Anthropogenic global warming (climate change) is a grave existential threat. Climatologists haven’t adequately articulated the threat to convey the urgency of this crisis. They will list the consequences of global warming in broad strokes; the anticipated rise in sea level, increased frequency of hurricanes, droughts, and floods, following a doubling of preindustrial levels of atmospheric CO2. But a cognitive dissonance persists because many people can’t reconcile the scope of tragic consequences with what they perceive as a meager rise in global average temperatures. They may say, “But it’s only a four degree rise in temperature over the next eighty years.” Many people can’t comprehend why a four degree rise in average global temperatures would be so catastrophic.

In the absence of substantive mitigation, implemented on a global scale, the minimum anticipated warming by century’s end is 4.3 degrees Celsius. So the numbers climatologists typically supply the media are in Celsius degrees.   This 4.3 number is equal to 8 degrees Fahrenheit. Also remember, these figures are the low end of possible scenarios envisioned by a consensus of climatologists that directly study climate and climate change. You may still be saying ” But it’s only 8 degrees, we can easily adapt”.

Climate change is not uniform geographically. Some regions have far greater vulnerability than other areas. The arctic has roughly three times the climate sensitivity than the global average. So with each one degree rise in global average temperatures, the arctic can expect a three degree rise. The interior of continents in the mid-latitudes have about double the sensitivity as the global average. So, that 8 degree Fahrenheit rise in global average temperatures becomes 16 degrees Fahrenheit where most readers of this post live. Some of you might still be saying that with just a little effort human populations can adapt to this level of warming, as if we are disconnected from the natural world.

It gets worse, much worse. It’s not the rise in average temperatures that kill you. It’s the extreme temperatures superimposed atop the rise in the average that kills you, and wipes out whole ecosystems.  Anthropogenic global warming doesn’t mean day to day weather variability “goes away”. It doesn’t mean that the seasons end. It doesn’t change the tilt of the Earth’s axis from 23.5 degrees with respect to the plane of the solar system. There will still be days in which the temperatures are as much as 20 degrees above or below average, just as occurs today. But I mean 20 degrees above or below the “NEW“, 16 degree higher average likely to exist at the conclusion of the 21st century.

So, what might this mean? Selecting a few cities in the interior of the United States can highlight the brutal consequences of a “business as usual”, no mitigation future. The historical average July temperature in Kansas City, MO is 91 Degrees. The average July and August temperature in Wichita Falls, TX is 97 degrees.  Now recognizing that these two locations will experience a rise in temperature that is double the global average, the new average mid-summer high temperatures for Kansas City and Wichita Falls are 107 degrees and 113 degrees respectively! But like I said before, it’s not the rise in the average that kills you, it’s the extremes superimposed atop the new, higher average that kills you. Once every ten years or so, Kansas City can expect to have at least one day each summer where the high temperature reaches 105 degrees. People and wildlife generally survive this 14 degree short term departure from the norm. Now, let us add 14 degrees to the expected increase in the average temperature by the end of the century: 107+14=121 degrees.  At this temperature, and with the high temperature immediately before and after this event likely to be only a few degrees cooler, wholesale ecological collapse will occur. Wholesale agricultural collapse will occur as well. Wildlife, vegetation, grazing ruminants, can’t retreat to air conditioned rooms. They die. And though humans can retreat to the safety of air conditioned rooms, it is only a reprieve. Humans are NOT separate from nature, we are intimately intertwined with nature. As nature goes, so do we, only delayed slightly. Nature bats last.

Civilization depends upon stability. Anthropologists believe that the end of nomadic ways of life, the agricultural revolution, and the rise of city-states are at least in part due to the stable climate Earth had experienced from the end of the Pleistocene about 10,000 years ago, until recently. Warming is now occurring at around 100 times the rate at which Earth came out of the last glacial maximum. A sixth mass extinction event is now a near certainty in the absence of some magical tehno-fix. This doesn’t justify inaction. Action now can mean the difference between 20% or up to 95% extinction over the next few centurys, depending on how long it takes us to get serious about climate change mitigation. So everyone, 4 degrees is a very big deal.