Friday, June 12, 2015

Connecting CMOs, ppms, and joules

I have often been asked questions like how many cubic miles of CO2 do we produce when we burn a cubic mile of oil, and how many ppms does that represent. In this post, I will make some simplifying, yet reasonable, assumptions to provide answers to these and other questions.

In round numbers, one cubic mile of oil weighs 3.8 billion tons and contains roughly 3.2 billion tons of carbon. Burning this quantity of oil produces 153 quadrillion Btu of energy, which we have defined as 1 cmo. This combustion produces about 12 billion tons or 2.7*1014 moles of CO2. As a gas, the volume of CO2 is depends on the pressure and other variables. But let’s say we condense it into a liquid. Liquid CO2 has a density of close to that of water. As a liquid the amount of CO2 from burning a cubic mile of oil will occupy 3 cubic miles. If we burn coal to get an equivalent amount of energy, we produce 17 billion tons of CO2, which as a liquid would take up 4.3 cubic miles.  Burning a cmo worth of natural gas will generate 7.5 billion tons of CO2—about 1.9 cubic miles of liquid CO2.

To determine by how much the concentration of CO2 in the atmosphere changes when we burn a cmo of oil, we need an estimate of the number of moles of gas in the earth’s atmosphere. Here’s a guesstimate. The radius of the earth is 4000 miles, and so its surface area, 4*pi*r2, is approx. 200 million square miles, and if we assume that the atmosphere extends to only 5 miles, the volume of atmosphere is 1 billion cubic miles. If we assume that the pressure in this 1 billion cubic miles is 1 atmosphere and 27°C (it is not, but then the atmosphere also extends to over 60 miles) we can estimate the number of moles of gas in it using the ideal gas equation, PV = nRT. The number turns out to be 1.7*1020 moles. Thus, CO2 introduced from burning a cmo of oil corresponds to 2.7*1014/1.7*1020 or about 1.5 ppm of the atmosphere.

Table. Volume of liquid CO2 produced from burning of 1 cmo of various fossil fuels and its concentration if it all ended up in the air.

Volume Liquid CO2 (mi3)
Conc. in Air (ppm)

The world is currently releasing about 36 billion tons of CO2 each year from combustion of coal, oil, and natural gas, and that would correspond to about 4.5 ppm. The global CO2 level though is rising at the rate of about 2.5 ppm a year or about half the value estimated. That is because about half of the emitted CO2 ends up in the oceans and thus increasing their acidity. The increased acidity makes it harder for corals, oysters, and plankton to develop their shells with potentially dire consequences for the entire food chain!

An estimated 530 billion tons of carbon have been burnt since the start of the industrial revolution. The expected rise in atomspheric CO2 concentration, if all of it stayed in the air, would have been 245 ppm.  The observed rise of 120 ppm (current concentration of 400 ppm minus 280 ppm, the concentration in 1860) jibes well with the assumed 50% staying in the air.

The greenhouse gas effect of the CO2 in air amounts to increasing the radiative forcing by roughly 0.5 W/m2. That seems like a small perturbation compared to solar insolation of 1000 W/m2 (at high noon). There is a nice video describing how you can measure the solar insolation in your backyard with a simple experiment. The net heat gained by the earth in a year can be estimated by multiplying the surface area of the earth (41 1012 m2) by the radiative forcing (0.5 W/m2) times the number of hours (8760) in a year, a factor that corrects for the fact that only half of the earth’s surface is facing the sun at a given moment, and that the sun is not overhead all the time. The result is a net heat gain of 563 trillion kWh or 12.5 cmo! Since we are currently consuming 2.75 cmo of fossil fuels per year that the additional heat being trapped from the greenhouse effect is four-and-a-half times the energy released from burning of fossil fuels. There goes the theory that the global warming is solely due to the heat rejected by the engines.

Monday, April 20, 2015

Deepwater Horizon Disaster: Five Years Later

Five years ago today the BP Deepwater Horizon (DWH) oil well in the Gulf of Mexico burst into flames following a blow out. Eleven workers died in the accident and 11 others were injured. Oil and gas gushed out for months from the broken pipe at the floor of the sea. The actual quantity of the spill was difficult to ascertain initially, and estimates ranged from 10,000 to 100,000 barrels per day. After the fact, it was determined that the maximum rate of spill was about 62,000 barrels a day and over the three-month period of the spill, 4.9 million barrels of oil had poured out. Even though this figure is questioned as it is important to the litigation and fines that BP has to pay, the range of discrepancy has narrowed—somewhere between 3.2 and 4.2 billion barrels. Researchers are still trying to figure where most of the oil went, because only about a quarter of amount has been accounted for.
Over 600 miles of the coastline were affected. Fishery and tourism are major industries of the region, and suffered enormous losses. The damage to the environment, to the local flora and fauna, and the destruction of their habitat was catastrophic in scope. There was a marked decline in the population of shrimp, oysters, and various fish, and the concern was that with the loss of much of their habitat, populations of pelicans, turtles, and dolphins would also collapse. People feared that seafood from the region would be contaminated with toxins threatening the industry. In the immediate aftermath of the tragedy the headlines screamed of the irrevocable damage to the fragile ecology of the area—that the place would forever turn into a wasteland.
Now, forever is a very long time. Not to minimize the catastrophe that the DWH blowout was, it seemed to me though that the alarmist response was uncalled for, and it distracted attention from the real restorative work that needed to be done. Deepwater Horizon was only one of several major events in which large amounts of oil were discharged into seas and oceans and these accidents could provide some valuable lessons.
A year following the DWH blowout, I wrote a post about the accident. I looked at what happened after four specific incidents of major oil spills:  Amoco Cadiz, Ixtoc 1, Exxon Valdez, and the sabotage by Iraqi army following the first Gulf War in 1991.  I also noted that about 10 million gallons of oil naturally seeps in the Gulf of Mexico every year. The main conclusion I drew was that as tragic as these events have been for the people and animals directly affected, they also provide a strong testament to the resilience of the environment as recovery of the environment, and that we would expect the Gulf of Mexico to also recover in three to five years.
I have been reviewing many of the articles about the aftermath of the disaster. Some of the noteworthy findings are:
·      The Food and Drug Administration tested seafood from the Gulf of Mexico for contaminants but has found few problems with toxicity.
·      Studies on the fate of the oil show that the oil-eating microbes, which are endemic to the region because of the natural oil seepage, feasted on the oil spill and biodegraded the oil. The sharp increase in the population of these microbes could have reduced the dissolved oxygen and adversely affect other species, but that scenario did not play out.
·      Fish and shrimp populations have rebounded to pre-disaster levels, and the seafood industry has largely recovered. However, oyster harvests have not yet recovered, possibly because of their limited mobility to move to oil-free areas.
·      Tourists have returned to the region bringing with them the anticipated economic recovery.
To be sure there are still many unanswered questions particularly about the long-term effects. The general point I want to emphasize is that as with previous cases of oil spills, nature has once again bounced back. It is not an excuse to be lackadaisical about oil spills. Safety has to be number one on the minds when drilling for oil in the seas, as it should be in many other industrial operations. Safe operating procedures and disaster preparedness have to be constantly improved as new information becomes available. At the same time we should recognize that oil is not an acute toxin and oil spills do not spell the demise of the region. Nature is remarkably resilient, and that’s worth celebrating.

Tuesday, February 24, 2015

Getting Real About Energy in Cubic Miles of Oil

Today, with plummeting oil prices and news reports of US oil production poised to exceed that of Saudi Arabia’s, there is a perception on the street that there is no energy crisis. Yet just a few years ago, we were all talking about one. Have things changed so dramatically so fast? We paid considerable attention to the energy crisis following the oil crunch in the 1970s, but then oil prices plunged, and public attention waned, and with it the efforts at conservation and improving fuel efficiency of vehicles. However, the underlying situation and the challenges facing us had not changed, and nor have they changed this time. A crisis is a terrible thing to waste, and we seem to be doing it all over again.  I recently spoke about it with Artist Michael Killen.

Meeting the global demand for energy remains a daunting task, and the energy sources we choose to employ will have a profound effect on the lives of billions of people around the world. People have to be involved in making the choice, or the choice will be made for them. For a sustained, informed public debate on this subject, it is necessary to have a common language that is readily understood by the specialist and the non-specialist. A Cubic Mile of Oil (Oxford University Press, 2010) provides a language to talk plainly yet intelligently about energy, and how to assess our future needs and evaluate our progress.

Energy use is essential to our well-being—it is our sustenance. We use it in all aspects of living: growing food, manufacturing, transportation, communication, lighting, heating and cooling, earning our livelihoods, for entertainment, and more. All these tasks require energy, and we derive it from many different sources such as oil, coal, natural gas, hydro power, nuclear fission, and wind and solar power. Unfortunately, energy from these sources is expressed in different and often unfamiliar units, which makes it hard to assess their relative contributions. We use kilowatt hours for electricity, gallons or barrels for oil, cubic feet for gas, British thermal units (btus) or tons for coal, and so on—it’s a veritable tower of Babel! 

Further, each of these units represents a relatively small amount of energy, and in order to express energy use at a global or national scale, we have to use mind-numbing multipliers like millions, billions, trillions, and even quadrillions. To overcome this problem, my colleague Hew Crane came up with the idea of expressing energy units from all the different sources in one large volumetric measure that is commensurate with the scale of global energy challenge and one for which we can form a mental image. The approximately 90 million barrels of oil the world currently consumes daily adds up to a little over a cubic mile of oil in a year, or one CMO. A CMO thus becomes a very convenient unit to express annual global energy production and consumption. Imagine a pool a mile long, a mile wide, and mile deep, and you have a cubic mile. That’s more than a thousand times the volume of a typical sports arena.

In 2013, the global consumption of oil was 1.1 cubic mile. The world consumed an additional CMO of energy from coal, about three-quarters of one CMO from natural gas, and roughly a quarter of one CMO each from hydrothermal, nuclear power, and wood burning, yielding a grand total of 3.5 CMO. All combined, solar, wind, and biofuels produced less than a tenth of a CMO in 2013. How much will we need in the future? That depends on how seriously we take the UN millennium goals for human development. Between 1981 and 2005, China lifted over 600 million people from poverty, reducing the poverty rate from 85% to 16%. Concomitantly, the infant mortality rate declined from 2100 deaths per day to 770 per day. This achievement was made possible by quadrupling energy consumption. 

Global statistics on poverty are stark: 1.4 billion people subsist below the poverty level, defined by the World Bank as living on $1.25/day; infant mortality is 17,000 children a day; 2.4 billion people rely on wood, charcoal, or dung as their primary source of energy, and women and young girls spend more than 6 hours each day collecting fuel and water and completing other chores that deprive them of opportunities for advancement through education and entrepreneurship. Roughly 1.5 billion people have no access to electricity. Even after implementing measures to conserve and markedly improving energy efficiency, it is estimated that annual global energy consumption will have to increase by several CMO/yr to remove the scourge of poverty and to allow all people to lead healthy, productive lives. 

The challenge of supplying energy to the world’s population is really overwhelming. Even at a modest growth rate of 2% per year (i.e., a doubling every 36 years), the world’s energy demand by 2050 will be over 7 CMO per year. As we seek solutions to the energy crisis, we have to ensure they scale to the CMO per year level¾if not, we will just be nibbling at the edges. When you consider what it takes to develop an infrastructure capable of producing even one CMO of energy, it becomes evident there are no easy solutions, and it will take an enormous effort sustained over many decades to effect meaningful change. 

The slide below illustrates how many power plants it will take to develop capacity for producing 1 CMO/yr.  For each resource, it shows the total number of plants and the rate at which they must be built in order that in fifty years we will have enough of them to produce 1 CMO/yr. Because such analyses are highly dependent on the size and availability factors, I have also included those details. The numbers are truly sobering.

In case you are wondering about the impact of continued use of fossil fuels on climate change, please read my post from June 2012, where I discuss the need for a differentiated approach and a focus on things that matter. And oh, did I mention it is also time to seriously look at nuclear again. Speaking of nuclear power, I was recently informed that this unit was also used by President Jimmy Carter, although—being a navy man—his preference was cubic nautical miles!