FINAL REPORT - International Joint Commission

FINAL REPORT
Climate Change Analysis
Four climate change scenarios were also used to test the plans to ensure that none of the candidate plans
would fail the Board’s guidelines under the potential change in climate that is predicted to occur due to
increased greenhouse gases in the atmosphere. No one knows for sure how this change in the climate will
affect water supplies, but generally warmer temperatures and increased precipitation are expected in the
Great Lakes–St Lawrence River basin. The amount of climate change will depend on the quantity of
greenhouse gases that accumulate in the atmosphere in the coming decades, and how quickly they build up.
In addition to this uncertainty in future greenhouse gases, the complexity of the earth’s climate system limits
scientists’ ability to completely model these changes. Nonetheless, several global climate models (GCMs)
have been developed to simulate the changes that might be expected under different assumptions about the
magnitude of future greenhouse gas increases. Each of these GCMs differs somewhat in how it models
the complex interconnected processes that are taking place in the atmosphere, the oceans and on land and
that affect climate. Recognizing this uncertainty in both future greenhouse gas amounts and the results of
different models, the Study Board asked that four different climate change scenarios be selected: the most
warming and wettest conditions, the least warming and wettest conditions, the most warming and driest
conditions and the least warming and driest conditions. Details about the selection of the GCMs and
greenhouse gas assumptions are reported in Mortsch et al (2004).
The four climate scenarios were labeled: warm and dry (C1); not as warm but dry (C2); warm and wet
(C3); and not as warm but wet (C4). The changes from base temperature, precipitation, humidity, wind
speed and solar radiation for each of these four scenarios were used to adjust the historical recorded
series of these properties of the climate. These changed climate series were restricted to 37 years in
length because of the limited available recorded values of these parameters in parts of the study area.
These 37-year climate sequences were then used as inputs to the hydrologic models to produce estimates
of potential future water supply conditions under the four possible climate change scenarios. Since the
supply sequences run for only 37 years, and the Shared Vision Model was set up to use 101-year-long
sequences, the 37-year sequences were repeated to fill in the 101 year sequence. This process lends an
artificial repetitive nature to the resulting supplies, as shown in Figure 46. As a result, the Plan Formulation
and Evaluation Group did not run the Integrated Ecological Response Model for the climate-change sequence
because the repetition of the 37-year supplies would have misrepresented the wetland plant calculations,
which are driven by flooding history. So only the economic damages are presented for climate change.
Figure 46: Five-year moving average of the net total supply (NTS) sequences for the four climate
change scenarios (C1-C4)
78 Options for Managing Lake Ontario and St. Lawrence River Water Levels and Flows