More Environmental Astronomy

Even though we don't understand the Earth and its ecosphere as a being, in many respects, it acts like on, and the assumption that it does, called the Gaia hypothesis, is a reliable way to make good predictions about how the global ecosystem will respond to stress factors, including extraterrestrial impacts. This hypothesis predicts that Earth is robust in the long term and that life will find a way to stabilize things in the long run even though that are factors that could screw it up. 

Of course, on these time scales, the "long term" may be too long to be relevant to humans.

The Gaia hypothesis postulates that life regulates its environment to be favorable for its own survival. Most planets experience numerous perturbations throughout their lifetimes such as asteroid impacts, volcanism, and the evolution of a star's luminosity. For the Gaia hypothesis to be viable, life must be able to keep the conditions of its host planet habitable, even in the face of these challenges. 

ExoGaia, a model created to investigate the Gaia hypothesis, has been previously used to demonstrate that a randomly mutating biosphere is in some cases capable of maintaining planetary habitability. However, those model scenarios assumed that all non-biological planetary parameters were static, neglecting the inevitable perturbations that real planets would experience. To see how life responds to climate perturbations to its host planet, we created three climate perturbations in ExoGaia: one rapid cooling of a planet and two heating events, one rapid and one gradual. The planets on which Gaian feedbacks emerge without climate perturbations are the same planets on which life is most likely to survive each of our perturbation scenarios. Biospheres experiencing gradual changes to the environment are able to survive changes of larger magnitude than those experiencing rapid perturbations, and the magnitude of change matters more than the sign. 

These findings suggest that if the Gaia hypothesis is correct, then typical perturbations that a planet would experience may be unlikely to disrupt it.

Olivia D. N. Alcabes, Stephanie Olson, Dorian S. Abbot, "Typical Climate Perturbations Unlikely to Disrupt Gaia Hypothesis" submitted for publication to MNRAS (June 3, 2019).

Environmental Concerns In Space

It isn't too son to consider environmental issues in the solar system beyond Earth.

"How much of the Solar System should we reserve as wilderness, off-limits to human development?" 

We argue that, as a matter of policy, development should be limited to one eighth, with the remainder set aside. We argue that adopting a "1/8 principle" is far less restrictive, overall, than it might seem. One eighth of the iron in the asteroid belt is more than a million times greater than all of the Earth's estimated iron reserves and may suffice for centuries. A limit of some sort is needed because of the problems associated with exponential growth. Humans are poor at estimating the pace of such growth, so the limitations of a resource are hard to recognize before the final three doubling times which take utilization successively from 1/8 to 1/4 to 1/2, and then to the point of exhaustion. Population growth and climate change are instances of unchecked exponential growth. Each places strains upon our available resources. Each is a problem we would like to control but attempts to do so at this comparatively late stage have not been encouraging. Our limited ability to see ahead suggests that we should set ourselves a 'tripwire' that gives us at least 3 doubling times as leeway, i.e. when 1/8 of Solar System resources are close to being exploited. At a 3.5 percent growth rate for the space economy, comparable to that of the iron use from the beginning of the Industrial Revolution until now, the 1/8 point would be reached after 400 years. At that point the 20 year doubling time of a 3.5 percent growth rate means that only 60 years would remain to transition the economic system to new "steady state" conditions. The rationale for adopting the 1/8 principle now is that it may be far easier to implement in principle restrictions at an early stage, rather than later, when vested and competing interests have come into existence.

Martin Elvis, Tony Milligan "How much of the Solar System should we leave as Wilderness?" (May 24, 2019)

22,000 Years Of Climate Change And History In One Comic

xkcd has an excellent comic summing up 22,000 years of climate change and the associated pre-historic and historical events taking place along the way in one oversized comic.

Two bits of commentary are in order.

First, xkcd has repeatedly demonstrated that often there is just no good substitute for drawing something to scale, even if that means it won't fit on the confines of an ordinary sized comic, or an ordinary sized piece of paper or book.  This is just such a case.

Second, while the comic is largely spot on when it comes to historical dates, the smoothing in the temperature diagram (which the author, in fairness, acknowledges is present in the comic) comes at the cost of a pretty important feature of the data from the period of about 40,000 to 10,000 years ago, which is that the temperature was wildly unstable and oscillated dramatically over much of that time frame, which is one important reason that farming had trouble establishing itself. It is hard to establish agriculture when one generation one set of crops work, and two generations later, an entirely different climate prevails.

To recap:

The key paleoclimate data are presented in the chart below.

 

Ignoring for the moment their simulated data in light gray bar graph form: 

Estimated dates of some well-studied cases of the initial emergence of cultivation are on the horizontal axis (8, 54, 55). Climate variability (Left) is an indicator of the 100-y maximum difference in surface temperature measured by levels of δ¹⁸O from Greenland ice cores (SI Appendix). A value of 4 on the vertical axis indicates a difference in average temperature over a 100-y period equal to about 5 °C.  

As the chart indicates, intermittent periods of wild temperature variation over the span of just a few generations was the norm for the entire Upper Paleolithic era (about 40,000-50,000 years ago), after which temperatures became much more stable starting at the beginning of the Holocene era about 10,000 years ago when farming first emerged in the Fertile Crescent and China and the middle latitudes of the Americas (farming arose independently at later times in the New Guinea Highlands, Sub-Saharan Africa and the Eastern United States).

This feature is material to the presentation because the big point of the comic is to show how extreme and unprecedented rapid climate change in the present is relative to the past.  And, compared to the last 10,000 years that is correct.  Moreover, there is extremely solid evidence showing that climate change now is man-made, which was not true of climate instability from 40,000 to 10,000 years ago. But, this pretty important detail does make for a more complicated story.

This rapid fluctuation during the last glacial maximum around 20,000 to 22,000 years ago also helps explain while the world experienced an intense population bottleneck at the time even though much of it was not covered with ice.

And, this rapid fluctuation may have been a driver of mass migrations across the globe by Upper Paleolithic populations whose existing habitats became uninhabitable again and again.  This placed Upper Paleolithic modern humans under severe selection pressure for adaptability, which is a trait that it is fair to say distinguished us more from other archaic human populations, like Neanderthals, that did not survive, than straight "IQ".

Missing Species Probably Mostly In Biodiversity Hotspots

Six regions already identified by conservation scientists as hotspots -- Mexico to Panama; Colombia; Ecuador to Peru; Paraguay and Chile southward; southern Africa; and Australia -- were estimated . . . to contain 70 percent of all predicted missing species.

From here, citing Lucas N. Joppa, David L. Roberts, Norman Myers, Stuart L. Pimm. Biodiversity hotspots house most undiscovered plant species. Proceedings of the National Academy of Sciences, 2011; DOI: 10.1073/pnas.1109389108.

I'm somewhat surprised that such a large swath of Latin America figures so prominently, or that southern Africa and Australia, which have had a British colonial presence for so long would still be expected to have so many undiscovered species. I would have expected more undiscovered species in Southeast Asia and the Congo basin.