Title: Impact of climate change on site characteristics of eight major astronomical observatories using high-resolution global climate projections until 2050
Authors: C. Haslebacher , M.-E. Demory, B.-O. Demory, M. Sarazin, and P. L. Vidale
First Author’s Institution: Center for Space and Habitability and Department of Space
It has become clear that every place on the planet will have to deal with some effect of anthropogenic climate change in the coming decades. People in astronomy, however low in number, have a disproportionately large impact both on a personal level as well as in terms of infrastructure. Luckily, there are many ways for improvement.
However, now that the environmental change motor has started, every part of society will need to solve the problems coming with its increasing effects. Will astronomers also see some major changes coming through? Now we can wonder, what about our observatories? While looking away from Earth, would they see the environment changing?
Short answer: Yes
For the long(er) answer, merily read along! Now, to be fully clear, we are talking about the ground-based observatories here on Earth. The ones in space don’t really have an atmosphere or climate change to consider once they’re up there (although getting them there certainly doesn’t help solving the problem).
Today’s study took a detailed look into eight major observing sites (also shown in Figure 1):
- Mauna Kea, Island of Hawaii, USA
- San Pedro Mártir in Baja California, Mexico
- Cerro Paranal, Cerro Tololo and La Silla, Chile
- La Palma, Canary Islands, Spain
- Sutherland, South Africa
- Siding Spring, Australia
In order to have a really great ground-based observing site, a few local characteristics are desirable. We need the air as dry as possible, more moisture only decreases the quality of the observation. A large elevation is also optimal (less atmosphere = less trouble). Also, as few clouds as possible would be optimal; the sun isn’t very able to pierce through thick clouds, stars or other objects at night don’t do much better sadly. Another eagerly sought-after property is good astronomical seeing: this tends to be better on mountain tops, so many observatories are built on mountains. Also, many astronomers like a good view (pun intended). The above eight observing sites have these properties in abundance, so many of the world’s most impressive telescopes can be found there.
Alright, the local properties at these sites are great for astronomical observations. But the question is: will it be the same in a few decades given the current accelerated global warming? This is what the authors of this paper studied. To do so, they looked at the following measurable quantities:
- Air temperature: influencing almost every other quantity in this list, it is also relatively easy to measure.
- Air humidity: local amount of water vapor in the air. If this is very high (like with mist), the telescope’s electronics are unlikely to take it well. Typically, telescopes are designed to shut down automatically when humidity becomes too high.
- Precipitable Water Vapor (PWV): imagine a column from the surface where the telescope stands on all the way to the upper atmosphere, and then take all the water in that column. If this is high, your telescope will see less good.
- Cloud cover: may be relatively self-explanatory! More clouds means less observing.
- Seeing: essentially driven by the local turbulence in the atmosphere. Lower turbulence leads to better seeing.
Although many of these quantities are monitored at the observing sites, most of the data has been collected for too short a time to make a confident conclusion about the impact of climate change happening on a decade scale.
So, we need more
Data! Data! Data!
One way to get loads of predictions to build upon is with simulations. In climate science, these are called Global Climate (or General Circulation) Models (GCM). The current ones, almost 70 years since the first GCM hit the market, are pretty powerful.
In this study, the authors used the PRIMAVERA models in the worst-case scenario, making a distinction between the models that incorporate ocean effects (coupled) models and those that don’t (atmospheric).
Another powerful tool used in climate science is a reanalysis, a climate simulation augmented with – often much more sparse – measurements serving as a good transition between empirical data and full simulations like GCMs. The authors made use of all three – measurement (also called in situ) data, reanalyses and GCMs – to see the impact on quantities described above.
An example of this is shown in Figure 2, showing the atmosphere temperature trend for the Mauna Kea site, where the temperature is clearly rising steadily.
An increasing temperature is coupled with a lot of other problems, but a direct consequence is an increased failure rate of the electronics of a telescope facility. This will become more and more frequent with rising temperatures. Not only the rising temperature will cause problems, also the local atmospheric water content at the observing sites is likely to increase as well. This leads to lower quality observations because of high water vapor in the air, along with decreased observation times as humidity becomes a bigger problem.
Currently, most observing sites do not take into account the effects of climate change when a new facility is built. As most of these effects will only accelerate in the coming decades, it will be increasingly important to have good estimates of the building site’s future conditions in order to mitigate environmental change effects on future telescopes.
Astrobite edited by Lina Kimmig & Clarissa Do Ó
Featured image credit: Wikimedia Commons