Double Atmospheric CO2 (Which We're On Track For) And The Best-Case Outcome Is A 4.7F Increase

[hatrack]

EDIT

Climate scientists have been trying to narrow down how, exactly, the climate will respond to increasing levels of carbon dioxide (CO2) for well over a century. We call this “climate sensitivity” — in essence, how sensitive the climate is to our emissions. In 1979 a major report suggested that global surface temperatures would ultimately rise somewhere between 2.7 and 9.1 degrees Fahrenheit (1.5 and 4.5 degrees Celsius) if the amount of CO2 in the atmosphere was doubled. Thirty-five years later, the Intergovernmental Panel on Climate Change gave the same range in their most recent assessment report.

A four-year effort led by 25 experts in the field has finally been able to give us a better understanding of how sensitive the climate actually is. By combining lines of evidence from physics-based studies, historical temperature records and records from the Earth’s more distant past — such as during the last ice age — we find that if the amount of CO2 doubles in the atmosphere, the world will likely warm between 4.7F and 7F (2.6C and 3.9C).

Such warming may not sound too bad — after all, what difference does a few degrees make? A lot, it turns out. If we go back to the depths of the last ice age, 20,000 years ago, we find that the global average temperature of Earth was only about 9F (5C) colder than today. That was enough of a difference to lower sea level by 300 feet and build up ice sheets thousands of feet thick covering much of North America. That Earth was basically a different planet.

We now know that a worst-case scenario of high future emissions and high sensitivity risks warming comparable to the warming since the end of the last ice age, occurring over the next one or two centuries. That would impose extremely difficult challenges to human society and natural ecosystems.

It is not inevitable that we will double carbon dioxide in our atmosphere — we control whether we do better or worse than that. We can cut our emissions rapidly enough to avoid doubling CO2 this century, given the political will to do so, and still limit warming below the internationally agreed-upon guardrail value of 3.6F (2C). Alternatively, if our emissions continue increasing, we could end up tripling rather than just doubling atmospheric CO2 by the end of the 21st century. How much warming occurs is up to us, and by narrowing the range of climate sensitivity, we now have a better idea of the consequences of our actions.

EDIT

https://thehill.com/opinion/energy-environment/509095-study-rules-out-catastrophic-scenarios-from-global-warming-but-the

[Boomer]

1. It is not inevitable that we will double carbon dioxide in our atmosphere

Not inevitable in the most literal sense of the word, but pretty damn likely based on the evidence of human behavior.

[hatrack]

2. 3 ppm/year (more or less) and in the absence of actual reductions, just a matter of time

.

[NickB79]

3. If we factor in other GHG's, we're almost there already

Our CO2e is pushing 600 ppm by some estimates, given how much methane, nitrous oxide, etc, has vented in recent years.