Geoengineering and Terrestrial Systems

Transcription

1 Geoengineering and Terrestrial Systems Rob Jackson IGBP meeting 31 January, 2011 William H. Schlesinger Duke Biology

2 Solar Radiation Management (Shepherd et al. 2009): 1) Stratospheric injection of sulfates or other chemicals; regional or global scale 2) Albedo management through brightening of ecosystems or plants, most often proposed for deserts or crops 3) Space reflectors global scale reduction in solar radiations 4) Cloud brightening, primarily over the oceans (not considered further here.

3 Carbon Dioxide Removal (CDR) on land: 1) Land-use management to protect or enhance sinks. 2) Biomass for energy use and carbon capture and storage (CCS) 3) Enhanced natural weathering (e.g., distributing silicate minerals). Comparable in scale to current mining activities. Ecological effects include mining disturbance (land, streams, etc.) and likely increases in soil ph. Not examined further here. 4) Industrial CO 2 removal primary issues are chemical wastes and carbon sequestration/storage underground or in oceans (not examined further here)

4 For terrestrial ecosystems, you can rarely alter solar radiation without changing the carbon balance, and you can t normally manipulate the carbon balance without altering albedo and the energy balance. Jackson et al Env Res Letters; Jackson & Salzman 2010 IS&T

5 For sunlight management, some possible direct ecological effects of a high CO 2, low T world: 1) Enhanced growth of weedy species on land and reduced plant diversity (e.g., Smith et al. 2000; Mohan et al. 2006). 2) Modestly greater global NPP based on the balance of increased photosynthesis and reduced respiration, in some sense the analog of FACE experiments today. Experiments, modeling work, and data synthesis are needed here. 3) Ocean acidification is certain, with possible disruption of trophic structure, primary production, and reef-building organisms. Which freshwater ecosystems, such as the Great Lakes, are particularly vulnerable to acidification? 4) Changes in soil chemistry, ph, and possibly rates of weathering. Again, the high-co2 literature can help here, but more work needed.

6 Sunlight Management, Stratospheric Dust or Mirrors: Advantages: relatively inexpensive, likely feasible, fairly cheap 1) The Pinatubo analogy M tons of SO 2 into the stratosphere. The earth cooled by ~1 F for over a year. Pinatubo also caused a global drought and reduced river flows and soil moisture (Trenberth and Dai 2007). Precipitation is more sensitive to sunlight than T is. 2) Stratospheric chemistry. Offsetting a doubling of CO 2 could delay recovery of the Antarctic ozone hole by 30 to 70 years and increase Arctic ozone depletion throughout this century (Tilmes et al. 2007). Altered UV radiation affects ecosystems (e.g., Caldwell et al. 2003). 3) Possible global or regional effects on weather patterns. Relatively stronger effect of sunlight reduction in the tropics than at the poles. Potentially reduced amplitude of seasonal cycle, altered T gradients. Uncertain effects on monsoons and climate patterns; simulations by Lunt et al suggest a reduced intensity of El Niño events. Especially true if we geoengineer regionally, particularly the arctic alone.

7 Sunlight Management, Stratospheric Dust or Mirrors: (continued) 4) Balance of diffuse and direct-beam radiation. Reducing sunlight by a few percent will reduce primary production in some systems, but not everywhere. Unclear regional and global effects on NPP (e.g., Pinatubo). 5) The termination problem. Terrestrial ecosystems will be harmed more by abrupt climate change than by gradual change in most cases. 6) Acid Rain unlikely to be a major ecological issue because the quantities will be <10% and likely <1% of global deposition.

8 Solar Radiation Management through Crop Brightening Currently feasible. Lenton and Vaughan (2009 Atm Chem Phys Disc) estimate a possible benefit of -1 W m -2 if all cropland albedo increases by 0.08 and if savanna and grassland albedo increases by See other papers (e.g., Woodward et al Current Biology). Ecological Research Needs: 1) Photosynthesis. In which systems would this help, harm, or have no effect on yields (i.e., light-limited ecosystems)? 2) Water use. In which systems would this aid in drought tolerance, a major thrust of current breeding? 3) Energy-balance effects and climate feedbacks (e.g., convection; strongly scale-dependent).

9 SRM through Albedo or CDR through Afforestation in Deserts 1) Gaskill (2004) proposed covering all deserts with a reflective polyethylene-aluminum surface to double albedo to 0.8. Global benefit: W m-2. Cost U.S. $Trillions/yr. 2) Ornstein et al. (2009 Climatic Change) proposed turning the Sahara and Australian deserts into forests by irrigation with desalinated seawater. Cost U.S. $Trillions/yr; requires a land area the size of the U.S. to offset global fossil fuel emissions. Doomed to fail, and an ecologically terrible idea. In CA, opposition to single concentrated solar facilities has been strong.

10 1) CO 2 Removal : Land-use management to protect sinks Reducing Emissions from Deforestation and Degradation (REDD). Deforestation and forest degradation contributes ~1.2 Pg C to the atmosphere each year, approximately one-seventh of fossil fuel emissions (van der Werf et al Nature Geosciences) Co-benefits: In addition to C storage, benefits include biodiversity, water recycling, and, likely, additional biophysical cooling.

11 Uncertain terrestrial sink of ~200 ppm CO 2 by We must narrow this uncertainty. Friedlingstein et al. 2006; C4MIP comparison. Eleven coupled climatecarbon models varied by almost 200 ppm CO 2 purely on the effects of climate change. Most models varied by ppm in 2100.

12 Norby et al PNAS How long will the stimulation of NPP by CO2 persist? and how long must experiments be run to answer that question?

13 Land-use management to enhance sinks: Afforestation and forest management For U.S. mitigation, a carbon price of $50 per tco 2 e could lead to afforestation of 16M ha of cropland (Jackson and Baker 2010 BioScience), even with the Renewable Fuel Standard in place. You cannot alter C storage on land without altering water cycling and availability. Change in annual runoff (mm) (mm) Jackson et al Science Plantation age (years)

14 Land-use management to enhance sinks: Afforestation and forest management. Land-use change alters albedo and the energy balance along with carbon. We need research on full radiative accounting for land-based activities. Southeastern U.S. Albedo Month Jackson et al ERL

15 Difference in July shortwave albedo paired pixels Mean difference in summer albedo is fairly modest (0.03)

16 Difference in January shortwave albedo Mixed forests versus grasslands Mean difference in albedo is 0.16, but strongly bimodal (0.05, 0.25)

17 2) CO 2 Removal: Biomass Energy and C Capture & Storage One of only a few opportunities to go carbon negative on a large scale; Shepherd et al. (2009 Royal Soc.) estimate the potential as large, a cumulative ~100 ppm of atm. CO 2. Includes the need for safe and affordable CCS technologies. Ecological Research Needs: 1) Competition for land use (food, biofuels, etc.) 2) How much of the unharvested C would have gone to soil C pools? 3) Sustainability and biodiversity where will the biomass come from? 4) Some negatives land-area intensive; low-density energy source; transportation costs; loss of soil nutrients through time. While industrial CO 2 removal may be more benign and will require far less land, biological removal by plants will probably be cheaper and is available now.

18 Biomass Available Now: Waste to Energy with CCS Chandel et al., in prep; 60% of waste from 5 largest landfills per state

19 Other possible drivers of WTE-CCS besides a carbon price Chandel et al., in prep

20 What is the fate of forest biomass and native habitats?

21 Which biomass is most vulnerable to loss naturally? And can we preferentially use it? MOD14CMG product for Veron et al., submitted

22 Annual electricity demand and energy released in fires Between 2003 and 2006, global fires consumed ~8500 PJ y -1 of energy, equivalent to ~47% of global electricity consumption and >100% of national consumption in 55 countries. Fire energy release: Ag- Non-ag Current electricity demand