Why We Must Phase out Coal Emissions

My grandchildren began to influence me when I realized that policy makers were ignoring the message from the climate science, or rather that politicians were developing the fine art of greenwash — they would say favorable words about the environment and stabilizing climate, but their actions were inconsistent with that goal.

Politicians would be happy if scientists just tell them there is a climate problem and then go away and shut up. Let them decide what they want to do.

But I decided that I did not want my grandchildren, some day in the future, to look back and say, “Opa understood what was happening, but he did not make it clear.”

What is clear is that we cannot burn all the fossil fuels. There is a limit on how much carbon we can put into the atmosphere.

When we inject a pulse of carbon dioxide into the atmosphere by burning fossil fuels, the carbon dioxide begins to disappear quite rapidly.

After 25 years, about half of it has been taken up by the land and ocean, mostly by the ocean. However, the ocean will not take up the full carbon dioxide emissions, because the carbon dioxide entering the ocean exerts a “back pressure” on the atmosphere — it can come back out. Until the excess carbon is deposited on the ocean floor as carbonate sediments, the ocean will not take up all of the fossil fuel emissions, and formation of those sediments takes thousands of years.

The climate and geophysical facts yield a remarkably well-defined and important conclusion. The story is summarized in the two parts of this figure.

The bar graph shows the carbon contained in all fossil fuels, with purple indicating portions that have already been burned. The blue portions are estimated economically recoverable reserves, which each have substantial uncertainty.

What is economically recoverable depends strongly upon policies, e.g., whether fossil fuels are subsidized or, in contrast, a growing carbon price is adopted.

Coal: The IPCC reserve estimate for coal is almost surely too large, and even the World Energy Council (WEC) estimate may be too high. But there is more than enough coal to take the world far into the realm of dangerous climate change.

Oil & Gas: Oil and and gas reserves that are actually exploited might be kept closer to the IPCC estimates via a rising price on carbon emissions. The larger reserve estimates of the Energy Information Administration (EIA) may be realistic if a policy is pursued to extract every last drop of oil in the ground from public lands, off-shore areas, the deep ocean and polar regions.

Unconventional Fuels: Unconventional fossil fuels, such as tar sands, oil shale and methane hydrates, potentially contain an even greater amount of carbon, but most of these could be left in the ground — if a sufficiently high price on carbon emissions is established.

The second chart compares actual atmospheric carbon dioxide history with carbon cycle simulations based on a dynamic-sink pulse-response function representation of the Bern carbon cycle model (Joos et al., 1996; Kharecha and Hansen, 2008).

The important point is that atmospheric carbon dioxide will peak at a value somewhere in the range 400 ppm to 425 ppm — if coal emissions are phased out by 2030 and if unconventional fossil fuels are not used significantly.

Improved forestry and agricultural practices could bring carbon dioxide below 350 ppm by the end of this century via actions that draw down atmospheric CO2 — if IPCC estimates for oil and gas reserves are valid, meaning a sufficient price is placed on carbon emissions to discourage extraction of every last drop of oil and gas.

These graphs tell us unambiguously that we must phase out coal emissions rapidly, not develop the unconventional fossil fuels, and not even go after every last drop of oil on the planet if we want our children and grandchildren to have a chance of inheriting a planet that is not spiraling out of their control.