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The MEC project assesses the activities of the seven sectors (Coasts, Wetlands, Infrastructure, Water Supply, Public Health, Energy Demand, and Institutional Decision-Making) through the use of climate change scenarios. These scenarios are not predictions, but rather descriptions of possible futures, which reflect understandings of the relationships within a climate system. The climate scenarios that are incorporated into the project represent a range of scientists’ best estimates of future climate conditions. These scenarios are developed using historical climate information and projections generated through mathematical models of the global climate system; all scenarios are specific to the New York metropolitan area.


Historical trends of temperature and precipitation over the last century are shown in Fig. 1 below.

Fig. 1. Observed average annual temperatures for the 1900s (oF), averaged over 23 stations in the MEC region. There is variability in the average temperatures of the past century, but there is also an overarching warming trend. The average temperature in the MEC region over the last century has increased by almost 0.2 degrees Fahrenheit per decade. Precipitation levels in the MEC region have increased by an average of almost 0.1 inch per decade over the past century.

Figure 2 reflects a possible future climate if the temperature and precipitation trends were to continue as they have been over the last century, without major changes in the climate system. The Current Trends Scenario does not assume any additional greenhouse gas or aerosol sulfate increases beyond what is implicitly present in the Current Trends Scenario.

Fig. 2. Current Trends Scenario: Projected temperature change (oF), compared to current levels (1961-1990) if the historical trend (1900-present) continues over the 2000s.


Other climate change scenarios are based on projections by global climate models (GCMs). These mathematical models simulate future temperature and precipitation changes in response to projected increases in CO2 and other greenhouse gases. GCMs project climate scenarios on a global scale, from which regional scenarios are extracted. The GCM scenarios used in the MEC study come from two sources: the United Kingdom Hadley Centre (HC) and the Canadian Centre for Climate Modeling and Analysis (CC). The MEC project utilizes the GCM scenarios that are distributed by the US Global Change Research Program (USGCRP) in its mandate for the U.S. National Assessment of the Potential Consequences of Climate Variability and Change for the Nation.

Global Climate Models simulate how climate responds to specific forcings such as changes in greenhouse gases and sulfate aerosols. Two of the scenarios account for the effects of greenhouse gases on the climate: HCGG (Hadley Centre Greenhouse Gas) and CCGG (Canadian Centre Greenhouse Gas). The other two scenarios consider both the greenhouse gases and the sulfate aerosols that are emitted as by-products of industrial activities: HCGS (Hadley Centre Greenhouse and Sulfate) and CCGS (Canadian Centre Greenhouse and Sulfate).

Because greenhouse gases create a warming effect as they trap heat in the atmosphere and sulfate aerosols create a cooling effect as they reflect and scatter solar radiation, the scenarios that incorporate only greenhouse gases forecast higher temperatures than those that include both greenhouse gases and sulfate aerosols.

Through linear interpolation between GCM grid-boxes, climate scenarios were initially obtained for several of the cities in the MEC study region. Because the cities are relatively close to each other, there is little difference between the city forecasts. Therefore, the MEC study decided to use the GCM projections for the mid-point of the study region.


Table 1 compares the bases of the five climate scenarios.
CURRENT TRENDS Projection of historical temperature and precipitation trends (1900-1990)
HCGG Hadley Centre, with forcing from greenhouse gases
HCGS Hadley Centre, with forcing from greenhouse gases and sulfate aerosols
CCGG Canadian Centre for Climate Modeling and Analysis, with forcing from greenhouse gases
CCGS Canadian Centre for Climate Modeling and Analysis, with forcing from greenhouse gases and sulfate aerosols

Figure 3 and Figure 4 illustrate the projections of the five scenarios for the MEC region. These five scenarios provide the range of future possibilities upon which the MEC Assessment bases its research.

Fig. 3. MEC projections of future temperature changes (oF), compared to average (1961-1990) temperatures in the MEC region. HCGG=Hadley Centre Greenhouse Gas; HCGS=Hadley Centre Greenhouse gas and Sulfate aerosols; CCGG=Canadian Centre Greenhouse Gas; CCGS= Canadian Centre Greenhouse gas and Sulfate aerosols.

Fig. 4. MEC projection s of future precipitation changes for the MEC region, as percentages, compared to the current (1961-1990) regional average. HCGG=Hadley Centre Greenhouse Gas; HCGS=Hadley Centre Greenhouse gas and Sulfate aerosols; CCGG=Canadian Centre Greenhouse Gas; CCGS= Canadian Centre Greenhouse gas and Sulfate aerosols.

If the average warming trend that emerges from the past century were to continue over the next century (the basis of the Current Trends Scenario), the average annual temperature for the MEC region would increase by almost 1.0 degrees F by the 2020s, 1.5 degrees F by the 2050s, and over 2 degrees F in the 2080s. If the average precipitation trend from the past century were to continue over the next century (Current Trends Scenario), there would be an average of a 1% increase in precipitation by the 2020s, a 1.6% increase by the 2050s and a 2.3% increase by the 2080s.

The HCGG scenario forecasts future temperature increases of 2.58oF in the 2020s, 4.37oF in the 2050s and 6.25oF in the 2080s. According to the HCGG scenario, the MEC region can expect 5% more precipitation in the 2020s, almost 14% more in the 2050s and 30% more precipitation in the 2080s, as compared to the average precipitation over the past 30 years.

The HCGS scenario projects future temperature increases of 1.68oF in the 2020s, 2.63oF in the 2050s and 6.25oF by the 2080s. The average annual precipitation forecasts from the HCGS scenario are: an 8.63% increase in the 2020s, a 10.37% increase in the 2050s and a 21.57% increase in the 2080s.

The CCGG scenario forecasts average annual temperature increases of 3.45oF in the 2020s, 6.52oF in the 2050s and 10.15oF in the 2080s. The CCGG projects very little change in precipitation over the next century: in the 2020s, precipitation would increase by 9% compared to the average precipitation over the past 30 years. The precipitation levels for the 2050s would be a slight .13% higher than the average for the past 30 years, followed by a forecast of .07% increase in annual precipitation in the 2080s.

The CCGS scenario projects an average annual temperature increase of 2.10oF for the 2020s, an increase of 4.80 oF in the 2050s and an increase of 6.47 oF in the 2080s. These temperature increases accompany projections of precipitation decrease over the century with a 1.40% increase in precipitation in the 2020s, a -15.62% precipitation decrease in the 2050s and a —2.07 decrease in precipitation levels, as compared to the past thirty years.


The five scenarios used in the MEC Assessment vary in the magnitude of the projected temperature changes, but they all follow a warming trend, with the GCM models projecting overall higher temperature changes than the current trend (1900-1990). The Current Trends Scenario’s projected temperature changes are lower than temperature changes projected by the GCM scenarios because the GCM scenarios account for increasing feedback from greenhouse gases that act as forcing mechanisms to warm the Earth’s atmosphere.

While each of the five future scenarios provide a distinct projection of precipitation change, it is important to note that the precipitation projections of the GCM scenarios do not agree either in magnitude or direction (as opposed to the projected temperature changes, which agree in direction, but not magnitude). The Hadley Centre’s scenarios show increasing levels of precipitation while the Canadian Centre projects decreasing precipitation over time.

Through the use of a range of plausible scenarios, the MEC assessment researchers are able to project possible impacts created by climate variability and change as well as to evaluate the MEC region’s responses. An assessment exercise such as the MEC study is useful in enabling preparedness for extreme climate events in the present as well as readiness for a changing future climate.

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