My research is interdisciplinary, arbitrarily divided here into several overlapping areas...

Evolution of the Earth System

Our existence here is the product of four billion years of continual evolution, which requires four billion years of continually habitable conditions. A major theme of my research is trying to understand both how and why this happened. Earth is unique in our solar system not only as the only planet with life, but also as the only planet which provides a habitat for life as we know it. The paradigm of Earth System Science arises from the argument that these are intertwined. This was argued first by Vernadsky with his concept of the biosphere and later independently brought to wide attention in the west by Lovelock with the Gaia hypothesis.

Specifically, I have worked on:
The nature of the Great Oxidation
  The transition from a reducing to oxidising atmosphere around 2.4 billion years ago, delayed some hundreds of millions of years from the origin of oxygen producing photosynthesis. I demonstrated that there are two distinct stable steady states for atmospheric oxygen in the presence of oxygenic photosynthesis: a low oxygen state with less than 1 ppm oxygen and a high oxygen state with at least 0.1% oxygen. The transition between these is non-linear and geologically rapid, occuring with the formation of the ozone layer.
The global nitrogen budget and changing atmospheric inventory We performed the first comprehensive reassessment of the global nitrogen budget for several decades. There are substantial reservoirs of nitrogen in the continental crust and in the mantle. Mantle nitrogen is not primordial, but subducted. The major mechanism for putting nitrogen in rocks is substitution of NH4+ for K+, indicating that the nitrogen in the solid Earth is geological in origin. The existence and nature of these reservoirs implies that atmospheric nitrogen has varied over time and may well have been two to three times the present level during the Archean.
The Faint Young Sun Paradox The Earth received around 20% less energy from the Sun in the Archean than today, yet geological evidence is for a temperate climate. The mechanism of this warming, through a stronger greenhouse effect and/or a lower albedo, remains subject of intense debate. I have contributed to this debate in two ways. First, by showing that a higher nitrogen inventory was likely on early Earth, and that this would have caused net warming through pressure broadening of the adsorption lines of greenhouse gases. Second, I conducted a comprehensive evaluation of the possible role that clouds could have within solutions to the Faint Young Sun paradox. By fully exploring phase space, I was able to put constraints on which proposed solutions are, and are not, feasible. 

Earth and Planetary Atmospheres

From a background in Earth meteorology and oceanography, I later came to learn that other planets had really really interesting atmospheres. If we are to study the evolution of Earth's atmosphere, then comparative planetology provides us with an exceptionally strong tool. My main tool here is atmospheric radiative transfer and simple climate models, applied to diverse atmospheric conditions.

Specifically, I have worked on:
The runaway greenhouse If a terrestrial planet becomes sufficiently warm, its atmosphere will become water vapour rich and a hard limit on the amount of thermal radiation which can be emitted will emerge. If more solar radiation is absorbed than the maximum thermal emission, the planet will heat uncontrollably, the so-called runaway greenhouse. Along the way, the whole ocean will evaporate and all life will become extinct. This is the history of Venus and the future of Earth. I have showed that the runaway greenhouse may be possible with amount of energy that Earth receives from the sun today, and that either decreasing the amount of cloud reflection or strongly increasing greenhouse gas concentrations could trigger it. 
Climatic effects of clouds Clouds have huge leverage on planetary climate, but are fickle beasts. Introducing condensate into the atmosphere has a strong and non-linear effect on the radiation field and thus climate. They both absorb thermal radiation, contributing a greenhouse effect and a warming, and reflect sunlight, reducing absorbed energy and thus cooling. Whilst a clear-sky atmosphere can be treated as a coupled thermodynamics-radiative transfer problem, clouds should require that dynamics are included to find where condensation occurs. This makes simple climate models less applicable, but non-simple climate models contribute a host of difficulties. I've used explored the parameter space for clouds for Early Earth climate (see above), and contributed that treating clouds on brown dwarfs as patchy (as Earth clouds are) gives a better fit to observations. 
Radiative transfer codes I've run a handful of different codes. What developers of these know, but many users seem not to, is that any "off the shelf" RT code will have been designed for specific conditions. Take the code outside its design range, and performance will deteriorate. Best to talk to the developer, or test the code yourself against something you know will work. 


A plurality of worlds has long been envisaged around other stars. In recent years, extrasolar planets have been detected. The grand question is: do any of these planets harbour life? The only practical method of life detection on extrasolar planets is by atmospheric analysis (Lovelock, 1962): one must examine the spectra of the atmosphere, observe that disequilibrium exists and determine that the only possible cause of that disequilibrium is life. To do this, one must understand how planetary atmospheres evolve, both with and without life.

Specifically, I have worked on:
The Habitable Zone In what region of circumstellar space might planets be habitable? This may guide where we may search for life on other planets in the future. My work has highlighted that there are several different regions of stable climate which overlap - and that the boundaries of these depend upon atmospheric inventories of carbon dioxide and nitrogen, which are biologically controlled. Thus habitability depends on inhabitance. 

Other things I've done along the way...

Geoenginering As we transfer carbon from buried organic carbon to atmospheric carbon dioxide on an industrial scale, we are partaking in the greatest global change experiment. The result will certainly be a global scale warming and most likely a major disruption to existing ecological, social and economic systems. A proposed range of solutions is to deliberately engineer Earth's climate to attempt to counteract our more careless actions with CO2 emissions. Some proposed schemes have received insufficient study; all are potentially dangerous.
Physical Oceanography I was on the shipboard party of the RRS James Clark Ross for cruise JR97 to the Weddell Sea and Fimbul Ice Shelf doing physical oceanography. Physical Oceanography was a major focus as an undergraduate. 
Meteorology The other half of my undergraduate degree, now coming back to be part of my work more. Victoria has one of the densest urban meteorology networks available through the UVic Victoria Schools Weather Network - so there is lots of interesting potential associated with this.