Capturing CO2 from ambient air - David Keith

Chapter 1
Introduction
The climate is changing. For decades it was a matter of debate, a point of uncertainty, whether humans
could fundamentally alter the earth’s climate system. Now it is an observable fact: we can, we have, and
we will continue to do so. Last year, 2005, was the hottest on record, continuing an accelerating warming
trend that has brought the global mean temperature up 0.8 ◦ C over the past century (Hansen et al., 2006).
But the changes we see are not only in temperature. Severe damage to ecosystems and harm to humans can
now be attributed to climate change, including extensive bleaching of coral reefs (Sugden, 2005), massive
loss of forests due to pine beetle infestation (Carroll et al., 2003; Gan, 2004), increased forest fire activity
(Westerling et al., 2006), and increased intensity of hurricanes (Webster et al., 2005; Emanuel, 2005).
The principle cause of this climate change is the emission of carbon dioxide (CO2) to the atmosphere
when humans burn fossil fuel. The combustion of coal, oil, and natural gas has fueled two centuries of
economic development across the world. Today, 80% of global energy use relies on fossil fuel (IPCC,
2005). Fossil fuel use is integral to the functioning of society at every level: the manufacturing of every
manner of consumer good, the movement of people and products, the maintenance of shelter from the
elements, the production of food, and the provision of water.
And yet, with every ton of carbon burned, the earth is altered in ways both predictable and unpredictable.
The changes in climate to come will likely threaten many people’s access to those basic services:
shelter, food, and water. Additionally, the irreversible damage to the world’s ecosystems, including the
extinction of a large fraction of the earth’s species, will be the most extensive civilized humans have ever
experienced (Thomas et al., 2004).
This leaves us in a difficult position; industrial society is built around fossil fuels, and yet their use
poses a grave and mounting threat. Fossil fuel use and the associated carbon emissions continue to grow
exponentially (see Figure 1.1). Many nations have begun programs to limit CO2 emissions, though current
measures are not sufficient to achieve dramatic reductions. Notably, the two largest emitters, China and
the United States, have no national regulation on CO2. Nonetheless, there is a general expectation that
further international agreements will be reached to limit CO2 emissions, and that a global market for
carbon emissions reduction will be developed. Such a market already exists in the European Union, and
has the effect of putting a value on CO2 emissions reduction.
There are various options available to meet regulatory demands. Energy conservation and efficiency
improvements are the lowest-cost near-term measures. Improvements in average vehicle fuel efficiency
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