Key Concepts: Being aware of the consequences of our society and industry on the Earth System, we can now be conscious (and conscientious) agents of global change. Adopting new technologies and procedures that can be scaled up over time might shift our society from carbon positive to carbon neutral. (Even better might be carbon negative, but sadly said technologies are not yet scaleable on an industrial level.)

Humans as Intentional Agents of Change

So are there ways we can--as individuals, as communities, and as societies--act in a fashion to lessen the effect of future global change and/or withstand better the changes we cannot prevent? (Incidentally, these represent "mitigation" and "adaptation", respectively. More about these below.)

You are no doubt already aware of, and maybe even actively work towards, many of these:

One useful way to think of the way we use natural resources as either "farming" or "mining":

Note that "farming" is by no means limited to crops, nor "mining" to minerals.

Think back to the case of Easter Island we saw last semester. The Polynesians who arrived there came from more tropical climate zones where trees grew very quickly, so for them chopping down trees was basically a "farming" technique. But Easter Island is colder than most of the Polynesian world, and trees grow very much more slowly there. As a consequence, over harvesting (that is, "mining") of trees for use in (among other things) the transportation and erection of the giant moai sculptures resulted in the island being deforested. And, as we saw, this took away their ability to do any serious fishing (previously their main protein source) or to escape from the rapidly degrading conditions on the island. Hence, lack of knowledge of their environmental limitations (in this case, that they were mining, rather than farming, trees) resulted in a collapse of their culture and extremely nasty times.

Carbon Neutrality vs. Carbon Negativity

Most of modern energy generation is carbon positive (which, sadly, isn't a good thing!). That is, the operation of these (generally fossil fuel-based) systems produces net emissions of greenhouse gases, which build up over time due to the long residence time of carbon dioxide. Much more beneficial would be carbon neutral: systems which do not result in net carbon emissions.

Carbon neutral systems come in two general flavors:

Even better than carbon neutrality is carbon negativity (again, despite the name, this is a Really Good Thing!!). This describes system whose use results in a net decrease in the carbon dioxide in the atmosphere (and thus sequestered somewhere else.) There are lots of naturally carbon negative systems: chemical weathering of rock; the dissolution and carbonate fluxes in the oceans; soil and coal formation; etc. The issue is that these systems have such slow flux rates compared to the actions of carbon positive emissions.

There are some artificial carbon negatives systems being investigated: biochar generation; carbon capture and sequestration at power plants; artificial trees. At present, though, none of these seem to be easily scaleable up to industrial scale. This is in part related to asymmetries in physical processes: oxidation is simply faster in many systems than reduction/fixation.

Adaptation vs. Mitigation & the IPCC
This semester we will see how Science can be employed to deal with the issues of climate change: specifically, with adaptation (the ability or potential to respond successfully to climate variability and change) and mitigation (the ability or potential to permanently eliminate or reduce the long-term risks and and hazards of climate change.) For example, reducing greenhouse gas sources or enhancing carbon sinks would be mitigation, while developing new crops that fare better in the new climate condition would be adaptation.

It's time to finally deal with one of the big players in the climate change realm: the Intergovernmental Panel on Climate Change (IPCC). It was established in 1988 by the World Meteorological Organization (WMO) and the United Nations Environmental Programm (UNEP). It is not a research nor a monitoring institution as such; instead, it is an organization for the coordination and cooperation of national research and climate institutions, academic scientists, independent researchers, and policy makers from all levels. Its primary function is to provide documents on the state of climate research for use by governments and international institutions. It aims to assess the scientific information related to:

In addition to various supplemental reports, the IPCC has so far presented five major Assessment Reports (1990, 1995, 2001, 2007), and the 2013-2104 5th Assessment Report. (AR6 is currently being developed, and scheduled for 2022.) These reports are organized by dozens of editors, with contributions of literally hundreds of scientists contributing to the various chapters of the different working groups:

Among many, many, many, many other things (mostly documenting different causes and implications of climate change), the IPCC reports uses a set of representative concentration forcing pathways (RCPs). These are different scenarios (or "storylines" (their word!)) for possible future development and ranges of expected changes and impacts. These are NOT predictions as such; rather, these are intended to represent general categories of possible futures. The 4th Assessment used a different set of emission scenarios, which you can read about in the 2000 Special Report on Emission Scenarios (it's not like intergovernmental bureaucrats are paid to come up with creative titles...). The new set of scenarios focus on the amount of total greenhouse gases in the atmosphere, rather than annual emissions as such in recognition of the fact we need to keep in mind the additive effect of past emissions.

To the right is a chart of the four RCPs, which look at past and projected gas concentrations from 1765 to 2300 CE. They are named for the total increase in radiative forcing (in W/m2) expected by 2100 compared to pre-industrial levels. (Image from Meinshausen et al. 2011. The RCP greenhouse gas concentrations and their extensions from 1765 to 2300. Climate Change 109:213-241. doi: 10.1007/s10584-011-0156-z)


Here are the models for total population, GDP, and energy use under these scenarios (from the same reference).

These four scenarios describe a generally-unrestricted growth scenario (RCP8.5, meaning that at 2100 there would be 8.5 W/m2 above preindustrial levels, or equivalent to about 1370 ppm CO2), two intermediate scenarios (RCP6 and RCP4.5, or equivalent to 850 and 650 ppm, respectively), and one with an aggressive effort to curtail emissions (RCP2.6, which assumes a peak at 3 W/m2 (490 ppm) before 2100 and a decline to 2.6). There are some sub-scenarios beyond these.

In terms of temperature changes, these scenarios suggest the following (temperatures are compared to the 1985-2005 average):

  • RCP8.5 +2.0 °C increase (range 1.4 to 2.6) by mid-century (2046-2065), and +3.7 (2.6 to 4.8) by the end of the century (2081-2100)
  • RCP6.0 +1.3 (0.8 to 1.8) and 2.2 (1.4 to 3.1)
  • RCP4.5 +1.4 (0.9 to 2.0) and 1.8 (1.1 to 2.6)
  • RCP2.6 +1.0 (0.4 to 1.6) and 1.0 (0.3 to 1.7)

For the longterm projections, RCP2.6 assumes "negative emissions" after 2070: that is, techniques and technologies in which human activity absorbs more greenhouse gases than they emit. Under the scenarios, RCP2.6 predicts CO2 at 360 pmm by 2300 (in other words, lower than today!), while RCP8.5 suggests 2000 ppm by 2250 (seven times preindustrial). In terms of temperature, that would be +0.0-1.2 °C increase from present in RCP2.6 for the late 23rd Century (2281-2300), while RCP has +3.0-12.6 °C increase (and thus encompasses near total global catastrophe!).


Update 2015: Sadly, it looks like RCP2.6 is not achievable; we missed our chance. Here is the current status for the RCPs, through the end of the century:

In order to have hit the RCP2.6 scenarios, emissions should have peaked by around 2011. They did not: they are still climbing (although there is a slow down in the rate of climb...). Keeping temperature under 2.0C by the end of the century looks extremely unlikely.

Again, the RCP scenarios are NOT predictions as such; the IPCC is not saying these are the only possible futures, nor are they listing probabilities of likelihood that any given one of these is the most likely future for the 21st Century. These are simply heuristic tools for the discussion of likely ranges of possible futures.

Over the different assessment reports, the evidence for the human role and the severity of that role in climate change has been steadily increasing, as noted:

By the way, in September of 2013 the scientists who contribute to the IPCC have already begun to wonder if their four-to-five year mega-reports are the best approach, or if they should instead concentrate on the smaller, but more rapidly produced, topical reports.

Stabilization Wedges
So WHAT DO WE DO ABOUT IT? One useful scheme has been suggested by S. Pacala and R. Socolow in an article in Science in 2004: stabilization wedges.

Pacal and Scolow set a goal of leveling off atmospheric CO2 at 550±50 ppm (around double pre-industrial's 280 ppm) by 2054 CE (i.e., within 50 years of the initial publication). Each "wedge" represents the introduction or expansion of new carbon sinks or of carbon-neutral technologies and methods to replace the current carbon-releasing ones.

They are "wedges" in that they start off at contributing a savings of 0 GtC/yr, but as they are expanded in use over time they ultimately reach 1 GtC/yr savings by 2054. Pacala and Socolow identified 15 specific different wedges (nor merely the technology, but the level to which they have to be adopted in order to reach 1 GtC/yr by 2054.) Pacal and Socolow calculated that only 7 would be needed to stabilize the levels. (Note that Pacala and Socolow did not incorporate the extremely-long residence time of carbon dioxide that Archer and others found, and other researchers estimate that it might require as many as 25 wedges to stabilize!), so the wedge plan might not actually achieve a total reduction in atmospheric levels towards 350 or 280 ppm at all. Still, halting the increase rather than heading for 750 or 1000 or higher ppm is a wonderfully good idea!!)

Other researchers have proposed additional "wedges" beyond those of Pacala and Socolow. We (and by "we", we actually mostly mean "you, the students") will be examining the actual science behind, and potential of, some of these mitigating strategies throughout the semester.

(Note: since no government acted when Pacala and Socolow first published, it is becoming progressively harder to reach these goals.) Dealing with climate and other global change require a long-term commitment of decades (or centuries, or longer) in order to succeed? Is this possible? Can humans dedicate themselves to plans that are longer than the business or election cycle?

Geoengineering: Hack the Earth?
Often we think about mitigating climate change by reduction in the output of greenhouse gases by means of more efficient use of energy and of generating power by means on carbon-free sources (solar, nuclear, tidal, geothermal, wind, etc.). But there are other opportunities out there. Some scientists and engineers have proposed extremely large-scale schemes to affect the Earth System as a means of mitigating climate change: geoengineering. After all, anthropogenic climate change is an inadvertent case of geoengineering, so we know we CAN affect the global Earth Systems! Here are some of the proposals:

At least some of these will almost certainly be used. However, there is always a great danger of the "law of unintended consequences" coming into play. In fact, some of these ideas have rather obvious potential drawbacks. In particular, anything which decreases insolation will necessarily cause a reduction in plant (including crop) growth, and thus endanger food productivity. Others rely on technologies in their infancy, which might result in various currently unknown environmental effects (for instance, what materials would we make artificial trees from, and what would be the impact of the mining, refining, and production of these materials?).

Can We Do It?
Historically, there most certainly is precedent for decades-long (or longer) commitments for projects by communities. For example, the great cathedrals of medieval Europe were not completed during the life time of the original designers, planners, and commissioning royalty and clergy. Notre Dame de Paris was begun in 1160 CE, but not completed until 1345! Clearly communities CAN make long-term plans and stick to them (most especially if it creates new long-term jobs and gives prestige and personal satisfaction to those involved.)

But history also warns us that societies can start major undertakings, only to abandon them even when they might bring great benefit. China in the late 14th and early 15th Centuries CE, during the Ming Dynasty and most directly under the admiralship of Zheng He, sent out massive "treasure fleets" to explore the Indian Ocean and Southeast Asian regions, establishing trading outposts and bringing back great wealth and knowledge to China. These involved vast expeditions (the 1st expedition consisted of 317 ships and 26,800 men; compare that to Columbus' mere three ships in his first voyage, or 17 ships and 1200 men in his second.) At the time China was easily the most advanced nation technologically, and had among the most sophisticated social and political structures. Had this Chinese Age of Exploration continued, they almost certainly would have found and colonized Australasia and the New World (where none of the native powers could have withstood them), and might well have overwhelmed the technologically-inferior spheres of Christendom and Dar al-Islam. However, when Zheng He and Emperor Yong Le died, a shift of politics within China caused that nation to be concerned primarily with internal affairs. The treasure fleets were burned as an "unnecessary expenses"; regulations against large vessels were created; and many records from the fleets and their discoveries were destroyed under Imperial orders. Chinese statesmen and bureaucrats emphasized short-term profits over long-term gains. As a consequence, China lost its potential to become the dominant world power; instead, relatively-backwards Europe managed to conquer the New World, gaining its gold and the biological wealth of crops that then fueled future European expansion.

So sometimes we can lose the world from short-sighted, inward-facing politics. Let us keep this in mind while confronting climate change.