CRUNCH TIME: Part Two

WARMER...THEN COOLER seems to have been the pattern of climate change. How could this be? We have seen that climate change can be non-linear. The earth cannot not just keep on gradually getting warmer because, once heat radiated exceeds heat received, the temperature will drop at some point to ensure equilibrium. How this might come about is an intriguing question.
In the meantime, much of the worry about the 'green house' effect appears to be related to the rise in sea levels as the Greenland ice sheet and, to a lesser degree, the Antarctic ice sheet melt. The ice sheet over Greenland is up to two miles thick; should it melt completely folk living near the coast would have enormous problems, not to mention huge loss of agricultural lands.
Burning fossil fuels, especially over the last 60 years, has dumped lots of carbon dioxide into the atmosphere while de-afforestation has removed significant carbon sinks. According to The Guardian (May 12), "Scientists at the Mauna Loa observatory in Hawaii say that CO2 levels in the atmosphere now stand at 387 parts per million (ppm), up almost 40% since the industrial revolution and the highest for at least the last 650,000 years." In addition, some scientists worry that methane currently locked up in sub-arctic tundras will be released as these areas unfreeze, adding more greenhouse gas.
Serious as gradual sea level rise will be, a more serious, precipitous outcome is in the offing. Fresh water melt from Greenland enters the north Atlantic just about where the cooled, saltier water of the Gulf Stream begins to sink to the ocean depths to turn southward. Large volumes of fresh water melt drawn into these gyres and mixed with the more saline current, have the capacity to prevent the downward sinking by lessening local sea water density. Depending on volume, this could slow or stall the great ocean conveyor. This would produce a succession of colder European winters and summers leading to widespread crop failures. It would also cause the ice sheets to begin to regenerate, adding another factor to the cooling trend.
A cooler Arctic region, coupled to the now relatively much warmer equator would accelerate the climate engine. The jet streams in the Northern Hemisphere would speed up and move more northerly, bringing wild weather and drought conditions where we now expect to grow crops. During the Little Ice Age, Europe experienced famine due to crop failures but this may have been somewhat reduced by the plagues.
Remember that, prior to the Twentieth Century, most people ate food produced locally, a large proportion of folk being employed in agriculture. Nowadays, in developed countries, just a few farmers produce food for the rest of us (ratio: one farmer per 70 or more non-farmers) and food is transported many hundreds of miles before we purchase it. Widespread crop failure, in conjunction with high transport costs, could prove catastrophic for millions.
Our most pressing concern may therefore be a sudden increase in the melt rate of the Greenland ice sheet dumping enough fresh water into the sea around Greenland and Labrador to stop the Great Ocean Conveyor.
Could continued extravagance in burning fossil fuels bring that about? You can bet your life on it! But then, we are betting somebody's life on it, are we not?