When it comes to global warming, what else don’t we know? What science does know, and what it can infer from studying archaeological records, already makes anybody who thinks the long-term habitability of earth is more important than short-term profits very worried.
One detail that may have been under-appreciated is meltwater. Melting ice sheets, especially in Greenland and Antarctica, is well understood to raise the sea level. But the effects might not be simply the additional water added to the oceans. In this scenario, the melted freshwater will additionally increase warming, thereby creating a feedback loop that will accelerate the loss of polar ice sheets, thus accelerating the rate of sea-level rise. How fast? Fast enough that the sea level could rise ‘several meters’, possibly six to nine meters, in 50 to 150 years.
Predictions of a future catastrophic rise in the oceans, threatening to drown many of the world’s biggest cities, are by now far from novel. Two other recent papers conclude that humanity has already committed itself to a six-meter rise in sea level because of the greenhouse gases already thrown into the atmosphere and the retention and later slow release of much of those gases by the world’s oceans. A study in the journal Science estimates that more than 444,000 square miles of land, where more than 375 million people live today, would be inundated by such a rise.
Compare that to the complacency of the world’s governments at the Paris Climate Summit in December 2015. Despite a thunder of plaudits from the corporate media, the governments committed themselves to goals that, even if achieved, would lead to a global temperature rise of nearly 3 degrees Celsius by 2100, with further increases beyond that. That is far beyond the goal of 1.5 degrees set at the summit. But even the summit’s actual modest goals are not necessarily attainable because peer pressure is the primary mechanism to induce compliance; there are no binding legal agreements.
The Atmospheric Chemistry paper says that sea level was at times six to nine meters higher than today approximately 115,000 years ago when the average global temperature “probably was only a few tenths of a degree warmer than today”. Ice-sheet stability may be a key to understanding rapid sea-level rise, the authors write.
The injection of added freshwater into the oceans from faster ice-sheet melting reduces the mixing of ocean waters, causing warmer water to remain at lower depths and thus making warmer water more available to melt the remaining ice shelves.
As a consensus for global warming emerges, there is less certainty that capping global temperature increase at 2 degrees would be ‘safe’; thus the Paris Climate summit’s surprise conclusion to set a goal of a 1.5-degree limit. To achieve such a goal, however, would, as noted above, require cuts to greenhouse-gas emissions far beyond anything pledged. The studies indicating that humanity has already committed itself to a six- to nine-meter sea-level rise imply that temperatures will rise past 1.5 degrees as greenhouse gas-generated heat trapped by the oceans is slowly released into the atmosphere over many decades, if not centuries.
There is no alternative to a massive change to industrial activity – no amount of re-forestation can come close to cancelling out the effect of industrial activity. Unfortunately, we live in an economic system that requires constant growth and offers no alternative work for those whose jobs would be eliminated were we to shut down the most polluting industries.
This article has been excerpted from: ‘No planet for optimists: coastal flooding may come sooner than we fear’.