Climate Change is a broad term that, as used on this site, comprises the totality of climate impact that is a consequence of human activity.*Whether GHG emissions, changes to albedo through deforestation, alteration of the carbon cycle of the oceans, etc. The climate is an extraordinarily complex system full of nonlinear interactions, and yet it is quite clear that humanity, in our domination of the globe and our attempts to control our own destiny, is directly and indirectly impacting climate in dramatic ways.
Let’s start by framing up the problem. As is explored throughout the pieces in the Musings section, the question “what is the root cause of our climate problem?” isn’t obvious, but we are quite confident that the manifestation of the challenge is most obviously expressed as a net flux of greenhouse gases into the atmosphere that contribute to a radiative forcing imbalance in addition to other, direct problems (i.e. ocean acidification) associated with the concentration of, in particular, carbon dioxide (CO2) in our atmosphere. GHG emissions are not the only vector of anthropogenic climate change*e.g. albedo change & biomass alteration, however they have the ‘benefit’ of allowing a quantitative framework for modeling the net influence to one of the principal issues: global temperature rise.*For a thorough introduction into the evidence for, and consequences of, anthropogenic climate change see the IPCC AR5 Synthesis Report
The principal greenhouse gases are CO2, CH4 (methane), N2O (nitrous oxide), and F-gases (i.e. HFCs and SF6) in rough order of importance as of 2020. These gases have net greater transmissivity to the solar spectrum than to the spectrum of radiation emitted from earth (hence they function, like a greenhouse, to ‘trap’ heat). The image below, provided by the IPCC AR5 report, shows the increased rate of emission of anthropogenic GHGs over time.
As of 2010, we were releasing ~50 billion tons of CO2-equivalent emissions (meaning that the radiative forcing of the emissions of all anthropogenic GHGs was equivalent to that of 50 billion tons of CO2 over a predetermined period, in this case 100 years – more on that later). This is, on a carbon basis, equivalent to approximately 13.6 billion tons of C. Is that big? The figure below shows an approximation of global carbon fluxes (natural and anthropogenic). While total carbon flux is approximately an order of magnitude larger than anthropogenic emissions, we are currently accumulating billions of tons of C in the atmosphere annually. This is because the sources of carbon exceed the sinks of carbon (i.e. nature can only absorb so much excess carbon so quickly). Anthropogenic emissions are the source of the imbalance in carbon flux that is causing an increase in concentration of greenhouse gases in the atmosphere.
This net imbalance of the flux of greenhouse gases ultimately contributes to global warming. The figures below show the scenarios of future anthropogenic emissions and the consequential likely impact to average global surface temperature.*Because we are a part of highly-complex ecosystems and are no longer a minor perturbation on the scale of the global carbon cycle, we are not only directly contributing to climate change through our emissions. The consequential alteration of ecosystems affects the ‘natural’ carbon cycle – unfortunately, most of the effects are positive feedback loops rather than negative feedback loops, meaning that we are pushing the system farther and farther from equilibrium. It’s worth noting that the grey scenario (baseline) is the ‘business as usual’ scenario, meaning that if we don’t actively change our behavior it is our probable future.
Again, we won’t go into detail on the full consequences of climate change, but a temperature change of >2 degrees C would be, most probably, catastrophic to our present way of life.*Most temperature change scenarios are probabilistic assessments of the likelihood of a given temperature rise for a given cumulated set of GHG emissions. This means that there is substantial variation in the possible outcomes of our emissions – a ‘4 degree C’ scenario might actually comprise possible worlds between, say, 2 and 10 degree C changes. This means that there exists substantial risk even at our present level of accumulated emissions.
So we know that we need to do something about our emissions, and we know that the magnitude of this change is massive. What are the sources of these emissions? The figure below shows a more detailed breakdown of the sources of anthropogenic emissions.
It’s worth noting that this is NOT a Sankey diagram of energy use (or, rather, it is incomplete with respect to energy) because the use of renewables with no direct GHG footprint is not reflected. However, from this diagram it is clear that the sources and uses of the fuels and process emissions that comprise our GHG footprint are highly varied and form the foundation of our economy. Radical transformation across the most fundamental sectors of our economy is required to adhere to the future emission scenarios that do not lead us to climate disaster.
We clearly need to get our GHG emissions under control. CO2 is the biggest offender, and most emissions scenarios that keep us below a 2 degree C increase above the pre-industrial world require us to actively remove carbon from the atmosphere. It it highly unlikely that we can achieve equilibrium with our environment in a condition that we would aspire to without addressing CO2. But the story is still incomplete. The largest positive climate feedback loop is the net energy imbalance of the planet (i.e. radiative forcing) which leads to global warming. It is the integrated energy imbalance that contributes to average temperature rise. Thus, the axis of time matters.
There are several variables associated with time that one must consider when contemplating the optimal course of action to give our species the greatest chance of survival. The first is ‘how long do we have before we reach a tipping point from which we cannot return?’ Unfortunately, we can’t know for certain at precisely what temperature rise or concentration of CO2 in the atmosphere a tipping point will be reached. However, we can provide ranges. The 2 degree scenario is the most commonly used target (though there is much debate about whether it is appropriate or already too high – the IPCC suggests that a 1.5 degree target is likely a safer bet) as a probabilistic statement that we are more likely than not to reach a tipping point if we surpass 2 degrees. It could happen at 1.5. It could happen at 4. There’s even an outside chance that there isn’t such a tipping point and a negative feedback loop will be activated of which we are yet aware. However, the best we can do is leverage our probabilistic assessments to provide a target.
The time-integrated effects of radiative forcing induce temperature change. The more radiative forcing present, the shorter amount of time we have to hit a 2 degree target. So what time frame is relevant for us to consider to avoid it? A lot less than 100 years.
The figure below shows the fraction of radiative forcing associated with the major GHGs:
Should the consideration of the axis of time actively change our behavior (i.e. would the optimal strategy to prevent climate disaster have path dependence)? Yes. Absolutely. There are things that we can do to give ourselves more time to solve the underlying problem of concentration of CO2. Examples include things like directly influencing radiative forcing (sometimes called geoengineering*A subject that the author believes deserves concentrated attention. Controlling radiative forcing by directly influencing large systems is not without risk, but there are very few credible scenarios whereby we do not ultimately require some form of ‘insurance’ to give ourselves the time to change our underlying infrastructure). But we should also consider our accounting of the relative importance of the greenhouse gases. Over a 100 year period, the Global Warming Potential (GWP) of the major GHGs stacks up as CO2 – 1, CH4 – 28, N2O – 265 (or 1, 34, and 298 respectively including climate feedbacks – see IPCC AR5 Chapter 8). Over a 20 year period, the GWPs stack up as CO2 – 1, CH4 – 86, N2O – 268). This is because different gases exhibit different atmospheric chemistry and consequently have different lifetimes and net effect on radiative forcing vs. time. Mitigating the emission of a ton of CH4 has 86 times the impact on integrated radiative forcing over a 20 year period than mitigating the emission of a ton of CO2.
Consequently, over short periods (but likely not indefinitely) we can buy ourselves more time before hitting our temperature tipping points by taking actions designed to have large net contribution to radiative forcing. However, we will eventually (and soon) need to address the CO2 elephant in the room.*There is some debate about the importance of the activity (i.e. concentration) of CO2 in the atmosphere (or oceans) independent of the impact on radiative forcing. Ocean acidification is an example of a negative externality of high CO2 concentration that might have detrimental ecosystem impact. However, the impact of radiative forcing is likely far greater than other CO2 concentration related effects of the great geoengineering effort that our humanity has undergone (i.e. fossil fuel burning civilization). Thus, it may be justified to eschew the CO2 issue in favor of more actionable effects directly reducing radiative forcing over the short to medium term. It is the author’s opinion that there is no way around us influencing the environment at a global scale through our choices – the question we will collectively need to answer is what framework we will use to make our choices.
To begin to answer the question of how we can go about solving the issues, we will need to understand why the issues exist in the first place. There are many dimensions to this question, including social, political, technical, and economic and untangling the massive complexity of the ‘why’ of our energy system is beyond the scope of any individual author (though perhaps Vaclav Smil comes closest in Energy and Civilization: a History).
I will leave the exploration of ‘why’ for Musings, but will briefly touch on some key points that outline the conversation: thermodynamics, cost, policy, and human behavior.
Thermodynamics
Energy is what lets us do things, and it turns out that we like to do things*Any anhedonists in the house?. What are the sources of energy that we could conceivably find to use?
There is (substantially) only one flux of energy to earth: solar energy. Light originating from fusion reactions in (dominantly) the Sun deposits, on average, roughly 1.3 kW m-2 of energy in the form of light onto the outer bounds of our atmosphere. Similarly, the dominant flux of energy from earth is radiation back into space (a combination of reflected light as well as emission from bodies of temperature greater than 0 K, including the surface of the earth at a rough average temperature of 288 K). If we consider flux of energy to the crust of the earth, then there are two sources: solar and geothermal energy (which is mostly gravitational potential from the formation of the planet + heat from the radioactive decay of unstable isotopes present in the Earth). Other sources of energy that we typically think of are free energies associated with stored energy. This stored energy may originate from solar or geothermal energy (i.e. wind and biomass), the formation of our planet and the gravitational potential energy that was converted to heat in the process (i.e. minerals in the crust that are reactive), the cores of stars (or supernovae, or the collision of neutron stars, or the interaction of cosmic rays… i.e. radioactive elements such as uranium with nuclear free energy), or the beginning of our universe and the formation of the earliest atomic species (i.e. low atomic mass species like hydrogen that constitute fuel for fusion).
When the state of a system of higher free energy is transformed to one of lower free energy, energy is released that lets us do ‘work’. The amount of energy released is dependent on the kind of transformation. As we’ve yet to have much success at harnessing antimatter, the highest energy density state transformations which we might seek to harness are nuclear in nature. There is an extraordinary amount of available free energy just in the hydrogen in our oceans, so why don’t we use 100% fusion energy to power our lives? We care about things other than energy density of our ‘fuels’ – in order for fuels to be of most use, we need them to be stable enough that they don’t spontaneously release energy in an unwanted fashion, but not so stable that we can’t easily access the free energy. Fusion, to date, has unfortunately fallen into that second category. The activation energy of fusion reactions is relatively high (meaning that we have to do a lot of work to get fusion to happen at conditions typical on Earth’s surface).
Because of their ease of use, relative stability, and reasonable energy densities, we have primarily relied on fuels that provide chemical free energy (i.e. energy is made usable by chemical reactions). Carbon (and hydrocarbons) is remarkably well suited to satisfy to-date human needs for sources of free energy.
CO2 is a fantastic molecule to generate when attempting to access the free energy of carbon chemistry. Oxygen is abundant in our atmosphere and CO2 has a relatively low energy of formation (meaning that significant free energy can be harnessed by reacting carbon-bearing molecules to CO2). This also means that it is a relatively stable molecule, for there aren’t many forms for carbon to take that are more energetically favorable, given our atmospheric conditions, than CO2 (but there are a few – this will be addressed in other posts).
Carbon chemistry has been selected by evolution to be the currency of energy – specifically, the vast majority of photosynthetic processes leverage carbon chemistry (i.e. carbon is the building block of life), with CO2 as an input. Thus, chemical free energies are available in the form of carbon-bearing molecules, and carbon bearing molecules are most-profitably used (if work is the desired outcome) when reacted to CO2.
There are other options we could use for chemistries, and indeed we could use other forms of stored free energy than chemical (e.g. nuclear), but it should be no surprise that we have defaulted to carbon. It has been selected for over the course of billions of years, and large amounts of stored free energy (i.e. fossil fuels) are readily plunderable for ‘free’ free energy.
Cost
Energy is the ultimate commodity (a joule is a joule). We default to selecting the lowest cost form of energy, all else being equal and given existent boundary conditions. We won’t go into detail about the various costs of energy here. At the risk of oversimplifying, energy costs are a function of the capex (and the cost of capital) and opex required for production. The energy yield ratio (i.e. how much energy is required to be put in to get a given amount of energy out) is a useful proxy for thinking about the cost entitlement of various sources of energy. Fossil fuels are energy ‘free’ for the taking – the major costs are extraction, transportation, and conversion. Solar energy is similarly ‘free’ – the primary cost is capex.
Lazard publishes an annual Levelized Cost of Energy comparison for the primary available sources of energy:
It is worth noting that the marginal levelized cost of energy (shown in gold) for paid-for capex can be significantly lower for certain sources of energy (e.g. nuclear and combined-cycle gas).
Only in the 2010s has the marginal cost of renewables been lower than that of conventional fossil generation sources. The figure below shows historical LCOEs.
The flipside of cost is value. We use energy to do things – it’s a means, not an end. The form, location, availability, and reliability of energy all matter and have value. Because human demand depends on factors in addition to energy-cost minimization, we value energy supply that maps onto our demand. Consequently, dispatchability (manifesting in the need to store energy for non-dispatchable sources such as renewables – we like the lights turning on when we flip the switch) is required by our current demand-management reality. This has additional cost.
While there are many complex dimensions of human choice that challenge the primacy of cost for the basis of why we choose a given energy system (i.e. historical choice of infrastructure, desire for on-demand energy, preferring electricity), it is still most reasonable to default to a presumption that for a given joule of delivered energy at a given time, most consumers choose the lowest-cost option.
Policy
The policy and regulatory environment (manifested in government and laws) establishes the boundary conditions of society and markets. Government itself may, to some degree, be a representation of the collective will of individual members of society and/or other agents that influence policy (e.g. corporations, wielders of military power, religious luminaries). Don’t worry, this won’t be turning into a political manifesto – the only point being made is that the rules that bound the behavior of agents in society are themselves mutable, and the policy and regulatory landscape affects our choices. This includes choices related to energy, climate, and, specifically, greenhouse gas emissions.
Capitalism has been highly adaptive over the past centuries and consequently has been selected for as the major global organizational framework for societies and markets. One of the principal challenges in climate relates to way that our values are expressed in the metrics optimized by markets. Today, in most places in most contexts, the products of the use of energy that generates CO2 have value in markets, but the systems that are harmed by the emission of CO2 (some of which provide ecosystem services) are not valued. Consequently, the negative value of CO2 is not substantially accounted for by present market frameworks.
It is a constant game of whack-a-mole to attempt to distill the complexity of human value systems into a set of metrics that could be optimized by markets and incentives. Indeed, we don’t have complete knowledge of what the impacts of our actions might be.*Climate change is a perfect example – in the 18th century we didn’t realize the impact that our industrialization through the use of fossil fuels would have on global climate (other than the rare prophet, i.e. Alexander von Humbolt) However, it is clear that the government (through policy and regulation) has a major role to play in establishing whether actions that contribute to climate change will be incentivized or disincentivized. We will not go into detail here about the policy frameworks that could help us change course regarding climate. Much smarter people have thought about these questions.
Human Behavior
Climate change is a problem by humans, for humans. It is the sum total of the individual actions of >7 billion people that comprises our effect on climate.*Though our individual agency may be limited – see Musings Human behavior (and the emergent behavior of societies) is the source of our climate problem. But it can thus be our solution as well. If we were to suddenly all choose to cease emissive behavior, there would be no more GHG emissions and climate change would be staved off. However, it turns out that we like things like eating, doing things with energy, convenience, infrastructure, etc. Finding a path between our emissive present and our hopeful future is a massive challenge. It is both depressing and comforting to realize that the forces against which we are struggling are of our own making. Human behavior – our values, our preferences, our beliefs – is a necessary lens through which to consider our current climate context and our potential paths forward.
4 Pillars, a Foundation, and Moving Forward
The theory of change that is implicit and emergent in the remainder of this site relies on the interconnectivity of four pillars on which we need simultaneous global action if we are to address climate change (Technology, Finance, Policy, and Culture) and rests on a belief that human behavior is the foundation for any agency that we have to affect our climate future.
This theory of change will be addressed explicitly in the Thoughts section.