Continued emissions of carbon dioxide to the atmosphere will affect climate and ocean chemistry. These consequences can be anticipated by consideration of basic physical principles, past climates, and calculations. Emission of 5,000 PgC (= amount of carbon in conventional fossil-fuel resources) over a few centuries could produce radiative forcing of climate of about 10 W m­^-2 which could be expected to produce global mean warming of ~4 to 12 °C. Warming in this range would have large biological and human consequences. It could threaten the ice sheets and lead to a long-term sea-level rise of 70 m. Ocean pH could decrease by 0.7 units, making the oceans more corrosive to carbonate minerals than they have been for many millions of years. From the perspective of geology and biological evolution, these changes would occur rapidly, overwhelming most natural processes that would buffer CO₂ changes occurring over longer time intervals, and thus may produce changes at a rate and of a magnitude that exceed the adaptive capacity of at least some biological systems. To find comparable events in Earth history, we need to look back tens of millions of years to rare catastrophic events.

This presentation discusses the forces shaping long-term future global energy demand and carbon emissions. The most important factors shaping future global energy demand and carbon emissions are population and technology. Population acts to set the scale of human activity, though there are many subtleties that work to either temper or magnify the basic scale effect. These factors, such as “tastes,” which temper the effect of population on energy demand are sometimes bundled under the heading “socio-economic” factors. Their effects can be significant.

Reversing the atmospheric buildup of carbon dioxide (CO₂) and other greenhouse gases will require a radical transformation in the world’s economies. Such changes are difficult to plan and imply coordination of policies on a scale not yet experienced. Not only is the task difficult, but the problem of climate change has many attributes that historically are associated with policy failure—namely, the perception of high immediate costs for uncertain and highly diffuse future benefits. This paper explores the historical experience with addressing partially analogous global challenges. The paper is pessimistic that societies will have much effect on their emissions trajectories in the next few decades, implying that substantial amounts of climate change are likely and the risk of abrupt changes in climate will also multiply. It is optimistic about the longer-term—the period from five decades on—when zero carbon technologies can diffuse into widespread use through the normal turnover of energy infrastructures.

Approximately 55 million years ago (Mya) at the boundary between the Paleocene and Eocene epochs (P-E boundary), the Earth experienced an extreme global warming event that persisted for several tens of thousands of years, and which triggered short- and long-term changes in marine and terrestrial ecosystems. Several lines of evidence suggest that the warming was caused by the sudden decomposition of marine methane hydrates which ultimately released >2000 gigatons of carbon (GtC) to the atmosphere. In theory, a large portion of this carbon would have been absorbed by the ocean, thereby lowering the ocean pH, and initiating a neutralization process involving the massive dissolution of seafloor carbonate. This process would enable the ocean to absorb and temporarily store additional carbon. Permanent sequestration of this excess carbon, however, would occur gradually through a number of negative feedback processes such as the burial of organic carbon. Quantitatively, the most important feedback should be the chemical weathering of silicate rocks, and eventual redeposition of carbonate on the seafloor. Here, I discuss the evidence used to constrain the magnitude of changes in ocean carbon chemistry 55 Mya, and implications for future carbon cycle feedbacks.