Is Climate Change Ever Good?

The cumulative effects of human actions over past centuries such as widespread deforestation and the abundant use of fossil fuels has caused changes in the present climate state that would otherwise not have occurred. This trend of an increase in the global average temperature shows no evidence of slowing into the future, which suggests that uncomfortable climate change will persist in the centuries to come. Most of the problematic aspects of climate change involve its negative impact on humans. This includes shifts in farmable regions of the world, destabilization of parts of the world due to fluctuating food prices, changes in flooding and drought patterns, and forced migration due to sea level rise.

A warming planet might pose problems for humans, but how would climate change affect the welfare of other species on Earth? In a recent paper titled “Is climate change morally good from non-anthropocentric perspectives?” and published in Ethics, Policy and Environment, Toby Svoboda and I examine the impact of climate change on non-human organisms. If we temporarily set aside the interests of humans, might it be possible that climate change provides net benefits to other organisms?

The context of this study is the belief by some people in “nonanthropocentrism” or “anti-humanism” as a philosophy. Such beliefs tend to place human interests beneath those of other organisms in Earth’s community of life. If such philosophical positions are accepted at face value, then this might suggest that climate change is in fact a good thing. Climate change might cause the decline of civilization and even a reduction in biodiversity, but it might allow other organisms to flourish as a result. The net effect could be a much more thriving planet, albeit one in which humans are worse off.

This is not to say that we should ignore the effects of climate change on humans. Instead, this analysis demonstrates that nonanthropocentrism and anti-humanism may be in conflict with modern attempts at mitigating climate change. Our analysis therefore challenges adherents of nonanthropocentric ethics to examine the extent to which non-human interests should take priority over the collective interests of human civilization.

Exomoon Atmospheres

As astronomers continue to search for potentially habitable planets orbiting other stars, some have also started to consider the possibility of habitable moons orbiting giant planets in such systems. Such exomoons could be the size of Mars, Earth, or even a few times larger, based on observations of similar large moons orbiting Jupiter and Saturn. A few scientific studies have demonstrated that exomoons should be expected in other planetary systems and could even be observable with the next generation of space telescopes.

I recently published a paper with RenĂ© Heller in Monthly Notices of the Royal Astronomical Society titled “Exploring exomoon atmospheres with an idealized general circulation model.” This study presents the first three-dimensional climate modeling of exomoon atmospheres. Exomoon atmospheres receive daily instellation from the host star of the planetary system, which would make them similar in climate to an Earth-like planet. But exomoons are also in synchronous rotation with the host giant planet (similar to the synchronous rotation of our moon around Earth). Exomoons therefore receive additional thermal energy at the top of their atmospheres from their host planet, in addition to the star. This configuration leads to a climate with warmer poles (a phenomenon known as “polar amplification”) and stronger dynamical energy transport.

Some exomoons atmospheres could enter a runaway greenhouse from the additional thermal energy of the host planet, but others should be able to maintain stable and potentially habitable atmospheres. Exomoons remain viable prospects in the search for life, and future astronomical surveys will gradually reveal the frequency of such worlds.

More on Mars Climate Cycles

Fluvial features on Mars seem to indicate that liquid water once flowed on the surface, yet climate theorists remain divided among how the red planet was able to sustain warm enough conditions in the distant past when the sun was fainter. Popular ideas include a dense greenhouse atmosphere of carbon dioxide, hydrogen, and other gases permitted a lengthy period of warmth. Another option suggests that periodic impacts caused enough warming to carve the features in a shorter time.

My co-authors and I have argued in previous papers that climate cycles on early Mars could have been driven by oscillations in the carbonate-silicate cycle, which would have provided transient warming from the accumulation of greenhouse gases by volcanoes and subsequent loss by weathering. In a new paper, we respond to a critique of the limit cycle hypothesis in our “Reply to Shaw.”

We acknowledge that the biggest obstacle to any explanation for warming early Mars with carbon dioxide is their ultimate fate: are there carbonate rocks buried underneath the martian regolith? If not, where did all the carbon dioxide go? Even so, we maintain that the early Mars climate cycle hypothesis remains consistent with observable geologic evidence and could have played at least a partial role in providing warm conditions on early Mars.

Circulation States of Synchronous Rotators

Some planets around low mass stars are expected to be in synchronous rotation, so that the star is continually fixed upon one side. This not only causes one hemisphere to experience permanent day and the other to reside in permanent night (with perpetual twilight along the “terminator” at the edges), but this also drives the climate into a regime fundamentally unlike any seen in the atmosphere of Earth.

In a recent paper titled, “Demarcating circulation regimes of synchronously rotating terrestrial planets within the habitable zone,” my co-authors and I analyze a set of climate model calculations to examine the dependence upon stellar effective temperature of the atmospheric dynamics of planets as they move closer to the inner edge of the
habitable zone. These results show that the surface temperature contrast between day and night hemispheres decreases with an increase in incident stellar flux. This trend is opposite that seen on gas giants, where the same forcing shows an increase in the day-night atmosphere temperature contrast.

We define three dynamical regimes in terms of the dynamical quantities known as the Rossby deformation radius (the ratio of buoyancy to rotation) and the Rhines length (the maximum extent of turbulent structures). The slow rotation regime is characterized by a mean zonal circulation that spans from the day to night side. Slow rotation requires that both the Rossby deformation radius and the Rhines length exceed planetary radius, which occurs for planets with rotation rate > 20 days. Rapid rotators show a mean zonal circulation that only partially spans a hemisphere, with banded cloud formation beneath the substellar point. The rapid rotation regime is defined by the Rossby deformation radius being less than planetary radius, which occurs for planets with rotation rate < 5 days. In between is the Rhines rotation regime, which retains a mean zonal circulation from day to night side but also features midlatitude turbulence-driven zonal jets. Rhines rotators are expected for planets with rotation rate between 5 to 20 days, where the Rhines length is less than planetary radius but the Rossby deformation radius is greater than planetary radius. The dynamical state can be inferred from observations of orbital period and spectral type of the host star as well as from comparing the morphology of the thermal emission phase curves of synchronously rotating planets. Such phase curves will be potentially useful tools for characterizing planets with the next generation of space telescopes.