Question 1

What are contrails (condensation trails)?

Accepted Answer

From contrails.org: 
Contrails are line-shaped ice clouds that form behind an aircraft when flying at high altitudes through regions with high humidity and low temperatures. The current scientific consensus is that contrails contribute to a large net warming effect on the climate. Historical CO₂ emissions from aviation are responsible for about 1.5% of anthropogenic global warming today. Contrails globally are estimated to add another 1-2% of additional climate warming.
For comparison, contrails contribute as much to global warming as a country the size of Germany or Japan!

See https://contrails.org/faq/ for more information on the science behind contrails.

Question 2

Aren't contrails just another name for chemtrails (the conspiracy theory)?

Accepted Answer

No. They both refer to the lines produced by planes in the sky but that is where the similarity ends (sorry, Lana Del Rey).

'Chemtrails' refer to a conspiracy theory which claims that nefarious governments are using commercial jets to spray chemicals to brainwash the public. It is completely unfounded.

'Contrails' refer to a scientifically established phenomenon in which water vapour and soot particles released by planes freeze and mix to form lines in the sky. Sometimes, these stick around long enough to act as a blanket over the planet, contributing to global warming in the same way that greenhouse gases do.

Please see contrails.org for more information on the science behind contrails and their effect on the climate.

Question 3

Are contrails really that bad for the climate?

Accepted Answer

This is the opening line of the March 2026 report by the Contrail Impact Mitigation Task and Finish Group, commissioned by the UK Government:

"Aviation's contrail climate impact is significant". It goes on to say: "There is consensus that contrails cause a net positive radiative forcing (warming)."

There is some uncertainty surrounding the exact extent of contrails' impact on the climate, partly because their effects do not last nearly as long as CO2. But one thing is clear: they are a problem. Most studies, reports and articles currently estimate that contrails represent 50% of aviation's total climate impact over a 20-year period, but some have it as high as 66%!

According to contrails.org: "Historical CO₂ emissions from aviation are responsible for about 1.5% of anthropogenic global warming today. Contrails globally are estimated to add another 1-2% of additional climate warming."

For comparison, contrails contribute as much to global warming as a country to size of Germany or Japan!

In any case, according to the precautionary principle (enshrined in international law by the 1992 Rio Declaration on Environment and Development), we shouldn't wait until we know exactly how bad the problem is before acting. Research and history shows that the earlier we act on environmental problems involving uncertainty, the better (European Environment Agency, 2013). Please bear in mind that the first report (by the IPCC) on the climate impact of contrails was published way back in 1999, so a lot of research has been done on this issue already.

Question 4

But aviation is only responsible for 2% of global emissions so why should I care?

Accepted Answer

Why you should be concerned about aviation's total climate impact:

Aviation, because it is proving so hard to decarbonise, is on course to be the highest emitting sector in the UK by 2040 (Climate Change Committee, 2025), and, when non-CO2 effects are acknowledged, accounts for 19% of the world's remaining temperature budget if we are to avoid a catastrophic 2°C temperature rise by 2050 (Smith et al, 2026).

Also, while it is true that aviation accounts for only around 2% of greenhouse gas emissions globally, in the UK it makes up 8% of total emissions. The environmental injustice of aviation is a worldwide trend. “Less than 20 percent of the world’s population has ever taken a single flight” according to former Boeing CEO David Muilenburg.

Why you should be concerned about contrails:

Contrails are estimated to have an annual impact on the climate comparable to a country the size of Germany or Japan!

A lot of the worst contrails are formed over the North Atlantic and Euope, so this is an issue which developed states like the UK, US, Canada and the EU have a responsibility to lead on resolving.

Aviation (particularly considering the impact of contrails) is therefore a significant contributor to global warming and environmental injustice.

Question 5

What about private jets?

Accepted Answer

Private jets produce contrails too!

A recent study by Imperial College, London, found that "jets produce more contrails than previously thought, potentially leading to outsized impacts on climate warming. Despite their smaller size, private jets create contrails as often as much larger aircraft. We already know that these aircraft create a huge amount of carbon emissions per passenger so the super-rich can fly in comfort."

For us, contrails represent another reason for why private jets should be regulated more heavily. But it is important that commercial planes are also regulated in this respect.

Question 6

What about aviation's other non-CO2 effects?

Accepted Answer

Aviation’s non-CO2 impact other than contrails includes the effects of Nitrogen Oxides (also called NOx), Soot particles (Aerosols), Sulphur Oxides (SOx), among others. Due to resource constraints, we are not able to concentrate on these other effects.