Prepared for 2010 lecture series at the Academy for Learning in Retirement,


I'd like to offer this outline for a series of four talks about the biology of global change. Originally the topic was the biological consequences of global (climate) change, but biology feeds back to climate via fluxes of C, water, and radiation (albedo and sensible heat effects), so a somewhat broader perspective is good.

This fills at least 4 lectures. One plan is to:

        Offer the outline

        Present some parts that are essential background, such as on the role of GHGs in warming and other climate changes and on plant physiological responses

        Ask for a consensus of attendees on which topics to focus upon

        Post any extra material online - eventually, I might be able to expand the material with useful links (a long job, but I've done this for other posted materials on my Website)


Might it also be worth recording the session in video? That could be posted.


I'm thinking of hands-on demos of some topics - e.g., a plant with a spotlight on it; I'd measure leaf T with an IR gun, then cut the base to prevent transpiration and see the rise in leaf T.


First major effect: Greenhouse gases (GHGs ) warming


Major focus on plants to begin with

Basis of almost all terrestrial food chains


What do physiology and physics tell us about effects on the individual plant?

Higher temperature altered photosynthetic rates (higher, in most situations)

damage, in some situations

almost no change in respiration (CO2 loss), in the long term

Changed precipitation regimes

Globally, total P goes up about 6% per degree C rise - observed

However, regionally it is both higher and lower; waterlogging & drought as extremes

In general, more water more productivity

Direct responses of plants to new levels of atmospheric CO2 itself (something lacking in animals)

Stomata (pores) reduce opening greater water-use efficiency, even as photosynthesis stays high or even increasesmostly cancelled by higher air T and still-higher leaf T

Mostly a benefit to dominant "C3" plants, vs. C4s (corn, sorghum, wild grasses primarily)

Different uptake and use of nitrogen from soil

Intrinsic: a reduction in nitrogen content, from "functional balance"

In most woody plants: still get higher photosynthetic rates (improved N-use efficiency);

not so in herbaceous plants, including grasses

Less "tasty" to insect pests? Crops: less nutritious for humans

Lower need for nitrogen partial escape from N limits on growth; more biomass

(mixed results in studies)

Highly idiosyncratic: changed uptake of N from soil, from much less to much more

We can't predict which species will do which (but I have some clues)

The relative competitiveness of species will change/is changing radically


Whole populations of plants and ecosystems - first, talk about (mostly) natural ecosystems

Where can each different species thrive in new conditions?

The "niche" is determined in good part by climate - climate zones are part of the map

Potential (fundamental) and realized niches

Besides climatic averages (temperature, precip.), plus soil type, etc.:

Niche is set by:

Competition among plants for resources (water, light, nutrients) altered; see above

Prevalence of diseases, pests new ranges for these now, esp. from changes in


Extreme events (sequences of high or low T, high or low water availability, high winds,


Extreme-event occurrences are shifted by climate change

Extreme events at biological scale are hard to characterize; we don't know their nature,


Basically, zones for most plants are shifting poleward, but with idiosyncratic differences among species

Natural distributions (biogeographic) will change

Can plants migrate there, and in time?

Migration occurs by dispersal of seeds or other propagules; mostly short range and

possibly not fast enough! (some extreme dispersals occur by wind and animal action)

Are plants adapted to the new conditions of soil, new incidences of pests and diseases in

their new climatic homes? An open question

Can plants adapt = change genetically?

To survive, compete, and reproduce, plants can stay in the game if they change some of their physiology and their patterns of growth and development

Can do this, if the genetic diversity is there - but the proper forms of genes (alleles) have been lost over the last 25 million years

Combinations of genes matter - genes are linked on chromosomes

This constrains how species can evolve

If adaptation to local conditions is strong, the possibility of adequate evolution is poor

Didn't plants (and other organisms) go through such changes in the past?

It takes many generations to replace genes (alleles) & this change in so many environmental conditions is faster than ever before, and involves more changes (more aspects of the environment than ever before)

Interesting note: some basic physiological patterns are very robust - how did plants in Ice Ages set their intake of CO2? Recent work by Joy Ward's group

Prediction of future genetics - and physiology, plant performance difficult!

Many current genotypes will be replaced big dieoffs ("excess genetic deaths"),

prominent for long-lived species such as trees

New patterns will emerge in timing and length of growing seasons in temperate zones

Spring (last frost) is earlier, fall (first frost) is later - here and globally

Will plants adjust their times of germination, flowering, senescence, and dormancy in an adaptive mode?

Not guaranteed - they use indirect signals of proper T regime, the photoperiod. Now the relation to proper T (e.g., frost-free times) has shifted

New patterns will emerge in the availability of resources (water, nutrients)



Precipitation regimes will change, as noted above

Altered timing - and natures - of El Nios, monsoons (here, India)

Usage by plants

Water-use efficiency up modestly a bit less use per day/week/month

Species differ there will be (big) winners and (big) losers

Longer growing season possibly more overall water use in an ecosystem

soil depletion (drought from usage)

Faster development (growing degree-days) potentially even faster water use

On balance: are we wetter or drier? Varies by region. Detected with satellites directly

measuring gravitational anomalies!

Nutrients - focus on nitrogen, which can be made available by biological fixation from air

Organisms that "fix" N2 from air are generally favored at high CO2

Will this, plus better efficiency in using N, make plants grow a lot more?

CO2 itself

Plants' uptake of CO2 accounts for about 20% of the extra CO2 we put in the air by using fossil fuels and doing deforestation they moderate the rise in CO2

In the long term: plants drove levels of CO2 down from 1000-2500 ppm to 180-280 ppm by being so successful in growing, esp. in making bits (lignins) that resist breakdown. These bits were buried and became coal. We're returning that carbon, but way too fast for them to adapt to the new availability (and for us to adapt to many new conditions)

Land area/ space to establish

Coastal plants (mangroves, etc.) - sea level rise inundation, saltwater intrusion

Importance for fish, incl. commercial! (less of a worry than massive overfishing, which

dooms most fish)

New patterns will emerge in ecological interactions with pests, diseasese, pollinators, seed dispersers

Pollinators - will they come out at the right time? Some disconnects seen already

Dispersers - ?? probably same distances moved

Pests (leaf eaters, phloem munchers, root eaters)

Many have expanded their geographic ranges

Timing and duration of pest occurrence has changed

Dramatic example: bark beetles in Western N. America, 2001-4

Warmer winter better overwintering of beetles

Longer summer an extra generation far more beetles

Drought (surprisingly, rare to occur with higher T) inability of plants to defend selves

Biggest timber loss in world history in British Columbia

Decay of dead trees is adding 0.3 Pg of C back into air (5% of annual world injection)


Main plant diseases are fungal, then bacterial, then viral

Some spread on own, on wind - favored by heat (so, expect greater incidence) and humidity (relative humidity is not changing, fortunately)

Some spread by vectors (insects) expanded ranges are already seen

We don't know who are winners and losers yet (expect more losers, by the way)

Agricultural systems

Fundamental changes in response to temperature, precipitation, pests, etc. are as above, for natural systems. Focus now on special aspects of agriculture

Water availability

Directly from precipitation: a bit more, if unevenly distributed, with less in some regions

From snowpack to rivers to irrigation - a mixed story

Globally, irrigation is applied on bout 10% of arable land but supports about 33% of global food production

Higher temperatures less snowpack in regions of more moderate temperatures (e.g., the Colorado Rockies)

Also, earlier snowmelt - before river flow can be used for irrigation?

Can't store the excess in reservoirs that are fairly full to capacity on average

What about moving planting dates earlier? Jury is out

Smaller glaciers in Himalayas, the source of 3 major rivers supporting (in part) 1 billion people in Asia - jury is out here, too

Pests and diseases, and their vectors

Overall: Need to move crops poleward as high temperatures, pests, and diseases move up

Where will we grow our crops with good enough soil, low disease/pest/weed incidence?

Where will our forests, ornamental trees, etc. be?

Will there be complete losers, niche gone from insufficiently fast migration?

Almost impossible to predict, I claim (link to my ppt for AGU 09 and our Eos article)

Crop production and quality

Global total: gains possible in theory, from increased precipitation and slight increase in water-use efficiency, sometimes related also to longer growing season

China has gained 8% in wheat production in North in 20 years

Qualifiers are serious

Too-early depletion of soil water at critical time for development of harvested parts

China's wheat gains are plateauing and will reverse

Poor adaptation of some crop genotypes to high T

Pest and disease incidence increasing

Direct effects of CO2 on competitors

Broadleaf weeds (C3 type plants) gain over major grass crops (C4 plants - maize,

sorghum, sugarcane)

CO2 makes weeds resistant to herbicide glyphosate (RoundUp) used widely on crops

(Note also that glyphosate reduces iron and manganese content of foods, to the

detriment of both plant and human nutrition, even as Monsanto pushes US govt.

to expand their GMO crops with glyphosate resistance in international aid)

Overall: big drops expected in tropics, where hunger and unrest are prevalent already

Case is uncertain in my view - not all of the relevant physiology has been accounted

Quality: look back at the section on the unavoidable reduction in nitrogen (protein) content as CO2 increases

This reduces food value to humans; makes it difficult to keep protein content sufficient in bread wheats already


Feedbacks of plant performance globally to climate

More plant growth, if it happens, increases the absorption of sunlight and warms the planet. The effect is notable only at high latitudes where trees replace snow. (Don't count on this)

Soil respiration increases with higher temperatures. Microbes in soil break down dead plant material and release CO2. (Respiration of live plants only changes a little, in contrast.)

Deforestation in Amazonia, SE Asia changes local climate, esp. precipitation. Amazonia has been predicted to have more or less rainfall, depending on the model used, but always to get hotter. In SE Asia, deforestation has little effect on precipitation, including the critical monsoon, because the moisture source is oceanic, not terrestrial.


Other big global changes that affect plants, wild and cropped:

Depletion of reserves of phosphate fertilizers

Deforestation - how it affects other vegetation

As a C source

As an alteration of global atmospheric water balance

Air, water, and soil pollution

Ozone in the lower atmosphere that we breathe and that plants experience

Generally a drop in productivity; minimal effect on quality of fruits, vegetables

Serious reductions in available water - China as an egregious example, from both diversion for industry and municipal use, plus pollution

Water wars? Food shortages?

Loss of native species and land races of crop plants, if only for crop breeding potential (vs. diseases, e.g. - need 90% effort of breeders on this, and new genes every 10 y or so; genetic engineering very little help here)

Related issue of genetic homogeneity, a continuing trend, even in light of 1970 S. corn blight

Exotic species introductions - massive topic in itself

Plants - kudzu, others, as examples

Diseases of plants - chestnut blight,

Pests of plants - Asian longhorned beetles


Animals and other organisms affected by global change

Extremely broad topic - besides climate and GHGs, there is land-use change (esp. deforestation, habitat fragmentation, pollution of water, soil, and air, etc.)

Let's limit it first to GHGs and climate change

Direct effects of higher CO2

On terrestrial organisms - minimal; our own respiration is at 20,000 ppm CO2, so a rise in external CO2 from 300 to 800 ppm is negligible

On marine organisms - huge! Ocean acidification aragonite undersaturation carbonate skeleton dissolution (corals, shellfish, diatoms)

Lowered N content in plants, for herbivore nutrition


Native species

Effects of temperature

On thermal limits and on water balance to cool evaporatively

Huge, for birds, bats - dieoffs in Australia

T and P

Disease and pest incidences

Potential changes in ocean currents - thermohaline circulation, for one

Other, non-climate effects

Vectors of animal diseases, incl. human diseases

Bird malaria in Hawaii

West Nile in US

Equine encephalitis

Humans: dengue, malaria, W Nile, Japanese encephalitis in US

Also, vectors, esp. mosquitoes

Extremely complex system

We never had to deal with so many coupled issues before, with necessary international linkages (and accompanying issues of sovereignty, equity)

Our uncontrolled experiment, as Roger Revelle called it back in the 1950's


What's being done? I have more work to do on this

For monitoring

Everything from field plots to global satellite surveys of biomass, productivity, species composition and species biogeographic ranges, pollinator activity, disease prevalence, etc.

Unfortunately, observations don't lead to substantial predictions of future changes. The models are far from complex and realistic enough, and proper models would need vastly greater amounts and types of data. Some progress in data amounts and richness is being made (NEON observatories, new satellites)

For prediction - see above

For mitigation = prevention of undesirable changes

In ultimate drivers, such as greenhouse gases

For adaptation (socioeconomic) - minimizing the adverse social, economic, and environmental effects of change that has occurred and will occur