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From Changing Landscapes in the Chicago Wilderness Region: A Climate Change Update to the Biodiversity Recovery Plan
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Past, Present and Future Climate Change

Milankovitch Cycles. Source:
Variability has been a natural part of the climate system throughout earth’s history, long before humans played any role in changing the climate. There are a multitude of complex interactions among the earth’s solar orbit (termed the “Milankovitch Cycles”), continental ice sheets, ocean circulation, volcanic emissions and other factors that have historically accounted for different scales and patterns of climatic variation (Bennett, 1990). Climate change refers to long-term scales occurring over many decades to millennia (e.g., 1500-year cold-warm cycles within the most recent glacial period of 74,000–14,000 years bp). This is the scale most relevant to evolutionary adaptation in organisms (Berteaux et al., 2004). On the other hand, shorter-term patterns, such as daily temperature fluctuations or the 2–7 year El Nino-Southern Oscillation cycles, represent what we refer to as weather (NASA, 2005).

Despite the enormous complexities of climate, significant changes have been documented in climate during the past 100 years. It has been reported that warming during the 20th century has resulted in the warmest period during the last 1000 years, with average global surface temperatures increasing by 0.8°C (Trenberth et al., 2007). Warmer temperatures are manifested in a variety of ways, such as nighttime low temperatures increasing more than daytime high temperatures, consequently decreasing the daytime range (Karl et al., 1996). Temperatures in the winter are rising faster than any other season, which can be beneficial to agricultural systems by lengthening the frost-free growing season (Field et al., 2007) while at the same time potentially harmful by increasing survival and reproduction of crop and forest pests (CCSP, 2009).

The International Panel for Climate Change (2007) concludes that this warming is at least, in part, the result of an enhanced greenhouse effect, and the extensive release of greenhouse gases into the atmosphere through human activities has very likely (i.e., probability of occurrence > 90%) played a large role in contributing to it (see probability table). The greenhouse effect occurs when certain atmospheric gases (e.g., carbon dioxide, methane, and nitrous oxide) absorb infrared heat emitted by the earth and, instead of allowing the heat to pass back out of the atmosphere to space, traps it and then emits the heat back toward the earth’s surface. The net result is that the earth warms, which is a natural and necessary phenomenon for life as we know it to exist on earth. However, the concentrations of heat-trapping gases found in the earth’s atmosphere today far exceed historical patterns.

Source: Marian Koshland Science Museum of the National Academy of Sciences.
For example, atmospheric CO2 is 38% higher today than the maximum concentration recorded during that past half million years (385 ppm compared to 280 ppm; Hönisch et al., 2009). In fact, CO2 levels have increased as much since the 1860’s as they did for a period of 10,000 years after the most recent advance of glaciers, a rate of change that is unprecedented in the earth’s recent history (Inkley et al., 2004; IPCC, 2007). Furthermore, greenhouse gas concentrations are expected to continue increasing, as much as 40% worldwide by 2030, if ways are not found to require mandatory emission reductions as the global economy recovers and continues to expand during the 21st century (US Energy Information Administration, 2009). As greenhouse gases in our atmosphere continue to increase, so will our air and water temperatures. Summertime average temperatures are projected to increase by 3.1–7.2°C (best range, extends from the midpoint of the lowest emission scenario to the midpoint of the highest; full range is 2–11.5°F) by the end of the century, leading to dramatic increases in the frequency of heat waves (IPCC, 2007; CCSP, 2009). Warming is expected to be greatest over land and at most high northern latitudes, and least over the Southern [formerly Antarctic] Ocean and parts of the North Atlantic Ocean (IPCC, 2007). There is, however, some evidence from the upper Great Lakes region indicating surface water temperature may be increasing even faster than air temperatures. This situation is thought to be triggering a range of system-wide impacts such as higher wind and current speeds and longer periods of lake stratification in this region (Austin and Coleman, 2007, 2008; Desai et al., 2009; Dobiesz and Lester, 2009).

It will be critical for policy and management guidelines to employ both mitigation as well as adaptation strategies to address climate change. This is because CO2 has a 120-year residency time in the atmosphere (Brasseur et al., 1999), meaning that while we can potentially reduce the magnitude of future climate change impacts through mitigation actions, we still have to adapt to the changes that are occurring as a result of what has already been done to the planet through large-scale industrial practices over the last 150 years.