Terrestrial Ecosystems, Complexity, and GeoEngineering: More Questions than Answers

IGBP Geoengineering WorkshopLa Jolla, CA

31 Jan – 2 Feb 2010

Anthony C. Janetos, DirectorJoint Global Change Research Institute

PNNL/UMD

Today’s Presentation

Talk primarily on the consequences of atmospheric geo-engineering schemes on ecological systemsImportance of understanding which effects are driven by temperature and precipitation and which are driven by CO2

Important also to understand which effects are on system function and which are on system structure and biological diversityWill not focus on engineering the biosphere, but will mention some possible unanticipated consequencesWill leave the idea that projections of ecosystem response are highly uncertain, in part because of complexityDo have some natural experiments to learn from

Various Schemes

Which Climate Effects Might Be of Concern?

Functional effects: climate and CO2 having an effect now on growing season length, on water resources, on fire and pest disturbances, and on primary productivityStructural effects: major structural elements of ecosystems, which plants are there

Population effects: differential response to CO2 and temperature, precipitationBiogeographic 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 1948-2002 with red circles indicating earlier runoff, and blue circles indicating later runoff. Bottom map shows projected changes in snowmelt-driven streams by 2080-2099, compared to 1951-1980, under a higher emissions scenario.91

7Global 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 CO2 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 CO2, nitrogen deposition, ozone, and forest disturbance on soil processes and soil carbon storage remains unclear.

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Functional Effects

Driven by changes in CO2, climate, and waterAlso see changes in growing season length and calculated changes in NPP, largely in mid-latitudesExpect 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 CO2, but this depends on the details of the models used to do the projections

Expect a strong interaction of climate and CO2 with respect to the major plant species that define ecosystems

Population Effects

Current CO2 (380 ppm) Potential Future CO2 (680 ppm)

Herbicide Loses Effectiveness at Higher CO2

The left photo shows weeds in a plot grown at a carbon dioxide (CO2) concentration of about 380 parts per million (ppm), which approximates the current level. The right photo shows a plot in which the CO2 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 CO2

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 knownBut the crop story is trickier – yield of major grains can be very sensitive to high temperatures at the time of seed setBut 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 seBut 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 forcingPossibly also increase depletion of stratospheric ozoneReduction of acceleration of hydrologic cycleIncrease in diffuse light…

Diffuse Light

We do know something about ecosystems’ functional response to diffuse light

Slowing of atmospheric CO2 increase after PinatuboHypothesized 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 CO2 not significantly alteredUncertain effects on precipitationIncrease in diffuse lightPinatubo-type response perhaps, but depends on

WaterWhether the increase in NPP can be sustainedRegional nature of light effects

Stratospheric Aerosol GeoEngineering

Structural Effects:Potentially changing climate component, but not CO2

Interaction changes in unknown ways

Population EffectsDifferential physiological effects don’t changeBut climatic ones might

Biogeographic EffectsUsually thought of as climate-drivenWould need to understand how regional and how persistent the engineering response was

What Could We Do to Find Out?

Experimental studiesChange climate but not CO2?This experimental protocol would need to be worked outPerhaps some analogues in soil warming experiments

Ecosystem process modeling studiesYes, but…VEMAP experience is sobering in this respect

Models diverged when forced because of differences in how they parameterized CO2 effectNot clear that ecosystem models are yet reliable enough to be used in this way

What Could We Do to Find Out?

Bioclimate envelope modelsAssume that current geographic ranges largely limited by climate

But often don’t account for differential responses to water, CO2, temperature changesSo if interaction changes, how would major plant species respond?

Dynamic Global Vegetation ModelsCombine functional components with rule-based components of response to climate for differential functional typesNot 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 carbonThis is not the only scheme out there, but is probably the major oneThere has been some discussion about growing more trees and then burying them to sequester the carbon, but area of land needed is problematicBut reason for growing woody plants is also strongly dependent on the policy environmentCarbon 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

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450 ppm Stabilization Scenario When ALL Carbon

is Valued (UCT)

450 ppm Stabilization Scenario When Terrestrial Carbon is NOT

Valued (FFICT)

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Final Thoughts

More questions than answersComplexity of ecosystems makes general principles elusiveFunctional and structural components each with unique responses to changes in climate and CO2

Models not yet constructed and understood to be quantitatively reliable for understanding changes that are clearly outside the range of natural variabilityBut even response to natural variability has revealed surprises