Ground-based astronomy is becoming impossible due to airfraft contrails

This article is from a time when the media was a little more honest, but nevertheless gets the time frame wrong.

I have long noticed that the the dark, starrry nights of my youth are well-and-truly a thing of the past even here Down-Under in a country that has had the clearest night skies anywhere in the world.

Telescopes 'worthless' by 2050

This photo is from the original article

BBC,

5 March, 2006

Ground-based astronomy could be impossible in 40 years because of pollution from aircraft exhaust trails and climate change, an expert says.

Aircraft condensation trails - known as contrails - can dissipate, becoming indistinguishable from other clouds.

If trends in cheap air travel continue, says Professor Gerry Gilmore, the era of ground astronomy may come to an end much earlier than most had predicted.

Aircraft along with climate change will contribute to increased cloud cover.

"You either give up your cheap trips to Majorca, or you give up astronomy. You can't do both"

Gerry Gilmore, University of Cambridge

The timescale is based on extrapolating air traffic growth figures. The BBC has learned that the calculations were made as part of preparations for an upcoming observatory project called the Extremely Large Telescope (ELT).

The ELT is intended to probe planets around nearby stars and look for extremely faint objects in the Universe.

Vision impaired

"It is already clear that the lifetime of large ground-based telescopes is finite and is set by global warming," Professor Gilmore, from Cambridge's Institute of Astronomy, told reporters recently in London.

"There are two factors. Climate change is increasing the amount of cloud cover globally. The second factor is cheap air travel.

"You get these contrails from the jets. The rate at which they're expanding in terms of their fractional cover of the stratosphere is so large that if predictions are right, in 40 years it won't be worth having telescopes on Earth anymore - it's that soon.

"You either give up your cheap trips to Majorca, or you give up astronomy. You can't do both."

Climate change is also expected to increase the amount of water vapour in the atmosphere through evaporation, contributing to overall cloudiness. The increase in cloud cover would affect both optical and infrared astronomy, which would have to be carried out from space.

Radio astronomy would continue to be ground-based.

Identical appearance

Contrails often present little more than a transient nuisance to astronomers; but when certain weather conditions prevail, they can break to look like natural clouds.

Holger Pederson, an astronomer at the Nils Bohr Institute in Copenhagen, Denmark, who has studied contrails, explained: "You can recognise the jet contrails when they are young. So you can stop your observation and then restart as soon as the contrail has passed the field of view of the telescope.

Satellite imagery can be used to monitor contrail evolution

"Worse is when the contrails last for hours. Then they degrade into something you can hardly distinguish from natural cirrus clouds."

Dr Hermann Mannstein, of the German Aerospace Centre (DLR), agreed astronomy would become more difficult, but said there was an upper limit on the contrail problem.

Contrails form where the air is highly saturated with water vapour, but will not form if the air is too dry

"You don't clog the whole sky. You have a certain proportion of the sky, in time and space, that can be affected," he said.

Restriction zones

But Professor Gilmore countered: "There are places where you get relatively fewer clouds - that's where we put our telescopes - but there is nowhere on Earth that you don't get clouds and aeroplanes.

"Already, around the major observatories, there are local laws to prevent aeroplanes flying within quite large distances," he told the BBC News website.

Professor Gilmore said sites where observatories are located, such as the Canary Islands, Hawaii and South America, are also attractive holiday destinations, and likely centres for future air traffic growth.

He added that the projections did not factor in the effects of global warming, which are likely to exacerbate the problem.

Mr Pederson said too few satellites built up image data on how contrails evolved over time.

"We may underestimate the amount of contrail-derived cirrus clouds," he said.

"We know from satellite imagery that clusters of contrails can last for two days. If carried by the upper jet stream through the troposphere, they can travel hundreds of kilometres."

There are several concepts under consideration for the European ELT, but the preferred design seems to be converging on a telescope that is some 30-60m in diameter.

A location has not been decided; but, despite the difficulties of access, Antarctica may become an option. The icy region has relatively clear skies, with a climate that is somewhat separate from other continents, and, crucially, is free from overflying commercial jets.

#AGU15 Accidental Geoengineering? Airline traffic may help create an icy haze that’s brightening U.S. skies

Whatsupwiththat,

16 December, 2015

SAN FRANCISCO, CALIFORNIA —The data just didn’t seem to make sense. That’s often the story right before scientists make a leap in understanding. In this case, scientists had some evidence that skies in the continental United States have been brightening, after several decades of so-called “dimming.”

Brightening and dimming are overly simplified words that signify increases and decreases in how much light from the Sun (measured as “irradiance” in watts/m2) reaches the planet’s surface—and these measurements are often analyzed under cloud-free conditions.

For the observed dimming under clear skies, convention would point to aerosols. Levels of these tiny particles, associated with pollution, had been rising for decades prior to the 90s and began falling after that thanks to pollution controls. That could make today’s skies brighter than those in the 70s or 80s—and it could also warm the climate, as more direct radiation reaches the surface.

But when Chuck Long, a Cooperative Institute for Research in Environmental Sciences (CIRES) researcher at the NOAA Earth System Research Laboratory, and his colleagues dug a bit deeper, something didn’t add up.

If the recent clear sky “brightening” trend were due to cleaner air and fewer aerosols alone, it should be accompanied by an increase in direct downwelling shortwave radiation, one part of solar radiation reaching the surface directly from the Sun. That didn’t happen, Long reported during the American Geophysical Union fall meeting in San Francisco.

Instead, Long and his colleagues found that at the continental United States sites they analyzed, direct downwelling shortwave radiation remained roughly steady between 1995 and 2007, under cloud-free skies. Rather, it was the diffuse shortwave radiation that increased. That simply couldn’t happen if fewer aerosols alone were the reason behind the brightening. If anything, fewer aerosols should mean less diffuse shortwave radiation, because particles in the atmosphere can bounce light around and back to space.

So the scientists dug deeper, and in a provocative new analysis, not yet published, Long suggests that a high-altitude “ice haze,” created by water and other emissions from aircraft, is responsible. “I’m talking about a sub-visual contrail-generated haze of ice, which we do not classify as a cloud but gives blue sky more of a whitish tint.” Long said.

The finding—if verified—could mean that we are in essence already conducting a geoengineering experiment on the atmosphere, adding ice particles that change the way solar radiation reaches Earth’s surface. Understanding the overall impact of those changes on warming or cooling at the surface will take more research, Long said.

The hypothesis has some circumstantial support in other datasets, Long and his colleagues have found: The brightening trend is closely correlated with U.S. Federal Aviation Administration commercial flight hours during 1995-2007; those aircraft emit both water and the particles necessary to crystalize that high-altitude water into ice.

Moreover, a preliminary study using spectral solar data from an Oklahoma site shows that the clear skies had an overall “whitening” trend during the study years, an indication of increased scattering.

Professor Martin Wild of the Institute for Atmospheric and Climate Science at ETH Zurich, Switzerland, has been tracking Earth’s changeable energy budgets. He and his colleagues detected upswings in sunlight reaching the Earth surface (i.e., “brightening”) since the mid-1980s, which marked a recovery from substantial downswings in prior decades, a discovery published in Science. “We care about dimming and brightening because these phenomena may not only affect global warming, but also affect plant growth, glacier melt, the water cycle, solar power, and much more,” Wild said.

Wild said he’s interested in the new hypothesis, which will require more investigation, but which could help researchers to better understand the origins of dimming and brightening, a phenomenon with broad environmental and socioeconomic implications.

CIRES is a partnership of N​OAA​ and C​U-Boulder.