Often, when looking at global warming, I am shocked by how much we have failed to understand the context of the problem we’re dealing with. That context can be best described by a planet that, for the most part, makes dramatic responses to small degrees of forcing over relatively short periods of time. In the periodic switching of ice age to warmer inter-glacial, the small, gradual changes in Earth’s orbit and in the distribution of sunlight over the Earth’s surface have been enough to push large climate shifts of 5 degrees Celsius or more over the span of 300-1000 years.
In the case of human greenhouse gas emissions, we have something much more extreme. A rather large forcing, in the form of a 120 ppm CO2 increase over the course of 150 years (and continuing to increase at a growing rate), is now putting the world climate system in motion. Current world CO2 concentrations are now near 400 ppm. This enormous forcing and increase in CO2 has happened at a rate ten times faster than during any time in geologic history. And the consequences of this very large and growing forcing will be devastating unless that forcing is rapidly reduced.
Unfortunately, there are many who publicly consider this forcing as a static influence, a steady-state change. The studies only see human CO2 emissions in a vacuum. They seem to indicate that changes to Earth’s climate will be the result of this forcing alone and not result in powerful responses from Earth’s larger climate. A recent study entitled “Too Late for Two Degrees,” published by Price Waterhouse Coopers LLC, follows this view by predicting world-wide CO2 concentrations based on human additions only. But if you look at the fine print, they provide this chilling caveat:
This high-level analysis has rounded figures and made several simplifying assumptions, for example on carbon sinks, and ignored complex interactions in the carbon cycle (such as any feedback effects), consistent with the LCEI model described in Appendix 1. In table 10.8, the IPCC also provides the likely range of temperature outcomes at different CO2 equivalent concentrations. The likely range of temperature increase is greater at higher concentrations.
When one considers that there is at least enough carbon stored in Earth’s sinks to contribute more than three times the amount of CO2 as fossil fuels, is it really a good idea to ignore these sources? But even if these sleeping giants remain dormant, a highly unrealistic assumption, world temperatures are likely to increase quite a bit more than the PwC study and many others estimate.
IF human CO2 emissions resulted in no additional global warming feedbacks coming from Earth’s environment, we would still be in for some serious changes. According to geological history, a level of 400 ppm CO2 results in 3-4 degrees Celsius of warming and the melting of the Greenland and West Antarctic Ice sheets — adding about 75 feet to sea level. This geological evidence contrasts with the PwC study, which estimates a 2 degree Celsius increase at 450 ppm CO2. More likely, past history will be a better guide for future results than a broad-based study that makes sweeping assumptions.
Sadly, this underestimation of the effects of even static changes only begins to address how much the PwC study has underestimated broader human greenhouse gas impacts. The human influx of CO2 resulting in an initial level of 400 ppm and growing will likely result in far worse changes. In particular, these changes involve the feedbacks which the PwC study has, admittedly ignored. There is a substantial amount of water vapor that will end up in the atmosphere. This added water content will heat the climate further. There is a substantial amount of permafrost, containing methane and carbon dioxide, which will thaw and add to the CO2 and methane already in the atmosphere. There is a substantial amount of methane on the sea bed in the form of frozen hydrates. A portion of these reserves will thaw and add carbon dioxide and methane to the atmosphere. There are broad areas of ice that will melt, turning white, reflective surfaces into dark, absorptive surfaces, making the planet even warmer and speeding the release of carbon from frozen stores.
The result is, likely, that if CO2 levels remain at 400 ppm for an extended period — decades to centuries — that these Earth-based feedbacks will be enough to push worldwide CO2 levels as high as 500 or 600 ppm. The last time CO2 levels were this high, all the ice caps melted and sea levels were 250 feet higher than they are today. Temperatures were 5-6 degrees Celsius higher.
We are in danger of this consequence and all the radical, violent, and powerful weather and Earth changes that will occur as a result now. But, even worse, we continue to add human-based CO2 at the rate of 2.2 parts per million each year to the atmosphere and that rate is increasing. If we continue on this path, it is likely that worldwide CO2 levels will substantially exceed 1000 ppm by the end of this century. And the level of heating that would result from this degree of concentration would be beyond anything seen during any period in which Earth supported complex life.
So it is for these reasons that I tend to look with skepticism at studies alleging that it is possible for the world to avoid a 2 degrees Celsius rise in temperature. Many scientists agree that staying below this level would be enough to avoid the very worst impacts of climate change and keep world civilizations and their supportive base of food production viable. Such studies are based on the notion that cutting carbon emissions, if enacted fast enough, can result in reduced CO2 levels and prevent the feedbacks that result in the worst temperature increases. This is possible. It is possible if the Earth climate system is not as sensitive as geology would seem to indicate. It is possible if carbon sinks can rapidly begin to draw world CO2 levels down and that other sinks do not become sources too rapidly.
In my view, as noted above, these studies have tended to be a bit optimistic. Broad based action is required, certainly and urgently. But some degree of human carbon capture may also be required if we are to hope to retain a livable planet. To return CO2 levels to the safe zone of 350 ppm which is likely to result in the least amount of damage.
So you can understand why the PwC study brought a shiver up my spine. The study is based on, what seems to me, a flawed notion that if global CO2 levels are stabilized at 450 ppm, then a rise in temperatures of 2 degrees Celsius can be prevented. This notion, itself, is flawed, for the very reasons I described above. Stabilizing atmospheric concentrations at 450 ppm is a recipe for at least 3 degrees of additional warming and a likely environmental contribution of CO2 to result in world concentrations stabilizing around 600 ppm even under somewhat optimistic scenarios.
This PwC study’s assertion is that for human caused CO2 concentrations to stay below 450 ppm, global carbon intensity will need to fall by 5.1% each year from 2013 to 2050. The current global annual rate of carbon intensity reduction is .8%. So in order for human emissions to result in a stabilized level of 450 ppm CO2 (and likely environmental feedbacks bringing levels as high as 600 ppm CO2), worldwide rates of carbon intensity reduction would have to increase nearly sevenfold.
Even more alarming, current rates of carbon intensity reduction would result in over 1,400 ppm CO2 from human sources alone by the end of this century! But at this level it is almost certain that enough carbon to increase CO2 concentrations above 2,500 ppm CO2 will then be supplied from the world’s environment. At this level, Earth will almost certainly become unable to support complex life, much less human civilization. It will certainly be on a path toward a hellish environment reminiscent of Venus and not the blue planet we have known.
This range from a terrible increase to 450 ppm to a hellish increase to 1,400 ppm or more is not acceptable. Carbon intensity needs to fall by a range of 6-8 percent each year. Very rapid adoption and deployment of wind, solar, and electric vehicles will be necessary to achieve these reductions. Changes in agriculture will also likely be necessary. These changes would prevent terrible impacts. But some very difficult to deal with changes would still, likely, be in store. And, therefore, it may be necessary to also deploy atmospheric carbon capture and to explore ways to enhance the Earth’s albedo as well.
At all levels, a sense of urgency is necessary to deal with this growing crisis.