Milankovitch Theory of Climate Change The Earth changes its: a)orbit (eccentricity), from ellipse to circle at 100,000 year cycles, b)wobble (precession), affects timing of seasons with respect to perihelion, at 23,000 year cycles c) tilt (obliquity), from 22° to 24.5° at 41,000 year cycles. THESE FACTORS AFFECT GLOBAL CLIMATE BECAUSE OF GREATER LAND AREA IN THE NORTHERN HEMISPHERE

* Climate Change is Nothing New TODAY *NB: The temporal scale used to examine climate change is very important, as different patterns are revealed, depending on the timescale used. The rate of climate warming projected by the IPCC is believed to be very rapid compared to past climate changes

The Jurassic A much warmer Earth with more CO 2

The last glacial maximum

[insert fig 16-6] Temperature variation during the past two millenia

Berner RA and Kothavala Z GEOCARB III: A revised model of atmospheric CO2 over Phanerozoic time. American Journal of Science. 301: Climate and CO 2 Concentrations: 2 to 590 million years BP Current Global Mean Temperature & [CO 2 ] vap

Climate Change Carbon dioxide absorbs outgoing longwave radiation emitted by the Earth This causes temperature to rise on a global scale CO 2 -induced global warming first predicted by Arrhenius (1896) Concentrations have increased from 280ppm (preindustrial) to 390 ppm (2011)

Source: NOAA ABSORPTION K  TO SPACE=31 L  <K  !! Heat transfer 7+24=31 Compensates for radiation imbalance at surface L =69 L  TO SPACE= = =0 GREENHOUSE EFFECT HERE

Source: IPCC

Climate Change The Observed Record (IPCC) The 20 th century was unusually wet in much of North America.

Global Circulation Models

Future Scenarios Temperature Increase +2.5 to  C above climate normals (McGinn and Shepherd, 2003) THE YEAR 2050 IN SOUTHERN ALBERTA

Growing Degree Days Barrow and Yu (2005) In: Sauchyn (2007 ), with permission

Future Scenarios Precipitation Increase +3 to +36 % above climate normals (McGinn and Shepherd, 2003) More rain and less snow from autumn to spring (Lapp et al., 2005) THE YEAR 2050 IN SOUTHERN ALBERTA

Annual Moisture Index:  ET >  P Barrow and Yu (2005) In: Sauchyn (2007 ), with permission

SEASONAL FLOWS ( ) Annual flow projected to vary from -13 to +8% (mean -4%). Increased winter rain:snow ratio and above-freezing temperatures will increase winter runoff Earlier spring melt and increased evapotranspiration will decrease summer runoff CURRENTECHHADNCAR m 3 s -1 Pietroniro et al. (2006) In: Sauchyn (2007) OLDMAN RIVER FLOW PROJECTIONS

Carbon ‘Enrichment’ MORE EFFICIENT PLANTS? Faster growth rates Increased water-use efficiency lower stomatal conductance required to maintain c i Increased nitrogen-use efficiency? Impact of global change on WUE depends on net result of opposing effects of increased T a and VPD vs. elevated [CO 2 ] vap Will the same species be dominant in a 2xCO 2 environment?

Future Scenarios NET PRIMARY PRODUCTIVITY OF ALBERTA GRASSLANDS Ecosys Model accounts for both climate change and CO 2 enrichment (Li, Grant and Flanagan, 2004) Input Canadian Regional Climate Model II climate change projections (IS92a emissions scenario). Results Lengthened growing season Transpiration increases from higher temperatures were offset by increasing plant water-use efficiency caused by rising CO 2 Increased net primary productivity offset by increasing respiration, so that carbon sequestration only increased very slightly (2 g C m 2 y 1 ) under climate change N.B.: Climate change may alter interspecies competition/dynamics and cause migration. Rapid change may also reduce biodiversity.

Source: IPCC Enhanced photosynthesis

Meanwhile, we are detecting stratospheric cooling ! Why ? Ozone depletion Tropospheric [CO 2 ] increases