Potential climate engineering effectiveness and side effects during a high carbon dioxide-emission scenario

Abstract

The realization that mitigation efforts to reduce carbon dioxide emissions have, until now, been relatively ineffective has led to an increasing interest in climate engineering as a possible means of preventing the potentially catastrophic consequences of climate change. While many studies have addressed the potential effectiveness of individual methods there have been few attempts to compare them. Here we use an Earth system model to compare the effectiveness and side effects of afforestation, artificial ocean upwelling, ocean iron fertilization, ocean alkalinization and solar radiation management during a high carbon dioxide-emission scenario. We find that even when applied continuously and at scales as large as currently deemed possible, all methods are, individually, either relatively ineffective with limited (<8%) warming reductions, or they have potentially severe side effects and cannot be stopped without causing rapid climate change. Our simulations suggest that the potential for these types of climate engineering to make up for failed mitigation may be very limited.

Emissions reduction: Scrutinize CO2 removal methods

“…Counter-intuitively, afforestation at mid-latitudes and in northern, boreal forests may have a net warming effect, despite increasing the storage of carbon 7 . Also, as with bioenergy crops, it is difficult, if not impossible, to reliably quantify the effects of future climate change during 2050-2100.…”

“…It has fallen to other groups to review insights and gaps in our understanding of the influence of CO 2 -removal techniques on ecology [3][4][5] ; to make broad assessments of climate-engineering schemes 6 ; and to carry out comparative modelling studies 7 .…”

Assessing carbon dioxide removal through global and regional ocean alkalinization under high and low emission pathways

“…In the period 2020-2100, we undertook a number of AOA experiments using a fixed quantity of 0.25 Pmol yr −1 of alkalinity, a similar amount to that used by Keller et al (2014). Consistent with this study, we applied AOA in the surface ocean all year round in ice-free regions, set to be between 60 • S and 70 • N (note that this ignores the presence of seasonal sea ice in some small regions).…”

“…They estimated that to mitigate the associated 1.5 K warming difference, via reducing atmospheric CO 2 concentrations by ∼ 400 ppm, an addition of 114 Pmol of alkalinity (between 2018 and 2100) would be required, and it would come at the cost of very large (unprecedented) changes in ocean chemistry. Keller et al (2014) used an Earth system model of intermediate complexity (EMIC) to explore the impacts of AOA over the period 2020-2100 arising from a globally uniform addition of alkalinity (0.25 PmolALK yr −1 ), an amount based on the estimated carrying capacity of global shipping following Kohler et al (2013). Keller et al (2014) showed that AOA led to a reduction in atmospheric CO 2 of 166 PgC (or ∼ 78 ppm), a net surface air temperature cooling of 0.26 K and a global increase in ocean pH of 0.06 in the period 2020-2100.…”

“…Their primary purpose is to reduce atmospheric CO 2 levels, and thus most CDR methods will also reduce the impacts of ocean acidification, although some proposed techniques such as ocean pipes (Lovelock and Rapley, 2007) and micro-nutrient addition (Keller et al, 2014) may actually lead to a regional acceleration of ocean acidification in surface waters.…”