The question about range and forest fires and prehistory is an excellent example of one of the most important things about climate change that is so poorly understood by the public. Doing something to an ecosystem like burning it or chopping it down,only has a significant impact on our climate if that ecosystem does not grow back the same as it was, or we chop or burn much, much more of it than normal every year. If we change a forest to cropland, or pasture and grow cows, we lose biomass. It goes into the atmosphere and stays there as CO2. When it grows back, it takes about the same amount of carbon back out of the atmosphere that was lost to burning or decomposition. The carbon dioxide and the other greenhouse gases are cycled back into the environment and there is no net increase of greenhouse gases.
Burning fossil carbon (fossil fuels) is different. The plants that created that fossil carbon are not going to grow back. So, half of that fossil carbon dioxide stays in the atmosphere for greater than 300 years. A quarter stays there for greater than ten thousand years. So repeated forest and range fires caused by lightning have little effect on climate. Those burned ecosystems grow back and the carbon cycle continues. The same goes for man-caused forest and range fires, as well as forest product harvesting.
A particularity bad fire year may even have a cooling effect on climate because of the other pollutants (aerosols: nitrogen oxides and sulfates in smoke) that reflect the sun’s radiation back into space without it warming the planet through the greenhouse effect. This cooling is very short lived however because those pollutants stay in the atmosphere for only days. In the case of volcanic emissions (the same form of aerosol emission come from volcanoes as well) it takes a couple of years for these “cooling pollutants” to rain or fall out of the sky or otherwise be chemically changed into something else that does not cool (or warm) the planet.
The Terra Preta Conundrum — Biochar: Pre-Columbian disposal of spent ash and coals from cooking fires was done over thousands of years. The waste ash was placed in pre-Columbian peoples growing plots to sweeten the acidic soil, a practice still done today across the planet. This sweetening allowed plants to utilize fertilizer better (manure) and it works with organic techniques as well as chemical fertilizers. This process, over dozens of generations, resulted in a carbon rich soil of a quality not normally found anywhere else. To have this kind of agricultural impact by charring and burying organic material, and to sequester carbon in the process is the goal of the modern biochar technique. Carbon placed in the soil as such largely stays there for time frames that matter with our society and climate change (hundreds to several thousand years).
To demonstrate the scope of a global biochar carbon sequestration effort that would make a significant difference I will use the example of charring all of the plants on the face of Earth and burying them. I am definitely not suggesting anything of the sort, but using the scale of such a suggestion to make a point. The carbon mass of all plant life on Earth is about 500 gigatons. Earth can produce this amount of carbon every 50 or 100 years or at the rate of about 5 or 10 gigatons per year. If we cleared all the forests on the planet and replaced them with fast growing short-lived tree species maybe we could cut this down to 25 years. The charring process is only about 50 percent efficient. Half of the biomass is converted to biochar, the rest to gases that are emitted into the environment or need to be captured and sequestered like greenhouse gas emissions from coal electricity generation. This process then leaves us with 2 to 5 gigatons of carbon to mix into the top 6 or 12 inches of Earth’s soil in the biochar process.
We emit close to ten gigatons of carbon as carbon dioxide alone every year, not counting other greenhouse gases. So charring and burying every plant on earth would not come close to breaking even. Considering the process is only 50 percent efficient, the net impact of burning all plants on Earth is down to 2.5 to 5 gigatons per year before other inefficiencies and reality are added in. if we could sustain this process by chopping and burning 1/25 of the global plant biomass every year—fifteen times the land area of the United States—every year. Altogether, biochar is certainly not a major player in carbon sequestration, but it could likely help. Especially using agricultural waste from cellulosic alcohol production or the like.
The best evaluation I found of the total philosophy of biochar/bio-oil production, use, cogeneration and carbon emission avoidance from enhanced soil fertility was published in Nature Communications in August 2010. This research looks at the sustainable use of this technique to sequester carbon on a global basis. By a sustainable basis, what is meant is that the biochar process is accomplished without endangering food security, habitat or soil conservation. The bottom line is that a half gigaton of carbon sequestration annually is possible if biochar techniques were put into effect in a sustainable way in every possible place on the planet. Large scale cellulosic carbon production in the form or fast growing trees species, switchgrass, algae and such are not really considered because of their large natural resource requirements that make them relatively unsustainable.
Implementing this technology would be something that we could do on a scale relative to that which we as a global society implemented the use of something like indoor plumbing. It will take 100 years, but in the end the sequestration and emissions avoidance will be meaningful, as will the enhanced fertility of our agricultural lands. An example of what each of us can do individually? Compost those kitchen scraps!
But we can’t wait a hundred years for techniques like this to be implemented. The challenge we have is to reduce the atmospheric load of carbon. This load of carbon in the sky is equal to about half of all of the greenhouse gases ever emitted. It’s a big, big deal. But voices like the Heartland Institute, the same voices that tell us that climate change is not real, a conspiracy, a natural cycle or that it is good for us: these are the same voices that tell us the solutions will ruin our economies. The vast majority of climate specialist say nothing of the sort. The solutions to climate change will cost one percent of global GDP per year for 100 years. This is very similar amount of money to what we have spent for the last 100 years installing toilets and water treatment systems across the planet for the last 100 years. It is very similar to the U.S. annual military budget, or the amount of money we spend across the globe every year on advertising, or the amount of agricultural damages from normal weather every year in the U.S. alone. It is four times less than what we spend in the U.S. alone on health care based on the average from 2000 to 2010.
Biochar is one little piece of the total solution. But because we did not begin to reduce emissions twenty years ago when suggested prudent, reducing emissions alone will likely no longer be enough. We need to implement alternative energy far faster than we have been. We also must stop emitting greenhouse gases from the production of energy from fossil fuels. We need to reduce consumption, increase efficiency and develop atmospheric carbon removal processes already in the field proving stages. The latest science is beginning to tell us that reducing emissions to zero will not get the job done. If we had of started reducing emission twenty years ago, it would have been possible. Since then, we have increased our emissions by 50 percent. Since 1988 we have emitted nearly as many greenhouse gases as were emitted since mankind started emitting. As a consequence, it is very likely that we will have to reduce atmospheric greenhouse gases below their present values.
This Herculean task needs to be accomplished in about the next twenty years. The previous projections of 2100 was fine twenty years ago, and the most recent projections of 90 percent emissions reductions by 2050 are likely to fall by the wayside just as did the 2100 projections from the Kyoto Protocol era.
Woolf et al., Sustainable biochar to mitigate global climate change, Nature Communications, August 2010.