Thread by @KHayhoe

It's here! The Climate Science Special Report, the most up to date synthesis of climate science today, just dropped. science2017.globalchange.gov

Our climate science report is vol 1 of the 4th US National Climate Assessment. Here's what NCA is & why it matters: blog.ucsusa.org/rachel-licker/…

This new climate sci report was written by US federal scientists from relevant agencies + a few non-feds like me, @bobkopp & @radleyhorton.

Here is a thread on the most important findings of our new climate science report: science2017.globalchange.gov

1/ It confirms what we've known for decades:
Climate is changing
Humans are responsible
The risks are serious
The time to act is now

2/ Much of what we've learned in recent years suggests changes could be more extensive, more rapid, and more damaging than we thought.

Global temperature increased by about 1.8°F (1.0°C) from 1901–2016. This period is now the warmest in the history of modern civilization. /3

Human activities are the dominant cause of observed warming since the mid-20th century...there is no convincing alternative explanation. /4

Thousands of studies document changes in temperature; melting glaciers; diminishing snow cover; shrinking sea ice; rising sea levels; etc /5

Without major reductions in emissions, avg global temperature relative to preindustrial could rise 9°F (5°C) or more by end of century. /6

Atmospheric CO2 is now past 400 ppm-last seen about 3 million yrs ago, when both global avg temp + sea level were much higher than today. /7

The further and the faster the Earth system is pushed towards warming, the greater the risk of unanticipated changes and impacts. /8

Yet with significant reductions in emissions, the increase in avg global temperature could still be limited to 3.6°F (2°C) or less, YES. /9

The bottom line? We care about a changing climate because it exacerbates so many of the risks we already face today. /10

Questions about our new climate science report? We're teaming up w/ @AAAS for a FB Live chat @ 3E on Nov 8. Join us: facebook.com/AAAS.Science/v…