Terrestrial Ecosystems, Complexity, and GeoEngineering: More Questions than Answers IGBP Geoengineering Workshop La Jolla, CA 31 Jan – 2 Feb 2010 Anthony C. Janetos, Director Joint Global Change Research Institute PNNL/UMD

Today’s Presentation Talk primarily on the consequences of atmospheric geo- engineering schemes on ecological systems Importance of understanding which effects are driven by temperature and precipitation and which are driven by CO 2 Important also to understand which effects are on system function and which are on system structure and biological diversity Will not focus on engineering the biosphere, but will mention some possible unanticipated consequences Will leave the idea that projections of ecosystem response are highly uncertain, in part because of complexity Do have some natural experiments to learn from

Various Schemes

Which Climate Effects Might Be of Concern? Functional effects: climate and CO 2 having an effect now on growing season length, on water resources, on fire and pest disturbances, and on primary productivity Structural effects: major structural elements of ecosystems, which plants are there Population effects: differential response to CO 2 and temperature, precipitation Biogeographic effects: changes in distribution of plant and animal species

Functional Effects

Observed and Projected Trends in Peak Streamflow Timing Top map shows changes in runoff timing in snowmelt- driven streams during with red circles indicating earlier runoff, and blue circles indicating later runoff. Bottom map shows projected changes in snowmelt-driven streams by , compared to , under a higher emissions scenario. 91

7 Global Climate Change Impacts in the United States 77 Findings: Forest Land Resources Climate change has very likely increased the size and number of forest fires, insect outbreaks, and tree mortality in the interior west, the Southwest, and Alaska, and will continue to do so. Rising CO 2 will very likely increase photosynthesis for forests, but the increased photosynthesis will likely only increase wood production in young forests on fertile soils. Nitrogen deposition and warmer temperatures have very likely increased forest growth where adequate water is available and will continue to do so in the near future. The combined effects of rising temperatures and CO 2, nitrogen deposition, ozone, and forest disturbance on soil processes and soil carbon storage remains unclear. 7

Functional Effects Driven by changes in CO 2, climate, and water Also see changes in growing season length and calculated changes in NPP, largely in mid-latitudes Expect to see increases in forest growth in young forests on fertile soils

Structural Effects

Projected Shifts in Forest Types The maps show current and projected forest types. Major changes are projected for many regions. For example, in the Northeast, under a mid-range warming scenario, the currently dominant maple-beech-birch forest type is projected to be completely displaced by other forest types in a warmer future. 243

Structural Effects Largely modeled as response to climate more than atmospheric CO 2, but this depends on the details of the models used to do the projections Expect a strong interaction of climate and CO 2 with respect to the major plant species that define ecosystems

Population Effects

Current CO 2 (380 ppm) Potential Future CO 2 (680 ppm) Herbicide Loses Effectiveness at Higher CO 2 The left photo shows weeds in a plot grown at a carbon dioxide (CO 2 ) concentration of about 380 parts per million (ppm), which approximates the current level. The right photo shows a plot in which the CO 2 level has been raised to about 680 ppm. Both plots were equally treated with herbicide. 233

Population Effects Some (like the example shown) are clearly differential physiological responses to atmospheric CO 2 Some of this is well-understood (C-3 vs C-4 responses) But other examples, like mismatch between pollen production and pollinators, or sensitivity of plants during seed set are more complicated and poorly known But the crop story is trickier – yield of major grains can be very sensitive to high temperatures at the time of seed set But this is dependent on when the high temperatures occur, so we would want to understand how the geoengineering climate response affects distribution of extremes

Biogeographic Effects

Butterfly Range Shifts Northward As climate warms, many species in the United States are shifting their ranges northward and to higher elevations. The map shows the response of Edith’s checkerspot butterfly populations to a warming climate over the past 136 years in the American West. Over 70 percent of the southernmost populations (shown in yellow) have gone extinct. The northernmost populations and those above 8,000 feet elevation in the cooler climate of California’s Sierra Nevada (shown in green) are still thriving. These differences in numbers of population extinctions across the geographic range of the butterfly have resulted in the average location shifting northward and to higher elevations over the past century, illustrating how climate change is altering the ranges of many species. Because their change in range is slow, most species are not expected to be able to keep up with the rapid climate change projected in the coming decades. 244

Biogeographic Effects Usually understood as climate effects per se But also clearly differential responses among both animal and plant species to changes in the climate system (temperature and precipitation) Details of the natural history will matter

Effects of Adding Stratospheric Aerosols Idea is to counteract GHG changes in radiative forcing Possibly also increase depletion of stratospheric ozone Reduction of acceleration of hydrologic cycle Increase in diffuse light…

Diffuse Light We do know something about ecosystems’ functional response to diffuse light Slowing of atmospheric CO 2 increase after Pinatubo Hypothesized to be result of increase in photosynthesis (light effect) more than decrease in respiration (temp effect) Ecosystems stored more carbon as a result, and slowed atmospheric accumulation

Stratospheric Aerosol GeoEngineering Anthropogenic emissions of CO 2 not significantly altered Uncertain effects on precipitation Increase in diffuse light Pinatubo-type response perhaps, but depends on Water Whether the increase in NPP can be sustained Regional nature of light effects

Stratospheric Aerosol GeoEngineering Structural Effects: Potentially changing climate component, but not CO 2 Interaction changes in unknown ways Population Effects Differential physiological effects don’t change But climatic ones might Biogeographic Effects Usually thought of as climate-driven Would need to understand how regional and how persistent the engineering response was

What Could We Do to Find Out? Experimental studies Change climate but not CO 2 ? This experimental protocol would need to be worked out Perhaps some analogues in soil warming experiments Ecosystem process modeling studies Yes, but… VEMAP experience is sobering in this respect Models diverged when forced because of differences in how they parameterized CO 2 effect Not clear that ecosystem models are yet reliable enough to be used in this way

What Could We Do to Find Out? Bioclimate envelope models Assume that current geographic ranges largely limited by climate But often don’t account for differential responses to water, CO 2, temperature changes So if interaction changes, how would major plant species respond? Dynamic Global Vegetation Models Combine functional components with rule-based components of response to climate for differential functional types Not clear that they can do this kind of model experiment reliably

What About Engineering the Biosphere? Usually thought of as growing more woody plants for sequestering carbon This is not the only scheme out there, but is probably the major one There has been some discussion about growing more trees and then burying them to sequester the carbon, but area of land needed is problematic But reason for growing woody plants is also strongly dependent on the policy environment Carbon itself must be valued for forests and natural ecosystems to be maintained

The Land Use Implications of Stabilizing at 450 ppm When Terrestrial Carbon is Valued ppm Stabilization Scenario When ALL Carbon is Valued (UCT) 450 ppm Stabilization Scenario When Terrestrial Carbon is NOT Valued (FFICT)

Final Thoughts More questions than answers Complexity of ecosystems makes general principles elusive Functional and structural components each with unique responses to changes in climate and CO 2 Models not yet constructed and understood to be quantitatively reliable for understanding changes that are clearly outside the range of natural variability But even response to natural variability has revealed surprises