Tipping points, and climate futures

I have often been asked "Is it too late?". I interpret this as something like "Are we already past the point of no return?".

We can explore future outcomes:

by modelling, based on our best knowledge of how Earth "works", using our observations of how Earth works currently.
But what if *new processes* kick in when the temperature / $CO_2$ reaches not-yet-reached levels? What "tipping points" are out there?

Climate modelling

Models of increasing sophistication attempt to project into the future.

The models code what we know so far about how Earth works. But what will the humans do?

The IPCC has come up with a couple of different "scenarios (guesses) about what the humans will do for the scientists to put in their models and see what happens:

IPCC scenarios

The IPCC is the International Panel on Climate Change.

A group convened by the United Nations to study climate change and implications.
Includes scientists, but also diplomats and industry representatives.
Their bylaws require that their reports reflect the consensus of the group.

In the 2000 report, and the 2007 AR4 report, they used the following: scenarios A1, A2, B1, B2.

2014 AR5 report used "RCP" (Representative Concentration Pathways) RCPs. The numbers refer to the eventual, stable amount of "radiative forcing" in Earth's atmosphere. This is a measure of "what's the most goose down" we'll have in the "blanket" of GHGs in Earth's atmosphere when emissions stabilize.

According to the IEA's report for 2018 have global $CO_2 (eq)$ emissions begun to slow down yet?

Are we too late for any of those scenarios?

Here is a summary of many model calculations for the different RCPs:

Tipping points

Climate tipping points are sudden (relatively sudden), irreversible changes that have a large impact on Earth's climate.

Here's some good speculation about what tipping points might appear.
A very recent alarm from climate scientists about cascading tipping points [Nature].
"Hothouse Earth" - (Also "Greenhouse Earth") Google icehouse and greenhouse to find about this classification of climates on Earth stretching back to our distant past: Which one are we in right now? What defines whether Earth is in the greenhouse or icehouse state?
See also A cascade of tipping points looms [Yale, e360] is a news story about the Nature article above.

Some of the "tipping points" cited in the study above are new feedback cycles that may not be active yet, but could possibly kick on if temperatures get above a certain threshold, or stay above a certain threshhold long enough.

Because they have not yet happened, it is hard to make precise predictions about tipping points.
And for things like the Amazon, we can observe the loss of forest, but forest loss is not yet due to natural causes, but rather to human causes.

Goshen's emissions

Here is Goshen's emissions inventory

What about Earth's orbit changing...?!

See Milankovitch cycles at IU and on wikipedia

Quiz/test questions

The IPCC

whether human societies will prioritize financial gain, or ecological concerns.
whether there will be more or fewer volcanic eruptions in the next hundred years.
whether Republicans or Democrats are more likely to win control of Congress.
whether countries are more likely to act together, or on their own to address climate change.

What the authority of the IPCC is. Do countries have to obey its reports?

By what authority the IPCC operates.

Who decides (and how) what goes into the IPCC reports.

Temperature and Carbon-dioxide data from the past

have never been as high as they are now.
have been as high as 2-5 times as high as now.
have been more than 5 times as high as now.

So, what is so dangerous about $CO_2$ levels

How we know what $CO_2$ levels and temperatures have been in the recent, and long-ago past.

Where (and why) is $CO_2$ currently being measure?

Roughly what is the current concentration of $CO_2$ in Earth's atmosphere? What was the "pre-industrial" concentration?