Yesterday, I posted about observed water temperature increases at the Buffalo Water Treatment Plant site. To remove the seasonality from the data (and to better discern long-term trends), I converted all of the data since 1960 to an annual departure. The departure given for each year is relative to the average of a 1960-2012 base period. So far, 2012 has averaged 2.8C above the mean for the 1960-2012 period. The current warmest year on record is 1998 at 1.8C above the mean. The average annual water temperature has been increasing at 0.29C per decade since 1960.
Figure 1. Average annual water temperature departure at Buffalo, NY, 1960-2012. Note the steady trend towards warmer water temperatures.
Perhaps more stunning is the decrease in number of days with a water temperature of 32F during that period. These readings are taken 35′ below the surface, so when the surface is covered or substantially covered in ice, the water temperature is usually 32F. The chart shows that the annual number of 32F readings has been decreasing at a rate of more than 1 day per year! In recent years, the rate of change appears to be increasing. Both 2012 and 1998 had 0 such days, while 2002 had just one. By contrast, 1964 had 139 days, and 1971 138 days.
Figure 2. Number of days with likely ice cover per year, 1960-2012.
These graphics show an umistakable warming of the Lake Erie climate system. As the region continues to experience warming, winter ice coverage will continue its marked decline. The decrease in ice cover will itself greatly affect the climate of surrounding areas. This will be accomplished by two means: (1) the warmer, open waters will better modify arctic airmasses moving southeast from Canada; and (2) the warmer, open waters will contribute to increased cloudiness & precipitation, which will make conditions less favorable for extreme cold.
This effect is already apparent in data from observation sites downwind of the Great Lakes. I took a look at the coldest minimum annual temperature at the Youngstown-Warren Regional Airport in northeast Ohio. As a native of the area, this should be a good site to conduct this analysis, as it is a small airport with minimal traffic and little, if any, contamination from surrounding land use over the period being considered.
In the 1960s, the average minimum temperature was -8.0F; in the 1970s, -8.6F; in the 1980s, -11.3F; in the 1990s, -3.2F; in the 2000s, -2.3F; and in the 2010s, +0.0F. As you can see, the trend is definitely up, with fewer days of extreme cold. The USDA plant hardiness zone maps illustrate this to some extent, but they are already obsolete. According to the most recent update, released just last year and based on data compiled from 1976-2005, this area is in zone 6a, with an average minimum temperature between -5 and -10F. In the last 15 years, however, the actual average minimum temperature is just -1.2F, well within zone 6b (almost nearing the threshold of 0F for zone 7!). In fact, in the 2010s, the average minimum temperature is just 0.0F. This is based on just three years; nonetheless, it does include data from two (allegedly) “bitter” cold winters (2009-10 & 2010-11). In fact, those winters were not particularly cold and would have been milder than most winters in the 60s, 70s, & 80s.
Figure 3. Mean extreme annual minimum temperature at Youngstown-Warren Regional Airport, Vienna Twp., OH, 1960-2012.
Closer to Lake Erie and in more urbanized areas, zone 7 temperatures are already evident. Since 1998, the average minimum temperature at Cleveland Hopkins International has actually been above 0F. While the official USDA plant hardiness map classifies no part of Ohio as zone 7, the more recent data from CLE and elsewhere on the Lake Erie shoreline suggests this may no longer be the case. For gardeners, this means you can probably begin experimenting with different plants that traditionally would not grow in northern Ohio and surrounding areas. If current trends continue, much of northeast Ohio, will likely be zone 7 by the 2020s. Should warming continue to increase in rate, as projected, and ice coverage continue to decline over the Great Lakes basin, the effects may be even more substantial. By mid to late century, I wouldn’t be surprised to see zones 8 or even 9+ begin to appear.
You seldom hear much about the actual effects of global warming or how global warming will manifest itself on the local or regional scale. This is how it will do so. Models project up to 6C of globally-averaged warming within the next century under a high emissions path, which would likely result in 9 or 10C of warming at mid-latitude landmasses, such as the Great Lakes region. Warming lake temperatures will provide a local positive feedback, particularly during the cold season. On a high emissions path, the subtropics will creep northward to encompass the majority of the Great Lakes region. In the far southern extent of the region, freezing temperatures may become the exception, rather than the rule during the winter months.