Global climate and CO2 have changed in the past naturally. How do we know we are responsible?

Isotopic ratios between C12 and C14 indicate fossil fuel combustion is the source of increasing CO2 concentration.

The half life of C14 is 5,730 years. Fossil fuels were formed millions of years ago. C14 in them will have decayed. If increasing carbon dioxide in the atmosphere is due to fossil fuel combustion, rather than some sort of natural change in current source-sink relationships, then the isotopic ratio should have changed over time due to the release of carbon with an enormously reduced C14 content. The reduced ratio is called the Suess effect. It is clearly evident.

What are the predicted biological impacts of the changes associated with global warming, and are some of these changes already apparent?

Hughes (2000) argued that changes are evident, and presented some of the patterns evident and expectedfrom global warming.

1. Plant growth physiology changes in increased CO2 atmospheres. Generally, growth rates increase, and warming lengthens the growing season for plants. The density of stomates decreases in many species, since fewer openings are necessary to take in sufficient CO2.

2. Species distributions change. Population sizes of native vascular plants on Antarctica have increased dramatically (by ~25x) from 1964-1990. Treelines have moved upward along mountain slopes since the turn of the 20th century. The ranges of non- migratory European butterflies have generally shifted northward by 35-240 kilometers (22 of 35 species, only 2 shifted southward). A number of meta- analyses indicate the extent of range shift. Parmesan participated in one of these, and found an average of 6.1km poleward shift per decade among 1700 species.

Birds have extended their distributions northward. In Britain, 59 bird species from the southern portion had extended distributions northward by an average of 19 km over 20 years (1968-72 compared with 1988-91).

3. Life cycles and the timing of critical seasonal events have changed. Egg laying in insects and birds, flowering and seed set in plants typically occur days earlier (an average of 2 days/decade in one study, 5 days in another).

Development may occur more rapidly, particularly in insects. Initial flight in holometabolous species (e.g. Lepidoptera) may occur earlier.

Whole communities may be affected. One example is the basis from which a whole discipline in ecology has grown – macroecology.

Loss of diversity of boreal small mammals from montane forests of the isolated mountain ranges in the Great Basin of the western is predicted in the U.S. (Brown 1995, 1998). A model of the loss was developed based on a doubling of CO2 and a 3o rise in average temperature. Boreal woodland will move up the mountain by 500m. That significantly decreases the habitat area available to the small mammals.

Using species-area relationships for these species that Brown had determined earlier, he was able to predict species losses on each of 19 mountain ranges.

Here is the diagram he used to portray the changes:

Brown is not alone in making this type of prediction. Here is the predicted vegetation change in the San Francisco Peaks of northern Arizona – note the total loss of alpine tundra at the highest elevations and a significant compression of spruce/fir forest that will (according to prediction) come to occupy the peaks.

Range shifts are also predicted for tree species of the Great Lakes region. Zapinski and Davis (1989, described in Brown 1998) determined that a number of Great Lakes area tree species had northern limits corresponding to the -15ºC January isotherm. They used the last post-glacial period to estimate the rate at which tree species could migrate, using an artificially high estimate of 100 km/century. Distributions on the next slide show the current distribution on the left, predicted distribution for the end of this century on the right. The gray area indicates the long-term potential distribution given sufficient time for dispersal into new areas.

It was possible to make those predictions because palynology has demonstrated how rapidly tree species moved after the Wisconsin glaciation. The migration patterns (with one portion erroneous) are in a figure from the text:

The effects of global warming will not be uniform over the earth’s surface (as well as the ocean depths). The method of predicting changes is to use GCM – General Circulation Models – that typically have two main components: atmospheric circulation models and ocean circulation models.

What sorts of information go into the components of the GCMs?

A(tmospheric)GCMs consist of a dynamical core which integrates the equations of fluid motion, typically for:

1. surface pressure 2. horizontal components of velocity in layers 3. temperature and water vapor in layers

Radiation input is generally split into solar/short wave and terrestrial/infra-red/long wave energy.

All modern AGCMs include parameterizations for:

1. convection 2. land surface processes, albedo and hydrology3. cloud cover

From all this come prognostic equations that are stepped forward in time and predict typically winds, temperature, moisture, and surface pressure.

Oceanic GCMs (OGCMs) model the ocean (with fluxes from the atmosphere imposed) and should contain a sea ice model.

Coupled atmosphere-ocean GCMs (AOGCMs) (e.g.HadCM3, GDFL CM2.X) combine the two models. These models are the basis for sophisticated model predictions of future climate, such as are discussed by the IPCC (International Panel on Climate Change).

Here is a compact diagram of what the models generally predict: