Robust

Across the central U.S., very heavy (greater than three inches per day) and extreme (greater than six inches per day) precipitation events increased in the period from 1979 to 2009 compared to the 1948 to 1978 period. Model projections for the central U.S. suggest a potential increase in these events, especially during winter months. Other future climate projections indicate that the Midwest may experience two to four more days of extreme precipitation by the end of the century.

Mean annual precipitation is projected to only increase by 0.7 inches under the GFDL A1FI scenario for the final 30 years of the 21st century compared to the 1971 to 2000 baseline. By contrast, annual precipitation is projected to increase under the PCM B1 scenario by an average of 3.8 inches. Changes in precipitation are projected to vary greatly by season. Both models project an increase in precipitation in winter and spring. They differ in projections for summer and fall. PCM projects an increase of 1.8 inches, while GFDL projects a decrease of 5.8 inches in summer.

Mean annual daily temperature across the region is projected to increase by 8.2 °F (4.5 °C) under the GFDL A1FI (high emissions) scenario and 2.3 °F (1.2 °C) under PCM B1 (low emissions) for the final 30 years of the 21st Century compared to the 1971 to 2000 baseline. The most dramatic increase in temperature is projected to be in winter for the PCM B1 scenario and summer for the GFDL A1FI scenario. No spatial variation in temperature changes across the Chicago Wilderness region is discernable.

All global climate models agree that sea level will rise. Sea levels have increased over the past century, and this trend is expected to continue. Additional warming is expected to increase global sea levels by up to 1m (3 ft) by the end of the century. In the Mid-Atlantic, sea-level rise is significantly greater than observed global sea-level rise, due to sinking of the land surface as it adjust to the melting of former ice sheets and the withdrawals of natural resources from underground.

Heavy precipitation events have increased substantially in number and severity in the across the Northeast over the last century, and many models agree that this trend will continue over the next century. Under the higher scenario (RCP8.5) the number of extreme events is projected to increase by two to three times the historical average in every region by the end of the 21st century, with the largest increases in the Northeast. Under the lower scenario (RCP4.5), these events are projected to increase by 50%–100%.

Seasonal differences in temperatures across the Mid-Atlantic and Northeast have decreased in recent years as winters have warmed three times faster than summers. By the middle of this century, winters are projected to be milder still, with fewer cold extremes, particularly across inland and northern portions of the Northeast. Warmer temperatures are expected to cause more winter precipitation to be delivered as rain. Snowfall, snow depth, and snow pack are all expected to be reduced.

Evidence at both global and local scales indicates that growing seasons have been getting longer, and this trend is projected to become even more pronounced over the next century. Warmer temperatures will result in fewer days with minimum temperatures below 32°F and a shorter freeze-free season. Winter or early-spring warmth has caused plants to start growing and emerge from winter dormancy earlier in the spring.

Temperatures in the Mid-Atlantic region (and across the broader Northeast) are projected to increase on average by 5.27 to 9.11 °F by the end of the century (2070 to 2099), with the greatest warming expected to occur during summer and fall. More warming (9.11 °F) is projected under a high climate scenario (RCP 8.5) and more moderate warming (5.27 °F) is projected under a moderate climate scenario (RCP 4.5).

Climate models under a high emissions scenario indicate temperatures will increase by 4.5F° to 10°F by the end of the century, whereas climate models under a low emissions scenario project temperature increases from about 3°F to 6°F by the end of the century.

Evidence at both global and local scales indicates that growing seasons have been getting longer, and this trend is projected to become even more pronounced over the next century. As seasons shift so that spring arrives earlier and fall extends later into the year, phenology may shift for plant species that rely on temperature as a cue for the timing of leaf-out, reproductive maturation, and other developmental processes. Longer growing seasons could also result in greater growth and productivity of trees and other vegetation, but only if balanced by available water and nutrients.