Session 3
NEPC 2011 Annual Meeting, Session 3
What will the Climate be like for our children and grandchildren?
Dr. Howard Skinner, plant physiologist, USDA-ARS Pasture Systems and
Watershed Management Research Unit, University Park, PA
Seven different scenarios showed what would happen with the release of varying levels of CO2 emissions over this century. Two of the scenarios of unbridled release of CO2 released 4 times more over year 2000 levels by the year 2100. One scenario there was a more gradual release of CO2 as some mitigation in combustion of fossil fuels occurred over the next 90 years. Emission of CO2, however, would still be 3 times higher by 2100 compared to year 2000. Two other scenarios caused only a doubling of CO2 emissions by 2100. One provided curbs in lower CO2 emissions immediately while the other did not trigger a reduction in emissions until the year 2050. At that point, the curbs were more drastic from there on out. The other two scenarios were more gradual in their approach to CO2 emissions the first few years out but eventually cut back drastically and actually lowered CO2 emissions to pre-2000 levels of 5 gigatonnes (Gt) [109 metric tons] carbon per year.
Under all 7 emissions scenarios atmospheric CO2 rose. Under the worst scenario of emissions, atmospheric CO2 levels would rise to over 900 parts per million (ppm) by year 2100 compared to 370 ppm in year 2000. The second worst scenario caused atmospheric CO2 to rise to over 800 ppm by 2100, the third to 700 ppm, and the fourth to just under 700 ppm. The 3 most benign scenarios kept atmospheric CO2 levels between 500 and 600 ppm.
As a result of these different levels of CO2 in the atmosphere, there would be a 3º C increase in world air temperatures by the year 2100 under the worst release scenarios of CO2 emissions. Even under one of the scenarios of reduced CO2 emissions, there would still be arise of 1.5º C in world air temperatures. Even if CO2 emissions levels were kept at year 2000 levels, there would be still be a rise in world air temperatures of 0.6º C by the year 2100.
The Earth’s surface has hot spots and cool spots so that the effect of rise in world air temperatures is not evenly distributed. Hence, the newer term, climate change, rather than global warming because even though there will be a general warming trend, it will not occur to the same degree everywhere. Rainfall patterns will remain non-uniform as they always have. However, the impact of climate change will be for rainfall patterns to shift and drought areas to expand from their present norms.
Temperature and rainfall predictions for eastern North America for 2080 to 2099 (based on 21 global models)
Temperature Rainfall
Low Mean High Low Mean High
Season Change º C Change %
Winter 2.1 3.8 6.0 2 11 28
Summer 2.1 3.3 5.4 -17 1 13
Annual 2.3 3.6 5.6 -3 7 15
As seen from the table above for the eastern North America temperatures, the high daily temperature is more affected by increasing atmospheric CO2 levels than is the daily mean or low temperature. The Northeast will have many more days above 90º F by 2040-2069 as compared to 1971-2000, with much of the Northeast having 40-50 days over 90º F. Looking at rainfall, summers will tend to be drier while winters will be wetter. This information is compiled from 21 global models.
The Northeast Climate Impacts Assessment map indicates the Northeast Region will generally be 3º C warmer in the years 2040-2069 compare to the years 1971-2000.
The 2040-2069 yearly growing season will be 4 to 6 weeks longer than it was during 1971-2000. Growing Season Length is the number of days between the last freeze in Spring and the first freeze in Fall. The freeze temperature used is 28º F. Interestingly enough, from a paper cited later by Jack Morgan, any production-enhancing effects of a lengthening of the growing season are small.
The projected change in North American precipitation for the years 2080-2099 is for a much wetter winter in the northern two-thirds of the continent while the southern third much drier. In spring, the much drier area will move northward with the upper half of the continent being wetter while the southern half much drier especially in the Southwest US. In the summer much of the continent will be much drier with very dry areas in the Southern Great Plains and the Pacific Northwest. Fall is the only season with minimal changes to precipitation, although the Great Plains with be drier.
The shift in climate will be pronounced at high CO2 emission levels. Western Pennsylvania is to become similar to northern Alabama weather of 1961-1990 by 2070-2099 and eastern PA similar to southern Georgia using the same time comparisons. New Hampshire will be similar to north central North Carolina around the cities of Greensboro and Winston-Salem by 2070-2099. Even at low emission levels, New Hampshire by 2070-2099 will be similar to northern Virginia of 1961-1990.