Soils and Global Warming

Transcription

1 Soils and Global Warming Reading: Lecture Notes Objectives: Introduce climate change Describe measured and expected effects on soil systems Describe prediction of climate change effect on food production. The World Has Warmed Globally averaged, the planet is about 0.75 C warmer than it was in 1860, based upon dozens of high-quality long records using thermometers worldwide, including land and ocean. Eleven of the last 12 years are among 12 warmest since 1850 in the global average. Understanding and Attributing Climate Change Anthropogenic warming is likely discernible on all inhabited continents Observed Expected for all forcings Natural forcing only Lecture 11, Soils and Global Warming 1

2 Human and Natural Drivers of Climate Change Carbon dioxide is causing the bulk of the forcing. On average, it lives more than a hundred years in the atmosphere and therefore affects climate over long time scales. What is Causing the Changes? What is a greenhouse gas? Nitrogen, O 2, and Ar make up for 99% of the atmosphere but are not greenhouse gases Water vapor, CO 2, CH 4, and N 2 O are greenhouse gases A greenhouse gas absorbs infrared radiation because of their dipole moment This dipole moment creates molecular vibration and bending and as a result the molecule absorbs infrared radiation Collisions transfer energy to heat the surrounding gas The N 2 O molecule Lecture 11, Soils and Global Warming 2

3 Industrial Revolution and the Atmosphere The current concentrations of key greenhouse gases, and their rates of change, are unprecedented. Carbon dioxide Methane Nitrous Oxide Land Precipitation is Changing over Broad Areas Smoothed annual anomalies for precipitation (%) over land from 1900 to 2005; other regions are dominated by variability. Another Look at the Problem: Extreme Events Lecture 11, Soils and Global Warming 3

4 More on Precipitation Projections of Future Changes in Climate New in AR4: Drying in much of the subtropics, more rain in higher latitudes, continuing the broad pattern of rainfall changes already observed. What Changes in the Soil System are Expected? Alterations to the carbon cycle Changes in soil water stored in the profile. Changes in mean soil temperature at the surface Temperature at the subsurface is a function of water content and organic carbon. Effects on roots and pests? Decrease in soil quality? Increase in soil erosion. Lecture 11, Soils and Global Warming 4

5 Carbon Losses Carbon was lost from soils across England and Wales over the period at a mean rate of 0.6% yr -1 (relative to the existing soil carbon content), reaching 2% yr -1 in soils with a carbon content greater than 10%. Source: Bellamy, P. H., P. J. Loveland, R. I. Bradley, R. M. Lark, and G. J. D. Kirk Carbon losses from all soils across England and Wales Nature 437: doi: /nature Source: Heimann, M. and M. Reichstein Terrestrial ecosystem carbon dynamics and climate feedbacks. Nature 451, doi: /nature06591 Simulated Global Changes in Soil Moisture Soils in mid and high latitudes will be drier in the summer and wetter in the winter (more snow). See report in the FT Wetherald, R. T., and S. Manabe, Simulation of hydrologic changes associated with global warming, J. Geophys. Res., 107(D19), 4379, doi: /2001jd001195, cm Lecture 11, Soils and Global Warming 5

6 Network of Soil Temperature Measurements Russia United States Long-Term Soil Temperature Records Minnesota Russia Source: Baker, J.M. and D.G. Baker Long-term ground heat flux and heat storage at a mid-latitude site. Clim. Change 54: Source: Zhang, T., Barry, R.G., Gilichinsky, D., S.S. Sorokovikov, V.A., and Ye, J An amplified signal of climatic change in soil temperature during the last century at Irkutsk, Russia. Clim. Change 49: Global Change in Surface Temperature Source: Pollack, H. N., Huang, S., and Shen, P-Y Climate change record in subsurface temperature: A global perspective. Science 282: Lecture 11, Soils and Global Warming 6

7 Extreme Precipitation Events The CO 2 Fertilization Effect The elevated concentration of CO 2 stimulates photosynthesis and reduces stomatal conductance 2.0 Other effects Improves water use efficiency Accelerates plant growth Changes the distribution of nutrients Reduces foliar concentration of nitrogen Kimball (1983): crop yields should increase 33% when [CO 2 ] doubles from 330 to 660 ppm Photosynthesis (mg CO2 m -2 s -1 ) Maize - C4 Wheat - C CO 2 concentration (μmol mol -1 ) Akita y Moss (1973) Lecture 11, Soils and Global Warming 7

8 General effects of [CO 2 ] on wheat yield Kimble (1983) Agron. J. 75: experiments Wheat yield increased 37% when [CO 2 ] increased from 330 to 660 ppmv Amthor (2001) Fields Crops Res. 73: lab and field experiments with wheat Non-limiting water and nutrients Ambient temperature Wheat yield increased 31% when [CO 2 ] doubled from 350 to 700 ppmv Amthor (2001) Greenhouse gases and agriculture Further synthesis from IPCC, WG III, Ch. 8 Agricultural lands (cropland, grasslands and permanent crops) occupy about 40-50% of the Earth s land surface (13.4 Bha) Agricultural activities resulted in emissions of GtCO 2 -eq yr -1 in 2005 (10-12 % of total global anthropogenic emissions of greenhouse gases) CH 4 contributes 3.3 GtCO 2 -eq yr -1 (50% of total) N 2 O contributes 2.8 GtCO 2 -eq yr -1 (60% of total) CO 2 contributes 0.04 GtCO 2 - eq yr -1 (~0% of total) Aerial views of managed landscapes Impact on Agricultural Productivity without Carbon Fertilization (percent) William R. Cline, Center for Global Development and Peterson Institute for International Economics Lecture 11, Soils and Global Warming 8

9 Impact on Agricultural Productivity with Carbon Fertilization (percent) William R. Cline, Center for Global Development and Peterson Institute for International Economics Research methods to study [CO 2 ] effects on plants Laboratory chambers Glasshouses Closed-top field chambers Open-top field chambers Free-Air Carbon Dioxide Enrichment (FACE) 50th_anniv/photo_album/PendallElise Effects of Climate Change on Agriculture Figure Atmospheric composition in these open-top field chambers (a) altered plant growth and physiology, and thereby also affected the amounts and forms of soil organic carbon. Increasing atmospheric CO 2 from low (360 mg/l, the ambient level) to high (500 mg/l, the level expected by 2050) enhanced photosynthesis in the plant, and thus increased the amount of fixed carbon available for translocation to the roots and eventually to the soil. (b) Increased root growth and exudation of carbon compounds contributed first to the active fraction of soil carbon as suggested by the pronounced effect after only 5 years of elevated atmospheric CO2. (c) The level of total soil organic carbon, most of which is stable humus, was also beginning to increase. Ozone, a pollutant at ground level, injures plants, reducing photosynthesis and therefore impacting the soil in a manner opposite that of CO2. The data suggest an interaction between the two gases, by which the full effect of CO2 is seen only when ozone is kept low. [Data from Weil et al. (2000); photo courtesy of R. Weil] Lecture 11, Soils and Global Warming 9

10 Conventional Management Steady State Improved Practice Carbon Sequestering Practice O D C B A Soils and Water, Spring 2008 Land Use change and soil management effects on SOM levels Cultivation Carbon oxidation and nutrient mineralization Erosion Wind and water Improved practices Agricultural systems Land use conversions 40 Summer fallow Soil Org. C (Mg ha -1 ) Practice Change Soil Measurement Years of Cultivation Wind erosion Soil Carbon Sequestration: A near term mitigation technology with significant but finite potential (40 Pg C) Net primary productivity Fresh soil organic matter 25 Organo-mineral complexes Adoption of no-till worldwide (Mha) No-till seeding in USA 0 USA Brazil Argentina Australia Canada Paraguay Others Izaurralde and Rice (2006) Agricultural management plays a major role in greenhouse gas emissions and offers many opportunities for mitigation Cropland Reduced tillage Rotations Cover crops Fertility management Erosion control Irrigation management Rice paddies Irrigation Chemical and organic fertilizer Plant residue management Rice fields in The Philippines No-till seeding in USA Agroforestry Better management of trees and cropland Maize / coffee fields in Mexico Lecture 11, Soils and Global Warming 10