Here is an explainer video. I'm using the fancy video set-up I use for teaching.
"Committed warming" is a standard calculation that asks how much warming you would get if you held the atmospheric composition fixed at today's values indefinitely.
This figure from the IPCC AR4 report shows about 0.6°C of committed warming in 2100 (the yellow line).
Our paper suggests that committed warming is larger than that — right now, we have experienced about 1°C of warming, and we are committed to 1.3°C of additional warming with fixed radiative forcing (although the error bars on this estimate are large).
This is not a prediction — holding atmospheric composition fixed is simply a convenient calculation models can do. It would be possible to have less future warming than we calculate if emissions go to zero soon.
Whatever the future emissions trajectory holds, however, our work suggests more future warming from our present climate than extrapolations from past warming (i.e., Mauritsen and Pincus, 10.1038/nclimate3357) or multi-model averages (as in the AR4).
Our calculation also emphasizes how hard it will be to keep warming below the Paris thresholds.
If people really want to achieve these targets, we need to accept the probability that we'll need to implement solar geoengineering.
My personal opinion is to not focus so much on these targets. In the end, there's nothing magical about them — there's no reason to think that warming of 1.99°C is much better than 2.01°C.
Another piece of good news is that much of this committed warming may be very slow to arrive. If we can reduce emissions quickly, then we may still break 2°C, but it may be centuries in the future.
So, if you want to minimize climate impacts, focus on getting emissions down to zero as fast as possible. Regardless of what we're committed to, there is always benefit in avoiding additional warming.
btw, here's a non-paywalled link to the paper: rdcu.be/cc2Cj
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There is no result that disqualifies climate economics more than this one. 8°C warming = loss of ~10% of GDP???? As a reminder, the last ice age was about 6°C cooler than today. Now imagine changes as big as those occurring over the next century or two. This result is absurd.
This plot shows GDP curves (growing at 2.5% and 2.46%) that differ by 4% in 2100. This is analogous to Lomborg's worlds with no global warming and a world that warms by 8°C in 2100!
8°C is getting close to temperatures during the Eocene, when there was no permanent ice on the planet.
NH land will warm more than the global average, so 8°C global avg. probably corresponds to something like 12°C (22°F) over NH land (and even more in the Arctic).
If you hear a "reasonable middle bro" who "cares deeply about the environment" but tells you that "climate change is not making hurricanes worse," they're gas-lighting you.
Let's examine the peer-reviewed science on this issue. From chapter 6 of the IPCC Ocean and Cryosphere report.
REPOST: I've been looking for a good figure showing Extreme temperatures have gone up. After searching without success, I made this, adapted from @DrJamesEHansen's 2012 PNAS paper. Data are from Berkeley earth.
[previous post had an error in the plot; corrected here]
The left plot shows the 1951-1980 June-July-August seasonal average for northern hemisphere land (30°N-60°N). The blue area is the coolest is 33% of temperatures, the white area or the middle 33%, and the red or the highest 33%.
The right plot shows the 2011-2020 temperatures. Over the decade, 88% of the seasonal averages would have been in the top third in the 1951-1980 period. Only 1.2% would have been in the coolest third. And 14% are warmer than ANY temperatures in the 1951-1980 period.
Climate models are based on physics. Their code describes the fundamental processes that we know drive atmospheric processes: radiative transfer, thermodynamics, the idea gas law, etc. 1/
Despite what you might hear, these models have been thoroughly tested. In fact, I’ve spent much of my career looking at model output and comparing to observations and I am constantly amazed how well climate models do. 2/
Now this doesn’t mean models do everything well. Some process are not simulated from first-principles — e.g., cloud microphysics, which occurs on too small a spatial scale for models to resolve. 4/
It should be noted that this is how climate science became politicized. When politicians started saying dumb things about climate science ("global warming stopped!"), it left scientists with a choice:
1) say nothing 2) publicly correct the misrepresentation of the science by politicians
Many in the scientific community chose #2, which I think was the morally responsible choice. But once you do this you've implicitly taken sides in the political debate.
There are multiple time scales on which CO2 is removed from the atmosphere. If you add a slug to the atmosphere, the first 50% is removed in 50 years, the next half (taking you down to 25% takes about 500 years, the next half (taking you down to 12.5%) takes 10,000+ years.
The decadal time scale is due to transport to land-biosphere & mixed-layer ocean, the century time scale is due to the slower process of transport to the deep ocean, and the very long time scales are the conversion of ocean carbonate to rocks.