Thread by @Sustainable2050

Reading IPCC's Special Report on The Ocean and Cryosphere
in a Changing Climate (#SROCC), published last week. You can find it here: ipcc.ch/srocc/home/

@IPCC_CH Less known than ice loss:
Snow cover is already shrinking too.
"Arctic June snow cover extent on land declined by 13.4 ± 5.4% per decade from 1967 to 2018, a total loss of approximately 2.5 million km2, predominantly due to surface air temperature increase (high confidence).

In nearly all high mountain areas, the depth, extent and duration of snow cover have declined over recent decades, especially at lower elevation (high confidence)."

"Permafrost temperatures have increased to record high levels (1980s-present) (very high confidence) including the recent increase by 0.29°C ± 0.12°C from 2007 to 2016 averaged across polar and high mountain
regions globally."

"Arctic and boreal permafrost contain 1460–1600 Gt organic carbon, almost twice the carbon in the atmosphere (medium confidence)."

"There is medium evidence with low agreement whether northern permafrost regions are currently releasing additional net methane and CO2 due to thaw. Permafrost thaw and glacier retreat have decreased the stability of high-mountain slopes (high confidence)."

Note that it's unclear whether thaw (definitely happening) of permafrost is already contributing to net methane and CO2 release to the atmosphere, contrary to what you sometimes read. It's complicated; try reading section 3.4.3 to get an impression.

"Between 1979 and 2018, Arctic sea ice extent has very likely decreased for all months of the year.
September sea ice reductions are very likely 12.8 ± 2.3% per decade. These sea ice changes in September are likely
unprecedented for at least 1000 years."

"Arctic sea ice has thinned, concurrent with a transition to younger ice: between 1979 and 2018, the areal proportion of multi-year ice at least five years old has declined by approximately 90% (very high confidence)."

"Feedbacks from the loss of summer sea ice and spring snow cover on land have contributed to amplified"warming in the Arctic (high confidence) where surface air temperature likely increased by more than double the global average over the last two decades."

And now for the hard part, the future ;)
I split IPCC's summary graph in two, since it just has too much information. First the top half:

All those graphs show historical (brown, purple) and calculated future (blue, pink) changes. The future changes are for two scenarios. Actually, I find the results for RCP2.6 very interesting; it's kind of a #ParisAgreement scenario, giving 2/3 chance of staying below 2°C.

The results for RCP8.5 (pink bands) are what happens if we don't reduce emissions, or if unknown feedbacks drive up atmospheric greenhouse gas concentrations anyway. Good warning to stay clear of that! Present emission reduction commitments are only a little bit better.

So let's zoom in on what could happen if we comply with the #ParisAgreement (RCP2.6).
Global mean air temperature rise: 1.6°C (quite some uncertainty).
Global mean sea surface temperature: Just a few tenths of a °C warmer than now. Not a huge further growth in marine heatwaves.

[NB: take your time to find the tick mark for 2020 ("you are here"); it's a bit to the right of the change from historical to projected values, due to the time lag in collecting data and using them in scientific publications.]

Under a #ParisAgreement scenario (RCP2.6):
The acidification of the ocean would hardly get worse than it is now, with already some recovery in the second half of the century. Same for oxygen decrease.
There would still be Arctic sea ice in September.

That's it for today. Overall conclusion: it's massively worthwhile to stick to the #ParisAgreement, for the world's ice and oceans as well, and all is not lost! (Note that it's also a massive challenge; it roughly means reducing global emissions to zero by 2050).