"21 thousand years ago, we were all under ice, miles deep. With climate we just don't know what's been triggered, and where the tipping points are."
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Climate change projections often focus on 2100. But the geological record shows that unless we rapidly reduce greenhouse gas emissions, we will be locking in drastic increases in temperatures and sea levels that will alter the earth not just for centuries, but for millennia.
— Why are we so concerned about the long-term threats global warming may pose to the stable climate that has nurtured human civilization over the past 10,000 years? Because by looking at previous eras of high, naturally occurring carbon emissions and cycles of glaciation and deglaciation, we can see what may well be in store for the earth should human-generated carbon emissions continue on a business-as-usual trajectory. And what’s coming down the road in but a few generations will be determined by the inescapable laws of chemistry and physics: Temperature increases lag behind C02 emissions, a crucial fraction of which can persist in the atmosphere for thousands of years. In turn, sea level increases lag well behind temperature increases. The end result is that the world’s oceans can be expected to continue rising for many thousands of years even after temperatures stabilize.
— These possibilities ought to be part of the calculus in decisions about energy, coastal development, and economic policy. Being blind to what the future will look like centuries from now ignores science. Sea level increases will not just miraculously stop in 2100, often our current end-year for forecasting. Indeed, sea level rise may be fast accelerating around then, especially in high-carbon scenarios. Research indicates that steadily accelerating sea level rise is possible and can become unstoppable for millennia because inertia in the climate system is enormous; a 2016 paper in Nature Climate Change, for example, indicated that sea levels could rise, far in the future, roughly 80 to 170 feet.
— Given current trends, keeping to the stated Paris Agreement goal of warming by no more than about 3.6 degrees Fahrenheit (2 degrees Celsius) looks quite unlikely. This is to say nothing of what the world might look like in 2200, 2300, or after, if global temperatures rise 7 to 10 degrees F over today’s levels, a realistic projection given current emissions trends. Such a climate would be scarcely recognizable. Catastrophic storms and vastly higher sea levels aside, temperatures 7 to 10 degrees F hotter than today’s would wreak havoc with the oceans, agriculture, and, in the warmest parts of the world, go beyond human endurance.
Jim |
