[m_mueller]

Here's a hint: 12 to 16 degrees of warming spaces out over 100 to 1000 years (why so unprecise? because we haven't got a good grasp of the incredibly complex machine with lots of explosive outcomes we're currently toying with - we can only infer from our best models, and the more precise they get, the worse the predictions become). That's 4 to 8 degrees because of our own greenhouse gases and an estimated additional 8 degrees from runaway warming effects that are getting triggered somewhere between +2 and +6.

Hint: That's 12 to 16 global average temperature increase. Ice age was only 4 degrees colder than now. 12 to 16 creates a desert planet. If I had to bet what brings humanity at least to the brink of extinction, it would be this.

There's basically one way out that's still realistic: Creating a more reflective atmosphere. But we only have one shot at this. I'm afraid that when +4 degrees already create utter chaos from rising sea levels, hurricanes, landslides and the following mass migration, the one shot won't be aimed well - it will be done by politicians pressured by screaming masses.

[pdonis]

> 12 to 16 degrees of warming spaces out over 100 to 1000 years

Where are you getting those numbers from?

[dredmorbius]

IPCC expressed in Farhenheit. 12°F == 6.7°C.

[dredmorbius]

I don't know, I haven't been following the IPCC closely.

However their latest executive summary is here:

http://report.mitigation2014.org/spm/ipcc_wg3_ar5_summary-fo...

"Without additional efforts to reduce GHG emissions beyond those in place today, emissions growth is expected to persist driven by growth in global population and economic activities. Baseline scenarios, those without additional mitigation, result in global mean surface temperature increases in 2100 from 3.7 °C to 4.8 °C com- pared to pre-industrial levels10 (median values; the range is 2.5 °C to 7.8 °C when including climate uncertainty, see Table SPM.1)11 (high confidence). The emission scenarios collected for this assessment represent full radiative forcing including GHGs, tropospheric ozone, aerosols and albedo change. Baseline scenarios (scenarios without explicit additional efforts to constrain emissions) exceed 450 parts per million (ppm) CO2eq by 2030 and reach CO2eq concentration levels between 750 and more than 1300 ppm CO2eq by 2100. This is similar to the range in atmospheric concentration levels between the RCP 6.0 and RCP 8.5 pathways in 2100.12 For comparison, the CO2eq concentration in 2011 is estimated to be 430 ppm (uncertainty range 340 – 520 ppm)13. [6.3, Box TS.6; WGI Figure SPM.5, WGI 8.5, WGI 12.3]"

[pdonis]

Didn't that number (which is the extreme upper end of the predicted range for the most extreme scenario the IPCC considered, and so not really the right number to quote anyway) get lowered in the AR5, to something like 4.8 degrees C?