How do we know what kinds of ecological effects to predict for a given climate change? That is, what evidence do we have about how organisms responded to climate changes in the past? One important source of information is the pollen record, as preserved in lake sediments or other strata. (The study of the pollen record is called "palynology.") As plant species increase or decrease on the landscape, their pollen also increases and decreases in abundance, and pollen grains under the right conditions can last for centuries. The palynological record tells us that when climate changed in the past (as documented inthe ice core data that we talked about before), plants migrated, following appropriate climates. For example, we know that at the end of the last ice age (10,000 yr ago) the spruce-fir forest that now spans Canada grew far to the south. As climate warmed at about 1 - 2 degrees C per 1000 years, the forests migrated orth at about 1 km per yr.
Similarly, we know that 6000-8000 yrs ago, summer temperatures in the Northern hemisphere hemisphere were about 1-2 degrees C warmer than now, and that, at that time, prairies extended hundreds of km to the east in the US, compared to their present location.
Fossil records can help us reconstruct the past fauna of places, and in company with paleoclimatology, can give us insights into how animals coped with climate changes of the past.
Migration was the fundamental response to past climate changes.
One concern now, however, is that the predicted changes will happen very fast compared to previous changes. We are looking at global mean temperatures increasing by 1.1 - 6.4 degrees C in about 100 years [IPCC's 2007 "most realistic" range] , compared with global mean increases of 1 - 2 degrees C per 1000 years in the past -- current rates are likely to be more than an order of magnitude faster than those ancient changes.
There are probably four basic ways of "coping:"
A. MIGRATE -- Whether this will be possible will depend on:
1. the rate and magnitude of climate change
2. species mobility (how fast they can move compared to how fast climate is changing (well see some data on this later))
3. where there is to go to
4. and whether there are corridors; migration
routes connecting present habitat with future habitat.
Connections with concerns about threats to biodiversity resulting from habitat loss and fragmentation of habitat (islands of suitable habitat, isolated from each other by intervening unsuitable habitat) are aggravated by the prospect of rapid climate change (or vice versa). Places that were suitable habitat in the past may not remain so, and it may be difficult (or impossible) to get to new areas.
For example, where do polar bears go when Arctic ice disappears in summer? They hunt seals and other marine mammals from sea ice that extends to the S in winter and contracts in summer. In summer, when they retreat to land, they don't eat much -- and aren't necessarily good competitors for other species of bears in the area. SO, short summers are good, from a polar bear's perspective. The West Hudson Bay sea ice is breaking up ~ 3 weeks earlier than 30 yr ago (Science 5 Jan 07), so bears must retreat to land earlier, and bears in the West Hudson Bay vicinity are skinnier and fewer cubs now survive. In fact, 25% of polar bear populations are declining (NRDC March/Apr 07) and this will worsen as sea ice contracts more and more in summers. Hence, polar bears were listed as threatened (=likely to become endangered if no action taken) under the Federal Endangered Species Act as of May 2008 .Listing SHOULD require development of a recovery plan that requires all Federal agencies to ensure that their actions don't put the bears at risk - concrete, measurable steps. Will listing really have this effect??
Migrations that are presumed to be in response to climate change have already been observed. For example, European forest plant species optimum habitat (as judged by plant abundance) has moved up in elevation - comparing ranges 1905-1985 versus 1986-2005 (Science 27 June 08). Many mobile species such as birds and butterflies have shifted ranges poleward by an average of ~ 6.1 km since the 1960's - based on an assessment of ~ 1,700 spp (Nature 2 Jan 03; cited in Science 12 March 04) Because plants and animals are interdependent, problems may arise if some move faster than others -- e.g., pollination or seed production and dispersal might suffer if plants don't move as fast as their pollinators and seed dispersers!
Inuit peoples of the far north are seeing
creatures that they have no words for - birds and insects that
have never been seen in their territory before, for example Reuters
Nov. 18, 2004)
B. ADAPT GENETICALLY. Whether this will be possible will depend on:
1. rate and magnitude of change
2. generation length in comparison to rate of climate change
3. population sizes (and the amount of genetic diversity that they contain for tolerance to climatic conditions) and,
4. population distributions (whether genes can "flow" between populations -- that is, whether organisms that have genetic makeups that allow them to tolerate changed climate conditions can move into other areas occupied by the species, and, in so doing, bring those favorable genotypes to that area).
As for migration, previously existing concerns about biodiversity related to small population sizes and isolation of one population from others ("habitat fragmentation"), become even more important when facing the prospect of global climate change. An increasing number of species are found in small, isolated populations owing to human influences (largely habitat destruction). These small, isolated populations with limited genetic diversity are likely to be more threatened than larger or interconnected populations, simply because the former will have less ability to adapt genetically to the changes. (If you arent sure what I mean by "adapt genetically" Im talking about an evolutionary change, similar to the evolution of pest resistance to pesticides that we talked about before.)
C. ACCLIMATE PLASTICALLY (This is, rather than genetically-based adaptation, just a matter of "getting used to" the changed conditions. It happens in all of us every year. When temperatures first drop into the mid-40s (F) in autumn, we feel like it is very cold, but, over winter, we acclimate to the colder conditions, and by spring, a 45 defree F day feels downright comfortable. This also happens when you spend time at high elevations -- your body acclimates to the lowered oxygen availability.) Whether this will happen depends on :
1. magnitude and rate of change compared to
2. physiological or behavioral plasticity in populations and individuals
A 47 yr study of Great Tits (birds!) in the UK showed that individual birds adjust their behavior in response to environmental cues, and these adjustments allowed their populations to closely track env'l changes. For example, breeding dates and egg-laying dates of individual birds vary with temperature, and date of food availability does too (Science 9May 08). This suggests that some potential for acclimation exists.
Other phenological changes (phenology refers to the timing of events in relation to dates or seasons) have also been observed. In many cases, it isn't clear if the changes involve adaptation (genetic changes in populations) or acclimation. Recorded changes include earlier leaf out, earlier migrations, earlier blooming times, longer growing seasons. As mentioned above relative to migration, open questions concern whether such changes will alter synchronization between trophic levels - e.g. how do hummingbirds survive if they arrive back in their summer territories before blooms are available .Community and ecosystem level impacts of such changes unknown!
D. EXTINCTION -- This will be the fate of organisms if the climate change is too fast or too extreme, such that none of the above are possible, or when there is no where to go (such as creatures who live in alpine areas, like pikas, when the climatic zone for alpine areas moves up right off the top of the mountain!)
Incredibly, models predict the extinction
of 18 - 35% of land species by 2050 owing to climate change and
the associated habitat losses, if present trends continue!!! (That
is, this % doesn't include other non-climate related causes of
extinction or habitat loss). Extinction has already occurred for
some species that couldn't move fast enough (citations in Science
18 July 08; Nature Jan '04).
1. Individual species will respond individually. Some may be able to acclimate, adapt, or migrate; some may not and some may survive with reduced numbers or geological ranges (similar to refugia during glacial periods).
2. Warming will affect entire communities of plants and animals, often in unpredictable ways. Some entire communities might shift range together, but, more often, new communities are likely to be created -- some species will stay, others will leave, and new ones will come. Whether ecosystem services remain intact (are able to be resistant) will depend on how severe the disruptions are.
3. Plants will be affected more directly than will animals (in general). Plants are strongly and directly affected by precipitation, temperature and [CO2], and individual plants can't move -- only their propagules can. However, effects on plants will often have effects on animals that depend on them. There are cases, however, where animals will be directly affected as well. For example, populations of the Adelie penguin in Antarctica have decreased by about 40% over recent decades. No one is sure why, or whether the decline is related to climate changes (natural or unnatural), but it may be that: (1) warming of the waters may have decreased their food supply (krill, which, in turn, depend on plankton), which would be an indirect effect or (2) heavier snowfalls (driven by warmer temperatures) may bury their eggs; a relatively direct effect.
4. Changes at high latitudes (e.g., the Arctic) are likely to be greatest, as warming is expected to be most extreme there. Thus, high latitude regions are likely to give us "early warning" signs for slower and more subtle global responses.
(See your assigned readings in Course Documents and articles listed on the supplementary reading list for more examples.)
1. Direct effects of increased CO2: "CO2 fertilization."
As you know, plants take up CO2 in photosynthesis. Under experimental conditions (as in a greenhouse) many plants are more productive (by as much as 30%) when grown in CO2-enriched atmospheres, particularly when conditions are both warmer and CO2-enriched. This enhanced productivity is sometimes jumped on as a benefit of increased [CO2], with claims that the world food situation will be enhanced under elevated CO2 and temperatures.
See any problems with this optimism?
Remember when we talked about "limiting factors" when we were talking about diminished crop responses to additional fertilizer? In nature (and in agricultural ecosystems) , plant productivity is affected by many things: light, water, temperature, nutrients, CO2, pathogens .The experiments that show enhanced plant productivity under enriched CO2 are usually conducted under conditions that are ideal for plant growth -- i.e., temperature, water and nutrients are not limiting. In these circumstances, growth IS CO2-limited. That is, plants may respond with increased productivity to enriched CO2 if something else isn't limiting at current levels. But, can we extrapolate from that increased productivity to what we would expect to see in the field -- either natural or agricultural -- and say that the world's food supply will be helped by increased [CO2]? In nature (or agriculture), production is unlikely to be primarily limited by CO2. If we wanted to try to set conditions so that plants could respond to enhanced CO2 (that is, to make CO2 the limiting factor) wed probably have to pump in even more water and nutrients than we are now to achieve yield increases. (That is, wed have to make those factors non-limiting.)
Further, in nature or agroecosystems, if crops respond positively to enhanced CO2, weeds may also respond positively to it!
Interactions with plant pathogens and pests may be altered under conditions of changed climate or elevated CO2 as well. I can imagine fungal diseases just "loving" warmer and moister conditions.
Many studies (but not all) indicate that increased productivity with increased CO2 is a transitory response. That is, the photosynthesis mechanism acclimates to higher CO2 and returns fairly quickly "normal" productivity. In addition, many studies now point to the fact that, while photosynthesis may speed up, respiration may speed apace, so that there is not in fact a net increase in productivity measured as increased biomass. Decomposition also speeds -- that is, the overall rate of biological cycling of carbon may be stimulated, without a net increase in carbon storage.
The statement that the world's food supply will be helped by increased CO2 ignores those effects and also ignores:
· increased problems with flooding
of coastal food producing areas
· increased drought and decreased recharge of groundwater owing to increased rates of evaporation
· incursion of salt water into formerly fresh ground water supplies (used for irrigation)
.changes in seasonal availability of water in areas that depend on snowpack for summer water
2. Effects related to increased temperatures and changes in moisture regime; shifts in forests as an example.
In many areas, plants are likely to be less affected by the changes in temperature than by resultant changes in water availability; its seasonal distribution, amount, and spatial distribution. (Both matter for many, of course.)
Trees grow where they do, in part, because conditions there are within their ecological tolerances; not too hot, not too cold, not too dry, not too wet. When environmental conditions change, species are likely to be affected first at the margins of their geographic range, where conditions may have been borderline anyway. Further, when conditions degrade for a species, the first thing to be affected will be often be its reproductive success. Frail seedlings won't be able to make it, while adults are better buffered by good roots, etc. Further, as mature individuals begin to be stressed, they may produce fewer seeds. These mature trees will persist for a while so initial effects will be subtle -- it will look like is all well. However, a closer look would reveal little or no regeneration. As conditions degraded further, even the well-buffered mature individuals may become increasingly stressed, making them more vulnerable to insects and disease (as we saw for ozone-stressed ponderosa pines and vulnerability to bark beetles).
Weakened and dying trees creat fuel loads, of course, with implications for forest fire frequency. Several models, including one developed by Dr. Ron Neilson here at OSU, predict that there will be huge forest fires in various parts of the country - including the NE US - as trees become stressed by climate changes (especially those related to water availability) and insects/diseases.
During the last ice age, spruce fir forests grew far to the south of their present distribution. As we saw earlier, forests shifted back north as climate warmed, coming out of that ice age. So, today, it is likely that species will also "try to" shift north or up (not consciously, of course, but through establishment of seedlings to the north of current centers of distribution). --
The questions are: will they be able to do it fast enough and are there places for them to go?
We know from pollen records that during past climate changes tree species migrated, "following" changes in climate. For example, when climate began warming about 15,000 yrs ago, species moved north at varying rates:
These rates were maxima for the species across geographic regions. That is, the rates werent limited by the rate at which climate was changing, but rather were limited by seed dispersal and colonization rates.
Now, each 1 degree C of temperature increase corresponds to a given climate zone moving at least 100-150 km to the North (in our hemisphere!)
So if temperatures increase by 1.1 to 6.4 degrees C over the next century, as is currently predicted, this would mean trees would have to migrate by 110 - 960 km N in that century if they are to remain in their current climate zone. For IPCCs mid-line estimate of about 3 degrees C of increase, zones would move N by 300 - 450 km over the coming century.
Do you see any problem when comparing these numbers to the migration rates given above? Yep, there is a problem -- the anticipated rate of change outstrips the migration rates that many species are capable of! (Some very well dispersed creatures -- including some animals -- will probably be able to move faster than trees...) Further, habitat fragmentation means that species probably wouldnt be able to migrate as fast as in the past, as there are impediments to migration beyond just disperal ability. IPCC has predicted, in fast, that deciduous forests of the NE US would be largely wiped out and replaced by grassland and savanna.
Further, other things matter besides simply getting seed to a new place. Are there sites for them in the new place? Are soil types suitable for them there? Are vital symbionts such as mycorrhizae there as well?
Migration to follow suitable climate may be easier in mountainous areas, where species can simply move up in elevation instead of having to move long distances in latitude. The dry adiabatic lapse rate is 10 C/1000 m, (it is, on average, about 10 degrees C cooler if you are 1000 m higher in elevation) so an increase of 3 degrees C in temperature would mean having to move up about 300 m in elevation. This may be more tractable, however, there may still be limitations due to soils, space and so forth. And, where will alpine plants and animals go? Alpine-dwelling animals like the pika may find that their habitat vanishes from the shorter mountains as climate warms, and they may be unable to migrate to higher peaks because of unsuitable habitat intervening.
Similar problems of dispersal and rate will apply to many understory plant species. We are likely to see animal migrations attempted too -- following plants and suitable environments. In the ancient past we know they did so. But today there is much fragmentation of habitat -- farms, roads, and cities are in the way. No one knows how many animals will be able to find their way to follow suitable climates.
A study of geographic ranges of 1,700 mobile species, such as birds and butterflies, reorted that their ranges have shifted poleward by about 6.1 km per decade since the 1960's (Nature, 2 June '03). Similarly, as mentioned previously, changes in phenology (timing of certain life stages or events, such as flowering or leaf-out) have recently been reported for many organisms. Will such changes affect the tight synchronization that exists between creatures -- e.g., will the insects that pollinate certain plants be present in the area when the plants are blooming -- or will those insects even still live in the same geographic area as do the plants that they pollinate?
Should -- or can -- humans assist migration?
Some people envision mega-scale ecosystem transplantation scenarios -- human intervention, as by, for example, moving plants or their seeds to the north or to higher elevations.
A few years ago when I was teaching about
this topic, the idea of actually attempting transplantation to
keep up with climate change was being talked about by just a few
"wild eyed" folks - is now getting closer to mainstream!!!
As an example, the reputable journal Science (18 July 08)
lays out an explicit decision tree for assessing likely success
of possible transplantations
It has also been pointed out
that gardens and nurseries have already essentially assisted migrations
- for 73% of native species found in nurseries, their commercial
northern range limits exceed their natural normal range limits
by an average of 1000 km!! (FEE 2008 (6)).
However, movement of organisms this can't start before the climate change has happened to a sufficient degree that the climate in the receiving area is appropriate. In the meantime, other things occupy the habitat. Further, it takes a long time for an ecosystem to develop, AND, we don't know how to assemble an ecosystem from scratch. The science of restoration ecology is in its infancy and we are increasingly realizing how little we know about how to put together an ecosystem .
Park and preserve managers should be considering climate change and the possible need of species to migrate when they are planning preserves and wildlife sanctuaries and setting goals for them. For example, the prospect of climate change strengthens the need to consider the availability of corridors linking areas. Further, we can't assume that we can establish a preserve to protect some particular threatened species; with climate change the area may be unsuitable for that particular organism. Our preserves may not preserve what we intended if climate changes! Thus, the prospect of climate has important implications for strategies to preserve biodiversity. It may be most important for us to preserve areas that may end up being suitable for who knows who rather than for particular target species.
3. Sea level rise and ocean warming.
Sea level has risen ~ 17 cm (10-25 cm) in this century (global mean), but all of the causes aren't understood, as discussed previously. There is also uncertainty about the magnitude of sea level rise that can be anticipated (18 - 59 cm is predicted by the end of the century [IPCC 2007} but many believe that it will probably be more than this. What consequences will be associated with a rise in sea level?
Something like 20% of the world's population
lives in areas that would be affected by sea level rise of this
magnitude - think how often population centers are coastal! Many
low lying S Sea islands have a greatly increased risk of flooding
with even a 4 INCH rise, which is <<<< IPCC's 2007
most OPTIMISTC scenario. Some projections are that the FL Keys
will be underwater by 2050.
Coastal wetlands are some of the world's most productive ecosystems and provide habitat for many plants and animals; many of these would be inundated. For example, Oregons coastal marshes in Coos and Tillamook Counties would be inundated by a 1 - 3 foot rise in sea levels (well within the range that is predicted to occur). Even a 1 rise would necessitate a costly realignment of HWY 101 along the coast, and would wreak havoc on many coastal developments.
75% of Louisiana's coastal wetlands would be flooded by a 1.5 foot rise, and it is estimated that a 1 foot rise would flood 20 - 40% of the US's coastal wetlands!! Not only are they likely to flood, but higher reaches will be affected by incursion of salt water into them. The Everglades ecosystem in Florida would be largely inundated by such sea level rises (as would be Miami).
There is increasing concern about the condition of coral reefs around the world, precipitated by the reports of large-scale "bleaching" events. Coral reefs are some of the most unique and diverse ecosystems on earth (likened to the tropical rainforests of the oceans). Yet many of them are imperiled, with an estimated >60% of them in imminent danger of death. (Dr. Mark Hixon here in OSU's Zoology dept, is one of the world experts on coral reefs and what is happening to them.)
"Bleaching" of corals happens when they experience stress, and expel the dinoflagellates (zooxanthallae) that make up part of the corals. (The zooxanthallae live in a symbiotic relationship with the coral animals, in which both partners -- the coral animals and their partners, the zooxathallae, benefit - basically the zooxanthallae help the animals in obtaining nutrients (they are photosynthetic) while the zooxanthallae are provided with a place to live.) When stressed physiologically, the zooxanthallae are expelled from the corals, causing them to bleach, or lose color (as well as vigor). In some cases, corals recover from bleaching; in other cases, they do not. Reports of such bleaching have been coming with increasing frequency in recent years, but no one has been certain of the causes. Recently, bleaching events have been more frequent, of greater geographic scope, and more severe than in the past, and have been nearly simultaneous in many places. Scientists now conclude that bleaching events are precipitated by both local-scale causes (e.g., sediments from near shore areas that can damage the corals) and larger, global-scale causes, such as ocean warming. The former is easier to deal with in many ways than is the latter!
During the strong El Nino event of 1997-98
(independent of global climate change or not??), severe bleaching
of corals was reported world wide, including from the Caribbean
(as much as 16% of the world's corals were affected). During this
time, temperatures of the Caribbean at 2 - 10 m depths increased
from their usual < 29 degrees C to over 30 degrees C. Correlation
or causation? And, if the latter, ocean warming induced by greenhouse
gases or natural variability? No one knows for sure, but the consensus
of scientific opinion is moving increasingly to believing that
this ocean warming does contain a "human fingerprint."
IPCC 2007 report predicts that we will
see ~ 2 C of ocean warming by the middle of this century, in which
case most reefs would be expected to bleach with widespread coral
mortality following within a few decades (particularly given additional
stress of acidification and pollution
). Corals' reproductive
organs are also damaged by warmer water whether they bleach or
not - they produce many fewer eggs and testes in warmer water
(e.g., when water temperatures are > 30 C).
*************As another example of potential effects associated with ocean warming: The California current in the Pacific runs from OR s to S CA, and has warmed 1.2 - 1.6 C since the 1950's. Zooplankton in that current have decreased 80% over last 40 yrs (they are temperature-sensitive and also depend on nutrient upwelling from cold deep water; the warmer water puts a density cap on upper layers so upwelling from deep, nutrient rich waters is lessened). Effects may be rippling up the food chain some species of fish and birds in the area are also declining. Some of the fish declines undoubtedly are a result of overfishing, but juveniles of some species (e.g. rock fish), that arent subject to fishing, are not surviving; these feed on zooplankton in their first year. Some zooplankton-dependent birds are in decline too, such as Cassin's Auklet, whose numbers have decreased 60% since the 1970's. This change in temperature of the ocean may be a natural temperature oscillation, but it nevertheless allows us to see a glimpse of what we might expect from global warming.
Dr. Mike Behrenfeld's lab in the Department of Botany and Plant Pathology here at OSU (2006 news release) has found that as mid- and low-latitude oceans warm, their water gets increasingly stratified (thermally; warm water floating in a "layer" on top of cooler denser water). A consequence is that productivity of phytoplankton, the base of the oceanic food chain, diminishes because they get separated on the surface (where they live because they need the light) from nutrients that are in deeper waters below. This was observed strongly during the 1997-98 El Nino and since the year 2000. Oceans have become increasingly thermally stratified and productivity of phytoplankton has diminished by as much as 30% in some areas .This also, of course, diminishes biological uptake of CO2 by oceans, which, you'll recall are one of the major sinks for CO2 emissions .
In the early 2000's a new concern arose - increased ocean uptake of atmospheric CO2 may be causing oceans to become more acidic. (Remember we talked about mechanisms by which oceans take up CO2 earlier?). According to the IPCC in its 2007 report, we've already observed an average decrease in pH of 0.1 pH units since pre-industrial times. (Remember that the pH scale is inverse - smaller numbers means more acidity. Also remember that the pH scale is logarithmic, tso a change of 0.1 pH units his actually represents a significant increase in acidity.
For example, the difference between pH 6 and pH 7 is a 10 fold difference in concentration of hydrogen ion - 10 times more at pH 6 than at pH 7.)
IPCC 2007 predicts that we'll see an average global decrease in ocean pH (increase in acidity) of 0.14 - 0.3.5 pH units over the 21st century as the oceans continue to take up more and more CO2. Recall that carbonic acid is formed as water equilibrates (or attempts to) with CO2 : H2O + CO2 -->H2CO3 (carbonic acid). This is a two way reaction but is currently running towards carbonic acid since CO2 content of the oceans is increasing.
Carbonic acid -- and a corresponding decrease in concentration of carbonate ion -- interferes with carbonate formation, and it happens that carbonate is a major constituent of corals and shelled creatures -- and many plankton. Ocean acidification can both interfere with shell formation, and, potentially can actually dissolve shells.
Experiments have shown that coral growth decreases as acidity increases (Science 13 June 08 and OSU This Week May 29, 08) Carbonic acid has a corrosive effect on aragonite, which is the form of calcium carbonate mineral that forms the shell of many marine creatures. The decrease in pH lowers the saturation state for carbonate minerals such as aragonite and calcite, so they begin to dissolve. The shift in pH is likely to be large enough by 2100 that shells will literally dissolve off the backs of some creatures (BioScience Nov 2007). Marine life has experienced such big and rapid changes in pH of their water only in rare catastrophic events in the geologic past. There is no controversy over the cause of this acidification -- it results from increased CO2 content of the oceans, which results from anthropogenic emissions of CO2 into thr atmosphere.
Some phytoplankton and zooplankton are also suspectible, but some types (phytoplankton called coccolithophores) secrete a form of calcium carbonate (calcite) that isn't as sensitive (see Science 18 April 2008 for details on coccolithophores). IAs I understand it, as CO2 concentration in water increases, the C-source favored by coccolithophores (bicarbonate ion) increases while the availability of carbonate ions, which is the C-source favored by corals and most shell fish, decreases.
(Note potential importance re CO2 sinks in ocean - seems to me like this would decrease the long-term storage of C in shells - except for coccolithophores .)
To move to notes on consequences of climate changes for humans and on policy steps that may be taken, click humans here. To move back to the previous section of these notes (on predictions for global climate changes), click predictions here, and to move to the master Table of Contents for these BI 301 home pages, click Contents. For reminders on how to navigate among and within these pages, click Navigate.
Page maintained by Patricia Muir at Oregon State University. Last updated (partially) Nov. 6, 2008.