like normal contrails - to us, at least. We have also been sent lots of links to websites and blogs claiming to expose the chemtrail conspiracy. The evidence on these blogs tends to consist of pictures and videos of vapour trails, all of which look exactly like normal contrails etc.

What we would require, in order to consider researching this alleged conspiracy, would be one of two things. Either clear statements from appropriate experts such as professors of atmospheric physics, fluid dynamics or aeronautical engineering, explaining how they determined that these apparent contrails are not in fact contrails but chemtrails, or, alternatively, clear statements from aviation workers detailing their experiences fitting, refilling and operating the systems used to disperse the chemicals from the planes. As there are literally millions of people working in the aviation industry around the world, many of whom are fairly low-paid, the chances of them keeping something like this quiet are fairly minimal, if it’s really happening.

If you would like to communicate with Greenpeace about chemtrails, as described in the OED or Wikipedia, please wait until you have what we would regard as evidence – statements from either properly qualified academics or appropriately experienced aviation workers supporting your concerns.

Please do not assume that a YouTube video or blog which convinced you will convince us. We’ve already seen them, and we weren’t convinced. Please do not think that accusing us of being part of the ‘chemtrail conspiracy’ will change our minds. We’re constantly accused by governments and security services of being in the pay of other governments and security services. It hasn’t changed the way we work and is unlikely to do so in the future.

Greenpeace require a reliable evidence base before campaigning on any issue. So far, we haven’t seen any evidence supporting the chemtrails hypothesis.