Dropping cause it’s hot: On climate change & Great Lakes levels

Falling Great Lakes levels have garnered a considerable amount of media coverage in the past few days. First, the New York Times featured a full-length piece on the issue on Monday, and The Plain Dealer followed up yesterday with a piece focused primarily on Lake Erie.

As the Times piece notes, the average monthly mean for the five lakes during this past winter reached its lowest level since officials began taking measurements in 1918. For Lake Erie, 2012 was the first year on record that water levels fell during every month.  According to the 2009 National Climate Assessment, the maximum ice coverage in the Great Lakes decreased by roughly 30% from 1973-2008. The prolonged winter and extremely wet spring this year is beginning to counter the effects of last year’s record drought, but these changes are clearly part of a long-term trend, which one season or  one year worth of precipitation cannot change.

Current lake levels, compared to long-term averages, for (left to right) Lakes Michigan & Huron, Lake Erie, and Lake Superior (courtesy of NOAA GLERL).

Current lake levels, compared to long-term averages, for (left to right) Lakes Michigan & Huron, Lake Erie, and Lake Superior (courtesy of NOAA Great Lakes Environmental Research Laboratory).

Both pieces noted the causes and likely effects of these changes for the Great Lakes region. By and large, however, they focused on the role of dredging. From the Times piece:

A measure of the drop in water levels can also be attributed to the engineering that makes Great Lakes shipping possible. The 1962 dredging of the St. Clair River may have lowered the water in Lake Huron and Lake Michigan by five inches, said John Nevin…Other dredging projects may have emptied 16 inches in all from the lakes, Mr. Nevin said.

In the comments section on his piece, Robert Smith, the PD reporter who covered the story, explicitly noted that he was focusing on dredging. Clearly dredging matters, and it will continue to into the future. It is a complicated issue, however, as it costs a considerable amount of money and is controlled by action from the Army Corps of Engineers and the US Congress, who appear to be engaged in a fight over who bears the burden for the issue.

The effects of the drop in lake levels will continue to take a significant toll on the Great Lakes. According to the US Department of Transportation (PDF), every 1″ drop in lake levels reduces the cargo capacity of a 1,000-foot bulk carrier by 270 tons. Given that the Great Lakes maritime trade industry is worth $34 billion annually, any long-term reductions in lake level will significantly hamper the regional economy.

Unfortunately, that’s precisely what climate models project. While neither piece directly addressed the issue (though the Times article does mention it in passing), climate change is likely to add to any natural and direct anthropogenic impacts on lake levels. As the Union of Concerned Scientists has noted (PDF), higher air temperatures contribute to the reduction of lake levels in two main ways. First, they will continue to reduce the extent of lake ice cover during the winter months, which provides a crucial buffer against surface evaporation on the open water. Secondly, higher surface temperatures themselves lead to greater rates of surface evaporation.

Projected changes in lake levels on the Great Lakes according to the Canadian global climate model (courtesy of the Second National Climate Assessment).

Projected changes in lake levels on the Great Lakes according to the Canadian global climate model (courtesy of the Second National Climate Assessment).

According to the First National Climate Assessment, mean annual temperatures in the Midwest are expected to increase by 3-6°C (5-10°F) by the end of the century. These changes will lead to wholesale climatic shifts in the region. According to the World Bank (PDF), in a 4°C warmer world (which, as I’ve noted, is becoming increasingly likely), the coolest months in the Central US by 2070 will be significantly warmer than the warmest months today. Even as early as 2030, summers in Illinois are projected to resemble current summers in Oklahoma.

As such, the effects of rising temperatures will likely outweigh projected increases in regional precipitation, contributing to the long-term decline of lake levels. The First National Climate Assessment projected a 5-6 foot drop in lake levels for all five of the lakes, while the Second Assessment (2009) revised these down to 1-2 feet, depending on the climate model used. Regardless of the projection, these declining lake levels will significantly increase the cost of shipping (PDF) on the Great Lakes by as much as 30%.

While we should be careful to neither attribute all ecological changes to climate change nor to blame direct anthropogenic environmental changes on the effects of climate change, it’s not wise to treat them as completely distinct phenomena. Climate change is currently adjusting the baseline for all weather-related phenomena; we have already forced global atmospheric concentrations of CO2 to their highest levels in human history and increased global average temperatures by roughly 0.8-1°C. Anthropogenic environmental changes and climate change will interact with one another and almost certainly create multiplicative effects over the next several decades. We need to recognize as such.

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